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	<title>DP Chemistry: Hess&#039;s Law </title>
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href="../19290/introduction-to-biochemistry--1.html">Introduction to biochemistry  </a></li><li><a href="../19287/proteins-enzymes--1.html">Proteins & enzymes </a></li><li><a href="../19291/lipids-1.html">Lipids</a></li><li><a href="../19299/carbohydrates--1.html">Carbohydrates </a></li><li><a href="../19305/vitamins--1.html">Vitamins   </a></li><li><a href="../19313/biochemistry-the-environment--1.html">Biochemistry & the environment </a></li><li><a href="../19336/proteins-enzymes-ahl--1.html">Proteins & enzymes (AHL)   </a></li><li><a href="../19347/nucleic-acids--1.html">Nucleic acids   </a></li><li><a href="../19361/biological-pigments--1.html">Biological pigments   </a></li><li><a href="../19366/stereochemistry-in-biomolecules-1.html">Stereochemistry in biomolecules</a></li></ul></li><li><a href="../19390/option-c--1.html" class="father">Option C </a><ul class="level-2"><li><a href="../19391/energy-sources-1.html">Energy sources</a></li><li><a href="../19407/fossil-fuels-1.html">Fossil fuels</a></li><li><a href="../19411/nuclear-fusion-nuclear-fission-reactions-1.html">Nuclear fusion & nuclear fission reactions</a></li><li><a href="../19429/solar-energy-1.html">Solar energy</a></li><li><a href="../19437/environmental-impact-global-warming-1.html">Environmental impact - global warming</a></li><li><a href="../19453/electrochemistry-rechargeable-batteries-fuel-cells-1.html">Electrochemistry, rechargeable batteries & fuel cells</a></li><li><a href="../19458/nuclear-fusion-fission-hl--1.html">Nuclear fusion & fission (HL)    </a></li><li><a href="../19470/photovoltaic-cells-and-dsscs-1.html">Photovoltaic cells and DSSCs</a></li></ul></li><li><a href="../19078/option-d-1.html" class="father">Option D</a><ul class="level-2"><li><a href="../19079/pharmaceutical-products-drug-action--1.html">Pharmaceutical products & drug action </a></li><li><a href="../19158/aspirin-penicillin--1.html">Aspirin & penicillin  </a></li><li><a href="../19174/opiates-1.html">Opiates</a></li><li><a href="../19184/ph-regulation-of-the-stomach-1.html">pH regulation of the stomach</a></li><li><a href="../19194/antiviral-medications--1.html">Antiviral medications </a></li><li><a href="../19211/environmental-impact-of-some-medications-1.html">Environmental impact of some medications</a></li><li><a href="../19254/taxol-a-chiral-auxiliary-case-study-1.html">Taxol - a chiral auxiliary case study</a></li><li><a href="../19258/nuclear-medicine--1.html">Nuclear medicine  </a></li><li><a href="../19273/drug-detection-analysis--1.html">Drug detection & analysis </a></li></ul></li></ul></li><li><a href="../16592/practical-scheme-of-work-ia--1.html">Practical scheme of work & IA </a><ul class="level-1"><li><a href="../16682/internal-assessment-1.html" class="father">Internal Assessment</a><ul class="level-2"><li><a href="../18892/scaffolding-the-investigation-1.html">&#039;Scaffolding&#039; the investigation</a></li><li><a href="../18896/timing-organisation--1.html">Timing & organisation </a></li><li><a href="../18905/choosing-the-research-question-1.html">Choosing the research question</a></li><li><a href="../18946/personal-engagement-1.html">Personal engagement</a></li><li><a href="../18950/exploration-1.html">Exploration</a></li><li><a href="../18957/analysis-1.html">Analysis</a></li><li><a href="../18965/evaluation-1.html">Evaluation</a></li><li><a href="../18966/communication-1.html">Communication</a></li><li><a href="../19882/internal-standardization-of-the-ia-1.html">Internal standardization of the IA</a></li><li><a href="../19901/submitting-the-samples-for-moderation-2.html">Submitting the samples for moderation</a></li><li><a href="../33754/ten-suggestions-for-ias-using-secondary-data-1.html">Ten suggestions for IAs using secondary data</a></li><li><a href="../37544/gaining-full-marks-for-a-databased-ia--1.html">Gaining full marks for a databased IA </a></li><li><a href="../19506/ia-example-marking-exercise--1.html">IA example & marking exercise </a></li><li><a href="../23929/genuine-examples-of-moderated-ia-reports-1.html">Genuine examples of moderated IA reports</a></li><li><a href="../25234/examples-of-teacher-marked-ia-reports--1.html">Examples of teacher-marked IA reports </a></li><li><a href="../37542/history-of-internal-assessment-1.html">History of Internal Assessment</a></li></ul></li><li><a href="../16598/mandatory-laboratory-components-1.html" class="father">Mandatory laboratory components</a><ul class="level-2"><li><a href="../16613/formula-of-magnesium-oxide--1.html">Formula of magnesium oxide </a></li><li><a href="../16612/determining-the-mr-of-an-unknown-gas-1.html">Determining the <i>M</i><sub>r</sub> of an unknown gas</a></li><li><a href="../16615/acid-base-titrations--1.html">Acid-base titrations </a></li><li><a href="../16616/a-green-acid-base-practical-1.html">A green acid-base practical</a></li><li><a href="../16617/analysis-of-aspirin-tablets-1.html">Analysis of aspirin tablets</a></li><li><a href="../16618/caco3-in-egg-shells-1.html">CaCO<sub>3</sub> in egg shells</a></li><li><a href="../16644/enthalpy-changes-1.html">Enthalpy changes</a></li><li><a href="../16631/reaction-rates-1.html">Reaction rates</a></li><li><a href="../16635/rate-dependent-factors-1.html">Rate-dependent factors</a></li><li><a href="../16636/determining-ea-for-a-reaction-1.html">Determining <i>E</i><sub>a</sub> for a reaction</a></li><li><a href="../16637/iodination-of-propanone-1.html">Iodination of propanone</a></li><li><a href="../18144/titrations-with-a-ph-meter-1.html">Titrations with a pH meter</a></li><li><a href="../18355/redox-titration-with-kmno4--1.html">Redox titration with KMnO<sub>4</sub> </a></li><li><a href="../16640/voltaic-cells-1.html">Voltaic cells</a></li><li><a href="../16659/3-d-molecular-modelling--1.html">3-D molecular modelling </a></li></ul></li><li><a href="../17168/other-good-practicals-1.html" class="father">Other good practicals</a><ul class="level-2"><li><a href="../17196/common-chemical-reactions-1.html">Common chemical reactions</a></li><li><a href="../227/elements-oxides-of-the-third-period--1.html">Elements & oxides of the third period </a></li><li><a href="../17239/the-halogens-1.html">The halogens</a></li><li><a href="../17162/boiling-points-of-mixtures-1.html">Boiling points of mixtures</a></li><li><a href="../17170/polarity-of-molecules-1.html">Polarity of molecules</a></li><li><a href="../18083/le-chateliers-principle--1.html">Le Chatelier&#039;s principle </a></li><li><a href="../19582/determining-kc-for-an-esterification-reaction-1.html">Determining <i>K</i><sub>c</sub> for an esterification reaction</a></li><li><a href="../18164/redox-reactions-of-vanadium--1.html">Redox reactions of vanadium </a></li><li><a href="../18351/chlorine-in-swimming-pools--1.html">Chlorine in swimming pools </a></li><li><a href="../18178/analysis-of-cuii-ions-in-solution--1.html">Analysis of Cu(II) ions in solution </a></li><li><a href="../18179/percentage-of-copper-in-brass-1.html">Percentage of copper in brass</a></li><li><a href="../18356/electrolytic-cells--1.html">Electrolytic cells </a></li><li><a href="../18598/reactions-of-organic-compounds-1.html">Reactions of organic compounds</a></li><li><a href="../18752/hydrolysis-of-halogenoalkanes-1.html">Hydrolysis of halogenoalkanes</a></li><li><a href="../18784/preparation-of-13-dinitrobenzene--1.html">Preparation of 1,3-dinitrobenzene </a></li><li><a href="../19022/determination-of-an-organic-structure-1.html">Determination of an organic structure</a></li><li><a href="../19887/preparation-of-nylon-66-1.html">Preparation of nylon 6,6</a></li><li><a href="../19343/determination-of-vitamin-c-content--1.html">Determination of vitamin C content </a></li><li><a href="../19342/hydrolysis-of-starch--1.html">Hydrolysis of starch </a></li><li><a href="../19159/preparation-purification-of-aspirin--1.html">Preparation & purification of aspirin </a></li></ul></li><li><a href="../18851/ict-in-practical-work-1.html" class="father">ICT in practical work</a><ul class="level-2"><li><a href="../18852/data-logging--1.html">Data logging </a></li><li><a href="../18853/software-for-graph-plotting--1.html">Software for graph plotting </a></li><li><a href="../18854/spreadsheets-for-data-processing--1.html">Spreadsheets for data processing </a></li><li><a href="../18855/databases-1.html">Databases</a></li><li><a href="../18856/computer-modelling-simulations--1.html">Computer modelling & simulations </a></li></ul></li><li><a href="../16594/group-4-project-1.html" class="father">Group 4 Project</a><ul class="level-2"><li><a href="../16595/practicalities-1.html">Practicalities</a></li><li><a href="../16596/reflective-statement--2.html">Reflective statement </a></li></ul></li><li><a href="../16666/a-new-laboratory-1.html">A new laboratory?</a></li></ul></li><li><a href="../16284/exams-1.html">Exams</a><ul class="level-1"><li><a href="../16286/essential-facts-1.html" class="father">Essential Facts</a><ul class="level-2"><li><a href="../16287/objectives-command-terms-1.html">Objectives & command terms</a></li><li><a href="../16288/grade-descriptors-1.html">Grade descriptors</a></li><li><a href="../16289/grade-boundaries-1.html">Grade boundaries</a></li></ul></li><li><a href="../16302/paper-1-multiple-choice-1.html" class="father">Paper 1 (Multiple Choice)</a><ul class="level-2"><li><a href="../16303/advice-to-students-paper-1-1.html">Advice to students (Paper 1)</a></li><li><a href="../31515/practice-paper-1-exams-1.html">Practice Paper 1 exams</a></li></ul></li><li><a href="../16305/paper-2-1.html" class="father">Paper 2</a><ul class="level-2"><li><a href="../16306/advice-to-students-paper-2-1.html">Advice to students (Paper 2)</a></li><li><a href="../16307/areas-of-difficulty-1.html">Areas of difficulty</a></li></ul></li><li><a href="../16313/paper-3--1.html" class="father">Paper 3 </a><ul class="level-2"><li><a href="../16314/advice-to-students-paper-3-1.html">Advice to students (Paper 3)</a></li><li><a href="../16342/data-response-questions-1.html">Data response questions</a></li><li><a href="../20054/experimental-work-questions-1.html">Experimental work questions</a></li></ul></li><li><a href="../16324/the-examination-process-1.html" class="father">The examination process</a><ul class="level-2"><li><a href="../16316/setting-the-exam-papers-1.html">Setting the exam papers</a></li><li><a href="../16317/predicted-grades-1.html">Predicted grades</a></li><li><a href="../16318/marking-the-papers-1.html">Marking the papers</a></li><li><a href="../16319/commenting-on-the-exams-1.html">Commenting on the exams</a></li><li><a href="../16320/grade-awarding-1.html">Grade Awarding</a></li><li><a href="../16321/enquiry-upon-results-1.html">Enquiry upon results</a></li><li><a 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Section A questions</a></li><li><a href="../17792/sl-questions-on-the-options-1.html">SL Questions on the options</a></li><li><a href="../24897/sl-quizzes-on-option-sub-topics--1.html">SL Quizzes on option sub-topics </a></li><li><a href="../17785/hl-multiple-choice-tests-on-individual-topics-1.html">HL Multiple choice tests on individual topics</a></li><li><a href="../24352/hl-multiple-choice-quizzes-on-sub-topics-1.html">HL Multiple choice &#039;quizzes&#039; on sub-topics</a></li><li><a href="../31520/hl-practice-paper-1-exams--1.html">HL Practice Paper 1 exams </a></li><li><a href="../17787/hl-questions-on-each-sub-topic--1.html">HL Questions on each sub-topic </a></li><li><a href="../20428/hl-paper-3-section-a-questions-1.html">HL Paper 3 Section A questions</a></li><li><a href="../17793/hl-questions-on-the-options-1.html">HL Questions on the options</a></li><li><a href="../24973/hl-quizzes-on-option-sub-topics-1.html">HL Quizzes on option sub-topics</a></li><li><a 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title="Equilibrium law ">Equilibrium law </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24660/mc-test-the-equilibrium-law-1.html" title="MC test: The equilibrium law">MC test: The equilibrium law</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../40961/equilibrium-law-questions-1.html" title="Equilibrium law questions">Equilibrium law questions</a></li></ul></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../18120/topics-8-18--1.html" title="Topics 8 & 18 ">Topics 8 & 18 </a></li><ul class="level-2 "><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18124/theories-of-acids-bases--1.html" title="Theories of acids & bases ">Theories of acids & bases </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right 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href="../40964/properties-of-acids-bases-questions-1.html" title="Properties of acids & bases questions">Properties of acids & bases questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18140/ph-scale-1.html" title="pH scale">pH scale</a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24668/mc-test-the-ph-scale-1.html" title="MC test: The pH scale">MC test: The pH scale</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../40971/ph-scale-questions-1.html" title="pH scale questions">pH scale questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18152/strong-weak-acids-bases-1.html" title="Strong & weak acids & bases">Strong & weak acids & bases</a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24670/mc-test-strong-weak-acids-bases-1.html" title="MC test: Strong & weak acids & bases">MC test: Strong & weak acids & bases</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../40972/strong-weak-acid-bases-questions-1.html" title="Strong & weak acid & bases questions">Strong & weak acid & bases questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18156/acid-deposition-1.html" title="Acid deposition">Acid deposition</a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24674/mc-test-acid-deposition-1.html" title="MC test: Acid deposition">MC test: Acid deposition</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../40983/acid-deposition-questions-1.html" title="Acid deposition questions">Acid deposition questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18160/lewis-acids-bases-1.html" title="Lewis acids & bases">Lewis acids & bases</a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24710/mc-test-lewis-acids-bases-1.html" title="MC test: Lewis acids & bases">MC test: Lewis acids & bases</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../40986/lewis-acids-bases-questions-1.html" title="Lewis acids & bases questions">Lewis acids & bases questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18250/acid-base-calculations-1.html" title="Acid base calculations">Acid base calculations</a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a 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</a></li></ul></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../18350/topics-9-19-1.html" title="Topics 9 & 19">Topics 9 & 19</a></li><ul class="level-2 "><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18365/oxidation-reduction-1.html" title="Oxidation & reduction">Oxidation & reduction</a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24725/mc-test-oxidation-reduction-1.html" title="MC test: Oxidation & reduction">MC test: Oxidation & reduction</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41033/oxidation-reduction-questions-1--1.html" title="Oxidation & reduction questions (1) ">Oxidation & reduction questions (1) </a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a 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questions</a></li></ul></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../18475/topics-10-20--1.html" title="Topics 10 & 20 ">Topics 10 & 20 </a></li><ul class="level-2 "><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18497/fundamentals-of-organic-chemistry--1.html" title="Fundamentals of organic chemistry ">Fundamentals of organic chemistry </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24749/mc-test-fundamentals-of-organic-chemistry-1.html" title="MC test: Fundamentals of organic chemistry">MC test: Fundamentals of organic chemistry</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41111/fundamentals-of-organic-chemistry-1-questions-1.html" title="Fundamentals of organic chemistry (1) questions">Fundamentals of organic chemistry (1) questions</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41112/fundamentals-of-organic-chemistry-2-questions-1.html" title="Fundamentals of organic chemistry (2) questions">Fundamentals of organic chemistry (2) questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18597/alkanes-alkenes-addition-polymers-1.html" title="Alkanes, alkenes & addition polymers">Alkanes, alkenes & addition polymers</a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24750/mc-test-alkanes-alkenes-addition-polymers-1.html" title="MC test: Alkanes, alkenes & addition polymers">MC test: Alkanes, alkenes & addition polymers</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41121/alkanes-questions-1.html" title="Alkanes questions">Alkanes questions</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41124/alkenes-questions-1.html" title="Alkenes questions">Alkenes questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18741/alcohols--1.html" title="Alcohols ">Alcohols </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24772/mc-test-alcohols-1.html" title="MC test: Alcohols">MC test: Alcohols</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41125/alcohols-questions-1.html" title="Alcohols questions">Alcohols questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18742/halogenoalkanes-benzene--1.html" title="Halogenoalkanes & benzene ">Halogenoalkanes & benzene </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24797/mc-test-halogenoalkanes-benzene-1.html" title="MC test: Halogenoalkanes & benzene">MC test: Halogenoalkanes & benzene</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41130/halogenoalkanes-benzene-questions-1.html" title="Halogenoalkanes & benzene questions">Halogenoalkanes & benzene questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18762/nucleophilic-substitution--1.html" title="Nucleophilic substitution ">Nucleophilic substitution </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24757/mc-test-nucleophilic-substitution-1.html" title="MC test: Nucleophilic substitution">MC test: Nucleophilic substitution</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41138/nucleophilic-substitution-questions-1.html" title="Nucleophilic substitution questions">Nucleophilic substitution questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18766/electrophilic-addition--1.html" title="Electrophilic addition ">Electrophilic addition </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24805/mc-test-electrophilic-addition-electrophilic-substitution-reacti-2.html" title="MC test: Electrophilic addition & electrophilic substitution reactions">MC test: Electrophilic addition & electrophilic substitution reactions</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41148/electrophilic-addition-questions-1.html" title="Electrophilic addition questions">Electrophilic addition questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18780/electrophilic-substitution--2.html" title="Electrophilic substitution ">Electrophilic substitution </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41149/electrophilic-substitution-questions-1.html" title="Electrophilic substitution questions">Electrophilic substitution questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18793/reduction-reactions--1.html" title="Reduction reactions ">Reduction reactions </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24811/mc-test-reduction-reactions-1.html" title="MC test: Reduction reactions">MC test: Reduction reactions</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41150/reduction-reactions-questions-1.html" title="Reduction reactions questions">Reduction reactions questions</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18797/synthetic-routes--1.html" title="Synthetic routes ">Synthetic routes </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24822/mc-test-synthetic-routes-1.html" title="MC test: Synthetic routes">MC test: Synthetic routes</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41152/synthetic-routes-questions--1.html" title="Synthetic routes questions ">Synthetic routes questions </a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18844/stereoisomerism--1.html" title="Stereoisomerism  ">Stereoisomerism  </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24817/mc-test-stereoisomerism-1.html" title="MC test: Stereoisomerism">MC test: Stereoisomerism</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41166/stereoisomerism-questions-1.html" title="Stereoisomerism questions">Stereoisomerism questions</a></li></ul></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../17285/topics-11-21--1.html" title="Topics 11 & 21 ">Topics 11 & 21 </a></li><ul class="level-2 "><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../17276/uncertainty-errors--1.html" title="Uncertainty & errors ">Uncertainty & errors </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24818/mc-test-uncertainties-errors-1.html" title="MC test: Uncertainties & errors">MC test: Uncertainties & errors</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../38869/uncertainty-error-questions--1.html" title="Uncertainty & error questions ">Uncertainty & error questions </a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../15014/graphical-techniques-1.html" title="Graphical techniques">Graphical techniques</a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24819/mc-test-graphical-techniques-1.html" title="MC test: Graphical techniques">MC test: Graphical techniques</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39387/graphical-techniques-questions--1.html" title="Graphical techniques questions ">Graphical techniques questions </a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../18968/spectroscopic-identification-of-organic-compounds-1.html" title="Spectroscopic identification of organic compounds">Spectroscopic identification of organic compounds</a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24820/mc-test-spectroscopic-identification-of-organic-compounds--1.html" title="MC test: Spectroscopic identification of organic compounds ">MC test: Spectroscopic identification of organic compounds </a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39388/index-of-hydrogen-deficiency-questions-1.html" title="Index of hydrogen deficiency questions">Index of hydrogen deficiency questions</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39351/identification-from-spectra-question-1-1.html" title="Identification from spectra - Question 1">Identification from spectra - Question 1</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39353/identification-from-spectra-question-2-1.html" title="Identification from spectra - Question 2">Identification from spectra - Question 2</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39354/identification-from-spectra-question-3-1.html" title="Identification from spectra - Question 3">Identification from spectra - Question 3</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39355/identification-from-spectra-question-4-1.html" title="Identification from spectra - Question 4">Identification from spectra - Question 4</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39356/identification-from-spectra-question-5-1.html" title="Identification from spectra - Question 5">Identification from spectra - Question 5</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39357/identification-from-spectra-question-6-1.html" title="Identification from spectra - Question 6">Identification from spectra - Question 6</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39358/identification-from-spectra-question-7-1.html" title="Identification from spectra - Question 7">Identification from spectra - Question 7</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39359/identification-from-spectra-question-8-1.html" title="Identification from spectra - Question 8">Identification from spectra - Question 8</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39360/identification-from-spectra-question-9-1.html" title="Identification from spectra - Question 9">Identification from spectra - Question 9</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39361/identification-from-spectra-question-10-1.html" title="Identification from spectra - Question 10">Identification from spectra - Question 10</a></li></ul><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../19027/spectroscopic-identification-of-organic-compounds-ahl--1.html" title="Spectroscopic identification of organic compounds (AHL) ">Spectroscopic identification of organic compounds (AHL) </a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../24821/mc-test-spectroscopic-identification-of-organic-compounds-ahl-1.html" title="MC test: Spectroscopic identification of organic compounds (AHL)">MC test: Spectroscopic identification of organic compounds (AHL)</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39375/identification-from-spectra-question-11-1.html" title="Identification from spectra - Question 11">Identification from spectra - Question 11</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39376/identification-from-spectra-question-12-1.html" title="Identification from spectra - Question 12">Identification from spectra - Question 12</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39377/identification-from-spectra-question-13-1.html" title="Identification from spectra - Question 13">Identification from spectra - Question 13</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39378/identification-from-spectra-question-14-1.html" title="Identification from spectra - Question 14">Identification from spectra - Question 14</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39379/identification-from-spectra-question-15-1.html" title="Identification from spectra - Question 15">Identification from spectra - Question 15</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39380/identification-from-spectra-question-16-1.html" title="Identification from spectra - Question 16">Identification from spectra - Question 16</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39381/identification-from-spectra-question-17-1.html" title="Identification from spectra - Question 17">Identification from spectra - Question 17</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../39382/identification-from-spectra-question-18-1.html" title="Identification from spectra - Question 18">Identification from spectra - Question 18</a></li><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a 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</div><section id="main-content"><div id="toc-1672970418" class="toc"><a href="#" class="toc-switcher" title="Show table of contents"><small><i class="fa fa-reorder"></i> Table of contents <span class="pull-right"><i class="fa fa-chevron-down"></i></span></small></a></div><h1><img alt="" src="../../../ib/chemistry/images/2014%20Core%20%26%20AHL/Topics-5---15/germain-hess.png" style="width: 2px; height: 3px;"><img class="ico" src="../../../img/icons/standard-1.png"> <img class="ico" src="../../../img/icons/higher-1.png"> 5.2 Hess&#39;s Law (2 hours)</h1><div class="pinkBg"><div><h2>Pause for thought</h2><p>Hess&rsquo;s Law is named after Germain Henri Hess (1802 &ndash; 1850) a Swiss national who moved with his family to Russia at the age of 3. He qualified as a doctor but later became a professor of chemistry at the St Petersburg Technical Institute. He was interested in minerals and analyzed one particular ore of silver telluride, Ag<sub>2</sub>Te, which is now called <a href="http://www.mindat.org/min-1881.html">hessite</a> in his honour.</p><hr class="hidden"><p style="text-align: center;"><img alt="" class="noborder" src="../../../ib/chemistry/images/2014%20Core%20%26%20AHL/Topics-5---15/germain-hess.png" style="width: 202px; height: 262px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;&nbsp; <img alt="" class="noborder" src="../../../ib/chemistry/images/2014%20Core%20%26%20AHL/Topics-5---15/hessite.png" style="width: 164px; height: 262px;"></p><p style="text-align: center;">Germain Hess &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Hessite</p><hr class="hidden"><p>Hess&rsquo;s Law states that the total energy change in a chemical reaction depends only upon the initial and final states and is independent of the reaction pathway. It used to be known as the Law of Constant Heat Summation and is in fact another way of stating the Law of Conservation of Energy.</p><hr class="hidden"><p>So how can Hess&rsquo;s Law be applied?</p><hr class="hidden"><p>There are basically three different methods that can be used to solve Hess&rsquo;s Law problems:</p><ul><li>Energy cycle</li><li>Enthalpy level diagram</li><li>Simultaneous equations</li></ul><p>So which is the best method to train students to use?</p><p>Energy cycle, enthalpy level diagram or simultaneous equations?</p><hr class="hidden"><p>Take as an example <a href="../16887/5-energetics-thermochemistry-1.html">Question 15 on the SL Energetics/thermochemistry multiple choice test</a>.</p><p><strong>Qu.15. </strong>The enthalpy change for the dimerization of two mol of nitrogen dioxide to form one mol of dinitrogen tetroxide is &ndash; 57 kJ.</p><p>2NO<sub>2</sub>(g) &rarr; N<sub>2</sub>O<sub>4</sub>(g)&nbsp; ∆<em>H</em><img class="ico" src="../../../img/icons/underground.png"> = &ndash; 57 kJ</p><p>The enthalpy change for the formation of one mol of NO<sub>2</sub>(g) from its elements is + 33 kJ</p><p>&frac12; N<sub>2</sub>(g) + O<sub>2</sub>(g) &rarr; NO<sub>2</sub>(g) ∆<em>H</em><img class="ico" src="../../../img/icons/underground.png"> = + 33 kJ</p><p>What is the enthalpy change for the formation of one mol of dinitrogen tetroxide from its elements?</p><p>N<sub>2</sub>(g) + 2O<sub>2</sub>(g) &rarr; N<sub>2</sub>O<sub>4</sub>(g)</p><hr class="hidden"><p><strong>1. Solution using simultaneous equations.</strong></p><p>To get N<sub>2</sub> on the left hand side start with the second equation and double it:</p><p>N<sub>2</sub>(g) + 2O<sub>2</sub>(g) &rarr; 2NO<sub>2</sub>(g) ∆<em>H</em><img class="ico" src="../../../img/icons/underground.png"> = + 66&nbsp; kJ</p><p>To get rid of 2NO<sub>2</sub> and to get N<sub>2</sub>O<sub>4</sub> on the right hand side add the first equation:</p><p>N<sub>2</sub>(g) + 2O<sub>2</sub>(g) &rarr; N<sub>2</sub>O<sub>4</sub>(g) ∆<em>H</em><img class="ico" src="../../../img/icons/underground.png"> = + 66 + (&ndash; 57) = + 9 kJ</p><p>Easy - but it does not really involve any chemistry.</p><hr class="hidden"><p><strong>2. Solution using an enthalpy diagram.</strong></p><p>The problem is that you need to put the reactants and products in the correct places on the diagram.</p><p style="text-align: center;"><img alt="" class="noborder" src="../../../ib/chemistry/images/2014%20Core%20%26%20AHL/Topics-5---15/enthalpy-diagram.png" style="width: 363px; height: 229px;"></p><p>Personally I do not find it very obvious from the information given even though there is no need to include the oxygen (as you do not know the answer beforehand) and students certainly do not find this easy.<br>Once the diagram has been drawn correctly it is easy to see that <em>x</em> is positive and is the difference in value between 66 and 57 kJ.</p><hr class="hidden"><p><strong>3. Solution using an energy cycle.</strong></p><p>Use the idea of <strong>A</strong> going directly to <strong>B</strong> or via <strong>C</strong>. In this case <strong>A</strong> is N<sub>2</sub>, <strong>B</strong> is N<sub>2</sub>O<sub>4</sub> and <strong>C</strong> is NO<sub>2</sub>.<br>In chemistry terms nitrogen can either be oxidized directly to N<sub>2</sub>O<sub>4</sub> or first to NO<sub>2</sub> which then dimerizes<br>to N<sub>2</sub>O<sub>4</sub>. (Again there is no need to include the oxygen in the cycle.)</p><p style="text-align: center; "><img alt="" class="noborder" src="../../../ib/chemistry/images/2014%20Core%20%26%20AHL/Topics-5---15/energy-cycle-for-n2o4.png" style="width: 184px; height: 200px;"></p><p>From the diagram (i.e. applying Hess&rsquo;s Law) it is easy to see that <em>x</em> = (2 x 33) + (&ndash; 57) = + 9 kJ</p><p>All three methods are correct but I think the energy cycle method is the easiest, the most elegant and demonstrates the best understanding of chemistry.</p><hr class="hidden"></div></div><hr class="hidden"><div class="box"><h2><strong>Nature of Science</strong></h2><p>Testing hypotheses. Hess&#39;s Law states that if the same products are formed from the same initial reactants then the energy change should be the same regardless of the number of steps. This is an example of where a hypothesis based on the law of conservation of energy and on atomic theory can be tested experimentally.</p><hr class="hidden"></div><hr class="hidden"><div class="box"><table align="left" border="0" cellpadding="10" cellspacing="0"><tbody><tr><td style="width: 50%;" valign="top"><h3><b><span style="font-weight: normal; "></span></b></h3><div class="yellowBg"><div><h2><b><span style="font-weight: normal; "><strong>Learning outcomes</strong></span></b></h2><p><span style="font-weight: normal; ">After studying this topic students should be able to:</span></p><p><b><span style="font-weight: normal; "><strong>Understand</strong></span></b></p><ul><li>Hess&#39;s Law states that the enthalpy change for a reaction that is carried out in a series of steps is equal to the sum of the enthalpy changes for the individual steps, i.e. it is independent of the reaction pathway.</li></ul><p><strong>Apply their knowledge to:</strong></p><ul><li>Apply Hess&rsquo;s Law to calculate enthalpy changes.</li><li>Calculate the value of &Delta;<em>H</em><sup>⦵</sup> for a reaction using data for &Delta;<em>H</em><sub>f</sub><sup>⦵</sup> values.</li><li>Determine the enthalpy change of a reaction that is the sum of multiple reactions with known enthalpy changes.</li></ul></div></div></td><td style="width: 50%;" valign="top"><h4><b><span style="font-weight: normal;"></span></b></h4><div class="yellowBg"><div><h4><b><span style="font-weight: normal;"><strong>Clarification notes</strong></span></b></h4><p>Values for enthalpies of formation can be found in Section 12 of the data booklet.</p><p>One application of Hess&#39;s Law is &Delta;<em>H</em> reaction = &Sigma;(&Delta;H<sub>f</sub><sup>⦵</sup><br>products) &minus; &Sigma;(&Delta;H<sub>f</sub><sup>⦵</sup> reactants).</p><hr class="hidden"><h4>International-mindedness</h4><p>There is a rather strange reference in the syllabus about recycling. It is not clear why this is under a sub-topic on Hess&#39;s Law but it states that although recycling materials is often an effective means of reducing the environmental impact of production, its efficiency in energy terms can vary in different countries.</p></div></div></td></tr></tbody></table></div><hr class="hidden"><div class="box"><table align="left" border="0" cellpadding="10" cellspacing="0"><tbody><tr><td style="width: 50%;" valign="top"><h2><span style=""><b><span style="font-weight: normal;"><strong>Teaching tips</strong></span></b></span></h2><p>I usually introduce this by asking students to write the equation for the formation of methane. If they have understood the definition they should write:</p><p style="text-align: center; ">C(s) + 2H<sub>2</sub>(g) &rarr; CH<sub>4</sub>(g)</p><p>I then ask them how they would determine &Delta;<em>H</em><sub>f</sub><sup>⦵</sup> for the reaction. They often try to devise some sort of apparatus to measure it directly but then realise that there is no way in which they can ensure that the only product of reacting carbon with hydrogen is methane and not some other hydrocarbon. They can however determine directly the enthalpies of combustion of carbon, hydrogen and methane. This leads to the concept of energy cycles and how the enthalpy of formation of methane can be determined indirectly.</p><p>Although the formal definition of Hess&#39;s Law is not required it is important to stress that it is just another way of stating the law of conservation of energy. If Hess&#39;s Law is not true then we could use an energy cycle to produce a perpetual motion machine - i.e. solve all the world&#39;s energy problems!</p><p>Stress throughout that the correct states are needed and that if one or more changes of state occur then this too needs to be incorporated into the energy cycle.</p><p>The topic lends itself to good practical work. Classic experiments are the hydration of copper(II) sulfate (see enthalpy changes right), the enthalpy of formation of metal oxides and the decomposition of potassium hydrogen carbonate. Some practicals available on the web attempt to verify Hess&#39;s Law by carrying out three separate reactions. For example, adding NaOH(s) to water, adding NaOH(s) to HCl(aq) and then adding NaOH(aq) to HCl(aq). However this seems to me to miss the point as it is better applied to reactions where the experimental value cannot be determined directly.</p><hr class="hidden"></td><td style="width: 50%;" valign="top"><h4><b><span style="font-weight: normal; "><strong>Study guide</strong></span></b>:</h4><p style="margin: 0px 0px 1em; padding: 0px; color: rgb(0, 0, 0); font-size: 1em;"><b><span style="font-weight: normal;"><img alt="" class="left noborder" src="../../../ib/chemistry/images/2014%20Basic%20information/New%20cover.jpg" style="width: 67px; height: 96px;"></span></b></p><p style="margin: 0px 0px 1em; padding: 0px; color: rgb(0, 0, 0); font-size: 1em;"></p><p style="margin: 0px 0px 1em; padding: 0px; color: rgb(0, 0, 0); font-size: 1em;"></p><p style="margin: 0px 0px 1em; padding: 0px; color: rgb(0, 0, 0); font-size: 1em;"></p><hr class="hidden"><p style="margin: 0px 0px 1em; padding: 0px; color: rgb(0, 0, 0); font-size: 1em;"><b><span style="font-weight: normal;">Page </span></b><span style="font-weight: normal;">4</span><b><span style="font-weight: normal;">0</span></b></p><hr class="hidden"><h2><strong>Questions</strong></h2><p><span style="font-family: 'Arial Narrow', Arial, Helvetica, sans-serif; font-size: 17px; color: rgb(0, 51, 102); font-weight: bold; "><b><span style="font-weight: normal;"> </span></b></span>For ten &#39;quiz&#39; multiple choice questions with the answers explained see <a href="../24582/mc-test-hesss-law-1.html" title="Core &amp; AHL » Teaching each topic &amp; sub-topic » Topics 5 &amp; 15 » Hess's Law » MC test: Hess's Law">MC test: Hess&#39;s Law</a>.</p><p style="margin: 0px 0px 1em; padding: 0px; color: rgb(0, 0, 0); font-size: 1em;">For short-answer questions which can be set as an assignment for a test, homework or given for self study together with model answers see <a href="../39546/hesss-law-questions-1.html" title="Core &amp; AHL » Teaching each topic &amp; sub-topic » Topics 5 &amp; 15 » Hess's Law » Hess's Law questions">Hess&#39;s Law questions</a>.</p><hr class="hidden"><h4><span style=""><b><span style="font-weight: normal;"><strong>Vocabulary list</strong></span></b></span></h4><p>Hess&#39;s Law<br>Law of conservation of energy<br>First law of thermodynamics<br>Enthalpy cycle</p><hr class="hidden"><h4><span style="color: rgb(0, 51, 102); font-family: 'Arial Narrow', Arial, Helvetica, sans-serif; font-size: 17px; font-weight: bold; "><b><span style="font-weight: normal;"><strong>IM, TOK, Utilization etc.</strong></span></b></span></h4><p>See <a href="../17270/topics-5-15--1.html">separate page</a> which covers all of Topics 5.</p><hr class="hidden"><h2>Practical work<span style="font-weight: normal; "></span></h2><p><a href="chemistry/practicals-for-sl-and-hl/enthalpy-changes.htm"><img class="ico" src="../../../img/icons/lab-1.png"> </a> <a href="../16644/enthalpy-changes-1.html" title="New 2014 programme (First exams 2016) » Practical scheme of work » Mandatory laboratory components » Enthalpy changes">Enthalpy changes</a></p></td></tr></tbody></table></div><hr class="hidden"><div class="greenBg"><h2 id="header-14">Teaching slides</h2><p>Teachers may wish to share these slides with students for learning or for reviewing key concepts.</p><div id="myCarousel-15" class="carousel slide" data-id="249"><!-- Carousel items --><div class="carousel-inner"><div class="active item"><a class="fancy" href="../../../tib-galleries/3-249/52-1.png" rel="gallery-249" title=""><img alt="" src="files/tib-galleries/3-249/52-1.png"></a><div class="carousel-caption"><p>Hess&#039;s Law: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-249/52-2.png" rel="gallery-249" title=""><img alt="" src="files/tib-galleries/3-249/52-2.png"></a><div class="carousel-caption"><p>Hess&#039;s Law: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-249/52-3.png" rel="gallery-249" title=""><img alt="" src="files/tib-galleries/3-249/52-3.png"></a><div class="carousel-caption"><p>Hess&#039;s Law: </p></div></div><div class="item"><a class="fancy" href="/files/tib-galleries/3-249/4.png" rel="gallery-249" title=""><img alt="" src="/files/tib-galleries/3-249/4.png"></a><div class="carousel-caption"><p>Hess&#039;s Law: </p></div></div><div class="item"><a class="fancy" href="/files/tib-galleries/3-249/5.png" rel="gallery-249" title=""><img alt="" src="/files/tib-galleries/3-249/5.png"></a><div class="carousel-caption"><p>Hess&#039;s Law: </p></div></div></div><!-- Carousel nav --><a class="carousel-control left" href="#myCarousel-15" data-slide="prev">&lsaquo;</a><a class="carousel-control right" href="#myCarousel-15" data-slide="next">&rsaquo;</a><div class="tib-indicators"><img class="" title="Click to view" style="margin: 10px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-249/52-1-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-249/52-2-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-249/52-3-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="/files/tib-galleries/3-249/4-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="/files/tib-galleries/3-249/5-thumb128.jpg"></div></div><p>&nbsp;&nbsp;</p></div><hr class="hidden"><div class="blueBg"><h2><span style="font-weight: bold;">Other resources</span></h2><p><strong>1.</strong> A tutorial which explains how to solve Hess&#39;s Law problems just by using simultaneous equations. It works, but in my view (see above), by ignoring the use of energy cycles it does not show any real understanding.</p><p style="text-align: center; "><object height="280" width="360"><param name="quality" value="high"><param name="allowScriptAccess" value="always"><param name="movie" value="http://www.youtube.com/v/iETCSFit-zA?version=3&hl=en_US&rel=0"><param name="allowscriptaccess" value="always"><embed allowscriptaccess="always" height="280" quality="high" src="http://www.youtube.com/v/iETCSFit-zA?version=3&hl=en_US&rel=0" type="application/x-shockwave-flash" width="360"></object></p><p style="text-align: center; "><iframe allowfullscreen="" frameborder="0" height="280" src="//www.youtube.com/embed/iETCSFit-zA?rel=0" width="360"></iframe></p><p style="text-align: center; "><a href="http://youtu.be/iETCSFit-zA">Hess&#39;s law (1) <img class="ico" src="../../../img/icons/video-1.png"><span class="anchor" id="video-1" name="video-1">&nbsp;</span> </a></p><hr class="hidden"><p><strong>2. </strong>Students teaching students. It could be worth showing this to students as they might appreciate it. Although quite thorough it does use three separate reactions simply to verify Hess&#39;s Law rather than using it to find out a value that cannot be determined directly.</p><p style="text-align: center; "><iframe allowfullscreen="" frameborder="0" height="280" src="//www.youtube.com/embed/ryNMjK6GuUQ?rel=0" width="360"></iframe></p><p style="text-align: center; "><a href="http://youtu.be/ryNMjK6GuUQ">Hess&#39;s Law (2) <img class="ico" src="../../../img/icons/video-1.png"><span class="anchor" id="video-2" name="video-2">&nbsp;</span></a></p></div></section></article><section id="media-extras"><div class="page-actions no-print navbar inline hidden-desktop"><div class="navbar-inner"><ul class="nav"><li><a class="presentation" href="#" onclick="return false;"><i class="fa fa-desktop"></i></a></li><li><a class="print-section-blog" href="#" onclick="return false;"><i class="fa fa-print"></i></a></li><li><a class="page-bookmarker" data-ticket="IB Docs (2) Team" data-pid="17689" href="#" onclick="return false;"><i class="fa fa-star"></i></a></li><li><a class="personal-notes" href="#" onclick="return false;"><i class="fa fa-file-text"></i></a></li><li><a class="" data-toggle="modal" href="#modal-feedback" onclick="return false;"><i class="fa fa-envelope-o"></i></a></li><li class="dropdown"><a class="dropdown-toggle" data-toggle="dropdown" data-target="#" href="#"><i class="fa fa-share-alt"></i></a><ul class="dropdown-menu" role="menu"><li><a class="" target="_blank" title="Share on Twitter" href="https://twitter.com/share?text=%22Hess%26%23039%3Bs+Law+%22+-+via+%40InThinker+%23chemistry%0A&url=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F17689%2Fhesss-law-"><i class="fa fa-twitter-square"></i><span>Twitter</span></a></li><li><a class="" target="_blank" title="Share on Facebook" href="https://www.facebook.com/sharer.php?u=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F17689%2Fhesss-law-&t=Hess's+Law+"><i class="fa fa-facebook-square"></i><span>Facebook</span></a></li><li><a class="" href="http://www.linkedin.com/shareArticle?mini=true&url=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F17689%2Fhesss-law-"><i class="fa fa-linkedin-square"></i><span>LinkedIn</span></a></li><li><a class="" href="https://plus.google.com/share?url=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F17689%2Fhesss-law-"><i class="fa fa-google-plus-square"></i><span>Google +</span></a></li><li><a class="" href="mailto:?subject=Hess's Law &body=Hess’s Law is named after Germain Henri Hess (1802 – 1850) a Swiss national who moved with his family to Russia at the age of 3. 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