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Latest updates

pH scale17 August 2022

The pH scale goes from 0 to 14 A question to consider: Does 10.0 mol dm-3 hydrochloric acid solution (see below) have a pH of minus 1?In this sub-topic pH is defined as being equal to minus the logarithm... more

Properties of acids & bases17 August 2022

The characteristic properties of acids are generally well known. Reactions of acids with reactive metals, metal oxides, hydroxides, carbonates and hydrogencarbonates are all obvious examples. Other less... more

Theories of acids & bases 17 August 2022

Have some sympathy for Svante Arrhenius, the Swedish chemist who won the Nobel Prize for Chemistry in 1903. Sub-topic 8.1 is titled "Theories of acids and bases" and yet the only theory covered in the... more

Equilibrium law 17 August 2022

A simple question, which would seem to be exactly what this topic is about, might be:What amount (in mol) of ethyl ethanoate will be formed in the equilibrium mixture if 2.0 mol of ethanoic acid and 1.0... more

Equilibrium 17 August 2022

Once you have explained the concept of dynamic equilibrium (as opposed to static equilibrium) it is worth challenging your students by asking them to suggest how it could be shown experimentally that... more

Activation energy17 August 2022

The relationship between the value of k, the rate constant, and temperature is given by the Arrhenius equation:k = A exp(–Ea/RT)where k is the rate constant, A is another constant sometimes known as... more

Collision theory & rates of reaction17 August 2022

Although students know the factors that affect the rate of a chemical reaction, it is very noticeable when marking the answers to Paper 2 questions that when they are asked to define the term rate of... more

Entropy & spontaneity 17 August 2022

Entropy is paradoxically probably one of the hardest and one of the easiest topics to teach! Hardest because a full understanding of entropy really requires knowledge of statistical thermodynamics; easiest... more

Energy cycles 17 August 2022

The idea of using an energy cycle to solve problems involving Hess's Law has already been introduced in sub-topic 5.2 Hess's Law. This Higher Level sub-topic involves the use of energy cycles that contain... more

Hess's Law 17 August 2022

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. He qualified as a doctor but later became a professor of chemistry... more