Which statement is correct for a reversible reaction when \({K_{\text{c}}} \gg 1\)?

A.     The reaction almost goes to completion.

B.     The reaction hardly occurs.

C.     Equilibrium is reached in a very short time.

D.     At equilibrium, the rate of the forward reaction is much higher than the rate of the backward reaction.

A

Which statement is always correct for a chemical reaction at equilibrium?

A.     The rate of the forward reaction equals the rate of the reverse reaction.

B.     The amounts of reactants and products are equal.

C.     The concentration of the reactants and products are constantly changing.

D.     The forward reaction occurs to a greater extent than the reverse reaction.

A

Iron(III) ions, \({\text{F}}{{\text{e}}^{3 + }}\), react with thiocyanate ions, \({\text{SC}}{{\text{N}}^ - }\), in a reversible reaction to form a red solution. Which changes to the equilibrium will make the solution go red?

    \({\text{F}}{{\text{e}}^{3 + }}{\text{(aq)}} + {\text{SC}}{{\text{N}}^ - }{\text{(aq)}} \rightleftharpoons {{\text{[FeSCN]}}^{2 + }}{\text{(aq)}}\)     \(\Delta {H^\Theta } =  + {\rm{ve}}\)

     Yellow\(\quad \quad \quad \quad \quad \quad \quad \quad \;\)Red

I.     Increasing the temperature

II.     Adding \({\rm{FeC}}{{\rm{l}}_3}\)

III.     Adding a catalyst

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

A

Which statement about chemical equilibria implies they are dynamic?

A.     The position of equilibrium constantly changes.

B.     The rates of forward and backward reactions change.

C.     The reactants and products continue to react.

D.     The concentrations of the reactants and products continue to change.

C

What happens to the position of equilibrium and the value of \({K_{\text{c}}}\) when the temperature is increased in the following reaction?

\[\begin{array}{*{20}{l}} {{\text{PC}}{{\text{l}}_5}({\text{g)}} \rightleftharpoons {\text{PC}}{{\text{l}}_3}({\text{g)}} + {\text{C}}{{\text{l}}_2}({\text{g)}}}&{\Delta {H^\Theta } = + 87.9{\text{ kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}} \end{array}\]

D

Which factor does not affect the position of equilibrium in this reaction?

2NO₂(g) \( \rightleftharpoons \) N₂O₄(g)     ΔH = −58 kJ mol⁻¹

A.     Change in volume of the container

B.     Change in temperature

C.     Addition of a catalyst

D.     Change in pressure

C

Consider the reaction between gaseous iodine and gaseous hydrogen.

\[\begin{array}{*{20}{l}} {{{\text{I}}_2}{\text{(g)}} + {{\text{H}}_2}{\text{(g)}} \rightleftharpoons {\text{2HI(g)}}}&{\Delta {H^\Theta } = - 9{\text{ kJ}}} \end{array}\]

Why do some collisions between iodine and hydrogen not result in the formation of the product?

A.     The \({{\text{I}}_{\text{2}}}\) and \({{\text{H}}_{\text{2}}}\) molecules do not have sufficient energy.

B.     The system is in equilibrium.

C.     The temperature of the system is too high.

D.     The activation energy for this reaction is very low.

A

Consider the equilibrium between N₂O₄(g) and NO₂(g).

N₂O₄(g) \( \rightleftharpoons \) 2NO₂(g)          ΔH = +58 kJ\(\,\)mol⁻¹

Which changes shift the position of equilibrium to the right?

\(\begin{array}{*{20}{l}} {{\text{I.}}}&{{\text{Increasing the temperature}}} \\ {{\text{II.}}}&{{\text{Decreasing the pressure}}} \\ {{\text{III.}}}&{{\text{Adding a catalyst}}} \end{array}\)

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

A

The equilibrium constant for N₂(g) + 3H₂(g) \( \rightleftharpoons \) 2NH₃(g) is K.

What is the equilibrium constant for this equation?

2N₂(g) + 6H₂(g) \( \rightleftharpoons \) 4NH₃(g)

A.     K

B.     2K

C.     K²

D.     2K²

C

What is the equilibrium constant expression, K_c, for the following reaction?

2NH₃(g) + 2O₂(g) \( \rightleftharpoons \) N₂O(g) + 3H₂O(g)

A.     \(\frac{{3\left[ {{{\text{H}}_2}{\text{O}}} \right]\left[ {{{\text{N}}_2}{\text{O}}} \right]}}{{2\left[ {{\text{N}}{{\text{H}}_3}} \right]2\left[ {{{\text{O}}_2}} \right]}}\)

B.     \(\frac{{{{\left[ {{\text{N}}{{\text{H}}_3}} \right]}^2}{{\left[ {{{\text{O}}_2}} \right]}^2}}}{{\left[ {{{\text{N}}_2}{\text{O}}} \right]{{\left[ {{{\text{H}}_2}{\text{O}}} \right]}^3}}}\)

C.     \(\frac{{2\left[ {{\text{N}}{{\text{H}}_3}} \right]2\left[ {{{\text{O}}_2}} \right]}}{{3\left[ {{{\text{H}}_2}{\text{O}}} \right]\left[ {{{\text{N}}_2}{\text{O}}} \right]}}\)

D.     \(\frac{{\left[ {{{\text{N}}_2}{\text{O}}} \right]{{\left[ {{{\text{H}}_2}{\text{O}}} \right]}^3}}}{{{{\left[ {{\text{N}}{{\text{H}}_3}} \right]}^2}{{\left[ {{{\text{O}}_2}} \right]}^2}}}\)

D

The equilibrium between nitrogen dioxide, \({\text{N}}{{\text{O}}_{\text{2}}}\), and dinitrogen tetroxide, \({{\text{N}}_{\text{2}}}{{\text{O}}_{\text{4}}}\), is shown below.

\[\begin{array}{*{20}{l}} {{\text{2N}}{{\text{O}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {{\text{N}}_{\text{2}}}{{\text{O}}_{\text{4}}}{\text{(g)}}}&{{K_{\text{c}}} = 0.01} \end{array}\]

What happens when the volume of a mixture at equilibrium is decreased at a constant temperature?

I.     The value of \({K_{\text{c}}}\) increases

II.     More \({{\text{N}}_{\text{2}}}{{\text{O}}_{\text{4}}}\) is formed

III.     The ratio of \(\frac{{{\text{[N}}{{\text{O}}_{\text{2}}}{\text{]}}}}{{{\text{[}}{{\text{N}}_{\text{2}}}{{\text{O}}_{\text{4}}}{\text{]}}}}\) decreases

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

C

What effect will an increase in temperature have on the \({K_{\text{c}}}\) value and the position of equilibrium in the following reaction?

\[\begin{array}{*{20}{l}} {{{\text{N}}_{\text{2}}}{\text{(g)}} + {\text{3}}{{\text{H}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2N}}{{\text{H}}_{\text{3}}}{\text{(g)}}}&{\Delta H = - 92{\text{ kJ}}} \end{array}\]

B

The difficulty index for this question was 58%, with incorrect responses distributed quite evenly over the distracters. It did however prove to be the best discriminator on the paper with a discrimination index of 0.64.

Which statement is correct when the system is at equilibrium at 350 °C?

A.     The concentrations of all reactants and products are equal.

B.     The concentrations of the reactants are greater than the concentration of the product.

C.     The reaction, as written, barely proceeds at this temperature.

D.     The reaction, as written, goes almost to completion at this temperature.

D

A comment was made that “barely” in answer C may have been difficult for those working in their second language. We acknowledge this, and will avoid its use.

What is the equilibrium constant expression, \({K_{\text{c}}}\), for the following reaction?

\[{\text{2}}{{\text{H}}_2}{\text{S(g)}} \rightleftharpoons {\text{2}}{{\text{H}}_2}{\text{(g)}} + {{\text{S}}_2}{\text{(g)}}\]

A.     \({K_{\text{c}}} = \frac{{{{{\text{[}}{{\text{H}}_2}{\text{S]}}}^2}}}{{{{{\text{[}}{{\text{H}}_2}{\text{]}}}^2}{\text{[}}{{\text{S}}_2}{\text{]}}}}\)

B.     \({K_{\text{c}}} = \frac{{{\text{[}}{{\text{H}}_2}][{{\text{S}}_2}{\text{]}}}}{{{\text{[}}{{\text{H}}_2}{\text{S]}}}}\)

C.     \({K_{\text{c}}} = \frac{{{\text{2[}}{{\text{H}}_2}{\text{]}} + {\text{[}}{{\text{S}}_2}{\text{]}}}}{{{\text{2[}}{{\text{H}}_2}{\text{S]}}}}\)

D.     \({K_{\text{c}}} = \frac{{{{{\text{[}}{{\text{H}}_2}{\text{]}}}^2}{\text{[}}{{\text{S}}_2}{\text{]}}}}{{{{{\text{[}}{{\text{H}}_2}{\text{S]}}}^2}}}\)

D

Consider the following reaction:

\({\text{2A}} \rightleftharpoons {\text{C}}\)     \({K_{\text{c}}} = 1.1\)

Which statement is correct when the reaction is at equilibrium?

A.     \({\text{[A]}} \gg {\text{[C]}}\)

B.     \({\text{[A]}} > {\text{[C]}}\)

C.     \({\text{[A]}} = {\text{[C]}}\)

D.     \({\text{[A]}} < {\text{[C]}}\)

D

One respondent felt that this question required too much mathematical analysis. 61.21% of the candidates, however, gave the correct answer. It is not too much of a step from [C] / \({{\text{[A]}}^{\text{2}}} = 1.1\) (Assessment statement 7.2.1) to realizing that [C] must be larger than [A] – and then there is only one possible answer.

Which is always correct for a reaction at equilibrium?

B

The value of the equilibrium constant, \({K_{\text{c}}}\), for a reaction is \({\text{1.0}} \times {\text{1}}{{\text{0}}^{ - 10}}\). Which statement about the extent of the reaction is correct?

A.     The reaction hardly proceeds.

B.     The reaction goes almost to completion.

C.     The products have a higher concentration than the reactants.

D.     The concentrations of reactants and products are the same.

A

What happens to the position of equilibrium and the value of \({K_{\text{c}}}\) in the following reaction when the temperature is decreased?

\({{\text{N}}_2}{{\text{O}}_4}{\text{(g)}} \rightleftharpoons {\text{2N}}{{\text{O}}_2}{\text{(g)}}\)     \(\Delta {H^\Theta } =  + 57.2{\text{ kJ}}\)

A

What will happen if the pressure is increased in the following reaction mixture at equilibrium?

CO₂ (g) + H₂O (l) \( \rightleftharpoons \) H⁺ (aq) + HCO₃⁻ (aq)

A. The equilibrium will shift to the right and pH will decrease.

B. The equilibrium will shift to the right and pH will increase.

C. The equilibrium will shift to the left and pH will increase.

D. The equilibrium will shift to the left and pH will decrease.

A

The reaction below represents the Haber process for the industrial production of ammonia.

\[\begin{array}{*{20}{l}} {{{\text{N}}_2}{\text{(g)}} + 3{{\text{H}}_2}{\text{(g)}} \rightleftharpoons {\text{2N}}{{\text{H}}_3}({\text{g)}}}&{\Delta {H^\Theta } = - 92{\text{ kJ}}} \end{array}\]

The optimum conditions of temperature and pressure are chosen as a compromise between those that favour a high yield of ammonia and those that favour a fast rate of production. Economic considerations are also important.

Which statement is correct?

A.     A higher temperature would ensure higher yield and a faster rate.

B.     A lower pressure would ensure a higher yield at a lower cost.

C.     A lower temperature would ensure a higher yield and a faster rate.

D.     A higher pressure would ensure a higher yield at a higher cost.

D

Which changes occur when the temperature is decreased in the following equilibrium?

\({\text{2BrCl(g)}} \rightleftharpoons {\text{B}}{{\text{r}}_2}{\text{(g)}} + {\text{C}}{{\text{l}}_2}{\text{(g)}}\)\(\,\,\,\,\,\)\(\Delta {H^\Theta } =  - 14{\text{ kJ}}\)

B

Which change will favour the reverse reaction in the equilibrium?

\[{\text{2CrO}}_{\text{4}}^{2 - }{\text{(aq)}} + {\text{2}}{{\text{H}}^ + }{\text{(aq)}} \rightleftharpoons {\text{C}}{{\text{r}}_{\text{2}}}{\text{O}}_{\text{7}}^{2 - }{\text{(aq)}} + {{\text{H}}_{\text{2}}}{\text{O(l)}}\;\;\;\;\;\Delta H =  - {\text{42 kJ}}\]

A.     Adding \({\text{O}}{{\text{H}}^ - }{\text{(aq)}}\)

B.     Adding \({{\text{H}}^ + }{\text{(aq)}}\)

C.     Increasing the concentration of \({\text{CrO}}_{\text{4}}^{2 - }{\text{(aq)}}\)

D.     Decreasing the temperature of the solution

A

Consider the following equilibrium reaction.

\[\begin{array}{*{20}{l}} {{\text{2S}}{{\text{O}}_{\text{2}}}{\text{(g)}} + {{\text{O}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2S}}{{\text{O}}_{\text{3}}}{\text{(g)}}}&{\Delta {H^\Theta } = - 197{\text{ kJ}}} \end{array}\]

Which change in conditions will increase the amount of \({{\text{S}}{{\text{O}}_{\text{3}}}}\) present when equilibrium is re-established?

A.     Decreasing the concentration of \({{\text{S}}{{\text{O}}_{\text{2}}}}\)

B.     Increasing the volume

C.     Decreasing the temperature

D.     Adding a catalyst

C

The following are \({K_{\text{c}}}\) values for a reaction, with the same starting conditions carried out at different temperatures. Which equilibrium mixture has the highest concentration of products?

A.     \(1 \times {10^{ - 2}}\)

B.     1

C.     \(1 \times {10^1}\)

D.     \(1 \times {10^2}\)

D

What is the equilibrium constant expression, \({K_{\text{c}}}\), for the following reaction?

\[{\text{2NOBr(g)}} \rightleftharpoons {\text{2NO(g)}} + {\text{B}}{{\text{r}}_{\text{2}}}{\text{(g)}}\]

A.     \({K_{\text{c}}} = \frac{{{\text{[NO][B}}{{\text{r}}_{\text{2}}}{\text{]}}}}{{{\text{[NOBr]}}}}\)

B.     \({K_{\text{c}}} = \frac{{{{{\text{[NO]}}}^{\text{2}}}{\text{[B}}{{\text{r}}_{\text{2}}}{\text{]}}}}{{{{{\text{[NOBr]}}}^{\text{2}}}}}\)

C.     \({K_{\text{c}}} = \frac{{{\text{2[NO]}} + {\text{[B}}{{\text{r}}_{\text{2}}}{\text{]}}}}{{{\text{[2NOBr]}}}}\)

D.     \({K_{\text{c}}} = \frac{{{{{\text{[NOBr]}}}^{\text{2}}}}}{{{{{\text{[NO]}}}^{\text{2}}}{\text{[B}}{{\text{r}}_{\text{2}}}{\text{]}}}}\)

B

An increase in temperature increases the amount of chlorine present in the following equilibrium.

\[{\text{PC}}{{\text{l}}_5}({\text{s)}} \rightleftharpoons {\text{PC}}{{\text{l}}_3}({\text{l)}} + {\text{C}}{{\text{l}}_2}({\text{g)}}\]

What is the best explanation for this?

A.     The higher temperature increases the rate of the forward reaction only.

B.     The higher temperature increases the rate of the reverse reaction only.

C.     The higher temperature increases the rate of both reactions but the forward reaction is affected more than the reverse.

D.     The higher temperature increases the rate of both reactions but the reverse reaction is affected more than the forward.

C

What is the equilibrium constant expression for the reaction below?

\({\text{2N}}{{\text{O}}_2}{\text{(g)}} \rightleftharpoons {{\text{N}}_2}{{\text{O}}_4}{\text{(g)}}\)

A.     \({K_{\text{c}}} = \frac{{{{[{\text{N}}{{\text{O}}_2}]}^2}}}{{[{{\text{N}}_2}{{\text{O}}_4}]}}\)

B.     \({K_{\text{c}}} = \frac{{[{{\text{N}}_2}{{\text{O}}_4}]}}{{[{\text{N}}{{\text{O}}_2}]}}\)

C.     \({K_{\text{c}}} = \frac{{[{{\text{N}}_2}{{\text{O}}_4}]}}{{2[{\text{N}}{{\text{O}}_2}]}}\)

D.     \({K_{\text{c}}} = \frac{{[{{\text{N}}_2}{{\text{O}}_4}]}}{{{{[{\text{N}}{{\text{O}}_2}]}^2}}}\)

D

Which equilibrium reaction shifts to the product side when the temperature is increased at constant pressure and to the reactant side when the total pressure is increased at constant temperature?

A.     \({{\text{N}}_{\text{2}}}{\text{(g)}} + {\text{3}}{{\text{H}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2N}}{{\text{H}}_{\text{3}}}{\text{(g)}}\)     \(\Delta {H^\Theta } < 0\)

B.     \({{\text{N}}_{\text{2}}}{{\text{O}}_{\text{4}}}{\text{(g)}} \rightleftharpoons {\text{2N}}{{\text{O}}_{\text{2}}}{\text{(g)}}\)     \(\Delta {H^\Theta } > 0\)

C.     \({{\text{H}}_{\text{2}}}{\text{(g)}} + {{\text{I}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2HI(g)}}\)     \(\Delta {H^\Theta } < 0\)

D.     \({\text{PC}}{{\text{l}}_{\text{3}}}{\text{(g)}} + {\text{C}}{{\text{l}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{PC}}{{\text{l}}_{\text{5}}}{\text{(g)}}\)     \(\Delta {H^\Theta } > 0\)

B

For the following reaction \({K_{\text{c}}} = 1.0 \times {10^{ - 5}}\) at 30 °C.

\[{\text{2NOCl(g)}} \rightleftharpoons {\text{2NO(g)}} + {\text{C}}{{\text{l}}_2}{\text{(g)}}\]

Which relationship is correct at equilibrium at this temperature?

A.     The concentration of NO equals the concentration of NOCl.

B.     The concentration of NOCl is double the concentration of \({\text{C}}{{\text{l}}_{\text{2}}}\).

C.     The concentration of NOCl is much greater than the concentration of \({\text{C}}{{\text{l}}_{\text{2}}}\).

D.     The concentration of NO is much greater than the concentration of NOCl.

C

There were two G2 comments on this question, both stating that the question was demanding. The question was answered correctly by 54.51% of candidates.

What is the equilibrium constant expression, \({K_{\text{c}}}\), for this reaction?

\[{\text{2NO(g)}} + {{\text{H}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {{\text{N}}_{\text{2}}}{\text{O(g)}} + {{\text{H}}_{\text{2}}}{\text{O(g)}}\]

A.     \({K_{\text{c}}} = \frac{{{\text{[}}{{\text{N}}_2}{\text{O]}} + {\text{[}}{{\text{H}}_2}{\text{O]}}}}{{{\text{2[NO]}} + {\text{[}}{{\text{H}}_2}{\text{]}}}}\)

B.     \({K_{\text{c}}} = \frac{{{{{\text{[NO]}}}^2}{\text{[}}{{\text{H}}_2}{\text{]}}}}{{{\text{[}}{{\text{N}}_2}{\text{O][}}{{\text{H}}_2}{\text{O]}}}}\)

C.     \({K_{\text{c}}} = \frac{{{\text{[2NO]}} + {\text{[}}{{\text{H}}_2}{\text{]}}}}{{{\text{[}}{{\text{N}}_2}{\text{O]}} + {\text{[}}{{\text{H}}_2}{\text{O]}}}}\)

D.     \({K_{\text{c}}} = \frac{{{\text{[}}{{\text{N}}_2}{\text{O][}}{{\text{H}}_2}{\text{O]}}}}{{{{{\text{[NO]}}}^2}{\text{[}}{{\text{H}}_2}{\text{]}}}}\)

D

Which are characteristics of a dynamic equilibrium?

I.     Amounts of products and reactants are constant.

II.     Amounts of products and reactants are equal.

III.     The rate of the forward reaction is equal to the rate of the backward reaction.

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

B

What is the equilibrium constant expression, \({K_{\text{c}}}\), for the formation of hydrogen iodide from its elements?

\[{{\text{H}}_{\text{2}}}{\text{(g)}} + {{\text{I}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2HI(g)}}\]

A.     \({K_{\text{c}}} = \frac{{{{{\text{[HI]}}}^2}}}{{{\text{[}}{{\text{H}}_2}{\text{]}} \times {\text{[}}{{\text{I}}_2}{\text{]}}}}\)

B.     \({K_{\text{c}}} = \frac{{{\text{[2HI]}}}}{{{\text{[}}{{\text{H}}_2}{\text{]}} + {\text{[}}{{\text{I}}_2}{\text{]}}}}\)

C.     \({K_{\text{c}}} = \frac{{2{{{\text{[HI]}}}^2}}}{{{\text{[}}{{\text{H}}_2}{\text{]}} + {\text{[}}{{\text{I}}_2}{\text{]}}}}\)

D.     \({K_{\text{c}}} = \frac{{{\text{[2HI]}}}}{{{\text{[}}{{\text{H}}_2}{\text{]}} \times {\text{[}}{{\text{I}}_2}{\text{]}}}}\)

A

\({K_{\text{c}}}\) expressions often leave much to be desired so it was encouraging to see that this was the easiest question on the paper with 93% of answers correct.

Consider this reaction at equilibrium.

     \({{\text{H}}_2}{\text{S(aq)}} + {\text{Z}}{{\text{n}}^{2 + }}{\text{(aq)}} \rightleftharpoons {\text{ZnS(s)}} + {\text{2}}{{\text{H}}^ + }{\text{(aq)}}\)     \(\Delta H < 0\)

Which change shifts the equilibrium position to the right?

A.     Adding sodium hydroxide

B.     Decreasing pressure

C.     Adding a catalyst

D.     Increasing temperature

A

Which combination of temperature and pressure will give the greatest yield of sulfur trioxide?

     \({\text{2S}}{{\text{O}}_{\text{2}}}{\text{(g)}} + {{\text{O}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2S}}{{\text{O}}_{\text{3}}}{\text{(g)}}\)     \(\Delta H =  - 196{\text{ kJ}}\)

B

Which statement describes and explains the conditions that favour the formation of hydrogen iodide?

A.     Increased temperature as the forward reaction is exothermic, and increased pressure as there are two gaseous reactants and only one gaseous product

B.     Increased temperature as the forward reaction is endothermic, and pressure has no effect as there are equal amounts, in mol, of gaseous reactants and products

C.     Decreased temperature as the forward reaction is exothermic, and decreased pressure as there are two moles of gaseous product but only one mole of each gaseous reactant

D.     Decreased temperature as the forward reaction is exothermic, and pressure has no effect as there are equal amounts, in mol, of gaseous reactants and products

D

The formation of nitric acid, \({\text{HN}}{{\text{O}}_{\text{3}}}{\text{(aq)}}\), from nitrogen dioxide, \({\text{N}}{{\text{O}}_{\text{2}}}{\text{(g)}}\), is exothermic and is a reversible reaction.

\[{\text{4N}}{{\text{O}}_{\text{2}}}{\text{(g)}} + {{\text{O}}_{\text{2}}}{\text{(g)}} + {\text{2}}{{\text{H}}_{\text{2}}}{\text{O(l)}} \rightleftharpoons {\text{4HN}}{{\text{O}}_{\text{3}}}{\text{(aq)}}\]

What is the effect of a catalyst on this reaction?

A.     It increases the yield of nitric acid.

B.     It increases the rate of the forward reaction only.

C.     It increases the equilibrium constant.

D.     It has no effect on the equilibrium position.

D

Which statement correctly describes the effect of a catalyst on the equilibrium below?

\[{{\text{N}}_{\text{2}}}{\text{(g)}} + {\text{3}}{{\text{H}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2N}}{{\text{H}}_{\text{3}}}{\text{(g)}}\]

A.     It increases the rates of both forward and reverse reactions equally.

B.     It increases the rate of the forward reaction but decreases the rate of the reverse reaction.

C.     It increases the value of the equilibrium constant.

D.     It increases the yield of \({\text{N}}{{\text{H}}_{\text{3}}}\).

A

What will happen when at a constant temperature, more iodide ions, \({{\text{I}}^ - }\), are added to the equilibrium below?

\[{{\text{I}}_{\text{2}}}{\text{(s)}} + {{\text{I}}^ - }{\text{(aq)}} \rightleftharpoons {\text{I}}_3^ - {\text{(aq)}}\]

A.     The amount of solid iodine decreases and the equilibrium constant increases.

B.     The amount of solid iodine decreases and the equilibrium constant remains unchanged.

C.     The amount of solid iodine increases and the equilibrium constant decreases.

D.     The amount of solid iodine increases and the equilibrium constant remains unchanged.

B

One G2 comment stated that the SL syllabus only requires students to consider Kc from the equation for a homogeneous reaction as outlined in AS 7.2.1. The respondent stated that the equilibrium as written involves two phases, (s) and (aq), and hence this would have confused candidates. 52% of candidates however did get the question correct and the question proved to be a reasonably good discriminator also, with a discrimination index of 0.45.

What happens when the temperature of the following equilibrium system is increased? 

CO(g) + 2H₂(g)  CH₃OH(g)         ΔH^θ = -91kJ

A

Consider the endothermic reaction below.

\[{\text{5CO(g)}} + {{\text{I}}_2}{{\text{O}}_5}{\text{(g)}} \rightleftharpoons {\text{5C}}{{\text{O}}_2}{\text{(g)}} + {{\text{I}}_2}{\text{(g)}}\]

According to Le Chatelier’s principle, which change would result in an increase in the amount of \({\text{C}}{{\text{O}}_2}\)?

A.     Increasing the temperature

B.     Decreasing the temperature

C.     Increasing the pressure

D.     Decreasing the pressure

A

Carbon monoxide and water react together in the industrial production of hydrogen gas.

\[{\text{CO(g)}} + {{\text{H}}_{\text{2}}}{\text{O(g)}} \rightleftharpoons {\text{C}}{{\text{O}}_{\text{2}}}{\text{(g)}} + {{\text{H}}_{\text{2}}}{\text{(g)}}\]

What is the impact of decreasing the volume of the equilibrium mixture at a constant temperature?

A.     The amount of \({{\text{H}}_{\text{2}}}{\text{(g)}}\) remains the same but its concentration decreases.

B.     The forward reaction is favoured.

C.     The reverse reaction is favoured.

D.     The value of \({K_{\text{c}}}\) remains unchanged.

D

What is the equilibrium constant expression, \({K_{\text{c}}}\), for the following reaction?

\[{{\text{N}}_{\text{2}}}{{\text{O}}_{\text{4}}}{\text{(g)}} \rightleftharpoons {\text{2N}}{{\text{O}}_{\text{2}}}{\text{(g)}}\]

A.     \({K_{\text{c}}} = \frac{{[{\text{N}}{{\text{O}}_2}]}}{{[{{\text{N}}_2}{{\text{O}}_4}]}}\)

B.    \({K_{\text{c}}} = \frac{{{{[{\text{N}}{{\text{O}}_2}]}^2}}}{{[{{\text{N}}_2}{{\text{O}}_4}]}}\)

C.    \({K_{\text{c}}} = \frac{{[{\text{N}}{{\text{O}}_2}]}}{{{{[{{\text{N}}_2}{{\text{O}}_4}]}^2}}}\)

D.    \({K_{\text{c}}} = [{\text{N}}{{\text{O}}_2}]{[{{\text{N}}_2}{{\text{O}}_4}]^2}\)

B

A