Define the term rate of reaction.

Describe the collision theory.

The Contact process involves this homogeneous equilibrium:

\[{\text{2S}}{{\text{O}}_{\text{2}}}{\text{(g)}} + {{\text{O}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2S}}{{\text{O}}_{\text{3}}}{\text{(g)}}\,\,\,\,\,\Delta H =  - 198{\text{ kJ}}\]

State and explain how increasing the pressure of the reaction mixture affects the yield of \({\text{S}}{{\text{O}}_{\text{3}}}\).

The Contact process involves this homogeneous equilibrium:

\[{\text{2S}}{{\text{O}}_{\text{2}}}{\text{(g)}} + {{\text{O}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2S}}{{\text{O}}_{\text{3}}}{\text{(g)}}\,\,\,\,\,\Delta H =  - 198{\text{ kJ}}\]

2.00 mol of \({\text{S}}{{\text{O}}_{\text{2}}}{\text{(g)}}\) are mixed with 3.00 mol of \({{\text{O}}_{\text{2}}}{\text{(g)}}\) in a \({\text{1.00 d}}{{\text{m}}^{\text{3}}}\) container until equilibrium is reached. At equilibrium there are 0.80 mol of \({\text{S}}{{\text{O}}_{\text{3}}}{\text{(g)}}\).

Determine the equilibrium constant (\({K_{\text{c}}}\)) assuming all gases are at the same temperature and pressure.

The Contact process involves this homogeneous equilibrium:

\[{\text{2S}}{{\text{O}}_{\text{2}}}{\text{(g)}} + {{\text{O}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2S}}{{\text{O}}_{\text{3}}}{\text{(g)}}\,\,\,\,\,\Delta H =  - 198{\text{ kJ}}\]

State the effect of increasing temperature on the value of \({K_{\text{c}}}\) for this reaction.

Outline the economic importance of using a catalyst in the Contact process.

change in concentration of reactant/product with time / rate of change of concentration;

Accept “increase” instead of “change” for product and “decrease” instead of “change” for reactant.

Accept “mass/amount/volume” instead of “concentration”.

Do not accept substance.

collision frequency;

two particles must collide;

particles must have sufficient energy to overcome the activation energy/\(E \geqslant {E_a}\);

Concept of activation energy must be mentioned.

appropriate collision geometry/orientation;

increases yield;

(equilibrium shifts to the right/products as) more gaseous moles in reactants/on left / fewer gaseous moles in products/on right;

\({\text{Eqm[}}{{\text{O}}_2}{\text{]}} = {\text{2.6 (mol}}\,{\text{d}}{{\text{m}}^{ - 3}}{\text{)}}\);

\({\text{Eqm[S}}{{\text{O}}_2}{\text{]}} = {\text{1.2 (mol}}\,{\text{d}}{{\text{m}}^{ - 3}}{\text{)}}\);

\({K_{\text{c}}} = \frac{{{{{\text{[S}}{{\text{O}}_3}]}^2}}}{{{{{\text{[S}}{{\text{O}}_2}{\text{]}}}^2}{\text{[}}{{\text{O}}_2}{\text{]}}}}\);

\({K_{\text{c}}} = 0.17\);

Award [4] for correct final answer.

Ignore units.

\({\text{(}}{K_{\text{c}}}{\text{)}}\) decreases;

catalyst increases rate of reaction / equilibrium reached faster / increases yield of product per unit time;

reduces costs / reduces energy needed;

Do not accept just “increases the yield”.

The definitions of rate of reaction in (a) were poor with many referring to a measure of time rather than a change in concentration. The collision theory was described successfully for the most part with “frequency of collisions” less frequently mentioned. In (c) (i) most realized that the number of moles of gases is important and thus gave a correct answer. Whilst the \({K_{\text{c}}}\) expression was often given correctly in (ii), the calculation of equilibrium mole concentrations was more testing, particularly that for \({\text{[}}{{\text{O}}_{\text{2}}}{\text{]}}\). Many were able to answer (iii) correctly. In part (d) many suggested that it is good to make more of something rather than relating this to a reduction in costs.

The definitions of rate of reaction in (a) were poor with many referring to a measure of time rather than a change in concentration. The collision theory was described successfully for the most part with “frequency of collisions” less frequently mentioned. In (c) (i) most realized that the number of moles of gases is important and thus gave a correct answer. Whilst the \({K_{\text{c}}}\) expression was often given correctly in (ii), the calculation of equilibrium mole concentrations was more testing, particularly that for \({\text{[}}{{\text{O}}_{\text{2}}}{\text{]}}\). Many were able to answer (iii) correctly. In part (d) many suggested that it is good to make more of something rather than relating this to a reduction in costs.

The definitions of rate of reaction in (a) were poor with many referring to a measure of time rather than a change in concentration. The collision theory was described successfully for the most part with “frequency of collisions” less frequently mentioned. In (c) (i) most realized that the number of moles of gases is important and thus gave a correct answer. Whilst the \({K_{\text{c}}}\) expression was often given correctly in (ii), the calculation of equilibrium mole concentrations was more testing, particularly that for \({\text{[}}{{\text{O}}_{\text{2}}}{\text{]}}\). Many were able to answer (iii) correctly. In part (d) many suggested that it is good to make more of something rather than relating this to a reduction in costs.

The definitions of rate of reaction in (a) were poor with many referring to a measure of time rather than a change in concentration. The collision theory was described successfully for the most part with “frequency of collisions” less frequently mentioned. In (c) (i) most realized that the number of moles of gases is important and thus gave a correct answer. Whilst the \({K_{\text{c}}}\) expression was often given correctly in (ii), the calculation of equilibrium mole concentrations was more testing, particularly that for \({\text{[}}{{\text{O}}_{\text{2}}}{\text{]}}\). Many were able to answer (iii) correctly. In part (d) many suggested that it is good to make more of something rather than relating this to a reduction in costs.

The definitions of rate of reaction in (a) were poor with many referring to a measure of time rather than a change in concentration. The collision theory was described successfully for the most part with “frequency of collisions” less frequently mentioned. In (c) (i) most realized that the number of moles of gases is important and thus gave a correct answer. Whilst the \({K_{\text{c}}}\) expression was often given correctly in (ii), the calculation of equilibrium mole concentrations was more testing, particularly that for \({\text{[}}{{\text{O}}_{\text{2}}}{\text{]}}\). Many were able to answer (iii) correctly. In part (d) many suggested that it is good to make more of something rather than relating this to a reduction in costs.

The definitions of rate of reaction in (a) were poor with many referring to a measure of time rather than a change in concentration. The collision theory was described successfully for the most part with “frequency of collisions” less frequently mentioned. In (c) (i) most realized that the number of moles of gases is important and thus gave a correct answer. Whilst the \({K_{\text{c}}}\) expression was often given correctly in (ii), the calculation of equilibrium mole concentrations was more testing, particularly that for \({\text{[}}{{\text{O}}_{\text{2}}}{\text{]}}\). Many were able to answer (iii) correctly. In part (d) many suggested that it is good to make more of something rather than relating this to a reduction in costs.