O-LevelChemistryRates of Reaction5070/21 · May/June 2023 · Q510 Marks
Ammonium chloride decomposes when heated to make hydrogen chloride and ammonia. This reaction is reversible. The forward reaction absorbs thermal energy. NH4Cl(s) ⇌ HCl(g) + NH3(g)
- (a)(i)An equilibrium mixture is formed when the reversible reaction happens in a closed system. State what is meant by the term equilibrium. Include ideas about rate of reaction and the concentrations of the reactant and products in your answer.[2]
- (a)(ii)Predict what happens to the position of equilibrium when the temperature is increased and the pressure remains constant. Explain your answer. prediction explanation[2]
- (a)(iii)Predict what happens to the position of equilibrium when the pressure is increased and the temperature remains constant. Explain your answer. prediction explanation[2]
- (b)Predict what happens to the rate of the backward reaction when the temperature is increased and the pressure remains constant. Explain your answer. prediction explanation[2]
- (c)Predict what happens to the rate of the backward reaction when the pressure is increased and the temperature remains constant. Explain your answer. prediction explanation[2]
Mark scheme
Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.
- 5(a)(i) (a reversible reaction) in which the rate of the forward reaction is the same as the rate of the backward reaction (1) and the concentrations of the reactants and the products do not change / are constant (1)
- 5(a)(ii) (position of equilibrium) moves to the right (1) because the reaction is endothermic / to minimise temperature increase by absorbing energy (1)
- 5(a)(iii) position of equilibrium moves to the left (1) because more moles of gas on product side / fewer moles of gas on reactant side (1)
- 5(b) rate increases because particles move faster / particles have more kinetic energy (1) more successful collisions / more collisions involve particles with equal or more than activation energy (1)
- 5(c) rate increases because more particles per unit volume (1) greater collision frequency (1)
Write your answer and get it marked
On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.
Sign up free →