AQA GCSE Chemistry (8462), Higher tier · The rate and extent of chemical change › Reversible reactions and dynamic equilibrium
Practise Effect of temperature changes. 13 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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The energy change for the forward reaction is +57 kJ/mol. What is the energy change for the reverse reaction?
−57 kJ/mol
What happens to the amounts of nitrogen and oxygen at equilibrium when the temperature is increased?
They decrease.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy3 marks
Nitrogen and oxygen react in a reversible reaction to form nitrogen monoxide: N2(g) + O2(g) ⇌ 2NO(g) The forward reaction is endothermic.
(a) The temperature is increased. What happens to the amount of nitrogen monoxide at equilibrium? Tick (✓) one box.[1]
It decreases.
It increases.
It stays the same.
(b) Give the reason for your answer.[1]
(c) What happens to the amounts of nitrogen and oxygen at equilibrium when the temperature is increased?[1]
Show the answer and mark scheme
(a)Answer: It increases.
(b)Answer: The forward reaction is endothermic, so increasing the temperature favours the forward reaction.
the forward reaction is endothermic, so increasing the temperature shifts the position of equilibrium to the right / favours the (endothermic) forward reaction
(c)Answer: They decrease.
they decrease
Question 2Medium6 marks
Nitrogen dioxide, NO2, is a brown gas. Dinitrogen tetroxide, N2O4, is a colourless gas. They are in equilibrium: N2O4(g) ⇌ 2NO2(g) A sealed tube containing the equilibrium mixture was put into hot water and the mixture became darker brown. The tube was then put into iced water and the mixture became paler.
(a) Is the forward reaction exothermic or endothermic? Explain your answer using the observations.[3]
(b) Explain why the mixture became paler in iced water.[2]
(c) The energy change for the forward reaction is +57 kJ/mol. What is the energy change for the reverse reaction?[1]
Show the answer and mark scheme
(a)Answer: Endothermic: in hot water the mixture became darker, so more NO2 formed; a higher temperature shifts the equilibrium in the endothermic direction.
endothermic
in hot water the mixture became darker brown, so more NO2 formed (the equilibrium shifted to the right)
increasing the temperature shifts the equilibrium in the endothermic direction
(b)Answer: Lowering the temperature shifts the equilibrium in the exothermic direction (to the left), so NO2 turns into colourless N2O4.
decreasing the temperature shifts the equilibrium in the exothermic direction (to the left)
so NO2 is converted into (colourless) N2O4
(c)Answer: −57 kJ/mol
−57 kJ/mol
Question 3Hard3 marks
The forward reaction in the industrial manufacture of an ester from an alcohol and a carboxylic acid is very slightly exothermic.
(a) Explain the effect of increasing the temperature on the equilibrium yield of ester.[2]
(b) Despite this, a moderately high temperature is used industrially. Suggest why.[1]
Show the answer and mark scheme
(a)Answer: The yield decreases slightly: increasing the temperature favours the endothermic (reverse) direction, shifting the equilibrium slightly to the left.
the equilibrium yield decreases (slightly)
increasing the temperature favours the endothermic (reverse) direction, shifting the equilibrium slightly to the left
(b)Answer: A higher temperature gives a much faster rate of reaction, so equilibrium (or a usefully high conversion) is reached in a practical amount of time.
a higher temperature gives a much faster rate of reaction, so a useful amount of ester forms in a reasonable time