AS LEVEL CHEMISTRY

2.3.2 RATES AND EQUILIBRIUM

TEST

Answer all questions
Max 50 marks

	
Name		……………………………………………………………..

Mark		……../50	……....%	Grade ………

1.	A group of students investigated the effect of concentration on the rate of a reaction. They used the reaction between magnesium carbonate and dilute hydrochloric acid and measured the rate at which the gas was collected.
(a)		An incomplete equation for this reaction is given below. Complete the equation by balancing it and inserting state symbols.
....MgCO3(.....) + ....HCl(.....)  ....MgCl2(.....) + ....CO2(.....) + ....H2O(.....)
[2]
(b)	The students added dilute hydrochloric acid to some magnesium carbonate. The students collected the gas and measured the volume, at regular intervals, until after the reaction was complete. They then plotted a graph of their results.

 	Use collision theory to explain the changes in the rate of the reaction as it proceeds.
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[3]
 [Total 5 marks]

2.	The diagram below shows the energy distribution of molecules at a particular temperature. Ea represents the activation energy of the reaction.

(i)	On the diagram, draw a second curve to represent the energy distribution of the same number of molecules at a higher temperature.
[2]
(ii)	Using your completed diagram, explain how an increase in temperature causes the rate of reaction to increase.
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[2]
[Total 4 marks]

3.	What is a catalyst?
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[Total 2 marks]

4.	In this question, one mark is available for the quality of written communication.
	What effect does a catalyst have on the rate of a reaction, and how does it achieve this effect?
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[4]
Quality of Written Communication [1]
[Total 5 marks]

5.	State two characteristics of a dynamic equilibrium.
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[Total 2 marks]

6.	Nitrogen dioxide, NO2, and dinitrogen tetroxide, N2O4, take part in the following equilibrium.
2NO2(g)  N2O4(g)	ΔH = –58 kJ mol–1
(a)	State le Chatelier’s principle.
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[2]
(b)	Describe, and explain, what would happen to the position of the NO2/N2O4 equilibrium if the following changes are made.
(i)	The temperature is increased.
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[2]
(ii)	The pressure is increased.
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[2]
(iii)	A catalyst is added.
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[2]
[Total 8 marks]

7.	A mixture of N2 and H2 was left until it had reached equilibrium as shown below.
	N2(g) + 3H2(g)  2NH3(g)	DH = − 92 kJ mol–1
	At that stage, N2, H2 and NH3 were present in the equilibrium mixture.
Explain how the following changes would affect the amounts of N2, H2 and NH3 present in the equilibrium mixture.
(i)	use of a catalyst
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[1]
(ii)	a higher temperature
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[2]
(iii)	a lower pressure
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[2]
[Total 5 marks]

8.	Methanol can be used as a fuel or as the feedstock for a variety of organic compounds. It is manufactured from carbon monoxide and hydrogen.
CO(g) + 2H2(g)  CH3OH(g)	DH = –129 kJ mol–1
(i)	Describe and explain how the composition of the equilibrium mixture is affected by increasing the temperature
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increasing the pressure in the reaction.
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[4]
(ii)	Describe and explain the effect of increasing the pressure on the rate of reaction.
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[2]
(iii)	The reaction is carried out by passing gaseous reactants over a transition metal catalyst.
	Suggest and explain the effect of a catalyst on the equilibrium position.
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[2]
[Total 8 marks]

9.	Ammonia, NH3, is made industrially by the Haber process. This is an equilibrium reaction.
N2(g) + 3H2(g)  2NH3(g) DH = –92 kJ mol–1
(a)	State the pressure and temperature that are used in the Haber process.
pressure ..........................................................................................................
temperature .....................................................................................................
[2]
(b)	Describe and explain why these conditions are a compromise between rate and equilibrium.
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[9]
[Total 11 marks]