CAIE A-Level Chemistry AS 7.1 Chemical Equilibria and Dynamic Equilibrium Questions

Practise defining dynamic equilibrium and predicting how temperature, concentration, pressure or a catalyst affects a system.

Exam points

state that forward and reverse rates are equal in a closed system while concentrations remain constant
use Le Chatelier’s principle to predict the direction of an equilibrium shift after a condition changes
interpret yield, composition or colour evidence without confusing equilibrium position with reaction rate

Covered syllabus points

7.1.1—What is meant by a reversible reaction 7.1.2—Le Chatelier’s principle as: if a change 7.1.3—Le Chatelier’s principle to deduce (from 7.1.4—Expressions for equilibrium constants 7.1.5—The terms mole fraction and partial pressure 7.1.6—Expressions for equilibrium constants 7.1.7—The Kc and Kp expressions to carry out 7.1.8—The quantities present at equilibrium 7.1.9—Whether changes in temperature, concentration 7.1.10—Conditions used in the Haber process

[Maximum number: 1]

When a sample of ammonium chloride is warmed it decomposes into ammonia and hydrogen chloride gas.

Figure for Question 1 — CAIE A-Level Chemistry AS

When the mixture of hot ammonia and hydrogen chloride gases hit a cold surface, a white solid of ammonium chloride reforms.

Which statements are correct?
1 Reaction 1 is in dynamic equilibrium.
2 Reaction 1 is reversible.
3 Reaction 1 is an endothermic reaction.

1, 2 and 3 are correct

1 and 2 only are correct

2 and 3 only are correct

1 only is correct

[Maximum number: 1]

Graphs can be drawn to show the percentage of ammonia at equilibrium when nitrogen and hydrogen are mixed at different temperatures and pressures.

Which diagram correctly represents these two graphs?

Figure for Question 2 — CAIE A-Level Chemistry AS

[Maximum number: 1]

The units of $K_{\mathrm{c}}$ for an equilibrium reaction are $\mathrm{mol}^{-1} \mathrm{dm}^{3}$ .
What could be the equation for the equilibrium?

1 $\mathrm{~A}(\mathrm{aq})+\mathrm{B}(\mathrm{aq}) \rightleftharpoons \mathrm{C}(\mathrm{s})+\mathrm{D}(\mathrm{aq})$
2 $\mathrm{P}(\mathrm{aq})+\mathrm{Q}(\mathrm{aq}) \rightleftharpoons \mathrm{R}(\mathrm{aq})$
3 $\mathrm{~W}(\mathrm{aq})+2 \mathrm{X}(\mathrm{aq}) \rightleftharpoons \mathrm{Y}(\mathrm{aq})+\mathrm{Z}(\mathrm{aq})$

1, 2 and 3 are correct

1 and 2 only are correct

2 and 3 only are correct

1 only is correct

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Covered syllabus points

Question 1

Question 2

Question 3