Edexcel IGCSE Chemistry reversible reactions and equilibria

Practise reversible-reaction questions by interpreting ⇌, defining dynamic equilibrium and predicting yield changes from conditions.

Exam points

State that ⇌ means a reversible reaction where the reaction can go both ways.
Define dynamic equilibrium using equal forward and reverse rates and constant concentrations.
Predict yield changes from temperature, pressure or catalyst changes in equilibria.

Covered syllabus points

3.17 Reversible-reaction symbol 3.18 Examples of reversible reactions 3.19C Dynamic equilibrium in a sealed container 3.20C Characteristics of dynamic equilibrium 3.21C Catalysts and equilibrium position 3.22C Temperature, pressure and equilibrium position

[Maximum number: 2]

(a)

Methanoic acid also reacts with propanol to form an ester.

The equation for the reaction is

\mathrm{HCOOH}+\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH} \rightleftharpoons \mathrm{HCOOC}_{3} \mathrm{H}_{7}+\mathrm{H}_{2} \mathrm{O}

[ 2 ]

(i)

State what is meant by the ⇌ symbol.

[ 1 ]

(ii)

When this reaction occurs in a sealed container, the reaction can reach dynamic equilibrium.

Give one characteristic of a reaction at dynamic equilibrium.

[ 1 ]

[Maximum number: 4]

Gaseous ethanol is manufactured by reacting ethene gas with steam.

This is the equation for the reaction.

(a)

The pressure on an equilibrium mixture of the three gases is decreased. All the other conditions are kept the same.

Predict the effect of this change on the yield of ethanol at equilibrium, giving a reason for your answer.

[ 2 ]

(b)

Predict the effect of adding a catalyst on the yield of ethanol at equilibrium, giving a reason for your answer.

[ 2 ]

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Covered syllabus points

(c) Reversible reactions and equilibria question 1

Question (a)

Question (i)

Question (ii)

(c) Reversible reactions and equilibria question 2

Question (a)

Question (b)