CAIE IGCSE Chemistry 6.3 Reversible Reactions and Equilibrium Topic Practice

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Covered syllabus points

6.3.1—Some chemical reactions are reversible6.3.2—Changing the conditions can change the6.3.3—Reversible reaction in a closed system6.3.4—Predict and explain, for a reversible6.3.5—Symbol equation for the production of6.3.6—Sources of the hydrogen (methane) and6.3.7—Typical conditions in the Haber6.3.8—Symbol equation for the conversion of6.3.9—Sources of the sulfur dioxide (burning6.3.10—Typical conditions for the conversion6.3.11—Typical Haber and Contact process

Question 1

[Maximum number: 1]

When the colourless gas N2O4\mathrm{N}_{2} \mathrm{O}_{4} is heated, it forms the brown gas NO2\mathrm{NO}_{2}.
When the reaction mixture is cooled, the brown colour fades and turns back to colourless.
Which type of reaction is described by these observations?

A

decomposition

B

displacement

C

reduction

D

reversible

Question 2

[Maximum number: 2]

Complete the equation for the thermal decomposition of hydrated cobalt(II) nitrate.

2Co(NO3)2∙4H2O→….CoO+….NO2+O2+….H2O2 \mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2} \bullet 4 \mathrm{H}_{2} \mathrm{O} \rightarrow \ldots . \mathrm{CoO}+\ldots . \mathrm{NO}_{2}+\mathrm{O}_{2}+\ldots . \mathrm{H}_{2} \mathrm{O}

Question 3

[Maximum number: 6]

Hydrogen iodide thermally decomposes into iodine and hydrogen. The reaction is reversible.

2HI( g) colourless gas →⇌I2( g) purple gas +H2( g) colourless gas \underset{\text { colourless gas }}{2 \mathrm{HI}(\mathrm{~g})} \rightarrow \underset{\substack{\mathrm{I}_{2}(\mathrm{~g}) \\ \text { purple gas }}}{\rightleftharpoons}+\underset{\substack{\mathrm{H}_{2}(\mathrm{~g}) \\ \text { colourless gas }}}{ }

Fig. 4.1 shows a gas syringe containing a mixture of hydrogen iodide, iodine and hydrogen gases. The gas syringe is sealed and the mixture is heated to 300∘C300^{\circ} \mathrm{C}. The mixture of gases reaches equilibrium and is purple.

Fig. 4.1

Fig. 4.1

Question (a)

(a)

State what is meant by the term equilibrium.

[ 2 ]

Question (b)

(b)

The pressure of the mixture is increased. All other conditions stay the same. The position of equilibrium does not change.

The colour of the gaseous mixture turns darker purple.
The temperature remains constant.

2HI( g) colourless gas =⇌I2( g) purple gas + colourless gas H2( g) colourless gas \underset{\text { colourless gas }}{2 \mathrm{HI}(\mathrm{~g})}=\underset{\substack{\mathrm{I}_{2}(\mathrm{~g}) \\ \text { purple gas }}}{\rightleftharpoons}+\underset{\substack{\mathrm{H}_{2}(\mathrm{~g}) \\ \text { colourless gas }}}{\text { colourless gas }}
[ 2 ]

Question (i)

(i)

Explain why the position of equilibrium does not change.

[ 1 ]

Question (ii)

(ii)

Suggest why the colour of the mixture of gases turns darker purple.

[ 1 ]

Question (c)

(c)

The temperature of the mixture of gases is decreased. All other conditions stay the same.

The mixture of gases turns lighter purple.
State what can be deduced about the forward reaction from this information.

[ 1 ]

Question (d)

(d)

Methanol is manufactured by reacting carbon monoxide with hydrogen.

CO( g)+2H2( g)⇌CH3OH( g)\mathrm{CO}(\mathrm{~g})+2 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{CH}_{3} \mathrm{OH}(\mathrm{~g})

The rate of formation of methanol increases when a catalyst is used.

[ 1 ]

Question (i)

(i)

State the effect on the position of equilibrium when a catalyst is used.

[ 1 ]
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