CIE IGCSE Chemistry

Topic Questions

IGCSEChemistryCIETopic Questions6. Chemical Reactions6.2 Reversible Reactions & Equilibrium

6.2 Reversible Reactions & Equilibrium

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11 mark

Water and a white solid are produced when blue copper(II) sulfate is heated. On the addition of water to the white solid, heat is released and the white solid turns blue.

Which row correctly describes the reaction and the blue copper(II) sulfate?

  type of reaction blue copper(II) sulfate
A non-reversible anhydrous
B reversible anhydrous
C non-reversible hydrated
D reversible hydrated

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21 mark

Steam and a blue solid are produced when pink cobalt(II) chloride crystals are heated. With the addition of water to the blue solid, heat is released and the blue solid turns pink.

Which row correctly describes the reaction and the pink cobalt(II) chloride crystals?

  type of reaction pink cobalt(II) chloride
A non-reversible hydrated
B reversible hydrated
C non-reversible anhydrous
D reversible anhydrous

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31 mark

Which of the following reactions cannot be reversed?

  • Melting ice

  • Thermal decomposition of hydrated cobalt(II) chloride

  • Combustion of propane

  • Hydration of anhydrous copper(II) sulfate

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41 mark

Reversible reactions occur when products formed in the forward reaction behave as reactants and proceed in the reverse direction to produce the original reactants again.

Which of the following statements is correct for a reversible reaction?

1 If the forward reaction is exothermic, then the reverse reaction must be endothermic
2 If the forward reaction is endothermic, then the reverse reaction must be exothermic
3 Both directions are exothermic
4 Both directions are endothermic

  • 1 and 2

  • 3 and 4

  • 1 only

  • 3 only

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51 mark

Which row correctly describes the conditions used in the Haber process?

  temperature / degree straight C pressure / atm catalyst
A 400 300 vanadium(V) oxide
B 450 200 iron
C 200 300 vanadium(V) oxide
D 300 200 iron

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61 mark

Nitrogen and hydrogen are the raw ingredients used in the production of ammonia, NH3.

Which row correctly describes the source of these reactants and the catalyst used?

  nitrogen hydrogen catalyst
A air methane vanadium pentoxide
B methane water finely divided iron
C methane water vanadium pentoxide
D air methane finely divided iron

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11 mark

The reaction for the production of ammonia is shown below.

N2(g) + 3H2(g) rightwards harpoon over leftwards harpoon 2NH3(g)

What is the effect of increasing pressure on the rate of production of ammonia and the percentage yield of ammonia?

  rate of production percentage yield
A increases decreases
B increases increases
C decreases increases
D decreases decreases

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21 mark

The production of sulfur trioxide during Stage 2 of the Contact process involves a reversible reaction. Which row describes the conditions of temperature and pressure and the percentage yield of sulfur trioxide?

  temperature / degree straight C pressure / atm percentage yield
A 150 1 - 2 70
B 450 1 - 2 98
C 450 200 98
D 150 200 70

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31 mark

Carbon monoxide and steam react together exothermically to produce the alcohol methanol, as shown in the equation.

CO(g) + 2H2(g) ⇌ CH3OH(g)

Both reactants and the product are gaseous. Which conditions of pressure and temperature would provide the highest yield of CH3OH?

  pressure temperature
A low low
B low high
C high low
D high high

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41 mark

The reversible reaction between nitrogen dioxide and dinitrogen tetroxide is shown.

2NO2(g) ⇌ N2O4(g)                   ΔH = -58 kJ / mol

Which of the following statements about the equilibrium mixture in this reaction is correct?

  • If the pressure is decreased the amount of N2O4 formed increases.

  • If the pressure is increased the amount of NO2 formed increases.

  • The decomposition of N2O4 is exothermic.

  • The decomposition of N2O4 is endothermic.

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51 mark

A part of the contact process involves the production of sulfur trioxide from the reversible reaction of sulfur dioxide and oxygen, as shown below.

2SO2(g) + O2(g) ⇌ 2SO3(g)              ΔH = -197 kJ / mol

Which of the following changes would increase the yield of SO3 at equilibrium?

1 Decreasing the temperature
2 Increasing the pressure
3 Decreasing the concentration of O2

  • 1 and 2

  • 1 and 3

  • 2 and 3

  • 1, 2 and 3

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61 mark

Which of the following statements best describes equilibrium position?

  • Equilibrium position refers to the concentration of reactants and products relative to one another at equilibrium.

  • Equilibrium position refers to the physical state of the reactants and products at equilibrium.

  • Equilibrium position refers to the relative reactivity of the reactants and products for a reaction at equilibrium.

  • Equilibrium position refers to the obtainable yield of product for the forward reaction only.

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71 mark

Which of the following statements best describes Le Chatelier’s Principle?

  • When a change is made to a system that is at equilibrium, the equilibrium position favours the endothermic reaction.

  • When a change is made to a system at equilibrium, the equilibrium position moves favours the exothermic reaction.

  • When a change is made to a system at equilibrium, the equilibrium position moves to oppose the change.

  • When a change is made to a system at equilibrium, the equilibrium position remains the same to restore balance to the system.

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81 mark

Which of the following factors affect the position of equilibrium for a reversible reaction?

1 Temperature
2 Surface area of solid reactants
3 Pressure
4 Concentration

  • 1 and 3

  • 1, 2 and 3

  • 2, 3 and 4

  • 1, 3 and 4

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11 mark

Hydrated cobalt(II) chloride undergoes thermal decomposition when heated to produce anhydrous cobalt(II) chloride and water.

CoCl subscript 2 bullet end subscript 6 straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon CoCl subscript 2 space plus space 6 straight H subscript 2 straight O

The addition of water to CoCl2 rehydrates the compound. Which row correctly describes the reverse reaction?

  reaction type colour change
A exothermic blue to pink
B endothermic blue to pink
C exothermic pink to blue
D endothermic pink to blue

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21 mark

Which of the following reactions is reversible?

  • Zn + CuSO4 → ZnSO4 + Cu

  • CuSO4•5H2O → CuSO4 + 5H2O

  • Fe + H2SO4 → FeSO4 + H2

  • KCl + AgNO3 → KNO3 + AgCl

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31 mark

Carbon and steam react together as shown in the equation.

C(s) + H2O(g) ⇌ CO(g) + H2(g)

Both of the products from the forward reaction are gaseous. Which conditions of pressure and temperature would provide the highest yield of H2?

  pressure temperature
A low low
B low high
C high low
D high high

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41 mark

The reaction between nitrogen and hydrogen in the Haber process involves a reversible reaction where an equilibrium is established between the reactants and the products.

Which one of the following statements correctly describes the conditions at equilibrium?

  • Both the forward and the reverse reactions have ended.

  • The concentrations of N2, H2 and NH3 are equal.

  • The concentrations of N2, H2 and NH3 are constant.

  • The rate of the forward reaction is different to the rate of the reverse reaction.

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51 mark

Which of the following statements about the Haber process is not correct?

  • A catalyst is used to increase the rate of the forward reaction.

  • Finely divided catalyst increases the surface area available for reaction.

  • Reacted N2 and H2 are recycled back into the reaction chamber.

  • High pressure is used as there are fewer gaseous moles in the products than in the reactants.

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61 mark

Which of the following statements correctly describes the effect of catalysts on the equilibrium position?

  • Catalysts affect the position of equilibrium but do not affect the rate at which equilibrium is reached.

  • Catalysts do not affect the position of equilibrium but increase the rate at which equilibrium is reached.

  • Catalysts affect the position of equilibrium and increase the rate at which equilibrium is reached.

  • Catalysts do not affect the position of equilibrium but decrease the rate at which equilibrium is reached.

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