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IGCSE · Practice questions · Reversible reactions and equilibrium

Balance in motion.

Six original Cambridge-style questions on reversible reactions and equilibrium: copper(II) sulfate and cobalt(II) chloride, dynamic equilibrium and changing conditions.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Oppose the change.

01
Recall
[3 marks]

Describe what is seen when blue hydrated copper(II) sulfate is heated, and when water is then added to the product. Write the equation, using the reversible symbol.

  • On heating, the blue crystals turn to a white powder (and steam is given off). ✓
  • When water is added, the white powder turns blue again and gets hot. ✓
  • CuSO4·5H2O ⇌ CuSO4 + 5H2O. ✓
02
Recall
[2 marks]

Describe a chemical test for water, giving the result.

  • Add the liquid to anhydrous copper(II) sulfate (or blue cobalt(II) chloride paper). ✓
  • It turns from white to blue (or the cobalt(II) chloride turns from blue to pink). ✓
03
Recall
[3 marks]

(Extended) State three features of a reaction at dynamic equilibrium.

  • The forward and reverse reactions happen at the same rate. ✓
  • The concentrations of reactants and products remain constant. ✓
  • It occurs in a closed system (nothing is added or removed). ✓
04
Analysis
[2 marks]

(Extended) For H2(g) + I2(g) ⇌ 2HI(g), predict the effect of increasing the pressure on the position of equilibrium. Explain your answer.

  • No effect on the position of equilibrium. ✓
  • There are two gas molecules on each side, so neither side is favoured by a change in pressure. ✓
05
Analysis
[3 marks]

(Extended) For CO(g) + 2H2(g) ⇌ CH3OH(g) the forward reaction is exothermic. State and explain the effect on the yield of methanol of (a) increasing the temperature and (b) increasing the pressure.

  • (a) The yield decreases: increasing the temperature moves the equilibrium in the endothermic direction, which is the reverse reaction. ✓
  • (b) The yield increases: there are 3 gas molecules on the left and 1 on the right, ✓
  • so higher pressure moves the equilibrium to the right, the side with fewer gas molecules. ✓
06
Explain
[2 marks]

(Extended) Explain why adding a catalyst to a reaction at equilibrium does not change the amount of product.

  • A catalyst increases the rates of the forward and reverse reactions equally. ✓
  • So the position of equilibrium does not change; equilibrium is only reached more quickly. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.