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WAEC WASSCE Chemistry 2021 past questions and answers

This 2021 WAEC WASSCE Chemistry set has 40 practice questions. Try these 5 free sample questions, tap a question to reveal the answer and explanation. Then practise the whole 2021 set with instant marking.

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Sample WAEC WASSCE Chemistry 2021 questions

1. Which change will increase the rate of a reaction without changing the overall chemical equation?
  1. Removing the catalyst
  2. Adding a suitable catalyst
  3. Reducing the temperature
  4. Using larger pieces of a solid reactant

Answer: B. Adding a suitable catalyst

A suitable catalyst provides an alternative pathway with lower activation energy and increases the reaction rate.

2. A reaction causes the mass of a flask and its contents to decrease by 2.4 g in 60 s as a gas escapes; what is the average rate of mass loss?
  1. 0.04 g s-1
  2. 0.25 g s-1
  3. 2.5 g s-1
  4. 144 g s-1

Answer: A. 0.04 g s-1

The average rate is 2.4 g divided by 60 s, which equals 0.04 g s-1.

3. In a sealed vessel at dynamic equilibrium, what is true of the forward and reverse reactions?
  1. Both reactions have stopped
  2. The forward reaction is faster
  3. The forward and reverse reaction rates are equal
  4. The concentrations of reactants and products are equal

Answer: C. The forward and reverse reaction rates are equal

At dynamic equilibrium the forward and reverse reactions continue at equal rates, so concentrations remain constant.

4. For the exothermic equilibrium N2(g) + 3H2(g) ⇌ 2NH3(g), what happens when the temperature is increased at constant pressure?
  1. The equilibrium shifts to the right and more ammonia forms
  2. The equilibrium position does not change
  3. The equilibrium shifts to the right because heat is a catalyst
  4. The equilibrium shifts to the left and less ammonia forms

Answer: D. The equilibrium shifts to the left and less ammonia forms

Increasing temperature favours the endothermic reverse reaction, shifting this exothermic equilibrium to the left.

5. What is the effect of adding a catalyst to a reversible reaction that has already reached equilibrium?
  1. It does not change the equilibrium composition
  2. It increases the yield of products only
  3. It decreases the yield of products only
  4. It permanently stops the reverse reaction

Answer: A. It does not change the equilibrium composition

A catalyst speeds up both directions equally and does not alter the equilibrium position or composition.

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