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A group of learners uses the reaction between powdered zinc and EXCESS dilute hydrochloric acid to investigate one of the factors that affects the rate of a chemical reaction. The balanced equation for the reaction is:
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
They conduct two experiments. The reaction conditions used are summarised in the table below.
5.1 Define reaction rate. (2)
5.2 Write down an investigative question for this investigation. (2)
5.3 Which curve, P or Q, represents the results of experiment I? Explain the answer. (3)
5.4 The average rate of the production of hydrogen gas, as represented by graph P, was 15 cm3 ∙s-1
Calculate the mass of zinc used. Take the molar gas volume at 25 °C as 24 000 cm3. (5)
5.5 In a third experiment (experiment III), 200 cm3 of a 0,25 mol∙dm-3 dilute hydrochloric acid solution at 35 °C reacts with the same amount of zinc powder as in experiment I and experiment II.
5.5.1 How will the heat of reaction of experiment II compare with that of experiment III? Choose from MORE THAN, LESS THAN or EQUAL TO. (1)
5.5.2 How will the activation energy of the reaction in experiment I compare with that of the reaction in experiment III? Choose from MORE THAN, LESS THAN or EQUAL TO. (1)
5.6 The rate of the reaction in experiment III is higher than that of experiment I. Fully explain this statement by referring to the collision theory. (3)
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