The student repeated the experiment using 0.20 mol/dm³ sulfuric acid instead of 0.40 mol/dm³ sulfuric acid. Excess zinc was used in each experiment.
Sketch a line on Figure 13 to show the results you would expect.

Changing the concentration of a reactant affects both the rate of the reaction and the total amount of product formed if that reactant is limiting. 1. **Effect on Rate:** The concentration of sulfuric acid has been halved. This means there are fewer acid particles per unit volume. According to collision theory, this will lead to fewer frequent successful collisions between the zinc and acid particles. Therefore, the rate of reaction will be slower. On the graph, a slower rate is represented by a less steep gradient. The new line should start at the origin but be shallower than the original line. 2. **Effect on Total Product:** The zinc is in excess, which means the sulfuric acid is the limiting reactant – it will run out first and stop the reaction. Since the volume of acid used is the same but its concentration is halved, there are half the number of moles of sulfuric acid reacting. According to the stoichiometry of the reaction (Zn + H₂SO₄ → ZnSO₄ + H₂), this will produce half the number of moles of hydrogen gas. The original reaction produced approximately 0.017 moles of H₂. Therefore, the new reaction will produce 0.017 / 2 = 0.0085 moles of H₂. The new line must level off at this value on the y-axis.