A student used the apparatus in Figure 3 to investigate the rate of the reaction between a metal and dilute hydrochloric acid - Edexcel - GCSE Chemistry - Question 2 - 2022 - Paper 1

To calculate the average rate of gas production, we use the formula:

$\text{Average Rate} = \frac{\text{Total Volume of Gas Produced}}{\text{Total Time}}$

The total volume of gas produced at 6 minutes is 60 cm³ and the total time is 6 minutes:

$\text{Rate} = \frac{60 \text{ cm}^3}{6 \text{ min}} = 10 \text{ cm}^3/\text{min}$

After 6 minutes, the rate of gas production decreases, as indicated by the graph in Figure 4, which starts to level off. This suggests that the reaction may be slowing down as the reactants are used up or the conditions for the reaction become less favorable.

The rate of reaction decreases over time because, as the reaction proceeds, the concentration of the reactants decreases. This results in fewer collisions between particles, leading to a slower rate of reaction. Additionally, as the reactants are consumed, the overall energy available for collisions decreases, further contributing to the decline in reaction rate.