This question is about rates of reaction - AQA - GCSE Chemistry - Question 1 - 2017 - Paper 1

The volume of oxygen produced at 25 seconds is approximately 12 cm³, based on the reading taken from the curve in part (i).

The reaction stops after approximately 45 to 50 seconds, where no additional oxygen is recorded.

The graph indicates that the line becomes less steep over time, demonstrating that the production of oxygen gas decreases, suggesting that the reaction slows as reactants are consumed. For example, during the initial 20 seconds, a significant volume of gas is produced, but in the last 20 seconds, the production rate drops significantly, indicating a decrease in the rate of reaction.

The mean rate of reaction can be calculated by taking the total volume of oxygen produced in the first 10 seconds, which is approximately 6 cm³, and dividing it by the time (10 seconds): $\text{Mean rate of reaction} = \frac{6 \text{ cm}^3}{10 \text{ s}} = 0.6 \text{ cm}^3 \text{ per second}$

1. The concentration of hydrogen peroxide should be kept constant; for instance, using the same molarity throughout the experiments.
2. The temperature at which the reaction occurs should also be controlled to ensure consistent reaction conditions.

Increasing the concentration of hydrogen peroxide means there are more particles of reactant present in the same volume. This results in a higher frequency of collisions between reacting particles, thereby increasing the likelihood of effective collisions that lead to reaction. More collisions generally lead to a higher rate of reaction.

Increasing the amount of catalyst results in a steeper graph or causes the graph to level off earlier. This happens because a catalyst provides an alternative pathway for the reaction with a lower activation energy, thereby increasing the rate at which products are formed without affecting the total volume of gas produced.