This question is about the rate of reaction between calcium carbonate and dilute hydrochloric acid - Edexcel - GCSE Chemistry Combined Science - Question 4 - 2021 - Paper 1

To complete the diagram, it should include:

• A delivery tube with a bung connected to the flask.
• The other end of the delivery tube should lead to a gas syringe or be submerged in water within an upturned measuring cylinder to collect the gas produced.

A water bath set to 45 °C could be used to maintain the temperature of the conical flask and its contents during the reaction.

To calculate the rate of reaction, first draw a tangent line at 100 seconds on the graph from Figure 6. Measure the rise (change in volume) and run (change in time) of this tangent:

• Rise: Increase in volume of gas.
• Run: 100 seconds (time).

The rate can be calculated as: $ext{Rate} = \frac{ ext{Rise}}{ ext{Run}}$ Ensure to express the result in appropriate units (e.g., cm³/s).

One other variable that needs to be controlled is the concentration of the hydrochloric acid used in the reaction.

Decreasing the temperature results in lower kinetic energy of the particles involved in the reaction. This leads to a slower movement of particles, which reduces the frequency of collisions between reactant particles. Consequently, fewer collisions occur with sufficient energy to overcome the activation energy barrier, thereby decreasing the rate of reaction.