A student investigates the temperature change in an exothermic reaction - OCR Gateway - GCSE Chemistry Combined Science - Question 12 - 2020 - Paper 1

The temperature shown on the thermometer is 20 °C.

To prove that the reaction is exothermic, the student should measure the temperature of the solution before and after adding the magnesium powder. If the temperature increases after the reaction, it indicates that the reaction releases heat.

The student would obtain an increase in temperature, confirming that the reaction is exothermic.

The reason could be that some heat escaped from the top of the polystyrene cup, which would lead to less heat being retained in the mixture, thus resulting in a smaller temperature change.

The reaction profile shows that the energy of the products is lower than the energy of the reactants. This indicates that energy is released during the reaction, characteristic of exothermic reactions.

Activation energy is the minimum amount of energy required for reactants to collide successfully and undergo a chemical reaction. It is represented as Eₐ on the reaction profile.