Required Practical: Temperature Changes — AQA GCSE Chemistry
This required practical measures the energy changes in reactions by recording temperature changes.
Aim
To investigate the temperature change in chemical reactions and identify them as exothermic (temperature rises) or endothermic (temperature falls). A common version investigates how the volume of one reactant affects the temperature change (e.g. acid + alkali neutralisation).
Method
- Measure a fixed volume of one reactant (e.g. dilute hydrochloric acid) into a polystyrene cup (a good insulator to reduce heat loss), and record the starting temperature.
- Add a measured volume of the other reactant (e.g. sodium hydroxide).
- Stir, and record the highest (or lowest) temperature reached.
- Calculate the temperature change (final − start).
- Repeat with different volumes of the second reactant and plot the results.
Results
- Exothermic reactions (e.g. neutralisation, displacement, combustion) cause a temperature rise.
- Endothermic reactions (e.g. some dissolving, citric acid + sodium hydrogencarbonate) cause a temperature fall.
- For neutralisation, the temperature change increases until the reactants are in the right proportions, then levels off or falls.
Improving accuracy
- Use a lid and a polystyrene cup to reduce heat loss.
- Stir to mix thoroughly and read the thermometer carefully.
Exam tips
- Use a polystyrene cup (insulation) to reduce heat loss.
- Calculate temperature change = final − start.
- Exothermic → temperature rises; endothermic → temperature falls.
- Control the volumes/concentrations; change only the independent variable.