GCSE Chemistry Temperature Changes required practical explained.

The temperature changes required practical asks GCSE Chemistry students to measure the energy transfer during a neutralisation reaction between an acid and an alkali. A fixed volume of acid is placed in a polystyrene cup, the starting temperature is recorded, and a measured volume of alkali is added. The thermometer shows how much the temperature rises, which tells students whether the reaction is exothermic or endothermic. Neutralisation reactions always release energy to the surroundings, so students expect the temperature to increase. The polystyrene cup acts as an insulator and reduces heat loss, making the measured temperature change closer to the true value for the reaction.

Aim

To investigate temperature change when acid reacts with alkali.

Method students should know

1. Measure a fixed volume of acid into a polystyrene cup.
2. Record the starting temperature.
3. Add a measured volume of alkali.
4. Place a lid on the cup and stir gently.
5. Record the highest or lowest temperature reached.

Variables

Independent variable

Volume or concentration of alkali.

Dependent variable

Temperature change.

Control variables

Volume of acid, Starting temperature, Insulation, Stirring method

Safety and common mistakes

• Wear eye protection.
• Clean spills immediately.
• Use dilute acid and alkali only.
• Using a glass beaker and losing heat quickly.
• Recording only the final temperature.
• Not identifying the maximum temperature.

Common questions students ask

Why is a polystyrene cup used instead of a glass beaker?

A polystyrene cup is a good thermal insulator. It reduces the transfer of heat energy from the reaction mixture to the surroundings, so the measured temperature change is closer to the true value. A glass beaker conducts heat away from the mixture, making the temperature change appear smaller than it really is.

How do you calculate temperature change in this practical?

Temperature change (ΔT) = final temperature − starting temperature. In an exothermic reaction such as neutralisation, the final temperature is higher than the starting temperature, so ΔT is positive. Always record the highest temperature reached, not just the temperature at the end of the experiment.

What is the difference between exothermic and endothermic in this context?

An exothermic reaction transfers energy to the surroundings, so the temperature of the reaction mixture increases. An endothermic reaction takes energy in from the surroundings, so the temperature decreases. Neutralisation reactions are always exothermic, so the temperature always rises when an acid and alkali react.

How do you improve the accuracy of the temperature change measurement?

Use a lid on the polystyrene cup to reduce heat loss from the top, repeat the experiment to calculate a mean temperature change, use a thermometer with a small scale interval, and record the maximum temperature reached rather than the temperature at a fixed time after mixing.