Edexcel iGCSE Chemistry -3.8 Practical: Temperature Changes in Reactions- Study Notes- New Syllabus

3.8 Practical: Investigating Temperature Changes in Chemical Reactions

Aim:

To measure temperature changes accompanying different types of chemical change and identify whether they are exothermic or endothermic.

Core Principle

• Exothermic → temperature increases
• Endothermic → temperature decreases

Temperature change is measured using a thermometer in an insulated container (usually a polystyrene cup).

Apparatus (General)

• Polystyrene cup (insulation)
• Beaker
• Thermometer
• Measuring cylinder
• Stirrer
• Balance (if required)
• Safety goggles

1. Salts Dissolving in Water

Example: Ammonium nitrate dissolving.   

Method:

• Measure a known volume of water into the cup.
• Record the initial temperature.
• Add a known mass of salt.
• Stir until dissolved.
• Record the lowest or highest temperature reached.

Observation:

• Temperature decreases → endothermic (e.g. \( \mathrm{NH_4NO_3} \)).
• Temperature increases → exothermic (e.g. \( \mathrm{CaCl_2} \)).

2. Neutralisation Reactions

Example:

\( \mathrm{HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)} \)

Method:

• Measure equal volumes of acid and alkali.
• Record initial temperature.
• Mix quickly and stir.
• Record maximum temperature.

Observation:

• Temperature increases.
• Reaction is exothermic.

3. Displacement Reactions

Example:

\( \mathrm{Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)} \)

Method:

• Place copper sulfate solution in cup.
• Record initial temperature.
• Add zinc powder.
• Stir and record highest temperature reached.

Observation:

• Temperature increases.
• Copper metal forms.
• Reaction is exothermic.

4. Combustion Reactions

Example: Burning ethanol.

\( \mathrm{C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O} \)

Method:

• Measure a known volume of water into a metal can.
• Record initial temperature.
• Burn fuel underneath.
• Record final temperature.
• Measure mass of fuel burned.

Observation:

• Temperature increases significantly.
• Reaction is exothermic.

Sources of Error (Exam Focus)

• Heat loss to surroundings.
• Heat absorbed by cup/thermometer.
• Incomplete combustion (for fuels).
• Delay in recording maximum temperature.