IGCSE · Practice questions · Exothermic and endothermic reactions

Follow the heat.

Six original Cambridge-style questions on exothermic and endothermic reactions: temperature data, examples, experimental method and the sign of ΔH.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Exo out, endo in.

Exothermic: energy to the surroundings; temperature rises.
Endothermic: energy from the surroundings; temperature falls.
Extended: ΔH negative for exothermic, positive for endothermic.
Reverse the reaction, reverse the sign of ΔH.

Recall

[2 marks]

State what is meant by an exothermic reaction and an endothermic reaction.

Exothermic: a reaction that transfers thermal energy to the surroundings, so the temperature of the surroundings increases. ✓
Endothermic: a reaction that takes in thermal energy from the surroundings, so the temperature of the surroundings decreases. ✓

Analysis

[4 marks]

A student mixes pairs of solutions and records the temperatures.

Mixture	Start / °C	End / °C
A	21	34
B	21	16
C	20	27
D	22	22

Calculate the temperature change for each and classify each as exothermic, endothermic or no detectable energy change.

A: +13 °C, exothermic. ✓
B: −5 °C, endothermic. ✓
C: +7 °C, exothermic. ✓
D: 0 °C, no detectable energy change. ✓

Recall

[2 marks]

Give one example of an exothermic reaction and one example of an endothermic reaction.

Exothermic: for example combustion of a fuel, neutralisation, or a metal reacting with an acid. ✓
Endothermic: for example thermal decomposition of calcium carbonate, photosynthesis, or dissolving ammonium nitrate. ✓

Explain

[3 marks]

Describe how a student could show that the reaction between hydrochloric acid and sodium hydroxide solution is exothermic.

Measure a known volume of acid into a polystyrene cup and record its starting temperature with a thermometer. ✓
Add the sodium hydroxide solution, stir, and record the highest temperature reached. ✓
A rise in temperature shows that the reaction is exothermic. ✓

Recall

[2 marks]

(Extended) Define enthalpy change, ΔH, and state its sign for an endothermic reaction.

The transfer of thermal energy during a reaction. ✓
ΔH is positive for an endothermic reaction. ✓

Explain

[2 marks]

(Extended) Hydrogen burns in oxygen with ΔH = −286 kJ/mol of water formed. State the value of ΔH for the decomposition of water into hydrogen and oxygen, per mole of water, and explain your answer.

+286 kJ/mol. ✓
The decomposition is the reverse reaction, so the energy change has the same size but the opposite sign. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.