Exothermic reactions
4 marks · NormalThe table shows temperature changes observed in four different reactions:
| Reaction | Temperature change (°C) |
|---|---|
| A: Displacement reaction | +16 |
| B: Dissolving ammonium chloride | -8 |
| C: Combustion of butane | +22 |
| D: Neutralisation reaction | +7 |
Identify the two exothermic reactions.
Explain your answer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Reactions A and C are exothermic. · must show A: Displacement reaction, +16°C, C: Combustion of butane, +22°C
(b) Exothermic reactions increase the temperature of the surroundings, so those with positive temperature changes are exothermic. · must show Temperature increase indicates heat release to surroundings
Must show: Correct reactions identified, Justification based on temperature change
Common mistakes: Choosing reactions with negative temperature change as exothermic
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Identifies reaction A (displacement) as exothermic.
B2 (a) · 1 mark · Identifies reaction C (combustion) as exothermic.
B3 (b) · 1 mark · Explains that exothermic reactions cause temperature to rise (heat released).
B4 (b) · 1 mark · Links positive temperature change to exothermic process.
Worked solution
a. Reactions A and C are exothermic.
b. Both these reactions show a positive temperature change, meaning heat is released into the surroundings, which is exothermic.