Comparing exothermic and endothermic reactions
Method:
- Measure 25 cmΒ³ of solution into a polystyrene cup (insulated)
- Record the initial temperature
- Add the second reactant and stir with the thermometer
- Record the maximum or minimum temperature
- Calculate ΞT (temperature change)
Exothermic test:
HCl + NaOH β Temperature rises
Endothermic test:
Citric acid + NaHCOβ β Temperature falls
Why use a polystyrene cup?
It's an insulator β reduces heat loss/gain to environment, making measurements more accurate.
Quick Check: In an endothermic reaction, what happens to the temperature of the surroundings, and why?
The temperature of the surroundings DECREASES. This is because the reaction absorbs energy from the surroundings β it takes in heat from everything around it to power the bond-breaking step. The surroundings lose thermal energy to the reaction, so they cool down.
This required practical covers Required Practical: Investigating Temperature Changes within Endothermic Reactions for GCSE Chemistry. Revise Endothermic Reactions in Energy Changes for GCSE Chemistry with 20 exam-style questions and 14 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 5 of 12 in this topic. Revise both the method and the reason for each step, because practical questions often test understanding rather than pure recall.
Practice questions for Endothermic Reactions
In an endothermic reaction, energy is:
Explain why a sports cold pack becomes cold when activated.