1.1.2—Endothermic vs. exothermic
- Syllabus
- First assessment 2025
- Objective
- 1.1.2
- Level
- HL
Endothermic and Exothermic
| Type | Energy direction | Surroundings temperature |
|---|---|---|
| Endothermic | Absorbed by the system | Decreases |
| Exothermic | Released by the system | Increases |
Classify from the direction of energy transfer, then check that the observed temperature change of the surroundings agrees.
Connect three representations: exothermic means energy flows out of the system, the surroundings warm, and ΔH for the system is negative; endothermic gives the opposite pattern and positive ΔH. State the observed part before inferring the reaction type.
Classifying Energy Changes
Assessment in practice
Representative question
Question 1
[Maximum number: 1]
Which statement about an exothermic reaction is correct?
A
Temperature decreases and the products have higher enthalpy than the reactants.
B
Temperature decreases and the products have lower enthalpy than the reactants.
C
Temperature increases and the products have higher enthalpy than the reactants.
D
Temperature increases and the products have lower enthalpy than the reactants.
D
Measuring Enthalpy Summary
Retrieve the route: define system/surroundings transfer, classify endothermic or exothermic, read stability from energy profiles, then calculate Q and ΔH with the correct sign.
Check the energy direction, surroundings temperature, reactant/product levels, moles, units, and ΔH sign.