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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
Products lie below reactants for an exothermic reaction and above them for an endothermic reaction, setting the sign of delta H.

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

[ 1 ]

Which statement about an exothermic reaction is correct?

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.