Energy Level Diagrams — Energetics | IGCSE Chemistry | Examo

Energy Level Diagrams — Energetics | IGCSE Chemistry | Examo

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 7% of your exam marks.

stable

Low

Stable7%

Calorimetry calculations and energy profile diagrams appear in nearly every series.

What an energy level diagram shows

An energy level diagram (sometimes called a reaction profile in later topics) plots the chemical energy of the species on the y-axis against the progress of reaction on the x-axis
A flat horizontal line at the left marks the energy of the reactants
A second flat horizontal line at the right marks the energy of the products
A vertical arrow between the two lines indicates the enthalpy change, ΔH

Reading the two cases

Diagram	Reactant level vs product level	Arrow direction	Sign of ΔH
Exothermic	Reactants higher than products	Arrow points down	ΔH negative
Endothermic	Reactants lower than products	Arrow points up	ΔH positive

The vertical gap between the two lines IS the magnitude of ΔH; longer arrows mean larger energy changes