Calculating Energy Changes — Energetics | IGCSE Chemistry | Examo

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4CH1

Energetics

Physical Chemistry · 3 question types

4CH1 Topics

Exothermic and Endothermic Reactions
Calorimetry Experiments
Calculating Energy Changes
Energy Level Diagrams
Bond Energy
Practical: Investigating Temperature Changes

Rates of Reaction8%

Reversible Reactions and Equilibria6%

Frequency legend

High (≥14%)

Above avg (10 to 13%)

Average (<10%)

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.

The heat-energy formula

Q = m c ΔT

Q = heat energy transferred, in joules (J)
m = mass of the substance being heated, in grams (g) — usually the mass of the solution, or the mass of water in a combustion experiment
c = specific heat capacity, the energy needed to raise the temperature of 1 g of substance by 1 °C. For water, c = 4.18 J g⁻¹ °C⁻¹
ΔT = change in temperature, in °C (the same numerical value as the change in kelvin)

Sign convention

If the temperature rises, the reaction is exothermic and ΔH is negative
If the temperature falls, the reaction is endothermic and ΔH is positive
After computing Q with positive numbers, attach the correct sign at the end

Energy per gram and molar enthalpy of combustion

For a fuel, the answers most often wanted are:
- Energy released per gram: Q ÷ (mass of fuel burnt)
- Energy released per mole (the molar enthalpy of combustion): ΔH = Q ÷ (moles of fuel)
These two values make different fuels easy to compare

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Calorimetry Experiments

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Energy Level Diagrams