Skip to content

Salam Academy

Sign in Create account

LearnCambridge97022025–2027Paper 4 · A Level Structured QuestionsThermodynamics

Paper 4 · Module

Thermodynamics

2 subtopics≈ 70 min in total

Start the module: Internal energy Open graphing calculator

Internal energy
The internal energy of a system is the sum of the random kinetic and potential energies of its molecules. It depends only on the state of the system (its temperature, volume, phase), not on how it got there. A rise in temperature means more random kinetic energy. During a change of state the potential energy changes while the temperature stays constant. For an ideal gas there are no intermolecular forces, so internal energy is all kinetic: $U=\tfrac32NkT$ .
≈ 30 min
The first law of thermodynamics
The first law is conservation of energy for a system: $\Delta U=q+W$ , where $q$ is the energy transferred to the system by heating and $W$ is the work done on the system. When a gas expands at constant pressure, it does work $p\Delta V$ on its surroundings, so $W=-p\Delta V$ . On a $p$ – $V$ graph, work is the area under the curve.
≈ 40 min