R2.3 Physical Equilibrium (IBDP Chemistry)

This PowerPoint lesson covers physical equilibrium for IBDP Chemistry (first examination 2025) and gives students a clear introduction to one of the key ideas needed for understanding reversible processes. It is designed to help students recognise the features of a physical system at equilibrium and explain why equilibrium is dynamic rather than static.

Physical equilibrium occurs during a physical change when the rate of the forward process is equal to the rate of the reverse process. In other words, particles continue to move between states, but there is no overall change in the observable properties of the system. This lesson helps students understand equilibrium through accessible examples such as water evaporating and condensing in open and closed systems and iodine subliming and depositing in a sealed container. These examples make the concept of dynamic equilibrium easier to visualise and explain.

This fully editable PowerPoint (.pptx) is ideal for classroom teaching, revision or flipped learning in the IB Diploma Programme. The lesson introduces key terms such as physical equilibrium, closed system, dynamic equilibrium and macroscopic property, then develops the idea that a closed system is required for equilibrium to be established. Students are guided to understand why equilibrium cannot be reached in an open system when matter escapes, and why at equilibrium the system appears unchanged even though particles are still changing state continuously.

The resource includes a retrieval starter activity, clear definitions, step-by-step explanations, real-world and laboratory-based examples, and opportunities for students to connect particle behaviour with visible observations such as constant water level or constant iodine colour. It is especially useful for helping students build strong conceptual foundations before moving on to chemical equilibrium.

File type included: editable PowerPoint (.pptx)
Last updated: 2026 – improved explanations of dynamic equilibrium, strengthened closed-system examples, and refined lesson flow to align with IB Chemistry first examination 2025.