This PowerPoint lesson covers orders of reaction and reaction mechanism for IBDP Chemistry HL (first examination 2025), helping students link experimental rate laws to reaction pathways and graphical data. It provides a clear, structured approach to understanding how concentration affects rate, how to identify zero, first and second order behaviour, and how the rate law can be connected to the rate-determining step.

In kinetics, the order of reaction shows how the rate depends on the concentration of a reactant. For example, a reaction may be zero order, first order or second order with respect to a particular reactant depending on how the rate changes when concentration changes. This lesson helps students understand that reaction order must be determined experimentally, not guessed from the balanced equation, and that the overall order is found by adding the individual orders together. It also introduces the rate constant, k, and shows how its units depend on the overall order of reaction.

This fully editable PowerPoint (.pptx) is designed for HL teaching, revision or flipped learning within the IB Diploma Programme. Students are guided through the characteristic concentration–time and rate–concentration graphs for zero, first and second order reactions, making it easier to identify patterns visually. The lesson then extends into reaction mechanisms, showing how the rate law can often be linked to the slow, rate-determining step. It also explains how intermediates must be removed from a proposed rate law so that the final expression is written only in terms of reactants.

The resource includes a retrieval starter, clear definitions, worked explanations, graph analysis, links between molecularity and elementary-step rate laws, and practice questions with answers. It is especially useful for preparing students for IB exam questions involving orders of reaction, units of k, graphical interpretation and the relationship between kinetics and mechanism.

File type included: editable PowerPoint (.pptx)
Last updated: 2026 – improved graph interpretation, clearer links between mechanisms and rate laws, and enhanced practice tasks aligned to IB HL assessment objectives.