MYP Chemistry: Factors Affecting Reaction Rate — FAQs

"Factors affecting reaction rate" is the MYP Chemistry topic covering how temperature, concentration, surface area, catalysts and light change how fast a reaction happens. In Years 4-5 you use collision theory to explain why each factor works, then design controlled experiments to test one variable at a time.

Five factors dominate MYP Chemistry: temperature, concentration (or pressure for gases), surface area of solid reactants, the presence of a catalyst, and light for photochemical reactions. Each one speeds up the reaction by raising either how often particles collide or how much energy those collisions carry.

Collision theory says a reaction only speeds up when particles collide more often, or collide with enough energy — the activation energy — to actually react rather than just bounce apart. Heating or concentrating a mixture increases both collision frequency and energy; a catalyst lowers the energy barrier instead.

Activation energy is the minimum energy particles need when they collide for a reaction to actually happen, rather than colliding and separating unchanged. It matters because most room-temperature collisions fail this test — which is exactly why heating a mixture, or adding a catalyst that lowers the barrier, speeds things up so much.

A strong investigation isolates one independent variable — say, acid concentration — while holding temperature, volume and surface area constant, and measures a clear dependent variable like gas volume or time to a colour change. State a hypothesis linked to collision theory before you start, not after you see the data.

Reaction rate investigations are typically assessed against Criterion B (Inquiring and Designing) and Criterion C (Processing and Evaluating), each out of 8 in MYP Years 4-5. Criterion B rewards a testable hypothesis and identified variables; Criterion C rewards accurate graphs, a collision-theory explanation of the trend, and honest evaluation of limitations.

The mistake I see most is changing two variables at once — temperature and concentration together — which invalidates the whole investigation. Others describe the graph ('it went up faster') without ever mentioning collisions, or write a hypothesis like 'rate will increase' with no reasoning attached to it.

Rate is the gradient of a graph of product formed (or reactant used) against time, usually in cm³/s. For initial rate, draw a tangent at time zero and find its gradient; for average rate, divide total change by total time taken.

Yes — reaction rate and collision theory are core Sciences content that can appear in the on-screen MYP eAssessment, assessed against the same four criteria used in class. Expect data-response tasks asking you to read a rate graph, identify controlled variables, or apply collision theory to an unfamiliar reaction scenario.

MYP treats reaction rate qualitatively — collision theory, graphs, controlled variables — while DP Chemistry, with first exams in 2025, adds rate laws, rate constants and reaction order with real calculations. According to the IB, DP's Reactivity 3 topic on reaction kinetics builds directly on the collision-theory foundation MYP Years 4-5 already covers.

Classic MYP practicals include marble chips reacting with hydrochloric acid (measuring CO2 gas volume), sodium thiosulfate and hydrochloric acid — the 'disappearing cross' reaction timed by colour change — and magnesium ribbon with dilute acid. Each isolates one factor: concentration, temperature or surface area.

Most struggles come from mixing up description with explanation — your child can say a graph rises faster, but hasn't linked it to collision theory (more frequent or more energetic collisions). It's rarely a maths problem; it's the written reasoning in Criterion C that usually costs the marks.

A solid grasp of collision theory and graph interpretation in MYP Years 4-5 is exactly what DP Chemistry's Reactivity 3 kinetics topic assumes from day one. Students who arrive without it spend the first weeks of DP relearning MYP content instead of moving straight to rate laws and Arrhenius calculations.

Look for Revision Notes summarising the five factors with collision-theory reasoning, Topical Worksheets with graph-reading and rate-calculation practice, and data-response questions styled like the eAssessment. On revisionprep.com you'll find MYP Chemistry Revision Notes and Topical Worksheets built around exactly these command terms and criteria.