Rates of Reaction: Collision Theory and What Changes a Rate
A reaction happens when particles collide often enough and hard enough. Concentration, surface area, temperature, pressure and catalysts each change one of those two things, and a rate is read as the gradient of a graph.
What a learner can do afterwards
- Explains each factor in terms of how often particles collide or how much energy they bring
- Works out a mean rate from a mass loss or gas volume graph, and says why the curve flattens
- Explains how a catalyst speeds a reaction up without being used up, using the activation energy
- Decides which of two curves on the same axes belongs to the faster run and justifies it
1 · Read
A reaction happens when particles collide with enough energy and the right facing. Most bumps fail one of those tests. The rate is really the count of successful crashes each second. Anything that raises that count speeds the reaction up.
Five dials tune the count. Higher concentration or gas pressure crowds particles, so meetings grow more frequent. Higher temperature gives more collisions enough energy and raises meeting rates. Powders beat lumps because more surface lies exposed, as marble chips in acid show. A catalyst opens an easier path with lower activation energy, and it is not used up.
Read rates off a graph of gas volume or mass loss against time. The mean rate is amount divided by time. If 60 cm3 forms in the first 30 s, the mean rate is 60 divided by 30, which is 2 cm3/s. Curves start steep and flatten as reactants drain away.
Compare runs on the same axes. The steeper starter is the faster run. If both curves level at the same total, the speed differed but the final amount did not. A catalyst does exactly this: quicker arrival, same harvest.
Collisions drive rates, five dials tune them, and graph slopes reveal the speed.
More to read
12.1 Chemical Reaction Rates
Rates clock chemistry. Track gas volume, mass loss, or colour change against time and plot curves. Steep starts flatten as reactants drain. Read slopes for speed at any moment, not just averages. One method per experiment keeps comparisons fair.
12.2 Factors Affecting Reaction Rates
Five dials rule speed. Heat energises collisions, concentration and gas pressure crowd them, surface area exposes more faces, catalysts open easier paths. Change one dial per test and graph the result. Marble chips in acid prove surface area; warm versus cold proves temperature.
12.7 Catalysis
Catalysts cheat barriers. Enzymes fold substrates into reacting shape; converters clean exhausts with platinum. Neither is consumed, so traces transform tonnes. Industry lives on catalysts: cheaper, cooler, faster. Find the barrier, lower it, reuse the helper.
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2 · Watch
En anglaisTake it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.