Reaction Rates
Rate measures how fast reactants disappear or products appear.
About this topic
Reaction rate is the change in concentration of a reactant or product per unit time, such as mol/(L·s). Rate = Δ[product]/Δt or −Δ[reactant]/Δt. It can be measured by monitoring colour, gas volume, mass loss, pH or conductivity, and the rate is faster at the beginning, then slows as reactants are used up.
On a graph of concentration against time, the slope of the tangent at any point gives the rate at that instant. The initial rate is the steepest. Factors affecting rate are explained by collision theory: concentration, temperature, surface area, catalysts and, for gases, pressure. Rates of different species are linked by the equation's coefficients; in 2H2O2 giving 2H2O + O2, oxygen forms at half the rate at which peroxide is consumed.
Worked example: if the concentration of a reactant falls from 0.80 M to 0.50 M in 30 seconds, the average rate of loss is 0.30 / 30 = 0.010 M/s. Applications include food preservation, drug shelf life, industrial optimisation and understanding how pollutants break down. Reaction rates in the body are controlled by enzymes.
A common misconception is that rate stays constant during a reaction, or that rate and extent of reaction are related. A fast reaction need not give more product, and a reaction can be thermodynamically favourable yet very slow, like diamond turning into graphite.
Key ideas
- Rate = Δconcentration/Δtime
- Affected by T, concentration, surface area, catalysts
- Measure with graphs
Quick check
Use cases: where Reaction Rates helps
- Homework: review the key idea behind Reaction Rates before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Reaction Rates without notes.
- Visual learning: play with the interactive lab to see how Reaction Rates changes when you adjust its inputs.
- Teaching a friend: explain Reaction Rates in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Reaction Rates?
Rate measures how fast reactants disappear or products appear.
What will I learn in Reaction Rates?
Rate = Δconcentration/Δtime. Affected by T, concentration, surface area, catalysts. Measure with graphs.
Is Reaction Rates part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Reaction Rates lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Reaction Rates?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.