Rates of Reaction
The rate of a reaction tells us how fast reactants are turned into products. We can measure it by looking at how quickly a change happens.
What is the rate of a reaction?
- The rate is how quickly reactants are used up or products are formed
- It can be measured in several ways, depending on the reaction
Measuring rate of reaction
Common methods:
- Change in mass over time (e.g. when a gas is given off)
- Volume of gas produced (using a gas syringe)
- Time taken for a colour change or precipitate to form
Rate of reaction formula
Rate = amount of reactant used or product formed ÷ time
- Units depend on what is measured (e.g. cm³/s or g/s)
Factors affecting rate of reaction
Factor | Effect |
Temperature | Higher temperature = faster rate (particles move faster) |
Concentration | More particles = more frequent collisions |
Surface area | More exposed particles = faster rate |
Catalyst | Speeds up reaction by lowering activation energy |
Pressure (for gases) | More particles in same space = more collisions |
Collision theory
For a reaction to happen:
- Particles must collide
- They must have enough energy (activation energy)
💡 Increasing rate = more frequent and/or more energetic collisions
Graphs of reaction rate
- A curve that starts steep and levels off
- Steepest at the start (fastest rate)
- Levels off when the reaction is complete
You can compare reactions using:
- Gradient = how fast
- Plateau height = how much product is made
Questions
- What does the rate of reaction measure?
- How does increasing temperature affect rate?
- What is the rate formula?
- What do catalysts do?
- According to collision theory, what must particles do to react?
Summary
- The rate of reaction shows how fast a chemical change happens
- Can be measured by mass change, gas produced, or colour change
- Higher temperature, concentration, pressure, or surface area = faster rate
- Catalysts speed up reactions without being used up
- Collision theory explains how particles must collide with enough energy