Rates of Reaction and Equilibrium
Factors affecting rate, collision theory, reversible reactions.
In this topic
Rates of Reaction
The rate of a reaction is how fast reactants are turned into products.
Rate = amount of product formed ÷ time OR amount of reactant used ÷ time
Collision theory: for a reaction to happen, particles must collide with sufficient energy (greater than activation energy) and the correct orientation.
Factors that increase rate: 1. Higher temperature: particles move faster, more frequent and more energetic collisions 2. Higher concentration (or pressure for gases): more particles in a given volume, more frequent collisions 3. Larger surface area (smaller pieces): more particles exposed to react 4. Catalyst: provides an alternative pathway with lower activation energy
Key Points
- Rate can be measured by: gas volume collected, mass lost, colour change, time for solution to become opaque
- Catalysts are NOT used up — they can be reused
- Different reactions need different catalysts
- On a graph: steeper line = faster rate
Example Questions
3Explain why increasing the temperature increases the rate of reaction.
At higher temperatures, particles have more kinetic energy and move faster. This means: 1) Collisions are more frequent — particles meet more often. 2) A greater proportion of collisions have energy greater than the activation energy, so more collisions are successful.
[3 marks]
3A student investigates the rate of reaction between marble chips and hydrochloric acid. Explain how using powdered marble instead of chips would affect the results.
Powdered marble has a much larger surface area than chips. More particles are exposed to the acid, so collisions between marble and acid particles are more frequent. The rate of reaction would be faster, producing gas more quickly. The same total amount of gas would be produced (same mass of marble).
[3 marks]