AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Factors which affect the rates of chemical reactions include: the…
Full specification wording
Factors which affect the rates of chemical reactions: Factors which affect the rates of chemical reactions include: the concentrations of reactants in solution, the pressure of reacting gases, the surface area of solid reactants, the temperature and the presence of catalysts.
Rate means how quickly reactants are used or products formed.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 1 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Rate means how quickly reactants are used or products formed. For a reaction to happen, particles must collide with at least the activation energy. Increasing the concentration of reactants in solution means more particles in the same volume, so collisions are more frequent and the rate rises. Increasing the pressure of reacting gases squeezes the same particles into a smaller volume, again increasing collision frequency. Increasing the surface area of a solid, for example using powder instead of a large lump, exposes more particles to collision. Raising temperature increases both collision frequency and the proportion of collisions with enough energy, so the effect is usually large. A catalyst provides an alternative pathway with lower activation energy, increasing the rate without being used up.
What earns the marks
- Rate is the change in amount of reactant or product per unit time, and it depends on the frequency and energy of collisions between particles.
- Increasing the concentration of reactants in solution increases the number of particles per unit volume, so successful collisions become more frequent and the rate increases.
- Increasing the pressure of reacting gases reduces the volume occupied by the same number of particles, increasing collision frequency and therefore the rate.
- Increasing the surface area of a solid reactant exposes more particles at the surface, so collisions with other reactants become more frequent and the rate increases.
- Increasing temperature raises the average kinetic energy of particles, so collisions are more frequent and a greater proportion exceed the activation energy, increasing the rate.
- A catalyst increases the rate by providing an alternative reaction pathway of lower activation energy, and it is not used up during the reaction.
Common mistakes and how to put them right
Saying that a catalyst increases the rate by giving particles more energy.
Put it right: A catalyst lowers the activation energy by providing an alternative pathway.
Confusing surface area with concentration when a solid is powdered.
Put it right: Powdering changes the exposed surface area of the solid, not the concentration of a solution.
Believing that increasing temperature only makes particles collide more often.
Put it right: It also greatly increases the proportion of collisions with energy at least equal to the activation energy.
Exam tips
- Link every factor back to collision frequency or collision energy rather than simply saying the reaction is faster.
- When comparing two experiments, state which factor changed, which factors were controlled, and how the changed factor alters collisions.
- Use the phrase activation energy correctly: particles must collide with at least this minimum energy for a reaction to occur.
Try the lesson
The start of the Factors which affect the rates of chemical reactions: Factors which affect the rates of chemical reactions include: the concentrations of reactants in solution, the pressure of reacting gases, the surface area of solid reactants, the temperature and the presence of catalysts. lesson, made from checked teaching notes for this specification point.
Have a go first
Which change increases the rate of a chemical reaction between a solid and a solution?
Listen
Rate means how quickly reactants are used or products formed. For a reaction to happen, particles must collide with at least the activation energy. Increasing the concentration of reactants in solution means more particles in the same volume, so collisions are more frequent and the rate rises. Increasing the pressure of reacting gases squeezes the same particles into a smaller volume, again increasing collision frequency. Increasing the surface area of a solid, for example using powder instead of a large lump, exposes more particles to collision. Raising temperature increases both collision frequency and the proportion of collisions with enough energy, so the effect is usually large. A catalyst provides an alternative pathway with lower activation energy, increasing the rate without being used up. A strong answer earns marks for these points. Rate is the change in amount of reactant or product per unit time, and it depends on the frequency and energy of collisions between particles. Increasing the concentration of reactants in solution increases the number of particles per unit volume, so successful collisions become more frequent and the rate increases. Increasing the pressure of reacting gases reduces the volume occupied by the same number of particles, increasing collision frequency and therefore the rate. Increasing the surface area of a solid reactant exposes more particles at the surface, so collisions with other reactants become more frequent and the rate increases. A common slip: Saying that a catalyst increases the rate by giving particles more energy. Instead, a catalyst lowers the activation energy by providing an alternative pathway. Exam tip: Link every factor back to collision frequency or collision energy rather than simply saying the reaction is faster.
See it
Key words
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Collision theory
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Activation energy
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Catalyst
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Rate
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See every definition
- Collision theory
- For a reaction to happen, particles must collide with at least the activation energy, and the rate depends on the frequency and energy of collisions between particles.
- Activation energy
- The minimum energy that particles must have when they collide for a reaction to occur.
- Catalyst
- A substance that provides an alternative reaction pathway with lower activation energy, increasing the rate without being used up.
- Rate
- The change in amount of reactant or product per unit time, meaning how quickly reactants are used or products formed.
Label the diagram
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