Rate: temperature (AQA GCSE Chemistry Combined Science): Revision Notes
Rate: temperature
How temperature affects reaction rates
Temperature has a big effect on how fast reactions happen. When you heat up reactants, the reaction goes faster. This happens because of collision theory.
Collision theory explains that particles must crash into each other with enough energy to react. The minimum energy needed is called activation energy.
What happens when you increase temperature
When you heat up reactants, several things happen:
- Particles move faster - they have more kinetic energy
- More frequent collisions - faster particles bump into each other more often
- Higher energy collisions - moving particles hit harder
- More successful reactions - more particles have enough energy to overcome the activation energy barrier
Think of it like this: cold particles move slowly like people walking. Hot particles move quickly like people running. Running people bump into each other more often and with more force.
This analogy helps visualise why temperature has such a dramatic effect on reaction rates. Just as running people have more collisions than walking people, heated particles interact more frequently and energetically.
The energy barrier
All reactions need a minimum amount of energy to get started. This is the activation energy.
At any temperature, reactant particles have different amounts of energy. Some have lots, some have little. Only the particles with enough energy can react when they collide.
When temperature increases:
- More particles have the minimum energy needed
- A higher proportion of collisions are successful
- The reaction rate increases
Key Concept: The activation energy barrier doesn't change with temperature - what changes is the number of particles that have enough energy to overcome it. This is why even small temperature increases can lead to dramatically faster reaction rates.
Testing temperature effects
You can investigate how temperature affects reaction rates using simple experiments. The key is to measure reaction rate (usually by tracking product formation) at different temperatures.
Worked Example: Zinc + Hydrochloric Acid Reaction
The reaction:
Method:
- Heat the hydrochloric acid to different temperatures (e.g., 20°C, 30°C, 40°C, 50°C)
- Add the same amount of zinc to each temperature
- Measure how much hydrogen gas is produced over time
- Compare the rates at different temperatures
Expected result: Hotter acid makes the reaction go faster - you'll see more gas produced in the same time period at higher temperatures.
Safety Requirements: Always wear safety goggles when heating acids. Keep experiments away from naked flames as hydrogen gas is flammable. Ensure good ventilation when working with acids.
Key Points to Remember:
- Higher temperature = faster reaction rate
- Heat makes particles move faster and collide more often
- More particles have enough energy to overcome the activation energy barrier
- You can test this by measuring gas production at different temperatures
- Always follow safety rules when heating chemicals