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3.1.5 - Kinetics | AQA A-level Chemistry | Summary Notes
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- Unit 3.1.5 - Kinetics
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AQA AS/A-level Chemistry - 3.1.5 - Kinetics - Concise summary notes - A+ Study Notes
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3.1.5 – KineticsCollision theory and activation energy
Collision theory states that chemical reactions can only occur when particles collide with sufficient energy, when
energy of colliding particles is greater than or equal to the activation energy and when particles are in correct
orientation
Most collisions don’t result in a reaction because either the particles don’t have sufficient energy or the particles are
in the wrong orientation
Activation energy is the minimum amount of energy needed for a successful collision between particles to start a
reaction
Rate of reaction
Rate of reaction is the change in concentration of reactants or products per unit time
To calculate rate of reaction from a graph at a specific point, calculate the gradient of the tangent to the curve at
that specific point
Initial rate of reaction is the rate of reaction at the start of a reaction where it is fastest
Factors affecting rate of reaction
The 5 factors affecting rate of reaction are:
- Temperature
- Concentration
- Pressure
- Surface area
- Presence of a catalyst/enzyme
Temperature affects rate of reaction because:
- Increasing temp. increases rate of reaction
- Particles gain more kinetic energy
- Particles move around faster
- More particles have energy greater than or equal to activation energy for successful collisions
- Particles collide more frequently
- Higher freq. of successful collision between particles
, 3.1.5 – Kinetics
A small increase in temperature result in a large increase in rate of reaction because:
- More particles have energy greater than activation energy
- Higher % of collisions result in reactions
- Rate of reaction increases with temp.
- Small increase in temp. produces large increase in number of particles with energy greater than activation
energy
Concentration affects rate of reaction because:
- Increasing conc. increases rate of reaction
- More particles in same volume of solution/liquid
- Particles closer together
- Particles collide more frequently
- Higher freq. of successful collisions between particles
Pressure affects rate of reaction because:
- Increasing pressure, increases rate of reaction
- Same number of particles in smaller volume of gas
- Particles closer together
- Particles collide more frequently
- Higher freq. of successful collisions between particles
Surface area affects rate of reaction because:
- Increasing SA, increases rate of reaction
- Reacting particles have more area to react with
- Particles collide more frequently
- Higher freq. of successful collisions between particles
A catalyst is a substance that increases the rate of a chemical reaction without being changed in chemical
composition or amount
A catalyst works by providing an alternative reaction pathway with lower activation energy
A catalyst affects rate of reaction because:
- Addition of catalyst, increases rate of reaction
- Provides alternative reaction pathway with lower activation energy
- Less energy needed for particles to have successful collision
- More particles have energy greater than or equal to activation energy for successful collisions
- Particles collide more frequently
- Higher freq. of successful collision between particles
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