5 - Kinetics Flashcards
How do chemical reactions occur?
When particles of substances collide
Define ‘activation energy’
The minimum amount of energy which particles need to collide to start a reaction
How does a reaction occur successfully?
Collisions must have energy greater than or equal to the activation energy
Why do most collisions not lead to a reaction?
Large majority of particles have insufficient energy to react when they collide
- Must have energies equal to or greater than the activation energy
What does the Maxwell-Boltzmann distribution show us?
Shows the spread of energies that molecules of a gas or liquid have at a particular temperature
How to draw a Maxwell-Boltzmann distribution:
- Curve must start at 0,0 as no molecules have 0 energy
- No maximum energy so curve does not touch the x-axis
- Not a bell curve
What happens to the distribution curve when temperature is increased?
- Curve shifts to the right
- Lower peak
What happens to the distribution curve when temperature is decreased?
- Curve shifts to the left
- Higher peak
Define ‘rate of reaction’
The speed the product is formed and the speed with which the reactant is used up
What happens to the rate of reaction when temperature is increased?
- More particles have greater then or equal to the activation energy
- Particles collide more frequently therefore more successful collisions
What happens to the rate of reaction when temperature is decreased?
- Less particles have greater then or equal to the activation energy
- Particles collide less frequently therefore less successful collisions
How can a small temperature increase lead to a large increase in rate?
Particles can gain energy through collisions
What happens to the distribution curve when concentration or pressure is increased?
- Shape unchanged
- Higher curve
- Area under curve will be greater as there is more particles
What happens to the distribution curve when concentration or pressure is decreased?
- Shape unchanged
- Lower curve
- Area under curve will be less as there is less particles
What happens to the rate of reaction when concentration or pressure is increased?
- More particles per unit volume
- Particles collide more frequently
- Higher chance of successful collisions
What happens to the rate of reaction when concentration or pressure is decreased?
- Less particles per unit volume
- Particles collide less frequently
- Lower chance of successful collisions
What is a ‘catalyst’?
A substance that speeds up a chemical reaction without being used up
How do catalysts work?
Catalysts provide an alternative route or mechanism with a lower activation energy to increase rate of reaction
What happens to the distribution curve when a catalyst is added?
Curve is unchanged, instead position of Ea shifts to the left
What happens to the rate of reaction when a catalyst is added?
- Rate of reaction increases as Ea is lowered
- More particles have energy greater than or equal to the Ea
What happens to the rate of reaction when surface area is increased?
- Larger area exposed for particles to collide
- More frequent and more successful collisions which increases rate of reaction
