5 - Kinetics

Question 1

How do chemical reactions occur?

Answer 1

When particles of substances collide

Question 2

Define ‘activation energy’

Answer 2

The minimum amount of energy which particles need to collide to start a reaction

Question 3

How does a reaction occur successfully?

Answer 3

Collisions must have energy greater than or equal to the activation energy

Question 4

Why do most collisions not lead to a reaction?

Answer 4

Large majority of particles have insufficient energy to react when they collide
- Must have energies equal to or greater than the activation energy

Question 5

What does the Maxwell-Boltzmann distribution show us?

Answer 5

Shows the spread of energies that molecules of a gas or liquid have at a particular temperature

Question 6

How to draw a Maxwell-Boltzmann distribution:

Answer 6

• 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

Question 7

What happens to the distribution curve when temperature is increased?

Answer 7

• Curve shifts to the right
• Lower peak

Question 8

What happens to the distribution curve when temperature is decreased?

Answer 8

• Curve shifts to the left
• Higher peak

Question 9

Define ‘rate of reaction’

Answer 9

The speed the product is formed and the speed with which the reactant is used up

Question 10

What happens to the rate of reaction when temperature is increased?

Answer 10

• More particles have greater then or equal to the activation energy
• Particles collide more frequently therefore more successful collisions

Question 11

What happens to the rate of reaction when temperature is decreased?

Answer 11

• Less particles have greater then or equal to the activation energy
• Particles collide less frequently therefore less successful collisions

Question 12

How can a small temperature increase lead to a large increase in rate?

Answer 12

Particles can gain energy through collisions

Question 13

What happens to the distribution curve when concentration or pressure is increased?

Answer 13

• Shape unchanged
• Higher curve
• Area under curve will be greater as there is more particles

Question 14

What happens to the distribution curve when concentration or pressure is decreased?

Answer 14

• Shape unchanged
• Lower curve
• Area under curve will be less as there is less particles

Question 15

What happens to the rate of reaction when concentration or pressure is increased?

Answer 15

• More particles per unit volume
• Particles collide more frequently
• Higher chance of successful collisions

Question 16

What happens to the rate of reaction when concentration or pressure is decreased?

Answer 16

• Less particles per unit volume
• Particles collide less frequently
• Lower chance of successful collisions

Question 17

What is a ‘catalyst’?

Answer 17

A substance that speeds up a chemical reaction without being used up

Question 18

How do catalysts work?

Answer 18

Catalysts provide an alternative route or mechanism with a lower activation energy to increase rate of reaction

Question 19

What happens to the distribution curve when a catalyst is added?

Answer 19

Curve is unchanged, instead position of E_a shifts to the left

Question 20

What happens to the rate of reaction when a catalyst is added?

Answer 20

• Rate of reaction increases as E_a is lowered
• More particles have energy greater than or equal to the E_a

Question 21

What happens to the rate of reaction when surface area is increased?

Answer 21

• Larger area exposed for particles to collide
• More frequent and more successful collisions which increases rate of reaction