6. The Rate and Extent Of Chemical Change

Question 1

How do you work out rate?

Answer 1

Rate = quantity of reactants used / time

or

Rate = quantity of products used / time

Question 2

What does the collision theory state?

Answer 2

In order for a chemical reaction to occur, particles must collide with sufficient energy

Question 3

What is activation energy?

Answer 3

The minimum energy particles must have for a reaction to be successful

Question 4

What happens as a reaction progresses?

Answer 4

The concentration of reactants decreases meaning the frequency of collisions between particles is reduced and so the reaction slows down

Question 5

How is the rate of a reaction increased?

Answer 5

• particles must collide more frequently

* particles must collide with more energy

Question 6

How do you achieve a higher rate of reaction?

Answer 6

Increase pressure, temperature, or concentration

Question 7

What is concentration?

Answer 7

The number of reactant particles in a given volume of liquid

Question 8

Does increasing temperature increase the number of reacting particles?

Answer 8

No, it just increases the chance of successful collisions

Question 9

Will the amount of product produced in the reaction be more, less, or the same at a higher temperature?

Answer 9

The same amount of product will be produced at all temperatures just at different rates

Question 10

What is a catalyst?

Answer 10

A substance that changes the rate of reactions, but is not changed chemically itself at the end of the reaction

Question 11

How do catalysts work?

Answer 11

• do not increase frequency of collisions or make collisions more energetic
• do provide an alternate reaction pathway to the products with a lower activation energy

Question 12

What is a reversible reaction?

Answer 12

Where the products of the reaction can react to produce the original reactants

Question 13

How can reversible reactions be represented?

Answer 13

A + B equilibrium arrow symbol C + D

Question 14

What does the double arrow on a reaction mean?

Answer 14

The reaction can go in either direction

Question 15

What happens if a reversible reaction in exothermic in one direction?

Answer 15

It is endothermic in the other

Question 16

What does it mean in a reversible reaction that the reaction is exothermic in one direction and endothermic in the other?

Answer 16

The energy absorbed in one direction is equal to the energy released in the other

Question 17

What is an example of a reversible reaction?

Answer 17

Hydrated copper sulphate <> anhydrous copper sulphate + water

Question 18

What always happens when a reversible reaction takes place in a closed system?

Answer 18

A state of equilibrium will be reached

Question 19

What is equilibrium?

Answer 19

When the amounts of reactants and products reach a balance - their concentrations stop changing

Question 20

What is a closed system?

Answer 20

When none of the reactants or products can escape

Question 21

How are the rates of the forward and backward reactions in a state of equilibrium?

Answer 21

The rate of the forward reaction is equal to the rate of the backward reaction

Question 22

Why are the conditions of equilibrium changed?

Answer 22

In industrial processes, to:

• maximise yield
• minimise cost
• minimise environmental impact

Question 23

What does the position of equilibrium depend on?

Answer 23

• temperature
• pressure
• concentration

Question 24

What is Le Chatelier’s rule?

Answer 24

If a system is at equilibrium and a change is made to any of the conditions then the system responds to counteract the change

Question 25

What is said when an equilibrium shifts so the forward reaction is favoured? (reactants -> products)

Answer 25

We say equilibrium is shifted to the right so more products are made

Question 26

What is said when an equilibrium shifts so the backward reaction is favoured? (products -> reactants)

Answer 26

We say equilibrium is shifted to the left so more reactants are made

Question 27

What happens when a change is made to a reaction which is in equilibrium?

Answer 27

The equilibrium position will move to minimise the change made

Question 28

What happens if you raise the temperature of a system (exothermic direction) in equilibrium?

Answer 28

• it will try cool itself down
• energy is taken in during endothermic reactions
• endothermic reaction is favoured and yield of endothermic reaction will increase

Question 29

What happens if you decrease the temperature of a system in equilibrium?

Answer 29

• it will try to heat itself up
• energy is given out during exothermic reaction
• exothermic reaction is favoured and yield of exothermic will increase
• equilibrium will shift in exothermic direction

Question 30

What happens if you raise the pressure of a system in equilibrium?

Answer 30

The system will try to reduce the pressure

Question 31

Which reaction will be favoured when a system in equilibrium has its pressure raised?

Answer 31

The reaction which has fewer molecules of gas produced will be favoured

Question 32

What happens if you lower the pressure of a system in equilibrium?

Answer 32

The system will try to increase the pressure

Question 33

Which reaction will be favoured when a system in equilibrium has it’s pressure lowered?

Answer 33

The reaction which has more molecules of gas produced will be favoured

Question 34

What happens to the position of equilibrium when concentration is increased?

Answer 34

The equilibrium is sent towards the opposite side

Question 35

What happens to the position of equilibrium when the concentration is decreased?

Answer 35

The equilibrium is sent towards the same side

Question 36

What does adding a catalyst do to equilibrium?

Answer 36

• doesn’t change equilibrium position
• both forward and backward reaction increase at the same rate
• equilibrium is reached faster