10 Reaction rates and equilibrium

Question 1

How do you calculate rate of reaction? (1 mark)

Answer 1

Measure change in concentration over time.

Question 2

How do you increase the rate of a reaction (according to collision theory)? (1 mark)

Answer 2

Need more frequent and successful collisions.

Question 3

How does increasing concentration affect the rate of reaction and why? (3 marks)

Answer 3

Increases because the number of particles in a given volume increases, meaning there are more frequent collisions, which in turn increases the number of successful collisions.

Question 4

How does increasing pressure affect the rate of reaction and why? (3 marks)

Answer 4

Increases because the number of particles in a given volume increases, meaning there are more frequent collisions, which in turn increases the number of successful collisions.

Question 5

How does increasing surface area of reactants affect the rate of reaction and why? (3 marks)

Answer 5

Increases, because more particles are exposed, which means collisions are more frequent.

Question 6

Describe what happens to rate of the reaction as time passes? (3 marks)

Answer 6

As time proceeds, reactants get used up so there are less frequent collisions and the rate of reaction decreases.

Question 7

Why are only some collisions effective? (3 marks)

Answer 7

The particles need to collide at the correct orientation and have enough energy to overcome the ‘activation barrier’ of the reaction.

Question 8

What is a catalyst?

Answer 8

A substance that changes the rate of a chemical reaction without undergoing any permanent change itself.

Question 9

How do catalysts increase the rate of chemical reaction? (1 mark)

Answer 9

Provide an alternate reaction pathway with a lower Ea.

Question 10

How do catalysts alter the position of equilibrium? (1 mark)

Answer 10

No effect.

Question 11

What is a homogenus catalyst? (3 marks)

Answer 11

Is the same physical state as the reactants, and reacts with the reactants to form an intermediate (which then breaks down and the catalyst is regenerated).

Question 12

What is a heterogenus catalyst? (1 mark)

Answer 12

Is a different physical state of reactants.

Question 13

Name 3 economic benefits of catalysts. (3 marks)

Answer 13

Lower operating temperatures and pressures.
Can improve properties.
Decreases time.
Exothermic reactions- allow reasonable yield in a reasonable amount of time.

Question 14

Name 3 environmental benefits of catalysts. (3 marks)

Answer 14

Save energy and decreases carbon dioxide emissions.
Allows alternative reactions with a higher atom economy.
Used in catalytic converters (in cars).

Question 15

What is the Boltzmann distribution? (1 mark)

Answer 15

The spread of molecular energies in gases.

Question 16

What does the area under the Boltzmann distribution show? (1 mark)

Answer 16

Total number of molecules

Question 17

Why does the Boltzmann distribution curve never meet the x-axis? (1 mark)

Answer 17

Because there is no maximum energy.

Question 18

What effect does an increase in temperature have on the Boltzmann distribution curve? (3 marks)

Answer 18

The average energy of molecules increases,
which means more collisions are successful and lead to a reaction,
so the curve flattens out so more area is past the Ea line.

Question 19

How does a decrease in temperature affect the Boltzmann distribution curve? (2 marks)

Answer 19

Makes the peak higher and the area past the Ea line decreases.

Question 20

How does a catalyst affect the graph for Boltzmann distribution? (1 mark)

Answer 20

Moves the Ea to the left (so more are is past the past the Ea line).

Question 21

Why does the Boltzmann distribution curve start at (0,0)? (1 mark)

Answer 21

No particles has no energy.

Question 22

What happens if you double the concentration of the reactants? (1 mark)

Answer 22

Double the amount of products produced.

Question 23

What is dynamic equilibrium? (1 mark)

Answer 23

Rate at which the forward reaction is the same as the reverse reaction.

Question 24

How does increasing temperature affect the position of equilibrium? (1 mark)

Answer 24

Moves it towards the endothermic reaction (to try and decrease the temperature).

Question 25

How does increasing concentration affect the position of equilibrium? (1 mark)

Answer 25

Moves it towards the side of the reaction you didn’t increase the concentration of.

Question 26

How does increasing pressure affect the position of equilibrium? (1 mark)

Answer 26

Moves it towards the reaction which produces less molecules (to try and decrease the pressure).

Question 27

Describe an experiment to establish the effect of H+ concentration on the reaction of potassium chromate with sulphuric acid.

Question 28

Describe an experiment to establish the effect of temperature on the reaction of chloride ions with cobalt ions.

Question 29

What is the equilibrium constant? (1 mark)

Answer 29

(C^c x D^d)/(A^a xB^b)
When aA + bB –><– cC + dD

Question 30

What does am equilibrium constant of 1 mean? (1 mark)

Answer 30

That equilibrium is halfway between the reactants and the products.

Question 31

What does am equilibrium constant of 1< mean? (1 mark)

Answer 31

That the equilibrium is towards the products.

Question 32

What does am equilibrium constant of 1> mean? (1 mark)

Answer 32

That the equilibrium is towards the reactants.

Question 33

What is the contact process? (1 mark)

Answer 33

The production of sulphuric acid.

Question 34

What catalyst is used in the contact process? (1 mark)

Answer 34

Vandium oxide (V2O5)

Question 35

What is the balanced equation for the reversible reaction in the contact process? (3 marks)

Answer 35

2SO2 (g) + O2 (g) –><– 2SO3 (g)

Question 36

What is included in the calculations for Kc in homogeneous reactions? (1 mark)

Answer 36

They are all the same physical state so all the reactants and products are included.

Question 37

What is included in the calculations for Kc in heterogeneous reactions? (1 mark)

Answer 37

There are different physical states, only gases and aqueous substances are included.