ES - Rates And Equilibris

Question 1

Explain why increasing the concentration of H2O2 increases the rate of reaction

Answer 1

More crowded particles
More frequent collisions

Question 2

Explain why increasing the temperature of of H2O2 increases the rate of decomposition
(Use a Boltzmann distribution)

Answer 2

More molecules have energy above activation energy

Question 3

Explain why Hugh pressures ad low temperatures would gibe the maximum equilibrium yield of methanol

Answer 3

High pressure because fewer moles of gas on the RHS

Low temp because it shifts the reaction in the direction of the exothermic
And forward reaction is exothermic

Question 4

Which way is equilibrium shifted if temp is increased?

Answer 4

In the direction of the endothermic reaction (yielding more reactants)

Question 5

How to tell if forward reaction is exothermic

Answer 5

H is negative

Question 6

Explain why the actual conditions used in the chemical industry might be different from high pressure and low temp

Answer 6

High pressures are too expensive
Too slow to use a low temperature

Question 7

Suggest 2 ways in which the use of catalysts helps chemical companies to make their processes more sustainable

Answer 7

Catalysts are not used up in reaction
Reactions take place at lower temperatures

Question 8

State Le Chatelier’s principle

Answer 8

When the conditions on a system in equilibrium are changed
the equilibrium moves to oppose the change

Question 9

What would happen to equilibrium if temp is increased

Answer 9

Move towards LHS
As reverse reaction is endothermic

Question 10

What happens to equilibrium if catalyst is added?

Answer 10

Nothing would change
Catalyst;lists speed up forward & reverse reactions by the same amount

Question 11

Explain how an increase in temp causes the rate of reaction to increase

Answer 11

Area under Fira-h exceeding Ea = number of molecules that can react
At higher temp the area under the curve greater than Ea is bigger
So more can react

Question 12

Use collision theory to explain the changes in the rate fop reactions as they proceed

Answer 12

• The concentration decreases
• Collisions decrease
• Reaction stops when all of one reagent is used up

Question 13

State and explain what effect using a weaker acid has on the rate of reaction

Answer 13

Rate of reaction decreases
Lower concentration of H+ in weak HCl

Question 14

3 features of a reversible reaction

Answer 14

• closed system
• concentrations remain constant
• rate of forward reaction = rate of reverse reaction

Question 15

What is meant by a catalyst?

Answer 15

A substance that lowers activation energy by providing an alternative route

Question 16

What is meant by homogeneous?

Answer 16

Catalysts in the same state as the reactants

Question 17

Using the fact that acids are needed to catalyse this reaction, deduce the formula of the ion that acts as the catalyst

Answer 17

H+

Question 18

Catalyst do not affect the position of an equilibrium. Explain why not

Answer 18

They alter the rate of the forward and reverse reaction by the same amount

Question 19

What goes on the Y axis of Boltzmann?

Answer 19

Number of molecules/particles

Question 20

Explain the effects of catalysts on the rate of reaction (with reference to the graph)

Answer 20

Greater proportion of collisions have greater than Ea

Question 21

Pressure for Haber process

Answer 21

50-1000 atm

Question 22

Temperature for Haber process

Answer 22

200-600 degrees Celsius

Question 23

Explain why the Haber process is a compromise between rate and equilibrium

Answer 23

Compromise as
If temp is too high, low yield
If temp it too low, slow rate
If pressure is too high, increases cost

Question 24

State and explain the effect on an equilibrium of a decrease in pressure

Answer 24

Decrease as particles are further apart
So there are less frequent collisions

Question 25

The forward reaction is exothermic. Explain how the graph supports this statement

Answer 25

As temp increases, conversions are decreasing
Equilibrium gas moved to LHS (endothermic direction)

Question 26

Suggest 2 reasons why it us necessarily to heat the calcium carbonate strongly to achieve decomposition

Answer 26

• To overcome activation energy
• Reaction is endothermic

Question 27

State and explain what happens to the composition of the mixture in the container when CO2 escapes

Answer 27

Moves to RHS
Le chatelier’s principle
Causes more products (compensation)

Question 28

Suggest why the conversion was such less than the theory suggested

Answer 28

Other products were formed

Question 29

Give two economically important processes that use catalyst and state their catalysts

Answer 29

Haber process - iron
Catalytic cracking - platinum

Question 30

What affect does a catalyst have on the rate of a reaction and how does it achieve this affect? (4)

Answer 30

Increases rate
By providing alternative route
Which decreases activation energy
By weakening bonds in the reactant
So more molecules have E > Ea