Unit 1: Section 5- Kinetics + RP3

Question 1

What is dynamic equilibrium?

Answer 1

The rates of the forwards and backwards reaction are the same, the concentrations of the products and reactants are constant.

Question 2

What is Le Châtelier’s Principle?

Answer 2

Equilibria will change their position to counteract any change in their conditions.

Question 3

How does increasing pressure effect equilibrium?

Answer 3

If the pressure of a system is increased, the equilibrium opposes the change by shifting to the side which produces the fewest moles of gas to reduce the pressure.

Question 4

How does decreasing pressure effect equilibrium?

Answer 4

If the pressure of a system is decreased, the equilibrium opposes the change by shifting to the side which produces the most moles of gas to increase the pressure.

Question 5

How does increasing temperature effect equilibrium?

Answer 5

If the temperature of a system is increased, the equilibrium shifts in the endothermic direction to oppose the change and reduce the temperature by absorbing heat.

Question 6

How does decreasing temperature effect equilibrium?

Answer 6

If the temperature of a system is decreased, the equilibrium shifts in the exothermic direction to oppose the change and increase the temperature by giving out heat.

Question 7

How does increasing the concentration of something effect equilibrium?

Answer 7

The equilibrium system will shift in the direction that reduces the concentration of that species.

Question 8

What happens if you change the pressure of a reaction where there are the same number of moles of gas on each side?

Answer 8

Changes in pressure will have no effect on the position of the equilibrium.

Question 9

What effect do catalysts have on the position of equilibrium?

Answer 9

Catalysts do not affect the position of equilibrium as they speed up the rate of the reaction of both the forward and backward reaction by the same amount. Catalysts will however cause the system to reach equilibrium more quickly.

Question 10

What is used in industry to maximise yield of chemical reactions?

Answer 10

Le Châtelier’s principle is used in industry to maximise yield

Question 11

What is the contact process?

Answer 11

Stage 1: S(s) +O2(g)→SO2(g)
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Stage 2: SO2(g) + 1/2 O2(g) ⇌SO3(g)

ΔH=−97 kJ mol −1 (dont need to know numbers)

Question 12

What temperature is need for the contact process and why?

Answer 12

Stage 2 of the contact process is exothermic so a low temperature is needed to increase the yield. However, a low temperature would cause a slow rate so a compromise is made of 450°C

Question 13

What pressure is needed for the contact process? (no numbers)

Answer 13

Having a high pressure would lead to high energy costs for marginal gains. This is because the effect of high pressure on yield is only slightly better.

Question 14

What is the Haber process?

Answer 14

N2(g) +3H2(g) ⇌2NH3(g)
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ΔH=−92kJ mol−1

Question 15

What catalyst is used in the Haber process?

Answer 15

Iron

Question 16

What temperature is needed for the Haber process and why?

Answer 16

The Haber Process is exothermic so a low temperature is needed to increase the yield. However, a low temperature would cause a slow rate so a compromise is made of 450℃.

Question 17

What pressure is needed for the Haber process?

Answer 17

Having a high pressure would lead to a higher yield as there are fewer moles of gas on the right. Therefore, high pressure is used. The pressure used is not too high because it would be expensive to maintain.

Question 18

What is the reaction for the hydration of ethene?

Answer 18

C2H4(g) + H2​O(g) ⇌ CH3CH2OH(l)

Question 19

What temperature is used for the hydration of ethene and why?

Answer 19

The hydration of ethene is exothermic so a low temperature is needed to increase the yield. However, a low temperature would cause a slow rate so a compromise is made of 300°C.

Question 20

What pressure is used for the hydration of ethene and why?

Answer 20

Having a high pressure would lead to a higher yield as there are fewer moles on the right so a high pressure is used. However, too high a pressure would lead to ethene being polymerised so a compromise of 60−70 atm is made.

Question 21

What is the reaction for the production of methanol?

Answer 21

CO (g) + 2H2(g) ⇌ CH3OH(g)

Question 22

What temperature is needed for the production of methanol?

Answer 22

The production of methanol is exothermic so a low temperature is needed to increase the yield. However, a low temperature would cause a slow rate so a compromise is made of 400°C.

Question 23

What pressure is needed for the production of methanol?

Answer 23

Having a high pressure would lead to a higher yield as there are fewer moles on the right so a high pressure is used. The pressure used is not too high because it would be expensive to maintain.

Question 24

What catalysts are used in the production of methanol?

Answer 24

Chromium and zinc oxides

Question 25

What is the equilibrium constant?

Answer 25

The equilibrium constant is a ratio that shows the relation between the concentration of products to the concentration of reactants.

Question 26

What does the higher the value of Kc mean?

Answer 26

the further to the right (i.e. towards the products) the equilibrium will lie

Question 27

What does the lower the value of Kc mean?

Answer 27

The further to the left (i.e. towards the reactants) the equilibrium will lie.

Question 28

How do you find Kc?

Answer 28

Divide the concentrations of the products by the concentration of the reactants.

Question 29

What is the only condition that effects Kc?

Answer 29

temperature

Question 30

What is the effect of an increased temperature on the Kc value of an exothermic forwards reaction?

Answer 30

The reaction will shift towards the reactants to oppose the increase in temperature. So, the equilibrium will shift to the left and the Kc value will decrease.