equilibria

Question 1

What are the two features of a dynamic equilibrium?

Answer 1

-the forward and backward reactions are occurring at the same rates.
- the concentration of the reactants and products stay constant.

Question 2

What is position of equilibrium?

Answer 2

If the position of equilibrium favours the reactants then it shifts towards the left, if it favours the products then it shifts towards the right.

Question 3

What is Le Chatelier’s principle?

Answer 3

It is used to find out how changing external conditions such as temperature and pressure on the position of equilibrium.

Question 4

What is effect of temperature on equilibrium?

Answer 4

If the temperature is increased the equilibrium will shift to oppose and move in the endothermic reaction to try to reduce the temperature by absorbing heat. Vice versa.

Question 5

What is the effect of pressure on equilibrium?

Answer 5

Increasing pressure will cause the equilibrium to shift towards the side with fewer moles of gas to oppose the change and thereby reduce the pressure.

Question 6

If the number of moles is the same on both sides then will changing pressure have any effect?

Answer 6

no

Question 7

Do low temperatures give a high or low yield?

Answer 7

Low temperature may give a higher yield of product but will also result in a slow rates of reaction.

Question 8

Does increasing pressure give a high yield?

Answer 8

Increasing pressure may give a high yield but also may result in a faster reaction

Question 9

What is the effect of concentration on equilibrium?

Answer 9

Increasing the concentration causes the equilibrium to shift to oppose this and move in the opposite direction to remove and decrease the concentration.

Question 10

What is the effect of catalysts on equilibrium?

Answer 10

A catalyst has no effect on the position of the equilibrium but it does fasten the rate at which equilibrium is achieved.

Question 11

What is the importance of equilibrium to industrial processes ( Haber costs, Contact process, Production of methanol from CO, hydration of ethene to produce ethanol ).

Answer 11

Low temperatures gives good yield but slow rate ; compromised temperature used. High pressure gives good yield and high rate : too high pressures would lead to high energy costs.
( Hydration of ethene to produce ethanol ) = High pressure leads to unwanted polymerisation of ethene to poly(ethene).

Question 12

What is the role of catalysts?

Answer 12

They speed up the rate, allowing a lower temperature to be used ( and hence lower energy costs ) but have no effect on position of equilibrium.

Question 13

In all cases what does high pressure lead to?

Answer 13

High pressure leads to high energy costs for pumps to produce the pressure and too high equipment costs to have equipment that can withstand high pressures.

Question 14

What does the term carbon neutral refer to?

Answer 14

An activity that has no annual carbon ( greenhouse gas ) emissions to the atmosphere.

Question 15

What two alcohols can be used as fuels ?

Answer 15

Methanol and ethanol

Question 16

Give an example of what can be carbon neutral ?

Answer 16

If carbon monoxide used to make methanol from the production of methanol from CO was extracted from the atmosphere then it could classed as carbon neutral. Would be only carbon neutral if the energy to carry out the reaction was not made by the combustion of fossil fuels.

Question 17

Can the unit of Kc change?

Answer 17

Yes.

Question 18

How do you calculate moles at equilibrium?

Answer 18

Moles of reactant at equilibrium = initial moles - moles reacted.

Moles of product at equilibrium = initial moles + moles formed.

Question 19

How concentration measured?

Answer 19

Concentration = moles / volume ( in dm^3).

Question 20

What is the effect of changing conditions on Kc .

Answer 20

The larger the Kc, the greater the amount of products. If Kc is small we say the equilibrium favours the reactants.

Question 21

Effect of temperature on position of equilibrium and Kc?

Answer 21

Both the position of equilibrium and the value of Kc will change if temperature is altered.

Question 22

When does Kc only change?

Answer 22

Kc only changes with temperature. Doesnt change with pressure or conc. And catalyst has no effect on Kc.

Question 23

What happens if the temperature is increased if the forward reaction is exothermic.

Answer 23

If the temperature is increased then the reaction will shift to oppose the change and move in the backwards endothermic reaction. The position of equilibrium shifts to the left. The value of Kc gets lower as there are smaller products.

Question 24

What is the effect of pressure on position of equilibrium and Kc.

Answer 24

The position of equilibrium will change if pressure is altered but the value of Kc stays constant as Kc only varies with temperature.

Question 25

What happens when the product side has fewer moles and the pressure is increased.

Answer 25

The reaction will shift to oppose the change and move in the forward reaction to the side with fewer moles of gas. The position of equilibrium shifts to the right. The value of Kc stays the same though as only the temperature changes the value of Kc.

Question 26

Why do catalysts have no effect on the value of Kc.

Answer 26

Catalysts have no effect on Kc as they speed up both forward and backward rates by the same amount.