Chemical Equilibirum

Question 1

What are the rules in an equilibrium system?

Answer 1

• The rate of forward reaction is equal to the rate of backward reaction
• The concentration of reactants and products do not change

Question 2

What does an equilibrium system being dynamic mean?

Answer 2

At equilibrium, both the forward and backwards reactions are taking place. As fast as the reactants are becoming products, the products are becoming reactants. Therefore, in an equilibrium system the concentrations of the reactants and products remain unchanged even though the forward and reverse reactions are still taking place

Question 3

What must a system be for it to remain in equilbirum?

Answer 3

Closed

Question 4

What is le Chatelier’s principle?

Answer 4

When a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change

Question 5

What does changing the concentration of a reactant or product in equilibrium do?

Answer 5

Change the rate of forwards or reverse reaction. The position of equilibrium will then shift to counteract this

Question 6

What happens if the concentration of A or B increases?

Answer 6

The equilibrium shifts to the right (towards C and D)

Question 7

What happens if the concentration of A or B decreases?

Answer 7

Equilibrium shifts to the left (towards A and B)

Question 8

What happens if the concentration of C or D increases?

Answer 8

Equilibrium shifts to the left (towards A and B)

Question 9

What happens if the concentration of C or D decreases?

Answer 9

The equilibrium shifts to the right (towards C and B)

Question 10

What is used to investigate the changes of equilibrium position with concentration?

Answer 10

The equilibrium between chromate ions and CrO4 2-

SEPERATE NOTES!

Question 11

What will changing the temperature of a system do to the equilibirum?

Answer 11

Change its position - the direction in which the equilibrium shifts depends on the sign of ΔH

Question 12

What does an increase in temperature do to the equilibirum?

Answer 12

Shift it in the endothermic direction - ΔH is positive

Question 13

What does a decrease in temperature do the equilibrium?

Answer 13

Shift the equilibrium in the exothermic direction - ΔH is negative

Question 14

What is used to investigate the change in equilibrium with temperature?

Answer 14

Cobalt chloride dissolved in water

SEPARATE NOTES!!!

Question 15

If the forward reaction is exothermic, what does an increase in temperature do?

Answer 15

Position of the equilibrium shifts to the left and more reactants are made

Question 16

If the forward reaction is exothermic, what does a decrease in temperature do?

Answer 16

Position of the electrons shifts to and the right and more products are made

Question 17

If the forward reaction is endothermic, what does an increase in temperature do?

Answer 17

Position of equilibrium shifts to the right and more products are made

Question 18

If the forward reaction is endothermic, what does a decrease in temperature do?

Answer 18

Position of equilibrium shifts to the left and more reactants are made

Question 19

What effect does an increase in pressure have on an equilibrium?

Answer 19

The equilibrium shifts to the side with fewer gaseous moles

Question 20

If the number of gaseous molecules is the same on both sides, what does an increase in pressure do?

Answer 20

Nothing

Question 21

What effect does a catalyst have on the equilibrium position?

Answer 21

It does not change the position of equilibrium - it speeds up the rates of forward and reverse reactions equally. However, it does increase the rate at which equilibrium is established

Question 22

What is the Haber process?

Answer 22

A process in how to make ammonia

N2 (g) + 3H2 (g) <=> 2NH3 (g)

Question 23

What is the change in enthalpy for the Haber process?

Answer 23

• 92 kJ mol^-1

Question 24

Is the Haber process exothermic or endothermic?

Answer 24

Exothermic

Question 25

What conditions would ideally make the highest yield of ammonia in the Haber process?

Answer 25

• A low temperature will push the equilibrium towards the ammonia
• A high pressure will push the equilibrium towards the ammonia

Question 26

Why can’t a low temperature be used in the Haber process?

Answer 26

It would produce a high yield but it would do so very slowly. It would take a long time for significant amounts of ammonia to form and the rate may be so slow equilibrium can’t even be established

Question 27

Why can’t a high pressure be used in the Haber process?

Answer 27

A very high pressure requires a very strong container and a large quantity of energy, increasing the cost of the process. Safety is also a concern, as a failure in steelwork could cause the leaking of hot gases including toxic ammonia

Question 28

What are the Haber process compromise conditions?

Answer 28

• Temperatures high enough to give a reasonable rate of reaction without shifting the equilibrium position too far to the right
• Pressure that is not a safety concern and not too expensive to run

these conditions are 350-500 degrees and 100-200 atm

Question 29

What is the notation for the equilibrium constant?

Answer 29

Kc

Question 30

How do you calculate Kc?

Answer 30

For the general reversible equation : aA + bB <=> cC + dD

where [ ] means concentration of

Question 31

What does a Kc value of 1 indicate?

Answer 31

The position of the equilibrium is halfway between the reactants and products

Question 32

What does a Kc value greater than 1 mean?

Answer 32

A position of equilibrium towards the products

Question 33

What does a Kc value less than 1 mean?

Answer 33

A position of equilibrium towards the reactants