7. Equilibrium

Question 1

What are the features of dynamic equilibrium?

Answer 1

• Requires a closed system
• Forward and reverse reactions are at the same rate
• Forward and reverse reactions concentrations remain constant.

Question 2

Define ‘yield’.

Answer 2

The amount of product in the equilibrium mixture, usually expressed as a percentage.

Question 3

Define a ‘homogeneous system’.

Answer 3

All reactants, products and catalysts are in the same phase.

Question 4

Define a ‘heterogeneous system’.

Answer 4

One of the chemicals is in a different state.

Question 5

State Le Chatelier’s principle.

Answer 5

• High pressure favours the side with the fewest moles of gas.

Question 6

How do catalysts affect equilibrium?

Answer 6

They don’t because they increase the rate of both reactions equally.

Question 7

What happens if you remove a substance from the equilibrium mixture?

Answer 7

The position of equilibrium will shift to replace the substance.

Question 8

What does Kc refer to?

Answer 8

The concentration of reactants.

Question 9

What does a large Kc mean?

Answer 9

Lots of products are formed.

Question 10

What is Kc affected by?

Answer 10

Only temperature and stochiometric coefficients.

Question 11

Kc= ?

Answer 11

[products]/ [reactants]

Question 12

What does it mean if Kc>1?

Answer 12

The products are favoured over reactants.

Question 13

What does it mean if Kc<1?

Answer 13

The reactants are favoured over the products.

Question 14

What does it mean if Kc=1?

Answer 14

The mixture contains appreciable amounts of both products and reactants.

Question 15

What is the effect on Kc if the coefficient is halved?

Answer 15

√Kc

Question 16

What is the effect on Kc if the coefficient is doubled?

Answer 16

Kc²

Question 17

What is the effect on Kc if the equation is reversed?

Answer 17

1/Kc

Question 18

What is the effect on Kc if the equations are added together?

Answer 18

The Kc values are added together.

Question 19

How does an increase in temperature affect an exothermic forward reaction?

Answer 19

• The equilibrium will shift in the endothermic direction (to the left)
• Yield of products decreases

Question 20

How does an increase in temperature affect an endothermic forward reaction?

Answer 20

• The equilibrium will shift in the endothermic direction (to the right)
• Yield of products increases

Question 21

What is the reaction quotient?

Answer 21

When a system is not at equilibrium, the ratio of concentrations of products and reactants differs from the Kc value.

Question 22

What does it mean if Q>K?

Answer 22

There are less reactants and more products than needed for equilibrium, so the reverse reaction will be favoured.

Question 23

What does it mean if Q<K?

Answer 23

The mixture contains more reactants and less products than needed for equilibrium, so the forward reaction is favoured.

Question 24

What does it mean if Q=K?

Answer 24

Equilibrium has been achieved so the rate of forward and backward reaction will be the same.

Question 25

What is the equation that links K and Gibbs Energy?

Answer 25

∆G= -RT lnK

Question 26

What does a negative ∆G value for a reaction indicate?

Answer 26

• The reaction is feasible/ spontaneous
• The equilibrium concentration of the products is greater than the equilibrium concentration of the reactants.
• The value of the equilibrium constant will be greater than 1.