10: Kp and the Equilibrium Constant

Question 1

When do we use Kp instead of Kc?

Answer 1

When looking at equilibrium between gases.

Question 2

What is partial pressure?

Answer 2

The pressure caused by one of the components in the system.

Question 3

Describe the partial pressure if gases are in equal quantities.

Answer 3

Partial pressure of all components will be the same.

Question 4

What are mole fractions?

Answer 4

The proportion of moles of a gas within the gas mixture

Question 5

Give the formula for mole fractions.

Answer 5

mole fraction = no. of moles of gas / total moles of gas

Question 6

If mole fraction is high, what is partial pressure likely to also be?

Answer 6

High

Question 7

Give the equation for partial pressure.

Answer 7

Partial pressure = mole fraction x total pressure

Question 8

How do catalysts affect Kp?

Answer 8

No effect on Kp. Increases the rate of the forward and backward reaction the same.

Question 9

How might an increase in temperature affect Kp?

Answer 9

Equilibrium shifts in the endothermic direction, so partial pressure of the substances in this direction all increase. Therefore, Kp increases.

Question 10

Why will a change in pressure have no effect on Kp?

Answer 10

Pressure rises for one molecule . This raises overall total pressure, so partial pressure of other molecules also rises. This means Kp does not change.

Question 11

Give an equation for Kp.

Answer 11

Kp = [partial pressure of reactants] / [partial pressure of products]