Kp

Question 1

Definition of homogeneous system:

Answer 1

A homogeneous system is one where all reactants and products are in the same phase

Question 2

What is total pressure?

Answer 2

Sum of the partial pressures of each different gas

Question 3

Equation for mole fraction:

Answer 3

Mole Fraction of A = Moles of Gas A in the mixture ÷ Total Moles of all gases

All mole fractions within a mixture should add up to 1

Question 4

Equation for partial pressure:

Answer 4

Partial pressure of A = Mole Fraction of A x Total Pressure

Question 5

Equation for Kp:
Eg: A + 2B ⇌ 3C + D

Answer 5

p(C)3 × p(D) ÷ p(A) × p(B)2

p(Products) ÷ p(Reactants)

DO NOT USE SQUARE BRACKETS FOR Kp EXPRESSION

Question 6

If Kp is greater than 1:

Answer 6

If Kp is greater than 1 it means the equilibrium is towards the right hand side (i.e. more products than reactants).

Question 7

If Kp is less than 1:

Answer 7

If Kp is less than 1 it means the equilibrium is towards the left hand side (i.e. more reactants than products).

Question 8

If Kp is exactly 1:

Answer 8

If Kp is exactly 1 it means the equilibrium is in the middle (i.e. equal amounts of products and reactants).

Question 9

What condition can change Kp value?

Answer 9

The only condition which can cause the Kp value to change is a change in temperature

Question 10

Units of Kp:

Answer 10

Pa / kPa / Atm

Top number - bottom number

Question 11

How would an increase in pressure affect the position of equilibrium?

Eg: N2(g) + 3H2(g) ⇌ 2NH3(g)
∆H = -92kJmol-1

Answer 11

• The equilibrium will shift to the RIGHT
• There are fewer gaseous moles on the right hand side
• The equilibrium will shift to oppose the increase in pressure

Question 12

How would an increase in temperature affect the equilibrium yield of the product?

Eg: N2(g) + 3H2(g) ⇌ 2NH3(g)
∆H = -92kJmol-1

Answer 12

• The equilibrium yield of the product will decrease
• The forward reaction is exothermic.
• The equilibrium will shift to oppose the increase in temperature

Question 13

How would a decrease in temperature affect the value of Kp?

Eg: N2(g) + 3H2(g) ⇌ 2NH3(g)
∆H = -92kJmol-1

Answer 13

• The value of Kp will increase.
• The forward reaction is exothermic.
• The equilibrium will shift to oppose the decrease in temperature.

Question 14

Effect of increasing temperature:

Forward reaction is exothermic

Answer 14

-Equilibrium shifts in the reverse direction, to favour the endothermic reaction, and so reduce the temperature.
-The yield of products decreases.
-The partial pressures of the products will decrease, therefore Kp will decrease

Question 15

Effect of decreasing temperature:

Forward reaction is exothermic

Answer 15

-Equilibrium shifts in the forward direction, to favour the exothermic reaction, and increase the temperature
-More products are formed.
-The partial pressure of the products will increase, therefore Kp will increase

Question 16

Effect of increasing temperature:

Forward reaction is endothermic

Answer 16

-Equilibrium shifts in the forward direction, to favour the endothermic reaction and reduce the temperature.
-More products are formed.
-The partial pressure of the products will increase, therefore Kp will increase.

Question 17

Effect of decreasing temperature:

Forward reaction is endothermic

Answer 17

-Equilibrium shifts in the reverse direction, to favour the exothermic reaction and increase temperature.
-The yield of products decreases.
-The partial pressures of the products will decrease, therefore Kp will decrease.

Question 18

Effect of adding a catalyst:

Answer 18

Adding a catalyst does not affect the value of Kp

A catalyst simply allows equilibrium to be reached sooner. A catalyst will affect the rate of reaction in both directions by the same amount.

Question 19

Effect of changing pressure on Kp:

Answer 19

Pressure does not affect the value of Kp

Question 20

Effect of increasing pressure on equilibrium:

Answer 20

Increase in pressure causes equilibrium to shift in favour of the direction with the fewer moles so that the pressure decreases.

Question 21

If Kp value changes:

Answer 21

If the Kp increases, the concentration of products will increase and the concentration of reactants will decrease
If the Kp decreases, the concentration of reactants increases and the concentration of products decreases

Question 22

Definition of dynamic equilibrium:

Answer 22

When a reversible reaction takes place in a closed system so that the rate of the forward reaction is equal to the rate of the reverse reaction
The temperature, concentrations of reactants and products and pressure are all constant at equilibrium.