19 Equilibrium

Question 1

What are the two main types of equilibria? (2 marks)

Answer 1

Homogeneous
Heterogeneous

Question 2

What is homogeneous equilibrium? (2 marks)

Answer 2

Species all the same state.
Everything is included in the equation for Kc

Question 3

What is heterogeneous equilibrium? (2 marks)

Answer 3

Species have different states.
Solids and liquids are not included in equation for Kc.

Question 4

Why are solids and liquids not included in a heterogenous Kc equation? (1 mark)

Answer 4

The concentration of solids and liquids are essentially constant.

Question 5

What do the values in the square brackets in the Kc equation represent? (2 marks)

Answer 5

Concentrationof species
At equilibrium

Question 6

What environmental factor affects K? (1 mark)

Answer 6

Temperature

Question 7

What happens to K when temperature increases, in an exothermic reaction? (1 mark)

Answer 7

Decreases

Question 8

What happens to K when temperature increases, in an endothermic reaction? (1 mark)

Answer 8

Increases

Question 9

Describe the effect of increasing the pressure on Kc for a reaction with less moles on the right. (3 marks)

Answer 9

An increase in pressure causes an increase in concentration.
Terms on the bottom of the Kc are more than on the top.
Therefore, the top if the expression increases and the bottom decreases until (the original) Kc is reached, and equilibrium restored.

Question 10

Describe what happens to Kp when the temperature is increased, in an exothermic reaction. (5 marks)

Answer 10

The system is no longer in equilibrium.
The expression is now greater than Kp.
Therefore, the partial pressure of the products must decrease and the partial pressure of the reactants must increase.
Until a new equilibrium is reached, with a new Kp.
Which is lower than the original.

Question 11

Describe what happens to Kp when the temperature is increased, in an endothermic reaction. (5 marks)

Answer 11

The system is no longer in equilibrium.
The expression is now less than Kp.
Therefore, the partial pressure of the products must increase and the partial pressure of the reactants must decrease.
Until a new equilibrium is reached, with a new Kp.
Which is greater than the original.

Question 12

What is the equation for mole fraction? (2 marks)

Answer 12

x(A) = no. of moles of A/ total no. of moles in gas mixture

Question 13

What is the equation for partial pressure? (2 marks)

Answer 13

Partial pressure = mole fraction of A x total pressure

Question 14

What is the relationship between partial pressures and total pressure? (1 mark)

Answer 14

Sum of partial pressures = total pressure

Question 15

What state does the expression for Kp only contain? (1 mark)

Answer 15

Gas

Question 16

What are the three acceptable units for partial pressure? (3 marks)

Answer 16

kPa
Pa
atm