5.1.2 - Equilibrium

Question 1

Equilibrium constant, Kc

Answer 1

• The large the value of Kc, the further the position of equilibrium towards the products
  c[] moldm-3

Question 2

Homogeneous equilibria

Answer 2

• Contains equilibrium species that all have the same state or phase

Question 3

Heterogeneous equilibria

Answer 3

• Contains equilibrium species that have different states or phases

Question 4

Calculating equilibrium quantities and Kc

Answer 4

1. Using the equation given, work out the equilibrium amounts of all equilibrium species using ICE
2. Find the equilibrium conc in moldm-3
   Divide the equilibrium amounts by the total volume in the reaction
3. Write the expression of Kc, substitute values + calculate Kc

Question 5

Equilibrium constant, Kp

Answer 5

• Equilibrium constant in terms of partial pressures
  p() atm

Question 6

Mole fraction

Answer 6

-Mole fraction of a gas is the same as its proportion by volume to the total volume of gases in a gas mixture.
Mole fraction x(A) = number of moles of A / total number of moles in gas mixture
- The sum of the mole fractions in a gas mixture must equal one

Question 7

Partial pressure

Answer 7

• The contribution that the gas makes towards the total pressure P
• The sum of the partial pressures of each gas equals the total pressure
  Partial pressure p(A) = mole fraction of A X total pressure P
  p(A) = x(A) X P

Question 8

3 rules of changing equilibrium

Answer 8

1. If conc of species increased - equilibrium shifts in direction that reduces the conc
2. If pressure increased - equilibrium shifts towards side with fewer gaseous moles
3. If temp increased - equilibrium position shifts in endothermic direction

Question 9

When do equilibrium constants change

Answer 9

• At a set temp, K is constant and doesn’t change despite any modifications to conc, pressure or presence of catalyst
• K does change if the temp is changed

Question 10

Effect of temp on equilibrium constants K

Answer 10

Exothermic reactions:
- equilibrium constant decreases with increasing temp
- raising temp decreases equilibrium yield of products

Endothermic reactions:
- equilibrium constant increases with increasing temp
- raising temp increases equilibrium yield of products

Question 11

What do catalysts affect

Answer 11

• Affect the rate of a chemical reaction not the position of equilibrium
• Speed up both the forward and reverse reactions in the equilibrium by the same factor
• Equilibrium is reached quicker