5.1.2 How Far?

Question 1

What is Kc?

Answer 1

[products]/[reactants]

Question 2

What does the value of Kc indicate?

Answer 2

• when Kc > 1 there are more products than reactants and equilibrium lies to the right
• when Kc < 1 there are more reactants than products and equilibrium lies to the left

Question 3

What happens to Kc when the temperature is increased?

Answer 3

• high temperature favours the endo direction and Kc will shift in that direction
• if Kc shifts away from the products then Kc will decrease

Question 4

What is the effect of a catalyst, pressure or concentration on Kc?

Answer 4

• Kc if only affected by temperature
• none of these will have a permanent effect

Question 5

What is Kp?

Answer 5

• used for gaseous equilibria
• use partial pressure p(A)
• use curly brackets
  Kp = (products)/(reactants)

Question 6

What happens to Kp with heterogeneous equilibria?

Answer 6

• liquids and solids are omitted from Kc because their concentrations are relatively constant

Question 7

How to calculate the mole fraction?

Answer 7

moles of gas A / total number of moles of gas

Question 8

What should mole fractions add up to?

Answer 8

1

Question 9

What is partial pressure?

Answer 9

• the pressure that an individual gas would exert if it occupied the reaction vessel on its own

Question 10

What is the equation for partial pressure?

Answer 10

• partial pressure = mole fraction of A x total pressure

Question 11

What should partial pressure add up to?

Answer 11

Total pressure

Question 12

What is homogeneous?

Answer 12

• all species in the same state or phase

Question 13

What is heterogeneous?

Answer 13

• species in different states or phases

Question 14

State and explain in terms of Kp how you would expect the equilibrium position to change

Answer 14

• equilibrium position shifts to the right / forwards / towards products
• ratio (in Kp expression) decreases or bottom of Kp expression increases more than top
• ratio (in Kp expression) shifts to restore Kp or top of Kp expression increases to restore Kp

Question 15

State and explain in terms of Kc how the equilibrium yield of SO3 would be different from the yield in the first experiment.

Answer 15

• Kc doesn’t change (with pressure/concentration)
• concentration of oxygen is greater or bottom of Kc expression is greater
• yield of SO3 increases and top of Kc expression increases and Kc shifts to restore