Equiibria and Kc

Question 1

What is meant by dynamic equilibrium?

Answer 1

• rate of forward reaction = rate of backwards reaction
• concentrations of reactants and products constant

Question 2

Give a reason why a high pressure of 50 MPa is not normally used in the Haber Process

Answer 2

Too expensive to generate

Question 3

State and explain, by using Le Chatelier’s principle, one advantage, other than cost, of using a temperature lower than 800 K

Answer 3

Yield of ammonia increases (1)
Exothermic reaction favoured (1)
System moves to raise temp / or oppose decrease in temp (1)

Question 4

Why is 800K a compromise temperature?

Answer 4

Balance between rate and yield (1)

Question 5

Kc for this equilibrium has no units.
State why the units cancel in the expression for Kc

Answer 5

equal number of moles

Question 6

use le chatelier’s principle to explain if high/low temp should be used to obtain highest possible yield of hydrogen.

CH4 + H2O —> CO + 3H2
enthalpy change = +206kj mol-1

Answer 6

• high temperature
• forward reaction = endothermic
• at high temperatures equilibrium shifts to the right

Question 7

explain in terms of particles why high operating pressure is used in industry

Answer 7

• increases rate of reaction
• higher pressure = higher concentration of particles
• so more collisions

Question 8

nickel catalyst is used. explain why catalyst is more effective when coated onto an unreactive honeycomb

Answer 8

• increase in surface area
• so more successful collisions

Question 9

The total volume of the mixture does not need to be measured to allow a
correct Kc value to be calculated. justify this statement

Answer 9

volume cancels out/equal number of moles on each side