Equillibrium

Question 1

If the Kc value is > 1 then:

Answer 1

products predominate and eqbm lies to the RHS

Question 2

Only factor that affects the value of Kc:

Answer 2

temperature

Question 3

2 features of dynamic equilibrium:

Answer 3

• forward and back reactions occuring simultaneously at equal rates
• the concentrations of prod & reactants remain constant

Question 4

Another 36.8 g sample of N2O4 was heated to the same temperature as in the original experiment, but in a larger flask. State the effect, if any, of this change on the position of equilibrium and on the value of Kc compared with the original experiment.
X <-> 2X

Answer 4

• position of eqbm shift to RHS
• Kc unaffected; only affected by temperature

Question 5

Define dynamic eqbm: (2)

Answer 5

• rate of forward = rate of backward,bot happening simultaneously
• conc. of products and reactants kept constant

Question 6

Many industrial ammonia plants operate at a compromise temperature of about 800 K.
(i) State and explain, by using Le Chatelier’s principle, one advantage, other than cost, of using a temperature lower than 800 K. (3)

Answer 6

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

Question 7

Format for eqbm position:

Answer 7

• state condition being changed
• the direction that eqbm will shift
• exothermic or endothermic
• state what this will oppose

Question 8

When do the units in Kc expression cancel out?

Answer 8

Equal no. of moles on each side of equation

Question 9

At high temperatures, nitrogen is oxidised by oxygen to form nitrogen monoxide in a reversible reaction as shown in the equation below.
..
N2(g) + O2(g) -> 2NO(g) ∆Hο
..
= +180 kJ mol–1
…
State and explain the effect of an increase in pressure, and the effect of an increase in temperature, on the yield of nitrogen monoxide in the above equilibrium.

Answer 9

• no change
• equal number of gaseous moles on either side
• both sides affected equally
• increases
• equilibrium moves to lower the temperature/oppose the change
• endothermic reaction favoured /forward reaction is endothermic

Question 10

State and explained the effect of using a catalyst on the yield of methanol in this equilibrium. (2)

Answer 10

no effect (on yield)

increases rate of both forward and reverse reactions equally