M3 ,, Chemical Equilibrium

Question 1

Dynamic equilibrium?

Answer 1

Dynamic equilibrium occurs when forward and backward reactions are occurring at equal rates. The concentrations of reactants and products stays constant and the reaction is continuous.

All reversible reactions reach an dynamic equilibrium state.

Question 2

Le Chatelier’s Principle?

Answer 2

states that if an external condition is changed the equilibrium will shift to oppose the change (and try to reverse it).

Question 3

Effect of Temperature increase on equilibrium?

Answer 3

If temperature is increased the equilibrium will shift to oppose this and move in the endothermic, backwards direction to try to decrease temperature. The position of equilibrium will shift towards the left, giving a lower yield of ammonia.

Question 4

Effect of Temperature decreases on equilibrium?

Answer 4

If temperature is decreased the equilibrium will shift to oppose this and move in the exothermic direction to try to increase the temperature by giving out heat.

Question 5

Effect of increasing Pressure on equilibrium?

Answer 5

If pressure is increased the equilibrium will shift to oppose this and move towards the side with fewer moles of gas to try to reduce the pressure . The position of equilibrium will shift towards the right because there are 3 moles of gas on the left but only 1 mole of gas on the right, giving a higher yield of methanol.

Question 6

Effect of Pressure decreasesing on equilibrium?

Answer 6

Decreasing pressure will cause the equilibrium to shift towards the side with more moles of gas to oppose the change and thereby increase the pressure.

Question 7

Effect of catalysts on equilibrium?

Answer 7

A catalyst has no effect on the position of equilibrium, but it will speed up the rate at which the
equilibrium is achieved.
It does not effect the position of equilibrium because it speeds up the rates of the forward and backward reactions by the same amount.

Question 8

Hager process?

Answer 8

N2 + 3H2 2NH3 H = -ve exo
T= 450oC, P= 200 – 1000 atm, catalyst = iron
Low temp gives good yield but slow rate: compromise temp used
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure

Question 9

Contact process?

Answer 9

Stage 1 S (s) + O2 (g)SO2 (g)
Stage 2 SO2 (g) +1⁄2O2 (g) SO3 (g) H = -98 kJ mol-1
T= 450oC, P= 1 to 2 atm, catalyst = V2O5
Low temp gives good yield but slow rate: compromise moderate temp used
High pressure gives slightly better yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure

Question 10

Production of methanol from CO?

Answer 10

CO (g) + 2H2(g) CH3OH (g) H = -ve exo T= 400oC, P= 50 atm, catalyst = chromium and
zinc oxides
Low temp gives good yield but slow rate: compromise temp used
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure.

Question 11

Hydration of ethene to produce ethanol?

Answer 11

CH2=CH2 (g) + H2O (g) CH3CH2OH(l) H = -ve
T= 300oC, P= 70 atm, catalyst = conc H3PO4
Low temp gives good yield but slow rate: compromise temp used.
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure.
High pressure also leads to unwanted polymerisation of ethene to poly(ethene).

Question 12

Effect of changing conditions on value of Kc?

Answer 12

The larger the Kc the greater the amount of products.
If Kc is small we say the equilibrium favours the reactants

Kc only changes with temperature. It does not change if pressure or concentration is altered.
A catalyst also has no effect on Kc