Marking criteria for option 2:
- (1) Initial n(P) and n(Q2) and n(PQ) from table.
- (2) Change in n(P) = equilibrium n(P) – initial n(P).
- (3) USING ratio: P : Q2 : PQ = 2 : 1 : 2.
- (4) Equilibrium n(Q2) = initial n(Q2) + change in n(Q2) and Equilibrium n(PQ) = initial n(PQ) - change in n(PQ).
- (5) Divide equilibrium amounts of P and Q2 and PQ by 2 dm3.
- (6) Correct Kc expression (formulae in square brackets).
- (7) Substitution of equilibrium concentrations into Kc expression.
- (8) Final answer: 10,889.
Marking criteria option 3:
- (1) Initial n(P) = 4 mol and n(Q2) = 2,4 mol and n(PQ) = 0.
- (2) Change in n(P) = equilibrium n(P) – initial n(P) = 2,8 mol.
- (3) USING ratio: P : Q2 : PQ = 2 : 1 : 2.
- (4) Equilibrium n(Q2) = initial n(Q2) + change in n(Q2) and Equilibrium n(PQ) = initial n(PQ) - change in n(PQ).
- (5) Divide equilibrium amounts of P and Q2 and PQ by 2 dm3.
- (6) Correct Kc expression (formulae in square brackets).
- (7) Substitution of equilibrium concentrations into Kc expression.
- (8) Final answer: 10,889.
Marking criteria option 4:
- (1) Initial c(P) and c(Q2) and c(PQ) from table.
- (2) Change in c(P) = equilibrium c(P) – initial c(P).
- (3) USING ratio: P : Q2 : PQ = 2 : 1 : 2.
- (4) Equilibrium n(Q2) = initial n(Q2) + change in n(Q2) and Equilibrium n(PQ) = initial n(PQ) - change in n(PQ).
- (5) Divide initial amounts of P and Q2 and PQ by 2 dm3
- (6) Correct Kc expression (formulae in square brackets).
- (7) Substitution of equilibrium concentrations into Kc expression.
- (8) Final answer: 10,889.
Or
Option 2
PQ | P | Q2 | |
Initial quantity (mol) | 3,2 | 0,8 | 0,8 |
Change (mol) | 0,4 | 0,4 | 0,2 |
Quantity at equilibrium (mol) | 2,8 | 1,2 | 1,0 |
Equilibrium concentration (mol∙dm-3) | 1,4 | 0,6 | 0,5 |
Reverse reaction:
Forward reaction:
Or
Option 3
P | Q2 | PQ | |
Initial quantity (mol) | 4 | 2,4 | 0 |
Change (mol) | 2,8 | 1,4 | 2,8 |
Quantity at equilibrium (mol) | 1,2 | 1,0 | 2,8 |
Equilibrium concentration (mol∙dm-3) | 0,6 | 0,5 | 1,4 |
Or
Option 4
P | Q2 | PQ | |
Initial concentration (mol∙dm-3) | 0,4 | 0,4 | 1,6 |
Change in concentration (mol∙dm-3) | 0,2 | 0,1 | 0,2 |
Equilibrium concentration (mol∙dm-3) | 0,6 | 0,5 | 1,4 |