In: Chemistry
An equilibrium mixture of PCl5(g), PCl3(g), and Cl2(g) has partial pressures of 217.0 Torr, 13.2 Torr, and 13.2 Torr, respectively. A quantity of Cl2(g) is injected into the mixture, and the total pressure jumps to 263.0 Torr (at the moment of mixing). The system then re-equilibrates. The appropriate chemical equation is
PCl3(g) + Cl2(g) <---> PCl5(g)
Calculate the new partial pressures after equilibrium is reestablished.
P PCl3 = ? torr
P PCl2 = ? torr
P PCl5 = ? torr
[pPCl3] = 6.80 torr
[pCl2] = 26.4 torr
[pPCl5] = 223.4 torr
Explanation
pressure equilibrium constant, Kp = [pPCl5]eq / [pPCl3]eq[pCl2]eq
Kp = (217.0 torr) / (13.2 torr) * (13.2 torr)
Kp = 1.2454
Total pressure = [pPCl5]eq + [pPCl3]eq + [pCl2]eq
Total pressure = (217.0 torr) + (13.2 torr) + (13.2 torr)
Total pressure = 243.4 torr
pressure Cl2 added = (total pressure after adding Cl2) - (total pressure before adding Cl2)
pressure Cl2 added = (263.0 torr) - (243.4 torr)
pressure Cl2 added = 19.6 torr
total pressure Cl2 = (13.2 torr) + (19.6 torr)
total pressure Cl2 = 32.8 torr
ICE table | PCl3 | Cl2 | PCl5 |
Initial | 13.2 torr | 32.8 torr | 217.0 torr |
Change | -x | -x | +x |
Equilibrium | 13.2 torr - x | 32.8 torr - x | 217.0 torr + x |
Kp = [pPCl5]eq / [pPCl3]eq[pCl2]eq
1.2454 = (217.0 torr + x) / [(13.2 torr - x) * (32.8 torr - x)]
solving for x, x = 6.4 torr
[pPCl3]eq = 13.2 torr - x
[pPCl3]eq = 13.2 torr - 6.4 torr
[pPCl3]eq = 6.80 torr
[pCl2]eq = 32.8 torr - x
[pCl2]eq = 32.8 torr - 6.4 torr
[pCl2]eq = 26.4 torr
[pPCl5]eq = 217.0 torr + x
[pPCl5]eq = 217.0 torr + 6.4 torr
[pPCl5]eq = 223.4 torr