Phosphorus pentachloride decomposes to phosphorus trichloride at high temperatur
ID: 1036810 • Letter: P
Question
Phosphorus pentachloride decomposes to phosphorus trichloride at high temperatures according to the reaction:
PCl5(g) ? PCl3(g) + Cl2(g)
At 250°C, 0.250 M PCl5 is added to a flask. If Kc = 1.80, what are the equilibrium concentrations of each gas?
[PCl5] = 1.25 M, [PCl3] = 0.474 M, [Cl2] = 0.474 M
[PCl5] = 0.0280 M, [PCl3] = 0.222 M, [Cl2] = 0.222 M
[PCl5] = 2.27 M, [PCl3] = 2.02 M, [Cl2] = 2.02 M
[PCl5] = 1.80 M, [PCl3] = 1.80 M, [Cl2] = 1.80 M
[PCl5] = 1.25 M, [PCl3] = 0.474 M, [Cl2] = 0.474 M
[PCl5] = 0.0280 M, [PCl3] = 0.222 M, [Cl2] = 0.222 M
[PCl5] = 2.27 M, [PCl3] = 2.02 M, [Cl2] = 2.02 M
[PCl5] = 1.80 M, [PCl3] = 1.80 M, [Cl2] = 1.80 M
Explanation / Answer
PCl5(g) ? PCl3(g) + Cl2(g)
Initial Conc. 0.250M 0 0
Change -x +x +x
Eq. Conc. (0.250-x) x x
Kc = 1.80
Kc = x2/(0.250-x)
1.80 = x2/(0.250-x)
Rearranging
x2+1.80x- 0.45 = 0
Solving the quadaratic equation
x = 1.80+-SQRT(1.80*1.80-4*1*(-0.45))
x = 0.222M
So the concentation of PCl3 and Cl2 are 0.222M and the equlibrium conc. of PCl5 is (1.80-0.222) 0.0280M
so the second option is correct ([PCl5] = 0.0280 M, [PCl3] = 0.222 M, [Cl2] = 0.222 M)