Question

1)Phosphorus pentachloride decomposes according to the chemical equation,A 0.170 mol sample of PCl5(g) is injected into an empty 2.10 L reaction vessel held at 250 °C. Calculate the concentrations of PCl5(g) and PCl3(g) at equilibrium. Kc=1.80 at 250 C

2)Carbon disulfide is prepared by heating sulfur and charcoal. The chemical equation is S2+C-CS2. How many grams of CS2(g) can be prepared by heating 19.4 moles of S2(g) with excess carbon in a 8.40 L reaction vessel held at 900 K until equilibrium is attained? Kc-9.40 at 900K

Answer 1

1)

molarity of PCl5 = 0.170 / 2.10 = 0.081 M

Kc = 1.80

PC5 ------------------> PCl3 + Cl2

0.081 0 0 ----------------> initial

0.081-x x x -----------------> equilibrium

Kc = [PCl3][Cl2]/[PCl5]

1.80 = x^2 / 0.081 -x

x^2 + 1.80 x - 0.1457 = 0

x = 0.0776

equilibrium concentrations:

[PCl5] = 0.081 - x = 0.0034 M

[PCl3] = x =0 .0776 M

[Cl2] = x =0 .0776 M

2 )

molarity of S2 = 19.4 / 8.40 = 2.31 M

S2 (g) + C (s) --------------------> CS2

2.31 -x x

Kc = x / 2.31 -x

9.40 = x / 2.31 -x

21.71 - 9.40 x = x

21.71 = 10.40 x

x = 2.087

molarity of CS2 formed = 2.087 M

moles = molarity x volume

= 2.087 x 8.40

= 17.53

mass = 17.53 x 76

mass = 1332.6 g

mass of CS2 formed = 1332 .6 g