In: Chemistry
The equilibrium constant K=0.36 for the reaction PCl5 (g) PCl3 (g) +Cl2 (g). (a) Given that 2.0 g of PCl5 was initially placed in the reaction chamber of volume 250 cm3, determine the molar concentration in the mixture at equilibrium. (b) What is the percentage of PCl5 decomposed.
PCl5 moles = mass / Molar mass of PCl5 = ( 2g) / ( 208.24g/mol) = 0.0096
volume = 250 cm3 = 250 ml = 0.25L
[PCl5] = ( 0.0096/0.25) = 0.0384 M
PCl5 (g) <------> PCl3 (g) + Cl2 (g)
Initial 0.0384 0 0
equilibrium 0.0384 -X X X
Kc = [PCl3] [Cl2] /[PCl5]
0.36 = ( X^2) / ( 0.0384-X)
X^2 + 0.36X - 0.01383 = 0
X = 0.035
at equilibrium [PCl3] =[Cl2] = 0.035M
[PCl5] = 0.0384-0.035 = 0.0034 M
b) % of PCl5 decomposed = 100 x ( PCl5 decomposed (i,e X) / PCl5 initial amount)
( 100 x 0.035/0.0384) = 91.15 %