Question

The reaction CH2Cl2 (g) --> CH4 (g) + CCl4 (g) has Kp = 1.33 at 400K. A 5.00L reaction vessel is evacuated, and 15.00 g of CH2Cl2 (l) is added to the flask. The CH2Cl2 (l) rapidly vaporizes and the reaction starts. a. What will be all of the partial pressures of the gases when equilibrium is reached? b. Sketch a graph showing the initial concentration of each gas and how they change as the mixture approaches equilibrium. Set-up your graph so that equilibrium is reacched two thirds of the way from the start to the end of the graph

Answer 1

[CH₂Cl₂] = 15.00 / (85 * 5) = 0.0353 M

P_CH2Cl2 = [CH₂Cl₂] R T = 0.0353*0.0821*400 = 1.16 atm

CH2Cl2 (g) --> CH4 (g) + CCl4 (g)

1.16 atm            0 atm           0 atm                 Initial

1.16 - x               x                   x                       Equilibrium

Kp = P_CH4 * P_CCl4 / P_CH2Cl2

1.33 = x * x / (1.16 - x)

1.54 - 1.33 x = x²

x² + 1.33 x - 1.54 = 0

Solving quadratic equation

x = [ - 1.33 +/- (1.77 + 6.16)1/2 ] / 2 = 0.743 atm

At equilibruim,

P_CH2Cl2 = 1.16 - 0.743 = 0.417 atm

P_CH4 = P_Cl2 = 0.743 atm