(12 pts) 11. A 2.00-L container at equilibrium at 550 K contains gases at the fo

Question

(12 pts) 11. A 2.00-L container at equilibrium at 550 K contains gases at the following concentrations: 0.1420 M CH,, 0.1420 M CCl, and 0.0380 M CH,Cl. The relevant reaction is shown below. CH,(g) + CCl,(g) 2 CH,C12(g) Suppose that l .530 g of CH,C, is added to the 2-L container above, and the system is allowed to return to equilibrium. Find the final concentration of CH,Cl, once equilibrium is restored. (The container remains at 550 K throughout.) Be sure to set up your work in an organized fashion so that you may receive some credit if you fail to solve the problem!

Explanation / Answer

Volume of container, V = 2 L

At constant temperature (550 K) equilibrium constant, Kc will remain constant.

CH4 (g) + CCl4 (g) --> 2 CH2Cl2 (g)

A)

Kc = [CH2Cl2]2/[CH4][CCl4]

= 0.0382 / (0.142 * 0.142)

= 0.0716

B)

Molar mass of CH2Cl2 = 84.93 g/mol

Moles of CH2Cl2 added = Mass of CH2Cl2 added / Molar mass of CH2Cl2

= 1.53 g / 84.93 g/mol

= 0.018

Initial [CH2Cl2] = 0.038 + 0.018 /V = 0.038 + 0.009 = 0.047 M

At new equilibrium:

CH4 (g) + CCl4 (g) --> 2 CH2Cl2 (g)

(0.142 + x) + (0.142 + x) --> (0.047 – 2x)

Kc = (0.047 – 2x)2 / (0.142 + x)2 = 0.0716

(0.047 – 2x) / (0.142 + x) = 0.2676

Solving we get,

x = 0.004

Final [CH2Cl2] = (0.047 – 2x)

= 0.047 – 2 * 0.004 = 0.039 M

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