Question

For the following reaction, Kc = 255 at 1000 K. CO (g) + Cl2 (g) ⇌ COCl2 (g)

Part A

If a reaction mixture initially contains a CO concentration of 0.1490 and a Cl2 concentration of 0.179 at 1000K. What is the equilibrium concentration of CO at 1000 K?

Part B

What is the equilibrium concentration of Cl2 at 1000 K?

Express your answer in molarity to three significant figures.

Part C

What is the equilibrium concentration of COCl2 at 1000 K?

Express your answer in molarity to three significant figures.

Answer 1

Data given : Kc =255

Let us first write the reaction

CO_(g)         + Cl_2(g)      -------->    COCl_2(g)

0.149                  0.179                               -

0.149-x                0.179-x                           x       

The Kc expression for the above reaction will be

Substituting the concentration in terms of x and the value of Kc

255 * (0.149-x)*(0.179-x) = x

255 ( 0.02667-(0.149+0.179)x+x²) = x

255 ( 0.02667-0.328x+x²) = x

6.80085-83.64x+255x² =x

255x² -84.64x +6.80085 =0

solving the above quadratic equation we get

x =0.1955, 0.13641

Here we both the roots positive but the 1^st root '0.1955' is not possible since the maximum amount of reactant present is 0.179 CL2 and 1 mole Cl2 = 1 mole COcl2, Hence maximum 0.179 M of CoCL2 can be formed.

Hence x=0.1955 can be discarded

Hence x =0.13641 M

Concentration of COCL2 =x =0.13641 M

Concentration of CO =0.149-x   =0.01259 M

Concentration of Cl2 = 0.179-x =0.04259 M