Question

The concentrations of reactants and products for a chemical reaction can be calculated if the equilibrium constant for the reaction and the starting concentrations of reactants and/or products are known.

Carbonyl fluoride, COF2, is an important intermediate used in the production of fluorine-containing compounds. For instance, it is used to make the refrigerant carbon tetrafluoride, CF4 via the reaction

2COF2(g)⇌CO2(g)+CF4(g),    Kc=7.40

If only COF2 is present initially at a concentration of 2.00 M, what concentration of COF2 remains at equilibrium?

Consider the reaction

CO(g)+NH3(g)⇌HCONH2(g),    Kc=0.640

If a reaction vessel initially contains only CO and NH3 at concentrations of 1.00 M and 2.00 M, respectively, what will the concentration of HCONH2 be at equilibrium?

Express your answer with the appropriate units.

Answer 1

Q1-

2COF2(g)⇌CO2(g)+CF4(g),    Kc=7.40

K = [CO2][CF4]/[COF2]^2

initially

[CO2] = 0

[COF2] = 0

[CO2] = 2

in equilibrium

[CO2] = 0 + x

[CF4] = 0 + x

[COF2] = 2 -2x

7.4 = (x)(x) / (2-2x)^2

sqrt(7.4) = x/(2-x2)

2.72*(2-2x) = x

5.44 - 5.44x = x

6.44x = 5.44

x = 5.44/6.44 = 0.8447

[COF2] = 2 -2x = 2-2*0.8447= 0.3106M

Q2.

similarly:

[CO] = 1

[NH3] = 2

[HCONH2] = 0

in equilbirium

[CO] = 1 - x

[NH3] = 2 - x

[HCONH2] = 0 + x

Kc = [HCONH2] / ([CO][NH3])

0.64 = x / (1-x)(2-x)

(1-x)(2-x) = 1.5625x

2-3x +x^2 = 1.5625x

x^2 -(3+1.5625)x +2 = 0

x^2 - 4.5625x +2 = 0

x = 0.4912

[CO] = 1 - 0.4912 = 0.5088

[NH3] = 2 - 0.4912 = 1.5088

[HCONH2] = 0 + 0.4912= 0.4912M