For the system 2A (g) + B( g) = 2C (g), if the initial concentration of pure C is 1.00 M, the equilibrium concentration is 0.40 M. What is the value of Kc?

Choose one answer.

a. 5.0

b. 0.45

c. 0.67

d. 2.2

e. 1.5

3 answers

Set up an ICE chart and solve. Post your work if you get stuck.
2A + B= 2C
I 0 0 1.00

C 2X X -2X

E 2X X 1.00-2X

KC= 0.40= C^2/ A^2*B

square root 0.40 (x*x)=1.00-2x
0.40(X)^2 SQUARE ROOT 0.40-1.00

I ended up with 0.09 but when I plugged it back in then I don't get any of the above answers. I don't know what I was doing wrong.
2A + B ==> 2C

If Ceq = 0.4 and it was 1.0 initially, it must have changed by 1-0.4= 0.6

Therefore, B must have changed by +0.3 and A must hav changed by 0.6 so the final concns are
A = 0.6 M
B = 0.3 M
C = 0.4 M
Plug those in and calculate Kc.