# Calculating the equilibrium constant at a initial pressure?

For the following reaction:

2 A(g) + B(g) ⇌ C(g)

Calculate the equilibrium constant K given the following information:

The initial pressure of A is 3.200 bar and the initial pressure of B is 3.355 bar

The equilibrium pressure of C is 0.798 bar

### 1 Answer

- hcbiochemLv 71 year agoFavorite Answer
Again, start with the expression for K. Since you are given pressures, this is often called Kp:

K = P(C) / [P(A)]^2 [P(B)]

Now, here, you are given initial pressures of A and B and an equilibrium pressure of C. So you need to find the equilibrium pressures of A and B. Since 0.798 bar of C was formed, thinking about the stoichiometry of the reaction, 0.798 bar of B had to be consumed, as did 2(0.798 ) = 1.596 bar of A. So, the equilibrium pressure of A is:

P(A) = 3.200 - 1.596 = 1.604 bar

And for B:

P(B) = 3.355 - 0.798 = 2.557

So, K for this reaction is:

K = (0.798) / (1.604)^2 (2.557) = 0.121

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