Question

Consider the following reaction:

2NOBr(g) 2NO(g) + Br2(g)

If 0.332 moles of NOBr, 0.377 moles of NO, and 0.375 moles of Br2 are at equilibrium in a 14.6 L container at 429 K, the value of the equilibrium constant, Kp, is ___.

[NOBr] = .332mol/14.6 L = .0227 M
[NO] = .377mol/14.6 L = .0258 M
[Br2] = .375mol/14.6 L = .02568 M

I'm aware of the Kc = [products]/[reactants] with respect to having the coefficients being the exponents; therefore Kc = ([.0258 M NO]^2[.02568 M Br2])/[.0227 M NoBr]^2 = 7.53E-4

I'm also aware of the Kc to Kp conversion via Kp = Kc(RT)^delta(n)
Delta n is 3 mols in total of the product - 2 mols of the reactant = 1, therefore

Kp = 7.53E-4(.0821*429)^1 = .265221681.
Is this right? I have done another problem, but it was wrong, so I'm betting I am wrong again.

Answer 1

Thanks for showing your work. It helps us spot the problem.
The set up for Kc is correct but the answer is not. I get something like 3.317E-2 (and I know that's too many significant figures) for Kc. My best quickest guess is that you're punching in x instead of divide or not squaring or something like that. Since the chemistry is right it must be a calculator problem.
The Kp looks ok except for the Kc value but the Kp answer is correct for the value of Kc you used.