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.
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.
Your calculations are correct! The equilibrium constant, Kp, is indeed 0.265221681. Good job!
Your approach for calculating the value of the equilibrium constant, Kp, is correct. However, there are some errors in your calculation.
First, when calculating the concentrations of NOBr, NO, and Br2, you should divide the number of moles by the volume expressed in liters. So the correct concentrations are:
[NOBr] = 0.332 mol / 14.6 L = 0.0227 M
[NO] = 0.377 mol / 14.6 L = 0.0258 M
[Br2] = 0.375 mol / 14.6 L = 0.0257 M
Second, when calculating Kc, the exponents should correspond to the coefficients in the balanced equation. In this case, the coefficients are 2 for NOBr, NO, and Br2. So the correct expression for Kc is:
Kc = ([NO]^2[Br2])/([NOBr]^2) = (0.0258^2 * 0.0257)/(0.0227^2) = 9.62E-4
Lastly, to convert Kc to Kp, you need to consider the stoichiometry of the reaction. In this case, the change in the number of moles, Δn, is 1 (2-2). The gas constant, R, is 0.0821 L * atm / (mol * K), and the temperature, T, is 429 K. So the correct conversion is:
Kp = Kc * (R * T)^Δn
= 9.62E-4 * (0.0821 * 429)^1
= 0.3217
Therefore, the value of the equilibrium constant, Kp, is approximately 0.3217.