So I have the reaction

Question

2HBr(g) <--> H2(g)+Br2(g)

I'm supposed to find the equilibrium constant, K, using free energy (G) values. The values in my textbook for G of H2 and Br2 were zero, and the value for HBr(g) was -53.5.

So, to find delta G I did products - reactants and got (0+0)-(2(-53.5)) and got that the delta G is +107.

Next I plugged that into the equation
deltaG = -RTlnK.

107kJ/mol(1000J/1kJ) = -8.314(298K)lnK
-43.2 = lnK
K=1.75x10^-19

I thought that should be the answer, but my homework says it's wrong. What am I doing wrong here? I've done several others of the same type of problem and gotten them right, so I don't know what the difference is.

Answer 1

Nevermind . . . the G value for Br2 isn't 0, which was throwing off my calculations. The answer ended up being 4.96x10^-20