1. The problem statement, all variables and given/known data For the equilibrium PCl5 <---> PCl3 + Cl2, all gases, Keq = 4.16e-2. The equilibrium concentration of PCl5 is 1.0 M, and both PCl3 and Cl2 are 0.204 M. If the volume of this closed system is doubled, what are the concentrations of each gas when a new equilibrium is reached? 2. Relevant equations Keq = ([product 1]^n * [product 2]^n) / ([reactant 1]^n * [reactant 2]^n) 3. The attempt at a solution old E: 1 M, 0.204 M, 0.204 M new E: PCl5: 1-x, PCl3: 0.204+x, Cl2: 0.204+x since the equilibrium would shift to the right where there's more moles. Now, when I try to solve it, I run into an obstacle: 4.16e-2 = ((0.204+x)(0.204+x))/(1-x) 4.16e-2 - 4.16e-2(x) = 0.0416+0.408x+x^2 0 = x^2 + 0.4496x 0 = x(x+0.4496) But x cannot be negative!