Hi, I'm completely out of ideas for this problem, and any help would be really appreciated. 1. The problem statement, all variables and given/known data At 850 degrees C and 1 atm pressure, a gaseous mixture of carbon monoxide and carbon dioxide in equilibrium with solid carbon is 90.55% CO by mass. Find the equilibrium constant for this reaction at 850 C. C(s) + CO2(g) <--> 2CO(g) 2. Relevant equations K=[products]/[reactants], PV=nRT(?) 3. The attempt at a solution Since the C concentration is solid, it is constant, so it is part of the equilibrium constant, so K will be = [CO]^2/[CO]. So I just need to determine how much the CO is from being 90.55% of the mass. I took the atomic weights of CO (~28 amu) and CO2 (~44 amu) and made an equation that would result in CO being 90.55% of the mass. 28x=(.9055)(28x+44y) X ends up being ~15 times greater than Y. This is where I'm stuck. I can use my X value to make a bunch of different amounts of CO and CO2 that have CO being 90.55% of the mass. My teacher hinted PV=nRT, but there is no given volume, and I see no way to use that equation with two unknowns. Also, the answer is K = .153. That doesn't help me though, since I need to show work.