This may belong in the Chemistry section but this is a problem from my Thermodynamics class, so I'll post it here and then move to the Chem section if need be. 1. The problem statement, all variables and given/known data Methane (CH4) is the principal constituent of natural gas and is often used to represent natural gas. Consider the operation of a natural gas fired water heater operating with 15% excess air. Assuming the fuel to be CH4 and the products of the reaction to be CO2, H2O, N2, O2 , and CO, calculate the concentration (percent by volume) of each product if the temperature in the products is 1000K. 2. Relevant equations CH4 + (a)(m)(O2 + 3.76N2 → bCO2 + cH2O + dN2 + eO2 + fCO 2CO2 [itex]\Leftrightarrow[/itex] 2CO + O2 where: a=moles for stoichiometric combustion m=excess air ratio (1.15 in this case) b,c,d,e,f = moles of products 3. The attempt at a solution To balance equation: From combustion reaction: C: 1 = b+f H: 4 = 2; c=2 O: 2*a*1.15 = c+2e+f N: 3.76*1.15*a*2 = 2d From dissociation reaction: 2b = 2f + e (2 CO2 makes 2CO and 1O2) I still only have 5 equations and 6 unknowns. There is also the equilibrium constant K that we are given a table of: [URL]http://upload.wikimedia.org/wikipedia/en/math/a/e/1/ae1ea56f2e557025e57022730f141861.png[/URL] [URL]http://upload.wikimedia.org/wikipedia/en/math/2/b/1/2b116a1f13940176246dd9e08a0c0be3.png[/URL] I know how to solve the problem when CO is not created. It becomes a much simpler problem. However, when CO enters the problem, I end up with not enough equations. Thanks for your help!