I'm having trouble forming a change of state equation for the following scenario: Microsoft Word - 5.60 PS 2 F15.

I'm having trouble forming a change of state equation for the following scenario: 

In a type of water heater, a flame of methane, (CH4), heats a container containing liquid water. Assume that 1.0 mole of CH4 and 10 moles of air (2 moles of O2 and 8 moles of N2) are used during the heating process. Assume also that complete oxidation of CH4(g) to CO2(g) and H2O(g) occurs. Assume that all the gases, including N2 (g) from the air, enter the heater at 298 K and leave at 498 K.