18. Methane, the main constituent of natural gas, burns in oxygen to yield carbon dioxide and water: CH4(g) + 2 O2(g) â CO2(g) + 2 H2O(l) Use the following information to calculate in kilojoules for the combustion of methane: CH 14(g) + O2(g) â CH20(g) + H2O(g) CH20(g) + 02(g)-CO2(g)+ H20(g) H2O(l) â H2O(g) 1°-·-275.6 kJ AHP =-526.7 kJ AH 44.0 kJ desired reaction. The important points are that: All the reactants [CH (g) and O24g)] must appear on the left All the products [CO2(g) and H200)] must appear on the right. All intermediate products [CH20(g) and H20(g)] must occur on both the left and the right so that they cancel. ·A reaction written in the reverse of the direction given [H2O(g) â H2O(1)] mtust have the sign of its Î11 Tip reversed If a reaction is multiplied by a coefficient [H2O(g) â H2O(l) is multiplied by 21, then ì¨1 for the reaction must be multiplied by that same coefficient.