HW 8.117

[Jennifer_Yee_3I]

One step in the production of hydrogen as a fuel is the reaction of methane with water vapor:
CH4(g) + H20(g) --> CO2(g) + 3H2(g) deltaH= -318 kJ
What is the change in internal energy for the production of 1.00 mol H2?

I'm wondering if someone could clarify why there is a net production of 2/3 mole of gas according to the solutions manual. Where does this come from?
Thank you!

[Rochelle Ellison 2H]

The problem is asking for the change in internal energy for 1 mol of H2 but the chemical equation shows the production of 3 mol H2. Therefore, you have to divide each of the stoichiometric coefficients by 3 mol so that the equation reads 1/3CH4(g) + 1/3H2O(g) → 1/3CO2(g) + H2(g). Now you can see that there were 2/3 mol of gas on the reactants side and 4/3 mol on the products side so the net production of gas is 4/3-2/3=2/3 mol.