What is the change in free energy (in kJ) at standard conditions or the combustion of 1.000g of H2(g) to form H2O(g)?

I know that the answer is -113kJ but I don't know how to get to this answer.

Question

What is the change in free energy (in kJ) at standard conditions or the combustion of 1.000g of H2(g) to form H2O(g)? 

I know that the answer is -113kJ but I don't know how to get to this answer.

anonymous · Answer

standard enthaply of formation of H2O is -241.5 kjmol^-
If 0.5 mol is produced energy change is -241.5*0.5
= - 120.75 kJ
I think this should be right

anonymous · Answer

Thats what I thought but I guess my next question is how do I know how many moles I have to multiply by -241.5kJ? I was using to 1g and dividing by the molecular weight of H (1.008) but this was not giving my -113kJ.

aaronq · Answer

do you have the balance equation and the molar enthalpy of combustion written down?

aaronq · Answer

balanced*

anonymous · Answer

2H2 + O2 yields 2H2O for combustion. Is that what I use?

anonymous · Answer

equation is H2 + 1/2 O2 ==== H2O
enthalpies are discussed for one mol