Question

How much heat energy is given off when one kilogram of hydrogen gas at 25C and one atmosphere is combined with enough oxygen gas to make liquid water at 25C?

Answer 1

Write the equation.
Balance it.
dH = delta H.
dHrxn = (n*dHf products) - (n*dHf reactants)

Answer 2

I think I need more help. I tried but I think I'm going in circles on this one and not thinking clearly at this point.

Answer 3

Look in your text, usually in the back of the book, and find the delta H formation values for these compounds/elements at 25 C. I think the value for liquid water, although I'm not sure, is about -285 kJ/mol. The value for elements is arbitrarily assigned zero.
So 2H2(g) + O2(g) ==> 2H2O(l)
Then dHrxn = (2*dHf H2O) - (2*dHf H2 + dHf O2)
Solve for dH rxn and that will be for 1 mol H2. Then scale it up to 1000 g H2.