# chemistry

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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?

• chemistry -

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

• chemistry -

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.

• chemistry -

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.

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