Find the enthalpy for 10.0g of NH3 when it is made from molecular hydrogen and molecular nitrogen. The answer is -27.2kj but I'm confused about how to find enthalpy if its in grams.

Answer 1

N2 + 3H2 ==> 2NH3
Look up delta Ho in your text for N2 (it will be zero) and H2 (it will be zero) and NH3 (I don't remember that number). Then plug that numbers into
dHrxn = (n*dHo products) - (n*dHo reactants) and solve for dHrxn/ That dHrxn will be 1 mol two mols of NH3 (2*17 = 34 g). Convert to 10.0 grams.
Post your work if you get stuck.