[Zoloft]

OK, so if I had C₃H₈(g) + 5O₂(g) ---> 3CO₂(g) + 4H₂O(g)

And I needed to find how much heat is released by burning 10 moles of propane, I would have to balance the equation, and in turn, that would give me like 10C₃H₈ +50O₂ ---> 30CO₂ + 40H₂0.

Anyway, I would then use Hess's equation and subtract the heat released by each reactant in their standard states (by multiplying by the moles per elements) from the heat released by their products.

Right?

[Astrokel]

You are correct if you are using deltaH_f. Alternatively, if you have got enthalpy change of your combustion of per mole of propane, you could just multiply it by 10.

[Mitch]

You can also factor out a 10 out of your coefficients.