Question

How many grams of C3H8 would you need to burn to obtain 511kJ of heat? (molar mass =44.1 g/mol) C3H8(g) + 5O2(g) 6 3CO2(g) + 4H2O(g) H=-2043kJ

Answer 1

I checked the molar heat of combustion of C3H8 (propane) and it's around 2200kJ/mol, so the H value looks about right. For this question, I would divide the amount of heat by the molar heat of combustion so that's 511/2043 so almost exactly 0.25 moles required. Multiply this by the number of grams per mole (molar mass) of C3H8 and you'll have your answer. Best wishes,