how many grams of ethylene would have to be burned to produce 450 kJ of heat?

Answer 1

You need the heat of combustion for ethylene.
C2H4 + 3O2 ==> 2CO2 + 2H2O

450 kJ/heat combustion per mole = # moles C2H4 burned.
Then # moles C2H4 x molar mass C2H4 = grams C2H4.

Answer 2

What is the mass of water that can be heated from 39 C to 80 C by the combustion of 150 g of methane. CH4 + 2O2 => CO2 + 2H2O Delta H= -890kJ