what is the formula to find the mass of propane that must be combusted to produce 188.3kj of energy?

Answer 1

Compute the heat of reaction per mole of combustion of C3H8 with O2. It should be in kJ per mole of C3H8.

Divide 188.3 kJ by the heat of reaction per mole. Assume the H2O ends up in liquid state at 298 K. This will give you the number of moles of C3H8 required. Convert that to mass of C3H8.

Each mole of C3H8 has a mass of 44.0 g.