Work out heat of combustion instantly with clear inputs, formula shown and shareable results.
Enthalpy of combustion is quoted per mole, so a mass of fuel must first be converted to moles before the heat release can be found. Burning 12 g of propane (44.1 g/mol, -2220 kJ/mol) releases about 604 kJ. Dividing the molar value by the molar mass gives the specific energy, which is the figure that matters when fuels are compared by mass.
Heat released
Q = (mass / molar mass) x |dHc|
Specific energy
kJ/g = |dHc| / molar mass
The enthalpy change is negative because the system loses energy; the heat delivered to the surroundings is the same magnitude, stated positively.
Whichever your molar enthalpy refers to. Standard combustion enthalpies assume liquid water products, which corresponds to the higher heating value.