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Molar enthalpy of combustion is the amount of energy released as heat when one mole of a substance undergoes complete combustion in the presence of oxygen, under constant pressure. Molar enthalpy of combustion can be used to determine the heat energy released during the combustion process.

Fuel value, also known as heat content or heating value, is defined as the amount of heat energy released during the combustion of a given amount of fuel. It is often expressed in units such as Joules per gram (J/g) or British thermal units per pound (Btu/lb).

Molar enthalpy of combustion is usually expressed in kJ/mol (kilojoules per mole), while the fuel value is expressed in J/g (Joules per gram) or Btu/lb. To convert between these units, we need to know the molecular weight of the fuel. Molecular weight is the mass (grams) of one mole of the substance.

To calculate the fuel value from molar enthalpy of combustion, follow these steps: 1. Convert molar enthalpy of combustion to energy per gram: Divide the molar enthalpy of combustion (kJ/mol) by the molecular weight (g/mol) of the fuel. This gives you the energy content in kJ/g. 2. Convert the energy per gram to the desired unit: If you want the fuel value in J/g, multiply the energy content obtained in step 1 by 1000 (1 kJ = 1000 J). If you want the fuel value in Btu/lb, multiply the energy content obtained in step 1 by 0.453592 (1 lb = 0.453592 kg), then multiply by 1000 to get the heat content in Btu/lb. Example: Let's consider a fuel with a molar enthalpy of combustion of 1500 kJ/mol and a molecular weight of 30 g/mol. 1. Convert molar enthalpy of combustion to energy per gram: 1500 kJ/mol ÷ 30 g/mol = 50 kJ/g. 2. Convert the energy per gram to the desired unit: a. J/g: 50 kJ/g * 1000 = 50,000 J/g. b. Btu/lb: 50 kJ/g * 0.453592 * 1000 = 22,679.6 Btu/lb. The fuel value of the given fuel is 50,000 J/g or 22,679.6 Btu/lb.