Question

The standard molar heat of formation of ethane, CO2, and water (\( \Delta H_f \)) are respectively -21.1, -94.1, and -68.3 kcal. The standard molar heat of combustion of ethane will be?

• A. 372 kcal
• B. 162 kcal
• C. 20 kcal
• D. 183.5 kcal

Hint:

Use Hess's law to calculate the heat of combustion from the standard enthalpies of formation.

Answer 1

The Correct Option is D

The heat of combustion can be calculated by using Hess's law and the enthalpy values for the formation of the products and reactants. The enthalpy of combustion is the sum of the enthalpies of the products minus the enthalpy of the reactants.