Question

A student calculated the standard enthalpy change of formation of ethane C2H6 using a method based on standard enthalpy change of combustion

Answer 1

To calculate the heat of combustion of ethanol (C₂H₅OH), you can use the enthalpies of formation for the products (CO₂ and H₂O) and the reactants (ethanol and oxygen). By subtracting the sum of the enthalpies of formation of the reactants from the sum of the enthalpies of formation of the products, you can determine the heat of combustion.

Step-by-step explanation:

The standard enthalpy of combustion can be used to calculate the heat of combustion of a substance. In this case, we want to calculate the heat of combustion of 1 mole of ethanol (C₂H₅OH). Using the enthalpies of formation provided: C₂H₅OH(I) = -278 kJ/mol, H₂O(I) = -286 kJ/mol, and CO₂(g) = -394 kJ/mol, we can calculate the heat of combustion.

The balanced equation for the combustion of ethanol is: C₂H₅OH(I) + 3O₂(g) → 2CO₂(g) + 3H₂O(I). According to the stoichiometry of the equation, for every 1 mole of ethanol combusted, 2 moles of CO₂ and 3 moles of H₂O are formed.

Using the enthalpies of formation, we can calculate the heat of combustion as follows:

Heat of Combustion:

1. Calculate the sum of the enthalpies of formation of the products (2CO₂ and 3H₂O)
2. Calculate the sum of the enthalpies of formation of the reactants (C₂H₅OH and 3O₂)
3. Subtract the sum of the enthalpies of formation of the reactants from the sum of the enthalpies of formation of the products to get the heat of combustion

Using the enthalpies of formation provided, the heat of combustion of 1 mole of ethanol is:

ΔH combustion = [2(-394 kJ/mol) + 3(-286 kJ/mol)] - (-278 kJ/mol)

Answer 2

C2H6 + 302 -------> 2C + 3H20