Question

Ethanol (C₂H₅OH) is currently blended with gasoline as an automobile fuel. calculate the standard enthalpy change for the reaction, assuming H₂O(g) as a product.

Answer 1

The standard enthalpy change for the combustion of ethanol is calculated using a balanced chemical equation and standard enthalpies of formation. The enthalpy change equals the sum of the enthalpies of formation of the products minus the sum of the enthalpies of the reactants. This calculation is essential for understanding the energy content of ethanol when used as a fuel.

Step-by-step explanation:

Calculating the Standard Enthalpy Change for Ethanol Combustion

To calculate the standard enthalpy change for the combustion of ethanol (C2H5OH), we use the balanced chemical equation and standard enthalpies of formation. The balanced equation for the combustion of ethanol is as follows:

C

2

H

5

OH(l) + 3O

2

(g) → 2CO

2

(g) + 3H

2

O(g)

Using standard enthalpies of formation from a referenced Appendix or textbook, the enthalpy change (ΔH°) for the reaction can be calculated using Hess's law:

ΔH° = [ΣΔH°f(products)] - [ΣΔH°f(reactants)]

For the combustion of 1 mole of ethanol:

This yields the combustion enthalpy for ethanol. For the density calculations of ethanol and heat comparisons with gasoline, you would multiply the combustion enthalpy by the density of ethanol (0.7893 g/mL) to find the energy per liter.

The theoretical distance an automobile can travel on a liter of ethanol compared to a liter of gasoline can then be approximated based on the respective heat of combustion and densities of the two fuels.