Ethanol (C2 H5 OH) is blended with gasoline as an automobile...

Ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ is blended with gasoline as an automobile fuel. (a) Write a balanced equation for the combustion of liquid ethanol in air. (b) Calculate the standard enthalpy change for the reaction, assuming $\mathrm{H}_{2} \mathrm{O}(g)$ as a product. (c) Calculate the heat produced per liter of ethanol by combustion of ethanol under constant pressure. Ethanol has a density of $0.789 \mathrm{~g} / \mathrm{mL}$. (d) Calculate the mass of $\mathrm{CO}_{2}$ produced per kJ of heat emitted.

Ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ is blended with gasoline as an automobile fuel.
(a) Write a balanced equation for the combustion of liquid ethanol in air.
(b) Calculate the standard enthalpy change for the reaction, assuming $\mathrm{H}_{2} \mathrm{O}(g)$ as a product.
(c) Calculate the heat produced per liter of ethanol by combustion of ethanol under constant pressure. Ethanol has a density of $0.789 \mathrm{~g} / \mathrm{mL}$.
(d) Calculate the mass of $\mathrm{CO}_{2}$ produced per kJ of heat emitted.

Key Concepts

Combustion Reaction Stoichiometry

This concept involves writing and balancing a chemical equation for a combustion reaction, where a fuel reacts with oxygen to form carbon dioxide and water. An understanding of stoichiometry is required to ensure that the masses and numbers of atoms for each element are conserved during the reaction. This is fundamental to predicting the amounts of reactants needed and the products formed.

Standard Enthalpy Change

In thermochemistry, the standard enthalpy change of a reaction can be determined using the standard enthalpies of formation of the reactants and products. By applying Hess’s Law, one calculates the overall energy change by subtracting the sum of the enthalpies of the reactants from that of the products. This concept is essential for evaluating the energy output of a reaction, as in the combustion of fuels.

Energy Density and Unit Conversions

This concept covers the conversion between mass, volume, and energy in the context of a substance’s properties, such as density. It includes using density to convert a given volume of fuel into mass, and subsequently, using stoichiometric and energetic data to determine the heat produced per unit volume. Mastering unit conversions is crucial for comparing energy outputs and designing efficient fuel systems.

Stoichiometric Product Yield Calculation

This concept refers to the use of balanced chemical equations to relate the moles of reactants to the moles (and corresponding mass) of products formed. In practical applications, such as determining the amount of CO2 produced per unit of energy output, stoichiometric calculations allow one to convert between chemical quantities and energy values. Understanding this relationship is key in assessing the environmental impact and efficiency of fuel combustion.

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