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Ch.5 - Thermochemistry
All textbooksBrown 14th EditionCh.5 - ThermochemistryProblem 79c
Chapter 5, Problem 79c

Ethanol (C2H5OH) is blended with gasoline as an automobile fuel. (c) Calculate the heat produced per liter of ethanol by combustion of ethanol under constant pressure. Ethanol has a density of 0.789 g/mL.

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1
Identify the chemical reaction for the combustion of ethanol: \[ \text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O} \].
Determine the molar mass of ethanol (C2H5OH) by adding the atomic masses of its constituent atoms.
Use the density of ethanol (0.789 g/mL) to convert 1 liter of ethanol to grams.
Convert the mass of ethanol obtained in the previous step to moles using the molar mass of ethanol.
Use the standard enthalpy of combustion for ethanol to calculate the heat produced per mole, then multiply by the number of moles to find the heat produced per liter.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Combustion Reaction

A combustion reaction is a chemical process in which a substance reacts rapidly with oxygen, releasing energy in the form of heat and light. In the case of ethanol, the reaction produces carbon dioxide and water as byproducts. Understanding the stoichiometry of this reaction is essential for calculating the heat produced during combustion.
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Combustion Apparatus

Heat of Combustion

The heat of combustion is the amount of energy released when a substance undergoes complete combustion with oxygen. It is typically expressed in kilojoules per mole (kJ/mol). For ethanol, this value can be found in tables of thermodynamic data and is crucial for determining the total heat produced when a specific volume of ethanol is burned.
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Density and Volume Conversion

Density is defined as mass per unit volume and is crucial for converting between the volume of a liquid and its mass. In this case, the density of ethanol (0.789 g/mL) allows us to calculate the mass of ethanol in a liter, which is necessary for determining the total heat produced during combustion based on the heat of combustion per mole.
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Related Practice
Textbook Question

Gasoline is composed primarily of hydrocarbons, including many with eight carbon atoms, called octanes. One of the cleanest–burning octanes is a compound called 2,3,4- trimethylpentane, which has the following structural formula: The complete combustion of one mole of this compound to CO2(g) and H2O(g) leads to ΔH° = -5064.9 kJ. (b) By using the information in this problem and data in Table 5.3, calculate H°f for 2,3,4-trimethylpentane.

Textbook Question

Diethyl ether, C4H10O(l), a flammable compound that was once used as a surgical anesthetic, has the structure The complete combustion of 1 mol of C4H10O(l) to CO2(g) and H2O(l) yields ΔH° = -2723.7 kJ. (a) Write a balanced equation for the combustion of 1 mol of C4H10O(l).

Textbook Question

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

Textbook Question

Ethanol (C2H5OH) is blended with gasoline as an automobile fuel. (d) Calculate the mass of CO2 produced per kJ of heat emitted.

Textbook Question

Methanol (CH3OH) is used as a fuel in race cars. (b) Calculate the standard enthalpy change for the reaction, assuming H2O(g) as a product.

Textbook Question

Methanol (CH3OH) is used as a fuel in race cars. (c) Calculate the heat produced by combustion per liter of methanol. Methanol has a density of 0.791 g/mL.