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Ch.5 - Thermochemistry
All textbooksBrown 15th EditionCh.5 - ThermochemistryProblem 81d
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Chapter 5, Problem 81d

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

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Identify the balanced chemical equation 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 standard enthalpy change (\( \Delta H^\circ \)) for the combustion of ethanol using standard enthalpies of formation.
Calculate the moles of \( \text{CO}_2 \) produced per mole of ethanol combusted from the balanced equation.
Use the \( \Delta H^\circ \) value to find the heat emitted per mole of ethanol combusted.
Calculate the mass of \( \text{CO}_2 \) produced per kJ of heat emitted by dividing the mass of \( \text{CO}_2 \) produced by the heat emitted.

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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 (usually a hydrocarbon) reacts with oxygen to produce carbon dioxide and water, releasing energy in the form of heat. In the case of ethanol, the reaction can be represented as C2H5OH + 3O2 → 2CO2 + 3H2O, illustrating how ethanol combusts to produce CO2 and H2O.
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Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It allows us to determine the amount of CO2 produced from a given amount of ethanol burned, using mole ratios derived from the balanced equation to convert between moles of ethanol and moles of CO2.
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Energy Release in Combustion

The energy released during combustion is typically measured in kilojoules (kJ) and is derived from the breaking and forming of chemical bonds. The heat emitted per mole of ethanol can be calculated using its enthalpy of combustion, which indicates how much energy is released when a specific amount of ethanol is burned, allowing for the calculation of CO2 produced per kJ of heat.
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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.

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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).

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Textbook Question

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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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.

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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.

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Textbook Question

Methanol (CH3OH) is used as a fuel in race cars. (d) Calculate the mass of CO2 produced per kJ of heat emitted.

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