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Ch.6 - Thermochemistry
Chapter 6, Problem 105b

Palmitic acid (C16H32O2) is a dietary fat found in beef and butter. The caloric content of palmitic acid is typical of fats in general. Which dietary substance (sugar or fat) contains more Calories per gram? The standard enthalpy of formation of palmitic acid is -208 kJ/mol and that of sucrose is -2226.1 kJ/mol. [Use H2O(l) in the balanced chemical equations because the metabolism of these compounds produces liquid water.]

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Key Concepts

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

Caloric Content of Macromolecules

Fats, such as palmitic acid, provide approximately 9 Calories per gram, while carbohydrates, like sugars, provide about 4 Calories per gram. This difference in caloric density is due to the higher number of carbon and hydrogen atoms in fats, which release more energy upon oxidation during metabolism.
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Standard Enthalpy of Formation

The standard enthalpy of formation is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. It provides insight into the stability and energy content of a compound. In this context, comparing the enthalpy values of palmitic acid and sucrose helps understand their energy release during metabolism.
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Metabolism and Energy Release

Metabolism refers to the biochemical processes that convert food into energy. During metabolism, fats and sugars undergo oxidation, producing energy and byproducts like water and carbon dioxide. Understanding these metabolic pathways is crucial for evaluating the energy yield of different dietary substances.
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Related Practice
Textbook Question

If 50.0 mL of ethanol (density = 0.789 g/mL) initially at 7.0 °C is mixed with 50.0 mL of water (density = 1.0 g/mL) initially at 28.4 °C in an insulated beaker, and assuming that no heat is lost, what is the final temperature of the mixture?

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Open Question
Calculate the caloric content of table sugar (sucrose, C12H22O11), given that the standard enthalpy of formation of sucrose is -2226.1 kJ/mol. For comparison, the standard enthalpy of formation of palmitic acid (C16H32O2), a dietary fat found in beef and butter, is -208 kJ/mol. Use H2O(l) in the balanced chemical equations, as the metabolism of these compounds produces liquid water.
Textbook Question

Palmitic acid (C16H32O2) is a dietary fat found in beef and butter. The caloric content of palmitic acid is typical of fats in general. Write a balanced equation for the complete combustion of palmitic acid and calculate the standard enthalpy of combustion. What is the caloric content of palmitic acid in Cal/g? The standard enthalpy of formation of palmitic acid is -208 kJ/mol and that of sucrose is -2226.1 kJ/mol. [Use H2O(l) in the balanced chemical equations because the metabolism of these compounds produces liquid water.]

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Open Question
Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. Use standard enthalpies of formation to calculate the amount of heat released per kilogram of methanol fuel and per kilogram of hydrogen fuel.
Textbook Question

Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. Which fuel contains the most energy in the least mass?

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Textbook Question

Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. How does the energy of these fuels compare to that of octane (C8H18)? 

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