Question

Compare fats and carbohydrates as energy sources in terms of the amount of energy released per mole, and account for the observed energy difference.

Short answer

Fats release more energy (33820 kJ/mol) compared to carbohydrates (2880 kJ/mol) because fats are more reduced.

Step-by-step solution

Understand the Energy Content of Fats and Carbohydrates

Fats and carbohydrates both serve as energy sources for the body, but they differ in the amount of energy they provide per mole. Fats typically contain more energy because they are more reduced compared to carbohydrates.

Calculate Energy Released from Carbohydrates

Carbohydrates, such as glucose, have an energy content of approximately 16 kilojoules per gram. To calculate the energy released per mole of glucose, we use its molar mass (180 grams/mol) and multiply: \( 180 \text{ g/mol} \times 16 \text{ kJ/g} = 2880 \text{ kJ/mol} \).

Calculate Energy Released from Fats

Fats, such as triglycerides, have an energy content of approximately 38 kilojoules per gram. Using the molar mass of a typical triglyceride (890 grams/mol), calculate: \( 890 \text{ g/mol} \times 38 \text{ kJ/g} = 33820 \text{ kJ/mol} \).

Compare the Energy Data

Compare the values obtained: carbohydrates release about 2880 kJ/mol, whereas fats release about 33820 kJ/mol. Fats provide significantly more energy per mole because they are more reduced and have more C-H bonds, which yield more energy when oxidized.

Account for the Energy Difference

The energy difference arises because the oxidation of more reduced molecules (such as fats, which have more hydrogen atoms per carbon) releases more energy. Fats are more energy-dense due to their chemical structure since the long carbon chains in fats store more energy as C-H bonds compared to the C-OH bond-rich structure of carbohydrates.

Key concepts

Fats vs. Carbohydrates

Understanding the energy content difference between fats and carbohydrates aids in comprehending why they serve distinct roles in energy storage and usage within the body. Fats typically provide more energy per unit weight than carbohydrates. This is primarily because fats are more structurally reduced, containing more carbon-hydrogen (C-H) bonds that, when oxidized, release substantial energy. Carbohydrates, like glucose, have prevalent carbon-oxygen (C-O) bonds. These bonds store less energy compared to the C-H bonds in fats.

When we refer to energy content, we note that:

• Fats: Approximately 38 kilojoules (kJ) per gram.
• Carbohydrates: Approximately 16 kilojoules (kJ) per gram.

This significant difference explains why fats are a more concentrated form of energy compared to carbohydrates. This property of fats makes them an efficient storage form of energy, utilized by the body for long-term energy requirements.

Molar Energy Calculation

Calculating energy content involves understanding the amount of energy released per mole of a substance. For both carbohydrates and fats, the calculation reflects their molar weights and their respective kilojoules per gram energy content.

To compute energy per mole:

• **Carbohydrates**: Use glucose as an example. With an energy content of 16 kJ/g and a molar mass of 180 g/mol, the calculation is: \( 180 \text{ g/mol} \times 16 \text{ kJ/g} = 2880 \text{ kJ/mol} \).
• **Fats**: Take triglycerides as a typical fat. With 38 kJ/g energy content and a molar mass of 890 g/mol, the calculation is: \( 890 \text{ g/mol} \times 38 \text{ kJ/g} = 33820 \text{ kJ/mol} \).

This molar energy calculation gives a quantitative understanding of the substantial energy density difference between fats and carbohydrates. Fats vastly surpass carbohydrates in terms of energy release per mole. This highlights their efficiency as a long-term energy source.

Oxidation of Biomolecules

Oxidation plays a pivotal role in energy release from biomolecules such as carbohydrates and fats. During oxidation, molecules undergo a transformation where electrons are transferred from the biomolecule to oxygen, releasing energy. The nature of the bonds in these biomolecules dictates the amount of energy released through this oxidation process.

Fats are more energy-dense compared to carbohydrates due to their molecular structure:

• **More C-H Bonds in Fats**: These bonds break during oxidation, releasing substantial energy. Fats, having longer carbon chains and more hydrogen atoms, generate more energy in comparison.
• **Less Oxygen Content in Fats**: This implies more hydrogens, making them more susceptible to oxidation compared to carbohydrates. Carbohydrates, with richer C-OH bonds, contain oxygen which contributes to less energy per molecular weight upon oxidation.

The increased number of bound hydrogen atoms in fats contributes to their higher energy yield upon oxidation, making them a potent energy source often used by organisms to meet prolonged energy needs.