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Calculate The Heat of Combustion of Glucose From The Following

Reviewed by Calculator Editorial Team

Glucose (C6H12O6) is a simple sugar that serves as a primary energy source for living organisms. When glucose undergoes combustion, it reacts with oxygen to produce carbon dioxide and water, releasing energy in the process. Calculating the heat of combustion provides insight into the energy content of glucose and its potential as a fuel source.

Introduction

The heat of combustion of glucose refers to the amount of energy released when one mole of glucose is completely burned in oxygen. This value is crucial in understanding the energy content of carbohydrates and their role in biological systems.

Glucose combustion follows this balanced chemical equation:

C6H12O6 + 6O2 → 6CO2 + 6H2O

The standard heat of combustion of glucose is typically reported as -2805 kJ/mol, meaning that burning one mole of glucose releases 2805 kilojoules of energy.

Formula

The heat of combustion (ΔHcomb) of glucose can be calculated using the following formula:

ΔHcomb = (ΔHproducts - ΔHreactants) × n

Where:

  • ΔHcomb is the heat of combustion (in kJ)
  • ΔHproducts is the sum of the standard enthalpies of formation of the products
  • ΔHreactants is the sum of the standard enthalpies of formation of the reactants
  • n is the number of moles of glucose

For glucose, the standard enthalpies of formation are:

  • Glucose (C6H12O6): -1273.2 kJ/mol
  • Oxygen (O2): 0 kJ/mol (by definition)
  • Carbon dioxide (CO2): -393.5 kJ/mol
  • Water (H2O): -285.8 kJ/mol

Example Calculation

Let's calculate the heat of combustion for 2 moles of glucose:

ΔHcomb = [(6 × -393.5) + (6 × -285.8)] - [1 × -1273.2] × 2
= [-2361 + (-1714.8)] - (-1273.2) × 2
= -4075.8 + 2546.4
= -1529.4 kJ

This means burning 2 moles of glucose releases 1529.4 kJ of energy.

Interpreting Results

The heat of combustion value provides several important insights:

  1. Energy Content: The negative value indicates an exothermic reaction, releasing energy to the surroundings.
  2. Fuel Efficiency: Glucose is an efficient fuel source, releasing significant energy per mole.
  3. Biological Importance: The energy released during glucose combustion powers cellular processes in living organisms.

Note: The actual heat of combustion may vary slightly depending on experimental conditions and the specific form of glucose used.

FAQ

What is the standard heat of combustion of glucose?

The standard heat of combustion of glucose is -2805 kJ/mol, meaning one mole of glucose releases 2805 kJ of energy when burned.

How does the heat of combustion relate to glucose's role in biology?

The heat of combustion explains how glucose provides energy for cellular respiration, which is essential for all living organisms.

Can the heat of combustion be used to calculate energy content in food?

Yes, the heat of combustion is often used to estimate the energy content of foods, particularly carbohydrates like glucose.

What factors can affect the measured heat of combustion?

Factors include the purity of the glucose sample, experimental conditions, and whether the measurement is conducted at constant pressure or volume.