The combustion of glucose, [tex]$C _6 H _{12} O _6(s)$[/tex], produces carbon dioxide, [tex]$CO _2(g)$[/tex], and water, [tex]$H _2 O ( g )$[/tex], according to the equation below.
[tex]$C_6 H_{12} O_6(s)+6 O_2(g) \rightarrow 6 CO_2(g)+6 H_2 O(l)$[/tex]
The enthalpy of the reaction is -2,840 kJ. What is the heat of combustion, per mole, of glucose?
A. -2,840 kJ / mol
B. -473.3 kJ / mol
C. 473.3 kJ / mol
D. 2,840 kJ / mol
Answer (2)
The balanced chemical equation represents the combustion of one mole of glucose.
The enthalpy change for the reaction is given as − 2 , 840 k J .
The heat of combustion per mole of glucose is equal to the enthalpy change for the reaction.
Therefore, the heat of combustion per mole of glucose is − 2 , 840 k J / m o l .
Explanation
Understanding the Problem The problem states that the combustion of glucose ( C 6 H 12 O 6 ) produces carbon dioxide ( C O 2 ) and water ( H 2 O ) according to the given balanced chemical equation:
C 6 H 12 O 6 ( s ) + 6 O 2 ( g ) → 6 C O 2 ( g ) + 6 H 2 O ( l )
The enthalpy of this reaction is given as − 2 , 840 k J . We are asked to find the heat of combustion per mole of glucose.
Determining the Heat of Combustion The heat of combustion is the amount of heat released when one mole of a substance is completely burned in excess oxygen. In this case, the balanced equation shows the combustion of one mole of glucose, and the enthalpy change for this reaction is given as − 2 , 840 k J . Therefore, the heat of combustion per mole of glucose is simply the given enthalpy change.
Final Answer Since the enthalpy change for the combustion of one mole of glucose is − 2 , 840 k J , the heat of combustion per mole of glucose is − 2 , 840 k J / m o l .
Examples
The heat of combustion is a crucial concept in various real-world applications. For instance, when designing engines or power plants that use fuels like glucose-derived ethanol, engineers need to know the heat of combustion to calculate energy output and efficiency. Similarly, nutritionists use the heat of combustion of carbohydrates, fats, and proteins to determine the caloric content of foods, which helps in planning balanced diets. In environmental science, understanding the heat of combustion is essential for assessing the energy released during wildfires and its impact on ecosystems. Knowing the heat of combustion allows for accurate energy balance calculations and informed decision-making in diverse fields.
The heat of combustion per mole of glucose is -2,840 kJ/mol, based on the enthalpy change provided for the combustion reaction. This value indicates the amount of energy released when glucose is burned in excess oxygen. Therefore, the correct option is A. -2,840 kJ/mol.
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