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At 25°C, the standard enthalpies of formation of CO₂(g), H₂O(l), and glucose(s) are −400 kJ/mol, −300 kJ/mol, and −1300 kJ/mol, respectively. What is the standard enthalpy of combustion per gram of glucose at 25°C?

1. +2900 kJ
2. −2900 kJ
3. −16.11 kJ
4. +16.11 kJ

Correct answer: −16.11 kJ

Solution

The standard enthalpy of combustion of glucose is calculated by taking the enthalpy of formation of the products (CO₂ and H₂O) and subtracting the enthalpy of formation of glucose. This results in a negative value, indicating that combustion is an exothermic reaction, and when divided by the molar mass of glucose, it yields approximately −16.11 kJ per gram.

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