The standard enthalpy of combustion is the enthalpy change when
Correct answer: A. one mole of a substance is burnt completely in excess oxygen under standard conditions
- A. one mole of a substance is burnt completely in excess oxygen under standard conditions
- B. one gram of a substance is burnt
- C. one mole of a substance is formed from its elements
- D. one mole of a substance is dissolved in water
Explanation
The definition specifies one mole, complete combustion and excess oxygen, and combustion values are always negative because burning releases energy. Incomplete combustion would give a different and smaller value, which is why excess oxygen is stipulated. Formation from elements is a separate quantity that may be positive or negative.
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About Enthalpy
Enthalpy is the heat content of a system measured at constant pressure, and its change indicates whether a reaction or physical process is endothermic or exothermic. The topic covers state functions, enthalpy diagrams, standard enthalpy of formation, combustion and neutralisation, and the relationship between ΔH and internal energy change.
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