For a reaction carried out at constant pressure, the heat exchanged is equal to the change in
Correct answer: B. enthalpy
- A. internal energy
- B. enthalpy
- C. entropy
- D. free energy
Explanation
Enthalpy was defined precisely so that its change measures the heat of a process at constant pressure, which is the condition of almost every reaction done in an open vessel. At constant volume, as in a bomb calorimeter, the heat measured is the change in internal energy instead, since no expansion work is done. This is why the two quantities differ slightly for reactions involving gases.
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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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