Enthalpy
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State
Enthalpy is a state function equal to internal energy plus pressure times volume; its change equals heat flow at constant pressure.
Show
The heat released by a Bunsen burner's flame equals its combustion reaction's enthalpy change, since it burns at roughly constant pressure.
Watch for
A reaction's heat measured in a sealed bomb calorimeter is not its enthalpy change, since pressure there can shift freely.