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The sum of the work done on/by a system and the heat given off/absorbed by a system is equal to the enthalpy of a reaction. This being said, when there is a constant pressure, the delta H value is simply equal to the heat transfer.
A slight correction to the previous definition. I believe that the sum of work and heat given off in a reaction is equal to change in internal energy (U). Enthalpy is related to heat given off in a reaction during a constant pressure. The heat given off in a reaction is generally denoted by q but in conditions of constant pressure (qp) this is enthalpy. Heat exchanged (q) is an overarching concept and the heat exchanged under a constant pressure condition is enthalpy.