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Symbol H. A thermodynamic property of a system defined by H = U+pV, where H is the enthalpy, U is the internal energy of the system, p its pressure, and V its volume. In a chemical reaction carried out in the atmosphere the pressure remains constant and the enthalpy of reaction, ΔH, is equal to ΔU+pΔV. For an exothermic reaction ΔH is taken to be negative.

Subjects: Chemistry.

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