Enthalpy is the amount of energy in a given reaction, we can calculate the heat of a system through the change in enthalpy (∆H).
The ∆H in physical state changes: 
The figure represents a change in physical state from solid to liquid (melting). It occurs when water goes through an enthalpy of fusion: melting ice resulting from an absorption of heat. The amount of heat needed for this process to occur is 7.3 KJ/mol (fusion of 1 mol of H2You)). Process equation:
H2O(s) → H2the (1) ∆H = + 7.3 KJ/mol
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Now pay attention to the image below:
Notice the steam coming out of the kettle, it demonstrates a change in physical state. The water inside the kettle was in a liquid state, but due to the absorption of heat it changed to a gaseous state. The heat required for the enthalpy of vaporization to occur in 1 mol of H2O(1) is 44 KJ/mol, according to the equation:
H2O (1) → H2the (v) ∆H = + 44 KJ/mol
By Líria Alves
Graduated in Chemistry
Brazil School Team
Physicochemical - Chemistry - Brazil School
Would you like to reference this text in a school or academic work? Look:
SOUZA, Líria Alves de. "Enthalpy of changes in physical state"; Brazil School. Available in: https://brasilescola.uol.com.br/quimica/entalpia-nas-mudancas-estado-fisico.htm. Accessed on June 28, 2021.