Enthalpy

Enthalpy is a concept used in thermodynamics to understand the total heat content of a system. It is a state function that depends only on the prevailing equilibrium state identified by the system's internal energy, pressure, and volume. It is an extensive quantity.

Definition

The enthalpy of a system is defined as the sum of its internal energy U and the product of its pressure P and volume V. The equation for enthalpy H is:

H = U + PV

Understanding Enthalpy

Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.

Enthalpy Change

The change in enthalpy (ΔH) of a reaction is a useful quantity, as it is directly measurable. It is the energy transferred from the system to its surroundings, or vice versa, in a process that takes place at constant pressure.

Enthalpy in Chemical Reactions

In chemical reactions, the enthalpy of reaction indicates whether a reaction is exothermic (releases heat, ΔH < 0) or endothermic (absorbs heat, ΔH > 0).

See Also

• Thermodynamics
• Internal Energy
• Pressure
• Volume
• Chemical Reactions

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  First law of thermodynamics for an open system
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  T-s diagram of nitrogen
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  Schematic of a throttling process
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  Schematic of a compressor