# Enthalpy

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The Enthalpy calculator compute the enthalpy energy based on the internal energy, pressure and volume.

INSTRUCTIONS: Choose units and enter the following:

• (U) This is the internal energy
• (p)  This is the pressure
• (V)  This is the volume

Enthalpy(H): The calculator returns the enthalpy in joules.  However this can be automatically converted to compatible units via the pull-down menu.

#### The Math / Science

The enthalpy[1] equation is always associated with the first law of thermodynamics[3], which states that energy can not be created or destroyed, thus it is to calculate the energy released or absorbed by the system. The system[4] is what we're interested in (such as the substance or matter), the environment around the system is called it's surroundings[5]. Energy is transferred  between the two and the enthalpy equation is the way to measure the energy change in the form of heat[6].

The enthalpy equation is defined by

H = U + P•V

where:

• H is the enthalpy (Joules)
• U is the internal energy (Joules)
• P is pressure (pascals)
• V is volume (m3,mL)

The enthalpy equation is a state function, which means its dependent on its variables, specifically temperature, pressure and internal energy[7].  If temperature and pressure were to be kept constant the equation will be ΔH=ΔU+PΔV. From this equation we can see that the enthalpy is dependent on the change of volume and internal energy. If pressure is kept constant than the equation becomes ΔH=q, from this we can observe whether the system absorbs or releases heat

## References

[2]Whitten, et al. 10th Edition. Pp.577

This equation, Enthalpy, is listed in 2 Collections.