# 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 equation is always associated with the first law of thermodynamics, 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 is what we're interested in (such as the substance or matter), the environment around the system is called it's surroundings. Energy is transferred  between the two and the enthalpy equation is the way to measure the energy change in the form of heat.

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.  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

Whitten, et al. 10th Edition. Pp.577

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