Enthalpy

Last modified by

WilliamC

on

Sep 29, 2022, 12:52:01 AM

Created by

Dasha

on

May 20, 2016, 4:43:03 PM

$H = U+(P*V)$

$(U) "Internal Energy"$

$(P)"Pressure"$

$(V) "Volume"$

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