Editing Enthalpy

[[Category: Physics]]
== Explanation ==
Enthalpy of a system is defined as the sum of the change in [[internal energy]] of the system and the amount of work done by that system to change the [[volume]] and [[pressure]] to accommodate itself in a state of equilibrium. As the internal energy of a system depends on different variables and cannot be accurately measured, Enthalpy was introduced as a [[thermodynamic potential]] to measure the total energy of a system. Mathematically, enthalpy '''H''' is related to the internal energy '''U''', volume '''V''' and pressure '''P''' as '''ΔH = ΔU + Δ(PV)''', and it is measured in the SI unit, joule.

== Frequently Asked Questions ==
=== Why enthalpy can't be measured directly? ===
As enthalpy is technically a measure of the sum of a system's internal energy and the energy required to accommodate itself, it is impractical and impossible to look for a reference point to begin the measure. Even at the [[absolute zero]] temperature scale, all systems would possess a minimum amount of energy called [[zero-point energy]]. So by convention, measuring the change in enthalpy with a reference point is easier and convenient in practice. For example, when you pour a litre of water into the ocean, you can tell that you had increased the quantity of the ocean by 1 litre, without knowing how many litres was initially in the ocean. This metaphor can help understanding why the change in enthalpy is convenient in reality.

=== How is enthalpy related to heat? ===
In a system at a constant pressure, the change in enthalpy is equal to the amount of [[heat]] transferred by the system. But enthalpy is a [[state function]], which means that the change in enthalpy does not depend on the path of the function. Only the initial and final state of the system matters. In contrary, heat is a path function that is exclusively governed by the temperature gradient of the system. Thus under constant pressure, the change in heat becomes equal to the enthalpy.