## What is Enthalpy?

The enthalpy of a system is a measure of the total energy in the system. It is the sum of the internal energy of the system and the work done on the system by external forces.

## Enthalpy – Definition

The enthalpy of a system is a measure of the system’s internal energy and the work needed to change its temperature. It is expressed in units of energy per unit of temperature.

## Enthalpy – Mathematical Equation

The mathematical equation for enthalpy is:

H = U + PV

Where H is enthalpy, U is internal energy, PV is pressure times volume.

## Enthalpy and Entropy

The change in entropy is a measure of how much disorder has been created in a system. The change in enthalpy is a measure of how much energy has been transferred into or out of a system.

## Enthalpy – Relation with Volume and Pressure

The enthalpy of a substance is a measure of the heat content of the substance. The enthalpy of a substance is a function of the temperature and pressure of the substance.

## Endothermic and Exothermic Reactions

Endothermic reactions are those where the system absorbs energy from its surroundings, while exothermic reactions are those where the system releases energy to its surroundings. In both cases, the change in energy of the system is measured.

## Change in Reaction of Enthalpy

The enthalpy of a reaction is the heat absorbed or released by the system. The change in the enthalpy of a reaction is the change in the heat absorbed or released by the system.