The total heat content of a system at constant pressure is equivalent to the internal energy (E) plus the PV energy.

Representation

Enthalpy of the system is represented by the symbol ‘H’

Equation

Enthalpy is defined by the equation:

H = E + PV

where, P and V are the pressure and volume of the system.

Equation

If H1 and H2 are the enthalpies of the system in the initial and final states,

This equation is the most general definition of ΔH.

Equation

When the pressure remains constant throughout the process, then

Enthalpy of Formation

The enthalpy of formation of a compound is defined as the change in enthalpy of the system when one mole of the compound is formed from its elements. It is denoted by ΔHf.

Enthalpy of Formation

For example:

The heat of formation of SO2 is -70.96 kCals.

Enthalpy of Neutralization

The enthalpy of neutralization of an acid at a given temperature is defined as the change in enthalpy (ΔH) accompanying the neutralization of one gram equivalent of the acid by a base or vice-versa in dilute solution at that temperature.

Enthalpy of Vaporization

defined as the heat change or enthalpy change when one mole of a liquid is converted into vapors or a gaseous state at its boiling point.

Enthalpy of Vaporization

For example, When one mole of water is converted into steam at 1000C or 373 K, the heat absorbed is 9.71kCal, which is the heat of vaporization of water. The change can be represented as

How to calculate enthalpy change?

The mass of your reactants, s, the specific heat of your product, and ∆T, the temperature change from your reaction, you are prepared to find the enthalpy of reaction using the formula ∆H = m x s x ∆T.