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Difference between Internal Energy and Enthalpy Heat

Table of Contents

Internal and enthalpy

Internal Energy (E) Enthalpy (H)
i. Internal energy is defined as the sum of different forms of energies associated with atoms, ions or molecules in a system also called molecular energy like kinetic energy, Potential energy, chemical bond energy etc. It is represented by E or U


E = KE + PE + bond energy + Nuclear energy + ……

ii. Internal energy of substance depends upon its chemical nature and its state of existence.

iii. The change in internal energy of a system is equal to the heat supplied to or absorbed by a system at constant volume

Qv = △ E

iv. The internal energy change doesn’t explain the nature of chemical change.

i. Enthalpy is defined as the heat content of a system. It is represented by H. It is state depended and path independed quantity.

Mathematically it is defined as H = E + PV.

Thus, enthalpy is the sum of internal energy and product of pressure and volume (also called pressure-volume work)

ii. Enthalpy of any substance depends upon its temperature and pressure.

iii. Enthalpy change is equal to the heat supplied to or absorbed or evolved in a system at constant pressure.

Qp = △ H

iv. The value of enthalpy change describes the nature of a chemical change. The -ve value describes the exothermic reaction and +ve value describes endothermic reaction.

Exothermic and Endothermic

Exothermic Reaction Endothermic Reaction
1. A chemical reaction in which heat energy is evolved after the chemical change is called exothermic reaction. 1. A chemical reaction in which heat energy is absorbed during the chemical change is called endothermic reaction.

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