Table of Contents
Internal and enthalpy
|Internal Energy (E)
|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
|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.