Internal Energy of a System

Each substance is associated with a certain amount of energy which depends on its chemical nature, temperature, volume, pressure etc. Thus internal energy of the system is simply the sum of all types of energies associated with the substance in the system. It is denoted by E or U.

E = E_T +E_K +E_P……

E_T \toTransitional energy

E_K \to  Kinetic energy

E_V \to irrational energy

E_N \toNuclear energy

E_P \to Potential energy

The exact measurement of internal energy is not possible so it is measured in terms of Internal energy change.

I.e.\Delta E or \Delta U

It depends only upon Temperature (for Ideal gas) Internal energy E’ is a state function hence \Delta E does not depend upon path or way of process or it depends upon initial and final states only.

For path I: Internal energy change is \Delta E_1

For path II: \Delta E_2 i.e.

Here \Delta E_1 = \Delta E_2

Internal energy

Internal energy

  • It is an extensive property.
  • \Delta is measured by using Bomb Calorimeter as follow
\Delta E = C \times \delta T \times \dfrac{M}{m}

M = molar mass; m = Mass of substance; C = Heat capacity of calorimeter; \Delta T = Rise in temperature

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