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.

$E = E_T +E_K +E_P$ ……

$E_T \to$ Transitional energy

$E_K \to$ Kinetic energy

$E_V \to$ irrational energy

$E_N \to$ Nuclear 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

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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