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  4. Internal energy is :

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Q. Internal energy is :

AFMCAFMC 2004

Solution:

Internal energy $(U)$ (also known as intrinsic energy) is a state function. A fixed quantity of any substance is associated with a definite amount of energy which depends upon chemical nature of substance is known as internal energy. The various energy which contribute towards internal energy are :
(a) Translational energy of molecules $\left(E_{t}\right)$
(b) Rotational energy of molecules $\left(E_{r}\right)$
(c) Vibrational energy of molecules $\left(E_{v}\right)$
(d) Electronic energy $\left(E_{e}\right)$.
(e) Nuclear energy $\left(E_{n}\right)$
(f) Interaction energy of molecules $\left(E_{i}\right)$
$u=E_{t}+E_{r}+E_{v}+E_{e}+E_{n}+E_{i}$
Change in internal energy $(\Delta u)$ of a reaction is
$\Delta U=U_{\text {product }}-U_{\text {reactant }}$
According to I law of thermodynamics
$\Delta U \neq q+W$
$q=$ heat energy
$W=$ work done
So internal energy is partly potential and partly kinetic.