Question

Internal energy is :

• A. partly potential and partly kinetic
• B. totally kinetic
• C. totally potential
• D. none of the above

Answer 1

Answer: (A)

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
$\Delta U\ne q+W$
$q=$ heat energy
$W=$ work done
So internal energy is partly potential and partly kinetic.