Question

In which process, there is no change in the internal energy of the system?
A.Isothermal
B.Adiabatic
C.Free expansion
D.Cyclic

Answer 1

Hint: Basically, in thermodynamics, the internal energy of the system refers to the energy that is contained within the system excluding the kinetic energy and potential energy. Moreover, it keeps account of the gains and losses of energy of the system that are basically due to changes in the internal state.

Complete step by step answer:
In chemistry, chemical thermodynamics refers to the study of interrelation of heat and work with chemical reactions or with physical changes of state. Moreover, chemical energy refers to the potential of a chemical substance to undergo a transformation through a chemical reaction.
Now, let’s study each of the options and determine the correct one. In the case of isothermal processes, the temperature of the system remains constant. The transfer of heat into or out of the system happens so slowly that thermal equilibrium is maintained. Further, in the case of adiabatic process, there is no transfer of heat and mass between a thermodynamic system and its surroundings. The third option is a free expansion process. It is an irreversible process in thermodynamics in which a volume of gas is kept in one side of a thermally isolated container, with the other side being evacuated. The last one is a cyclic process. This process involves the transfer of heat and work into and out of the system.
Now, internal energy refers to the energy associated with the random, disordered motion of molecules. Moreover, in case of isothermal, free expansion and cyclic process, there is no change in the internal energy of the system as temperature remains constant in these processes and as internal energy is a function of temperature, so there is no change in the internal energy of the system.
Hence, option A, C and D are correct.

Note:Don’t get confused with internal energy and kinetic energy. Basically, internal energy is the total energy contained by a thermodynamic system and it has two major components: kinetic energy and potential energy. The kinetic energy is due to the motion of the system’s particles. For example, vibration, rotations, translations etc.