Question

In a cyclic process, the change in internal energy of the system is
1. Positive
2. Negative
3. Zero
4. Cannot be determined

Answer 1

Correct Answer - Option 3 : Zero

The correct answer is option 3) i.e. Zero

CONCEPT:

• Cyclic process: It is a thermodynamic process where a system comes back to its initial state i.e. the system starts and returns to the same thermodynamic state.

• Internal Energy: The internal energy of a system is identified with the random, disordered motion of molecules;
  • The total (internal) energy in a system includes potential and kinetic energy.

The internal energy of an ideal gas is calculated by

U = nfRT/2

Change in internal energy is given by:

ΔU = nfRΔT/2

where n is the number of moles, f is the degree of freedom of gas, R is gas constant, and T is the temperature.

• Since the system return to the same state after each cycle, the change in internal energy is zero.
• In this case, the work done will be equal to the heat energy.

EXPLANATION:

• In a cyclic process (ΔT = 0 so ΔU = 0), the system remains the same after each cycle. Hence, the change in internal energy is zero.