Internal energy and entropy are state functions

Internal energy (U) and entropy (S) are thermodynamic properties that describe the state of a system. A state function is a property that depends only on the current state of the system and is independent of how the system reached that state. In other words, the value of a state function is determined solely by the initial and final states of the system, not the path taken to go from one state to another.

Internal energy (U)

Internal energy is a measure of the total energy of a system, which includes the kinetic energy of the particles within the system and the potential energy associated with their interactions. It is denoted by the symbol U and is a state function. The internal energy of a system can change during a process due to the transfer of heat (Q) and work (W) done on or by the system.

Entropy (S)

Entropy is a measure of the degree of disorder or randomness in a system. It is denoted by the symbol S and is also a state function. The entropy of a system can change during a process due to the transfer of heat and irreversible changes in the system.

Explanation of the correct statement

The correct statement is option B: Internal energy and entropy are state functions. This means that the values of internal energy and entropy depend only on the current state of the system and are independent of the path taken to reach that state.

The change in internal energy (ΔU) and the change in entropy (ΔS) between two states can be determined by calculating the difference in their values at the initial and final states:

ΔU = Ufinal - Uinitial
ΔS = Sfinal - Sinitial

Since internal energy and entropy are state functions, the values of Ufinal, Uinitial, Sfinal, and Sinitial are independent of the specific process or path taken to go from the initial to the final state.

This is not the case for options A, C, and D:

- Option A states that the internal energy changes in all processes. However, this is not true as the internal energy can remain constant in some processes, such as an isothermal process.
- Option C states that the change in entropy can never be zero. However, this is not true as the change in entropy can be zero for reversible processes.
- Option D states that the work done in an adiabatic process is always zero. However, this is not true as work can be done in an adiabatic process if there is a change in volume against an external pressure.

Therefore, the correct statement is option B: Internal energy and entropy are state functions.