# Interview Questions on Thermodynamics

Thermodynamics topic questions and answers for interview, competitive examination and entrance test.

1. What is the difference between heat capacity and specific heat of the material?
The heat capacity of material is the amount of heat transformed to raise unit mass of a material 1° in temperature.

The specific heat of material is the ratio of the amount of heat transferred to raise unit mass of a material 1° in temperature to that required raise unit mass of water 1° of temperature at some specified temperature.

For most of the engineering purposes, heat capacities may be assumed numerically equal to specific heat values.

2. Explain the rule to find specific heat for aqueous solutions.
For an aqueous solution of salts, the specific heat can be estimated by assuming the specific heat of the solution equal to that of the water alone. Thus, for a 15% by weight solution of sodium chloride in water, the specific heat would be approximately 0.85.
3. What do you understand by latent heat? Give examples of latent heats.
For pure substances, the heat effects accompanying changes in state at constant pressure (no temperature change being evident) are known as latent heats. Examples of latent heats are the heat of fusion, vaporization, sublimation and change in crystal form.
4. Define the term free energy and free enthalpy. What is their significance and importance?
Free energy (or Helmholtz function) is defined as f = u.T.s.

It is equal to the work during a constant-volume isothermal reversible nonflow process.

Free enthalpy (or Gibbs function) is defined as

g = h – Ts

(where u = internal energy, h = enthalpy, T = temperature, s = entropy)

Gibbs function is of particular importance in processes where chemical changes occur. For reversible isothermal steady-flow processes or for reversible constant-pressure isothermal nonflow processes, change in free energy is equal to network.

5. What is the polytropic process? Under which conditions polytropic process approaches isobaric, isothermal, and isometric process? In which reversible process no work is done ?
A polytropic process is one that follows the mathematical equation pvn = constant (‘p’ is the pressure, ‘v’ is the volume and index ‘n’ may have values from -∞ to +∞. This process approaches isobaric when n = 0, isothermal when n = 1, and isometric when n = ∞. No work is done in the isometric process.
6. Out of constant pressure and constant volume lines on TS diagram which line has higher slope? and whether the slope is constant or variable ?
Constant volume line. Slope is variable.
7. In which process fluid expands but no work is done?
Throttling process.
8. Whether superheated steam can be treated like ideal gas ?
Yes.
9. Which parameter remains constant in isochoric process ?
Volume remains constant.
10. In which process internal energy remains constant ?
Isothermal process.

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