Chemical Engineering Thermodynamics Interview Questions

Here are the top 50 commonly asked questions in Chemical Engineering Thermodynamics interviews. Whether you’re just starting your preparation or need a quick refresher, these questions and answers will help you tackle your interview with confidence.

Basic Chemical Engineering Thermodynamics Interview Questions with Answers

1. Who is the father of chemical engineering thermodynamics?

French engineer, Nicolas Sadi Carnot is known as the father of thermodynamics.

2. What is the need to study thermodynamics?

Thermodynamics describes the quantitative relationship of energy and work. These mathematical relationships are needed to determine real property values and in the calculations of heat and work in various processes in industries.

3. Which properties are called thermodynamic properties?

Pressure, temperature, volume, internal energy, enthalpy, entropy, Gibbs energy and Helmholtz energy are the eight thermodynamic properties.

4. What do you mean by a thermodynamic phase?

Thermodynamic phase refers to a homogenous material which can be separated from a non-homogenous material. The physical properties of a thermodynamic phase are essentially uniform.

5. What do you mean by a thermodynamic state?

Thermodynamic state refers to the condition of a system at a specific time which can be fully understood by a suitable set of thermodynamic parameters given according to the phase rule.

6. What are the types of thermodynamic processes?

There are four different types of thermodynamic processes. They are isobaric, isothermal, adiabatic and isochoric types of processes.


7 What are the types of thermodynamic properties?

Thermodynamic properties can be classified into extensive and intensive properties. Extensive properties depend on the amount of species whereas intensive properties are those which do not depend on the amount of species.

8. What is the first law of thermodynamics?

The first law of thermodynamics states that energy assumes many forms; the total quantity of energy is constant, and when energy disappears in one form it appears simultaneously in other forms.

9. What are the types of thermodynamic systems?

There are three types of thermodynamic systems: insulated, closed and open system. Insulated system allows transfer of mass, but not mass; closed system allows transfer of energy, but not mass. Open systems allow transfer of mass and energy through system.

10. Which scientist first identified the first law of thermodynamics?

James Joule, through a series of experiments, demonstrated that there exists a quantitative relationship between heat and work. This relationship is expressed in the form of the first law of thermodynamics.

11. What is thermodynamic work?

Thermodynamic work is the work done by a system on its surroundings, which is the energy transferred by the system to its surroundings in a way by which the system can spontaneously exert macroscopic forces on its surroundings.

12. How are the thermodynamic properties related?

The thermodynamic properties of pressure, volume and temperature are related through equations of state. These equations give complete relationship of pressure, volume and temperature. Other thermodynamic properties are expressed as functions of these properties.

13. What is the thermodynamic temperature scale?

Kelvin scale is considered to be the thermodynamic temperature scale. This temperature scale is independent of the characteristics of a substance and can be used comfortably in all calculations of heat and work.

14. What is second law of thermodynamics?

The second law of thermodynamics states that no apparatus can operate in a way that its only effect is the conversion of heat absorbed by a system completely into work.

15. Who invented the thermodynamic heat engine?

French engineer, Nicolas Sadi Carnot invented the thermodynamic heat engine. This engine has the maximum efficiency, in that the conversion of heat supplied to a system into work is maximum in this engine.


16. What is a thermodynamic heat sink?

A thermodynamic heat sink is a reservoir of heat which can absorb a significant amount of heat without significant change in temperature. Air is an example of heat sink.

17. What are the thermodynamic processes in a heat engine?

A heat engine consists of a reversible cycle of four thermodynamic processes. The four processes, in order, are adiabatic compression, isothermal expansion, adiabatic expansion, isothermal compression.

18: What is thermodynamic equilibrium?

Thermodynamic equilibrium denotes the absence of change in any property as well as the absence of tendency toward change on a macroscopic scale. The absence of tendency to change denotes the absence of any driving force.

19. What is the condition for thermodynamic equilibrium?

Thermodynamic equilibrium is reached when the driving forces become zero. The driving force for phase change is difference in chemical potential. Multiple phases at the same temperature and pressure are in equilibrium when the chemical potential is same in all phases.

20. What are the thermodynamic properties to account for non-ideality?

Non-ideality of gases is accounted by the introduction of fugacity coefficient. Non ideality of liquids is accounted by the introduction of the activity coefficient.


Intermediate Chemical Engineering Thermodynamics Interview Questions with Answers

21. What are the canonical variables of Gibbs energy?

The canonical variables for Gibbs energy are temperature and pressure. This implies that the Gibbs energy of a system can be fully understood by the temperature and pressure of the system.

22. What is enthalpy?

Enthalpy is the heat transferred through a system at constant pressure. It is obtained by the addition of flow work to the internal energy of the system. Absolute values of enthalpy cannot be calculated.

23. What is entropy a measure of?

Entropy is a measure of energy that is unavailable to do work. It represents the disorder or randomness in the arrangement of molecules in a system.

The limitations of Raoult’s law are that it cannot be applied to concentrated solutions and for mixtures containing a volatile solute. Raoult’s law does not account for change in the number of particles in the solution.

25. What is the property used to modify Raoult’s law?

The property used to modify Raoult’s law is activity coefficient. Activity coefficient is used to account for non-idealities in liquid phase solutions.

26. What does K-value measure?

The K-value is a measure of tendency of a species to partition itself between liquid and vapor phases. The K-value also gives us the knowledge of the tendency of a species to favor the vapor phase i.e., its volatility.

27. How can we find the saturation pressure for a given temperature?

The saturation pressure for a given temperature can be evaluated using any of the empirical relation which relate the two properties. An example of an empirical relation is given by Antoine’s law which relates the temperature with logarithm of saturation pressure.

28. What are the characteristics of ideal gas?

An ideal gas has three main characteristics: It should not have any intermolecular forces, the total volume of the gas molecules is negligible to the volume occupied by the gas and, all collisions between molecules are elastic.

29. What is chemical potential?

Chemical potential of a species is the measure of energy that can be absorbed or released as a result of change in the number of particles of that species. It represents the tendency to react or the tendency to transition into another phase.

30. What are the degrees of freedom at the triple point?

The triple point is the point where all three phases, solid, liquid and gas, coexist together. For a single component, the phase rule gives the degrees of freedom at the triple point as zero implying that the state is unique set of temperature and pressure.

31. What does entropy represent?

Entropy represents the direction of a process and spontaneity of a process. Entropy gives us information about the randomness in a system.

32. What does fugacity represent?

Fugacity of a species represents the pressure of a real gas as opposed to the
pressure of an ideal gas. Fugacity gives us a reference to establish an absolute standard of measurement up to zero pressure in the calculation of equilibrium criteria.

33. What is critical temperature?

The critical temperature of a substance is the temperature above which vapor of that substance cannot be liquified for any amount of pressure applied.

34. What is critical pressure?

The critical pressure of a substance is its saturation pressure at the critical temperature, above which liquid and gas phases cannot be distinguished.

35. Which properties are used to measure deviations from ideal gas measured?

Deviations from ideal gas measures in terms of residual properties. Residual properties measure the difference in property value of a real gas to that of an ideal gas.

36. What is compressibility factor? What does it represent?

Compressibility factor ‘Z’ is the ratio of volume of a real gas to the volume of an ideal
gas. It represents the degree of deviation of a real gas from an ideal gas.

37. What are mixtures which deviate from Raoult’s law called?

Mixtures which deviate from Raoult’s law are known as azeotropes. Mixtures with positive deviations are known as minimum boiling azeotropes and those with negative deviations are known as maximum boiling azeotropes.

38. For what concentrations can Henry’s law be applied?

Henry’s law can be applied for species which are in very low concentrations in the liquid phase. The pressure of the gas phase should be low so that it can be approximated as an ideal gas.

39. What are the two types of heat capacities?

There are two types of heat capacities: heat capacity at constant volume (Cv) and heat capacity at constant pressure (Cp). The two types of heat capacities are functions of temperature.

40. What is the partial molar Gibbs energy equal to?

The partial molar Gibbs energy is equal to the chemical potential of a species. Since the absolute value of Gibbs energy cannot be measured, the absolute value of chemical potential cannot be measured.

41. What do you mean by shaft work in the energy balance equation for an open system?

Shaft work is the work done by direct contact of material with the surrounding material at the boundary of the system. A system in equilibrium cannot initiate shaft work. Example of shaft work is turbine extracting energy from a flow.

42. What do you mean by ideal work? How is it calculated?

Ideal work is the work done in a change of state which is accomplished reversibly. Ideal work can be calculated as the shaft work needed or obtained by doing an entropy balance and setting the entropy generation term to zero.

43. Why are reduced temperature and pressure defined?

Reduced temperature and pressure are defined to check the variability of
compressibility factor with respect to these properties. The compressibility factor of different fluids is the same when they are compared in terms of their reduced temperature and pressure.

44. What is meant by dynamic equilibrium?

Dynamic equilibrium is the equilibrium achieved at the completion of reversible
chemical reaction. The concentration of both reactants and products does not change in a dynamic equilibrium.

45. What is the nature of chemical reaction equilibrium?

Chemical Reaction equilibrium is of a dynamic nature. The forward and backward reaction do not cease to occur but they proceed at equal rates of reaction.

46. What is the heat effect of mixing?

Heat effect of mixing refers to the enthalpy liberated or absorbed from a substance upon mixing due to the new interactions between the particles of the mixture.

47. Why can’t we calculate the entropy of an irreversible process?

Entropy cannot be calculated for an irreversible process as entropy change is not caused solely due to heat transfer. Since entropy is a state function, we can devise a reversible process between the two states and calculate the change in entropy.

48. What do you mean by a quasi-static process?

A quasi-static process is one in which every point of the process is in equilibrium with itself. The number of intermediate equilibrium steps tend to infinity and the process can be approximated as reversible.

49. What are the conditions when a real gas can be approximated to an ideal gas?

A real gas can be approximated to be an ideal gas at the conditions of low pressures and high temperatures.

50. What is STP condition?

STP condition refers to Standard Temperature and Pressure condition. This state is considered as a reference for ideal gas, with temperature 273K and pressure 1atm.

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