Chemical Process Calculation Interview Questions

Here are the top 50 commonly asked questions in Chemical Process Calculation 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 Process Calculation Interview Questions with Answers

1. What is Process Calculation?

Process calculation is the subject that deals with study of conversion, separation, material balance reactions and to carry out the basic as well as complex calculations which are useful in chemical engineering.

2. Which four fundamental quantities (with units) are used in solving process calculation problems?

The four fundamental quantities are used in solving process calculation problems are length, mass, time and temperature. Their fundamental units are meter, kilogram, second and kelvin respectively.

3. What are the different methods used to express the composition of mixtures in process calculation?

The different methods which are used to express the composition of mixtures of different components such as solids, liquids and gases in process calculation are Mass Per cent, Volume Per cent and Mole Per cent.

4. What is the concept of Normality in process calculation?

Normality is defined as the ratio of gram equivalent of solute to the volume of solution in litre i.e. number of gram equivalent of solute dissolved in one litre of solution. Normality is denoted by the symbol N.

5. What is meant by Molarity in process calculation?

Molarity is the ratio of gram moles of solute to the volume of solution in litre i.e. number of gram moles of solute dissolved in one litre of solution. Molarity is denoted by the symbol M.

6. How do you define the term Molality in process calculation?

Molality is the ratio of gram moles of solute to the mass of solvent in kilogram i.e. gram moles of solute dissolved in one kilogram of solvent. Molality is denoted by the symbol m.

7. What is the principle of Stoichiometry in process calculation?

In chemical reactions, the mass and volumetric relationships are generally presented together with the basic units for expressing the changes in mass and compositions. This relationship is called as the principle of stoichiometry.

8. When is the Raoult’s law valid in process calculation?

Raoult’s law is valid in process calculation when the mole fraction (xA) of the component (A) in the liquid phase is close to 1 i.e. the liquid phase is almost pure.

9. How do you define vapor pressure in process calculation?

The absolute pressure at which both the liquid and its vapor acquire the equilibrium at a given temperature is called as vapor pressure. All liquids and solids possess a definite vapor pressure at given temperature.

10. What is dimensional analysis method used in process calculation?

The method that is use to determine the relationships among the physical quantities by using the major fundamental quantities like length L, mass M, time T and temperature θ is called as dimensional analysis method.

11. What is the difference between boiling and normal boiling point in process calculation?

The boiling point is defined as the temperature of liquid at which both, the equilibrium vapor pressure and the total surrounding pressure of liquid surface are equal. Whereas the temperature of liquid at which the equilibrium vapor pressure is equal to the atmospheric pressure at sea level is called as normal boiling point.

12. What is meant by critical temperature in process calculation?

The maximum temperature at which the gas can be liquefied is called as critical temperature. It is also defined as critical state above which gases cannot be liquefied no matter how much pressure we are applying on it.

13. What is Dalton’s law that is used in process calculation?

Dalton’s law states that the total pressure that is exerted by the gaseous mixture is equal to the sum of different partial pressure of the gaseous component. This law shows the additive property of partial pressures.

14.How do you define the term humidity that is used in process calculation?

The ratio of mass of water vapor present in the air in kilogram to the mass of dry air in kilogram is called as humidity. It provides the information about the amount of water vapor present in the air. Humidity is denoted by H.

15. What is Wet Bulb temperature which is used in the study of process calculation?

When the bulb thermometer is covered by wet cloth, then the temperature of moist air is measured by ordinary thermometer and it is said to be Wet Bulb temperature. It is referred as WBT.

16. What are the four main plot curves of humidity chart used in process calculation?

The four main plot curves of humidity chart that gives information of amount of moisture present in dry air at given temperature are Humidity Vs Temperature curve, Humidity vs Humid heat line, Specific volume vs Temperature curve and Adiabatic cooling lines.

17. What are the various important operations carried out in the process industry?

The various important operations that are carried out in the process industries which are very useful and require less efforts are distillation, absorption, extraction, crystallization, drying, mixing and evaporation.

18. What are the different types of crystallizers that are used in process industries?

There are four different types of crystallizers that are used in commercial practice in the process industries are Agitated batch crystallizer, Swenson walker crystallizer, Krystal crystallizer, Vacuum crystallizer.

19. What is purging operation in process industry?

When two or more reactants are fed into reactor and one of the reactant is impure then that unwanted material remains in the recycle stream and prevent the attainment of steady state. The withdrawal of recycle stream under this condition is called purging operation.

20. What is recycle operation in process industry?

When reactants are fed in the reactor, some reactants remain unreacted. The product is taken out and unreacted reactants are separated from the product. The unit operation in which unreacted reactants are sent back and combined to the fresh feed is called as recycle operation.

Intermediate Chemical Process Calculation Interview Questions with Answers

21. What is saturated vapour pressure?

When the vapour of a liquid exists under conditions where its partial pressure is equal to the equilibrium vapour pressure, then it is known as saturated vapour pressure. At this condition the vapour is completely ready to condense.

22. What is unsaturated vapour pressure?

When the vapour of a liquid exists under conditions where its partial pressure is less than the equilibrium vapour pressure, then it is known as unsaturated vapour pressure. At this condition the vapour is not ready to condense and such vapour is called as superheated vapour.

23. What is vapour pressure of immiscible liquid mixtures?

The vapour pressure of immiscible liquid mixture is the sum of vapour pressure exerted by the individual components of the system without change in temperature. Depending on the temperature, each component of the mixture will add its own vapour pressure.

24. How can we achieve humidification?

Humidification can be achieved to the desired condition by spraying water into the circulation of air path, at a temperature higher than the wet bulb temperature and lower than the dry bulb temperature. Absorption refrigeration system is employed to achieve this condition.

25. What is the mechanism of dehumidification?

When the temperature of the surface is less than the dew point of the air, at this condition the condensation of moisture takes place. Hence, the temperature of the air falls. This is the mechanism of dehumidification.

26. What is distillate and residue in fractional distillation?

In fractional distillation, components are separated on the basis of their boiling points. So, the product obtained from the top is called distillate (overhead product) and the product removed from the bottom is called residue (bottom product).

27. When and how can you achieve supersaturation?

Supersaturation can be achieved when the solubility of a compound in a solvent exceeds the saturation solubility. It can be achieved by cooling the solution and by addition of a substance, which is more soluble in solvent than the solid to be crystallized.

28. What is solubility and solubility curve?

When a particular substance (solute) is dissolved in a particular solvent until it yields a saturated solution is called solubility. Solubility curve is the plot of temperature on x-axis and solubility (g of solute/100 g of solvent) on y-axis.

29. What are the various industrially used evaporators?

The various industrially used evaporators which are very useful and commercially practiced are vertical tube evaporator, horizontal tube evaporator and steam jacketed kettle etc.

30. What is the limiting reactant?

If two or more reactants are fed to a chemical reactor according to the stoichiometric proportion to produce the products, then the reactant that would disappear first at completion of reaction is called the limiting reactant.

31. What is an excess reactant?

If two or more reactants are fed to a chemical reactor according to the stoichiometric proportion to produce the products, then the reactant that would still remain at the completion of reaction is called an excess reactant.

32. What is selectivity?

The information regarding the amount of wanted product formed by desired reaction relative to amount of unwanted product formed by side reaction is called selectivity.

33. What is material balance with single and multiple chemical reaction?

If material balance of a system involves with a single chemical reaction to produce the product, it is called material balance with single chemical reaction and if it involves with two or more chemical reactions, then it is called material balance with multiple chemical reactions.

34. What are primary and secondary solid fuels?

The solid fuel which comes from the natural source is called primary solid fuel and which is derived from the natural solid fuel is called secondary solid fuel. The examples of primary solid fuels are coal, wood, etc. and of secondary solid fuels are charcoal, coke, etc.

35. What are primary and secondary liquid fuels?

The liquid fuel which comes from natural source is primary liquid fuel and which is derived from primary liquid fuel is secondary liquid fuel. The example of primary liquid fuel is petroleum and of secondary liquid fuels are Synthetic petrol, Diesel, Kerosene, etc.

36. What are primary and secondary gaseous fuels?

The gaseous fuel which comes from natural source is primary gaseous fuel and which is derived from primary gaseous fuel is secondary gaseous fuel. The example of a primary gaseous fuel is Natural gas and of secondary gaseous fuels are LPG, coal gas and biogas.

37. What is the composition of Natural gas?

The Natural gas contains 80% to 90% methane and the rest is ethane, propane, butane and pentane. It also contains small amount of other gases like light hydrocarbons, acetylene, oxygen, hydrogen and carbon dioxide.

38. What is the statement of Amagat’s law?

Amagat’s law states that the total volume which is occupied by the gaseous mixture is equal to the sum of volume of pure component of gases. It shows the additive property of pure component of volume of gases.

39. What does the value of ‘R’ display in the formula of ideal gas law?

In ideal gas PV=nRT, R is 8.314 J/mol K which display the value of universal gas constant at standard atmospheric pressure.

40. What are the various drying equipments used in industries?

The various drying equipments that are industrially used are named as Tray dryer, Drum dryer, Spray dryer, Vacuum dryer, Freeze dryer, Fluidised bed dryer respectively.

41. What is the vapour pressure of liquid?

The pressure exerted by the vapour at the condition where rate of condensation and the rate of vaporisation are equal and a dynamic equilibrium is attained is called as vapour pressure of liquid.

42. Which equation is used for showing effect of temperature on vapour pressure?

The effect of temperature on vapour pressure of liquid is shown by Clausius Clapeyron equation. If ideal gas law is obeyed by the vapour of the liquid, then the Clausius Clapeyron equation is more accurate at low temperature and low pressure.

43. What is Cox chart?

A plot that portrays the logarithmic vapour pressure of substance vs logarithmic vapour pressure of reference substance where both the values have same temperature is known as Cox chart.

44. What is meant by relative vapour pressure?

The ratio of vapour pressure of the solution to the vapour pressure of the pure solvent is known as relative vapour pressure where p is the vapour pressure of solution and Ps is the vapour pressure of the pure solvent.

45. What are the uses of adiabatic cooling lines?

Adiabatic cooling lines are mostly used to determine the humidity of wet bulb temperature and dry bulb temperature. During drying in adiabatic conditions, the adiabatic cooling lines shows the changes in humidity.

46. What is dew point temperature?

The temperature at which the dry air which is associated with water vapour becomes saturated and filled with moisture with respect to plane water surface is known as dew point temperature. It is denoted by D.P.

47. What is Dry Bulb temperature?

The temperature when measured by the ordinary thermometer is not affected by the moisture of the air that means it can be freely exposed to air is known the Dry Bulb temperature. It is referred as DBT.

48. What is saturated humidity?

When the vapour pressure of water in air is in the equilibrium condition with the liquid vapour at give temperature and pressure, then it is said to be saturated humidity. Saturated humidity is mainly denoted by Hs.

49. What is meant by relative humidity?

The ratio of actual partial pressure of water vapour in the mixture of air to the partial pressure of water vapour at saturation level is called as relative humidity. At saturation, the relative humidity is 100 percent and it is denoted by HR.

50. What is the influence of temperature on the solubility of substance?

If the solution is not saturated, then the substance dissolves in the solution. This process is continued until the solution become saturated, then supersaturated. And the state of supersaturation is only possible by reducing the temperature, hence influence of temperature on solubility of substance is important.

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