Differences between evaporation and other heat processes MCQs With Answer

Differences between evaporation and other heat processes MCQs With Answer — This concise overview helps B.Pharm students grasp evaporation relative to boiling, condensation, sublimation, and other heat-driven phenomena crucial in pharmaceutical processing. Learn key concepts like vaporization mechanisms, latent heat, equilibrium vapor pressure, effect of temperature, humidity, surface area, and pressure; and practical implications for drying, solvent removal, lyophilization, spray drying, and rotary evaporation. Emphasis on formulation stability, process control, and equipment selection makes the topic directly relevant to pharmaceutics and quality control. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What primarily distinguishes evaporation from boiling?

• Evaporation occurs throughout the liquid at a specific temperature
• Evaporation requires external nucleation sites
• Evaporation occurs only at the liquid surface below boiling point
• Evaporation requires the entire liquid to reach vapor pressure equality

Correct Answer: Evaporation occurs only at the liquid surface below boiling point

Q2. Which heat process involves phase change from solid directly to vapor?

• Evaporation
• Sublimation
• Condensation
• Boiling

Correct Answer: Sublimation

Q3. In pharmaceutical drying, which process most commonly uses controlled low temperature to avoid thermal degradation?

• Conventional boiling
• Spray drying at high inlet temperature
• Lyophilization (freeze-drying)
• Flash evaporation at atmospheric pressure

Correct Answer: Lyophilization (freeze-drying)

Q4. Which factor does NOT increase the rate of evaporation of a solvent at constant temperature?

• Increased surface area
• Lower ambient humidity
• Increased airflow over surface
• Higher ambient pressure

Correct Answer: Higher ambient pressure

Q5. Latent heat of vaporization is best defined as:

• Heat required to raise liquid temperature by 1°C
• Heat needed to convert a unit mass of liquid to vapor without temperature change
• Heat released when vapor condenses
• Heat lost during conduction

Correct Answer: Heat needed to convert a unit mass of liquid to vapor without temperature change

Q6. Which statement about boiling is TRUE compared to evaporation?

• Boiling occurs only at the surface
• Boiling can occur at any temperature if humidity is low
• Boiling involves bubble formation throughout the bulk liquid
• Boiling decreases vapor pressure

Correct Answer: Boiling involves bubble formation throughout the bulk liquid

Q7. In a rotary evaporator, the primary mechanism enabling solvent removal is:

• Conduction heating only
• Lowering boiling point by reduced pressure and increased surface area
• Mechanical agitation without pressure change
• Freeze-induced sublimation

Correct Answer: Lowering boiling point by reduced pressure and increased surface area

Q8. Which thermodynamic parameter describes equilibrium between liquid and vapor at a given temperature?

• Enthalpy of fusion
• Equilibrium vapor pressure
• Specific heat capacity
• Thermal conductivity

Correct Answer: Equilibrium vapor pressure

Q9. Which process is most appropriate for removing water from heat-sensitive biologicals without passing through liquid phase?

• Spray drying
• Vacuum oven drying at high temperature
• Freeze drying (lyophilization)
• Direct sun-drying

Correct Answer: Freeze drying (lyophilization)

Q10. Evaporation causes cooling of the remaining liquid primarily because:

• Heat of fusion is absorbed
• High-energy molecules escape reducing average kinetic energy
• Conduction removes heat quickly
• Ambient temperature rises

Correct Answer: High-energy molecules escape reducing average kinetic energy

Q11. Which is a kinetic factor influencing evaporation rate?

• Latent heat value
• Surface temperature only
• Molecular weight of solvent and diffusion rate
• Boiling point at 1 atm only

Correct Answer: Molecular weight of solvent and diffusion rate

Q12. How does reducing ambient pressure affect boiling point and evaporation?

• Raises boiling point and reduces evaporation
• Lowers boiling point and can increase evaporation rate
• No effect on boiling point or evaporation
• Only affects sublimation

Correct Answer: Lowers boiling point and can increase evaporation rate

Q13. Which statement differentiates vaporization and evaporation?

• Vaporization only refers to condensation
• Vaporization is a general term for phase change from liquid to vapor, including evaporation and boiling
• Evaporation is a type of condensation
• Vaporization does not involve latent heat

Correct Answer: Vaporization is a general term for phase change from liquid to vapor, including evaporation and boiling

Q14. In spray drying, solvent removal is primarily by:

• Sublimation of droplets
• Evaporation of solvent from atomized droplets into hot air
• Condensation onto cold surfaces
• Mechanical compression

Correct Answer: Evaporation of solvent from atomized droplets into hot air

Q15. Which material property increases equilibrium vapor pressure and thus tends to promote evaporation at a given temperature?

• Higher intermolecular forces
• Lower molecular volatility
• Higher volatility and lower boiling point
• Higher viscosity only

Correct Answer: Higher volatility and lower boiling point

Q16. Which process requires continuous input of heat equal to latent heat to maintain phase change?

• Convection without phase change
• Evaporation or boiling during vaporization
• Adiabatic compression
• Sublimation with no heat transfer

Correct Answer: Evaporation or boiling during vaporization

Q17. What is the effect of adding a non-volatile solute on evaporation of a solvent from solution?

• It increases solvent vapor pressure
• It lowers solvent vapor pressure (Raoult’s law) and decreases evaporation rate
• No effect on vapor pressure
• Causes immediate boiling

Correct Answer: It lowers solvent vapor pressure (Raoult’s law) and decreases evaporation rate

Q18. During condensation, heat is:

• Released to surroundings as vapor becomes liquid
• Ignored due to no phase change
• Used to increase vapor pressure

Correct Answer: Released to surroundings as vapor becomes liquid

Q19. Which instrument is most suitable for drying a small volume of heat-sensitive drug solution under reduced pressure?

• Open tray at room temperature
• Rotary evaporator under vacuum
• High-temperature oven
• Direct microwave without control

Correct Answer: Rotary evaporator under vacuum

Q20. Vapor pressure of a liquid increases with:

• Decreasing temperature
• Increasing temperature
• Fixed temperature and increased atmospheric pressure
• Adding non-volatile solute

Correct Answer: Increasing temperature

Q21. In the context of drying powders, which process is most likely to cause surface crusting and hinder internal moisture removal?

• Slow evaporation at low temperature
• Lyophilization
• Rapid surface evaporation leading to case hardening
• Subcritical boiling throughout the matrix

Correct Answer: Rapid surface evaporation leading to case hardening

Q22. Which equation relates the rate of evaporation to vapor pressure difference and mass transfer coefficient?

• Van’t Hoff equation
• Fick’s law of diffusion or mass transfer models
• Arrhenius equation
• Raoult’s law only

Correct Answer: Fick’s law of diffusion or mass transfer models

Q23. Which is TRUE about flash evaporation used in pharma processing?

• It slowly removes solvent at ambient pressure
• It involves rapid vaporization when pressure suddenly decreases
• It is identical to sublimation
• It is used for freeze-drying proteins

Correct Answer: It involves rapid vaporization when pressure suddenly decreases

Q24. The phenomenon where evaporation from a surface is slowed because the air immediately above becomes saturated is called:

• Boiling
• Boundary layer effect or saturated boundary layer
• Condensation
• Conduction inhibition

Correct Answer: Boundary layer effect or saturated boundary layer

Q25. Which heat transfer mode most directly supports evaporation by bringing thermal energy to a liquid surface?

• Radiation only
• Conduction through container only
• Convection providing heat and removing vapor
• Magnetic heating

Correct Answer: Convection providing heat and removing vapor

Q26. How does humidity affect evaporation during pharmaceutical drying?

• Higher humidity increases evaporation rate
• Higher humidity reduces evaporation rate by lowering vapor pressure gradient
• Humidity has no effect
• Only temperature matters

Correct Answer: Higher humidity reduces evaporation rate by lowering vapor pressure gradient

Q27. Which process would you select to separate volatile solvent from a non-volatile API without high thermal stress?

• Direct high-temperature drying
• Vacuum distillation or rotary evaporation at reduced pressure
• Open-air evaporation
• Microwave heating at uncontrolled power

Correct Answer: Vacuum distillation or rotary evaporation at reduced pressure

Q28. In an open system, evaporation reaches equilibrium when:

• Liquid temperature equals ambient temperature
• Rate of evaporation equals rate of condensation from surrounding vapor
• No molecules are escaping
• Latent heat becomes zero

Correct Answer: Rate of evaporation equals rate of condensation from surrounding vapor

Q29. Which describes the role of airflow in industrial evaporative dryers?

• Airflow only cools the product
• Airflow removes saturated vapor and supplies dry gas to maintain gradient
• Airflow increases vapor pressure
• Airflow prevents mass transfer

Correct Answer: Airflow removes saturated vapor and supplies dry gas to maintain gradient

Q30. When comparing evaporation and sublimation, which is correct?

• Evaporation is liquid to vapor; sublimation is solid to vapor
• Both are identical in mechanism and conditions
• Sublimation requires liquid phase first
• Evaporation occurs only in solids

Correct Answer: Evaporation is liquid to vapor; sublimation is solid to vapor

Q31. Which parameter must be overcome for bubble formation during boiling?

• Surface tension and surrounding pressure to allow nucleation
• Only ambient humidity
• Only the color of container
• Viscosity independent of pressure

Correct Answer: Surface tension and surrounding pressure to allow nucleation

Q32. Which process is LEAST suitable to concentrate a heat-sensitive antibiotic solution?

• Vacuum evaporation at low temperature
• Rotary evaporation with controlled bath temperature
• Prolonged open-air evaporation under sunlight
• Membrane concentration methods like reverse osmosis

Correct Answer: Prolonged open-air evaporation under sunlight

Q33. In terms of molecular energy distribution, evaporation preferentially removes:

• Lowest energy molecules
• Highest energy molecules at the tail of Maxwell-Boltzmann distribution
• Only those with zero kinetic energy
• All molecules equally

Correct Answer: Highest energy molecules at the tail of Maxwell-Boltzmann distribution

Q34. Which is an advantage of freeze-drying over conventional evaporation-based drying for pharmaceuticals?

• Faster for all formulations
• Better preservation of structure and bioactivity of thermolabile compounds
• Lower cost always
• Requires no specialized equipment

Correct Answer: Better preservation of structure and bioactivity of thermolabile compounds

Q35. Boiling point elevation caused by dissolved solute affects evaporation by:

• Lowering the temperature required for boiling of solvent
• Raising boiling point and reducing volatility of solvent
• Not affecting evaporation at all
• Turning evaporation into sublimation

Correct Answer: Raising boiling point and reducing volatility of solvent

Q36. For volatile organic solvents, which safety concern is greatest during evaporation in the lab?

• Loss of color only
• Fire and flammable vapor accumulation
• Increased viscosity
• Reduced vapor pressure

Correct Answer: Fire and flammable vapor accumulation

Q37. The Clausius-Clapeyron equation relates which two variables important for phase change processes?

• Viscosity and surface tension
• Vapor pressure and temperature
• Density and color
• Electrical conductivity and temperature

Correct Answer: Vapor pressure and temperature

Q38. Which drying method exploits both evaporation and convective heat transfer to rapidly remove solvent from droplets?

• Lyophilization
• Spray drying
• Cold pressing
• Crystallization

Correct Answer: Spray drying

Q39. Why is surface area critical to evaporation rate in tablet drying?

• Larger surface area reduces evaporation
• Larger surface area increases available sites for molecules to escape, increasing rate
• Surface area only affects chemical reactivity
• Only internal porosity matters, not surface area

Correct Answer: Larger surface area increases available sites for molecules to escape, increasing rate

Q40. Which is true about evaporation in closed containers?

• Evaporation continues indefinitely
• Vapor accumulates until equilibrium vapor pressure is reached and net evaporation stops
• Evaporation rate increases over time
• Pressure has no effect

Correct Answer: Vapor accumulates until equilibrium vapor pressure is reached and net evaporation stops

Q41. Which heat process is used when a solvent is removed by boiling under reduced pressure to avoid high temperatures?

• Freeze-drying
• Vacuum distillation
• Open-tray evaporation at room pressure
• Electrostatic drying

Correct Answer: Vacuum distillation

Q42. In drying kinetics, the constant rate period is governed mainly by:

• Internal diffusion only
• External mass transfer and evaporation from wet surface
• Chemical reactions
• Solid-state polymorphism

Correct Answer: External mass transfer and evaporation from wet surface

Q43. Which describes desorption-dominated drying in pharmaceuticals?

• Surface evaporation only
• Removal of bound water from within matrix requiring heat to break bonds
• Immediate boiling of solvent
• Condensation of solvent into matrix

Correct Answer: Removal of bound water from within matrix requiring heat to break bonds

Q44. Which method best prevents oxidation during solvent removal of oxygen-sensitive API?

• Open-air evaporation with fans
• Vacuum evaporation or inert gas purge (nitrogen) during drying
• Heating in presence of oxygen
• High-shear mixing in air

Correct Answer: Vacuum evaporation or inert gas purge (nitrogen) during drying

Q45. Which describes the key difference between evaporative cooling and conductive cooling?

• Evaporative cooling removes energy via phase change; conduction transfers thermal energy through material
• Both are identical processes
• Conduction involves mass loss
• Evaporation heats the remaining fluid

Correct Answer: Evaporative cooling removes energy via phase change; conduction transfers thermal energy through material

Q46. Which is a common measure of dryness in pharmaceutical powders post-evaporation drying?

• pH value
• Residual moisture content (e.g., % w/w by Karl Fischer)
• Color intensity
• Thermal conductivity only

Correct Answer: Residual moisture content (e.g., % w/w by Karl Fischer)

Q47. When comparing evaporation and condensation rates, what determines net mass flux between phases?

• Only boiling point
• The vapor pressure gradient between liquid surface and surrounding gas phase
• Color of liquid
• Surface tension alone

Correct Answer: The vapor pressure gradient between liquid surface and surrounding gas phase

Q48. Which laboratory technique uses sublimation to purify a compound with sufficient vapor pressure at moderate temperature?

• Chromatography
• Sublimation under reduced pressure using a cold finger
• Liquid-liquid extraction
• Direct evaporation at high heat

Correct Answer: Sublimation under reduced pressure using a cold finger

Q49. Which statement about energy requirements: evaporation vs boiling to remove a given mass of solvent?

• Both require heat equal to latent heat per mass; boiling may be faster due to bulk vaporization
• Evaporation requires no energy
• Boiling requires no latent heat
• Evaporation always uses more energy than boiling

Correct Answer: Both require heat equal to latent heat per mass; boiling may be faster due to bulk vaporization

Q50. In designing a drying process for a hygroscopic API, which approach best minimizes caking and loss of potency?

• Rapid high-temperature evaporation with no humidity control
• Controlled drying with reduced temperature, controlled humidity, and possibly inert atmosphere
• Leaving product in open air indefinitely
• Using only direct sunlight heating

Correct Answer: Controlled drying with reduced temperature, controlled humidity, and possibly inert atmosphere

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com