Latent heats MCQs With Answer

Latent heats MCQs With Answer provide B. Pharm students a focused revision tool on phase-change energetics and pharmaceutical applications. This concise, keyword-rich introduction covers latent heat, latent heat of fusion and vaporization, specific latent heat, enthalpy changes during melting, boiling, condensation, and sublimation, plus practical topics like freeze-drying, crystallization, thermal analysis (DSC/TGA), and pressure effects. Questions emphasize calculations (Q = mL), units (J/kg), measurement methods, and implications for drug stability, drying processes, and formulation design. Designed to boost exam preparedness and conceptual understanding, the set balances theory, calculations, and applied pharmaceutical examples. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the definition of latent heat?

• Energy required to change temperature of a substance
• Energy absorbed or released during a phase change without temperature change
• Energy lost by radiation from a surface
• The heat required to raise unit mass by 1 degree

Correct Answer: Energy absorbed or released during a phase change without temperature change

Q2. Which formula correctly represents the heat required for a phase change?

• Q = mcΔT
• Q = m + L
• Q = mL
• Q = L/ m

Correct Answer: Q = mL

Q3. What does ‘L’ represent in Q = mL?

• Latent heat per mole
• Specific latent heat per unit mass
• Specific heat capacity
• Latent heat flux

Correct Answer: Specific latent heat per unit mass

Q4. What are common units for specific latent heat in SI?

• J kg
• J kg^-1
• J m^-3
• W m^-2

Correct Answer: J kg^-1

Q5. The latent heat of fusion refers to which process?

• Vapor to gas transition
• Liquid to vapor transition
• Solid to liquid transition
• Sublimation from solid to gas

Correct Answer: Solid to liquid transition

Q6. The latent heat of vaporization refers to which process?

• Solid to liquid
• Liquid to vapor
• Gas to solid
• Melting of solids

Correct Answer: Liquid to vapor

Q7. Approximate specific latent heat of fusion for water is:

• 34 kJ/kg
• 334 kJ/kg
• 2260 kJ/kg
• 2.26 kJ/kg

Correct Answer: 334 kJ/kg

Q8. Approximate specific latent heat of vaporization for water at 100°C is:

• 334 kJ/kg
• 4184 kJ/kg
• 2260 kJ/kg
• 100 kJ/kg

Correct Answer: 2260 kJ/kg

Q9. Which technique directly measures latent heats and phase transitions in pharmaceutical solids?

• HPLC
• DSC (Differential Scanning Calorimetry)
• UV-Vis spectroscopy
• pH titration

Correct Answer: DSC (Differential Scanning Calorimetry)

Q10. In freeze-drying (lyophilization), which latent heat is most relevant?

• Latent heat of fusion
• Latent heat of vaporization (sublimation)
• Latent heat of condensation
• Specific heat capacity

Correct Answer: Latent heat of vaporization (sublimation)

Q11. During freezing of a drug solution, what happens to temperature while latent heat is removed?

• Temperature decreases continuously
• Temperature remains constant at freezing point until solidification completes
• Temperature increases due to exothermic reaction
• Temperature oscillates randomly

Correct Answer: Temperature remains constant at freezing point until solidification completes

Q12. Which statement about latent heat and polymorphism is true?

• Different polymorphs have identical latent heats
• Polymorph transitions can involve latent heat changes detectable by DSC
• Polymorphism has no thermal signature
• Latent heat only applies to liquids and gases

Correct Answer: Polymorph transitions can involve latent heat changes detectable by DSC

Q13. How does pressure generally affect the boiling point and latent heat of vaporization?

• Increasing pressure lowers boiling point and increases latent heat
• Increasing pressure raises boiling point and decreases latent heat
• Increasing pressure raises boiling point and may change latent heat value
• Pressure has no effect

Correct Answer: Increasing pressure raises boiling point and may change latent heat value

Q14. Which calorimetric method is commonly used alongside DSC to study mass changes during phase transitions?

• TLC
• TGA (Thermogravimetric Analysis)
• IR spectroscopy
• Mass spectrometry

Correct Answer: TGA (Thermogravimetric Analysis)

Q15. The heat released when vapor condenses to liquid is called:

• Latent heat of fusion
• Specific heat
• Latent heat of condensation
• Calorific value

Correct Answer: Latent heat of condensation

Q16. Which process requires latent heat input: sublimation, deposition, condensation, or freezing?

• Deposition
• Condensation
• Freezing
• Sublimation

Correct Answer: Sublimation

Q17. For a 10 g sample of ice melting at 0°C, using L = 334 kJ/kg, how much heat is required? (Choose closest)

• 334 J
• 3.34 kJ
• 33.4 kJ
• 334 kJ

Correct Answer: 3.34 kJ

Q18. Specific latent heat is an intensive or extensive property?

• Extensive
• Neither
• Intensive
• Depends on mass

Correct Answer: Intensive

Q19. Which of the following best describes sensible heat?

• Heat associated with a phase change without temperature change
• Heat stored in chemical bonds
• Heat that changes temperature of a body
• Latent heat per unit mass

Correct Answer: Heat that changes temperature of a body

Q20. In pharmaceutical drying, why is latent heat important?

• It determines the color of the drug
• It controls the rate of solvent evaporation and drying efficiency
• It is irrelevant to drying
• It only affects pH

Correct Answer: It controls the rate of solvent evaporation and drying efficiency

Q21. What is the effect of dissolved solutes on freezing point and latent heat of fusion?

• Solutes raise freezing point and increase latent heat
• Solutes lower freezing point (freezing point depression) and change energy required for freezing
• Solutes have no effect
• Solutes convert freezing to sublimation

Correct Answer: Solutes lower freezing point (freezing point depression) and change energy required for freezing

Q22. Which law relates pressure, temperature and latent heat across a phase boundary?

• Raoult’s law
• Clapeyron equation
• Henry’s law
• Beer-Lambert law

Correct Answer: Clapeyron equation

Q23. During crystallization of a drug, latent heat is:

• Absorbed from surroundings
• Released to surroundings (exothermic)
• Unaffected
• Only released if solvent is organic

Correct Answer: Released to surroundings (exothermic)

Q24. Which phase transition does not involve a liquid phase?

• Melting
• Condensation
• Sublimation
• Boiling

Correct Answer: Sublimation

Q25. Why is knowledge of latent heats important for spray drying in pharmaceuticals?

• It determines tablet hardness
• It helps estimate solvent removal rates and droplet temperature changes
• It controls active pharmaceutical ingredient potency
• It sets dissolution rates directly

Correct Answer: It helps estimate solvent removal rates and droplet temperature changes

Q26. If 50 g of water at 100°C vaporizes, how much heat is required? Use L = 2260 kJ/kg. (Choose closest)

• 113 kJ
• 226 kJ
• 11.3 kJ
• 2260 kJ

Correct Answer: 113 kJ

Q27. Latent heat values are useful in predicting which property important for lyophilization cycle design?

• Glass transition temperature of excipient only
• Sublimation rate and required condenser capacity
• Tablet disintegration time
• Color of final product

Correct Answer: Sublimation rate and required condenser capacity

Q28. Which instrument gives a direct measurement of heat flow vs temperature and can quantify latent heat?

• Gas chromatograph
• Differential Scanning Calorimeter
• Polarimeter
• Microscope

Correct Answer: Differential Scanning Calorimeter

Q29. What happens to latent heat of vaporization as temperature approaches critical point?

• It increases to infinity
• It decreases to zero at the critical point
• It remains constant
• It oscillates

Correct Answer: It decreases to zero at the critical point

Q30. Which term best describes energy required to break intermolecular forces during vaporization?

• Sensible heat
• Latent heat of vaporization
• Specific heat capacity
• Activation energy

Correct Answer: Latent heat of vaporization

Q31. In formulations, controlling latent heat release during crystallization can help prevent:

• Particle agglomeration and thermal hotspots
• Color fading only
• pH drift
• Microbial contamination

Correct Answer: Particle agglomeration and thermal hotspots

Q32. Which of the following is true about latent heat and microencapsulation solvent removal?

• Latent heat has no role in solvent evaporation
• Lower latent heat solvents evaporate faster at given conditions
• Higher latent heat always leads to faster drying
• Latent heat only affects solid drugs

Correct Answer: Lower latent heat solvents evaporate faster at given conditions

Q33. Which property is directly measured by TGA that complements latent heat data from DSC?

• Change in mass with temperature
• Change in refractive index
• Change in pH
• Change in viscosity

Correct Answer: Change in mass with temperature

Q34. For a binary solvent mixture, how does latent heat of evaporation compare to pure components?

• Always equals the average of pure components
• May vary nonlinearly due to interactions and vapor composition
• Is always larger than both pure components
• Is irrelevant for mixtures

Correct Answer: May vary nonlinearly due to interactions and vapor composition

Q35. Which phenomenon in freeze-concentration during freezing affects solute distribution and latent heat release?

• Ostwald ripening
• Freeze-induced phase separation
• Centrifugation
• Spray chilling

Correct Answer: Freeze-induced phase separation

Q36. A calorimetric peak on DSC at melting point corresponds to:

• Only sensible heat
• Latent heat of fusion
• Evaporation enthalpy
• Optical rotation

Correct Answer: Latent heat of fusion

Q37. Which of the following reduces the energy required for sublimation in a freeze-dryer?

• Increasing chamber pressure
• Decreasing condenser capacity
• Lowering shelf temperature while maintaining low chamber pressure
• Adding nonvolatile solutes

Correct Answer: Lowering shelf temperature while maintaining low chamber pressure

Q38. What is the latent heat change sign convention during freezing (liquid to solid)?

• Positive (absorbed)
• Zero
• Negative (released)
• Depends on pH

Correct Answer: Negative (released)

Q39. In calorimetric measurement, integration of peak area yields:

• Mass change only
• Total heat (enthalpy) associated with event, including latent heat
• Only temperature
• Viscosity change

Correct Answer: Total heat (enthalpy) associated with event, including latent heat

Q40. Which factor does NOT directly affect amount of latent heat required for a phase change of a sample?

• Mass of the sample
• Specific latent heat value of the substance
• Initial temperature far from transition point (after heating to transition, latent heat fixed)
• Color of the sample

Correct Answer: Color of the sample

Q41. Why is latent heat important in designing sterilization processes involving steam?

• Steam latent heat enables transfer of large quantities of energy to microorganisms for inactivation
• Latent heat only affects packaging color
• Steam does not carry latent heat
• Latent heat reduces temperature

Correct Answer: Steam latent heat enables transfer of large quantities of energy to microorganisms for inactivation

Q42. Which statement is true for latent heat during isothermal phase change?

• No heat is exchanged
• Heat is exchanged without temperature change until phase conversion is complete
• Temperature increases steadily
• Entropy decreases without heat exchange

Correct Answer: Heat is exchanged without temperature change until phase conversion is complete

Q43. In calorimetry, baseline correction is necessary because:

• It removes instrumental and sensible heat contributions to isolate latent heat peaks
• It increases sensitivity to color
• It measures pH changes
• Baselines are not used

Correct Answer: It removes instrumental and sensible heat contributions to isolate latent heat peaks

Q44. Which process releases latent heat: condensation, melting, vaporization, or sublimation?

• Vaporization
• Sublimation
• Melting
• Condensation

Correct Answer: Condensation

Q45. How does particle size influence drying in terms of latent heat requirements?

• Smaller particles dry slower due to higher latent heat
• Smaller particles dry faster due to higher surface area, but total latent heat per mass remains same
• Particle size has no effect on drying kinetics
• Larger particles always require less latent heat per mass

Correct Answer: Smaller particles dry faster due to higher surface area, but total latent heat per mass remains same

Q46. Which term describes heat required to melt one mole of a solid?

• Specific latent heat
• Molar enthalpy of fusion
• Heat capacity
• Combustion enthalpy

Correct Answer: Molar enthalpy of fusion

Q47. For an ideal pure crystalline drug, the melting peak on DSC is typically sharp because:

• Impurities broaden and depress melting point; pure crystals have narrow melting transitions
• Crystals never melt sharply
• DSC cannot detect melting
• Sharp peaks mean no latent heat involved

Correct Answer: Impurities broaden and depress melting point; pure crystals have narrow melting transitions

Q48. Which of the following is a direct pharmaceutical implication of latent heat during storage of frozen formulations?

• Latent heat is irrelevant to frozen storage
• Heat released during crystallization can cause local warming and destabilize sensitive actives
• Latent heat increases cryoprotectant concentration uniformly without issues
• Latent heat prevents microbial growth

Correct Answer: Heat released during crystallization can cause local warming and destabilize sensitive actives

Q49. When designing a condenser for a lyophilizer, which latent heat value is most critical?

• Latent heat of fusion of solute
• Latent heat of sublimation of ice
• Specific heat of shelf
• Latent heat of vaporization of organic solvent only

Correct Answer: Latent heat of sublimation of ice

Q50. Which property change accompanies latent heat absorption during melting of an amorphous excipient?

• Decrease in molecular mobility
• Transition through glass transition and increased molecular mobility before melting
• Immediate crystallization without mobility change
• Instant thermal decomposition

Correct Answer: Transition through glass transition and increased molecular mobility before melting

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