Q1. The heat of vaporization is __________-dependent.

1. Pressure
2. Temperature
3. pH
4. All of the above

ANSWER – B. Temperature

• Explanation: The heat of vaporization is temperature-dependent, yet for narrow temperature ranges and lower temperature Tr1.0, a constant heat of vaporization can be assumed. Because the substance is a supercritical fluid, the heat of vaporization decreases with increasing temperature and vanishes altogether at the critical temperature (Tr=1) because the liquid and vapor phases no longer exist above the critical temperature.

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Q2. _______ is most popular in grain drying.

1. Convection drying
2. Conduction drying
3. Freeze-drying
4. All of the above

ANSWER: A. Convection drying

• Explanation: The drying agent (hot gases) in contact with the wet solid is employed to supply heat and transport away the evaporated moisture in convection drying, and the heat is mostly transmitted to the wet solid through convection. Grain drying is most commonly done by convection. It can be carried out in batches or continuously. The continuous system includes tray and compartment dryers, pneumatic conveying dryers, rotary dryers, and tunnel dryers, whilst batch dryers include tray and compartment dryers and batch through circulation dryers.

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Q3. The boiling of water is an example of _____ type of heat transfer.

1. Conduction
2. Convection
3. Radiation
4. Both A and B

ANSWER: B. Convection

• Explanation – Because heat transfer in a system occurs owing to mass movement within the system, convection is connected with fluids. Boiling water is an example. The transfer of thermal energy in the form of the electromagnetic spectrum in a vacuum is known as radiation. The electromagnetic spectrum is generated at high temperatures. The transfer of vibrational energy from one molecule to the adjacent molecules intimately connected in a solid mass causes conduction heat transfer.

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Q4. _______ is a physical process in which a solid directly converts into a gaseous (vapor) state without going through a liquid state.

1. Evaporation
2. Sublimation
3. Condensation
4. Freezing

ANSWER: B. Sublimation

• Explanation – Sublimation is the conversion of a solid to a gaseous (vapor) state without passing through a liquid state. The amount of heat required to turn a unit quantity of solid into a gas at a given temperature is known as the latent heat of sublimation. For example, the amount of heat necessary to sublimate ice into vapor at 0°C is calculated to be 2,838 kJ/kg, which is the latent heat of sublimation of ice at 0°C. This process is important in the formation of ice and snow crystals in the atmosphere. This process is the polar opposite of deposition.

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Q5. The enthalpy of vaporization, (symbol ∆Hvap) is also known as ____.

1. Latent heat of vaporization
2. Heat of evaporation
3. Latent heat of sublimation
4. Both A and B

ANSWER: D. Both A and B

• Explanation – The enthalpy of vaporization (Hvap) is the enthalpy change necessary to convert a given quantity of a substance from a liquid to a gas at a particular pressure (often atmospheric pressure as in STP). It is frequently measured at a substance’s typical boiling point; while tabular values are normally corrected to 298 K, the correction is often less than the uncertainty in the measured value.

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