Moisture in a solid exerting an equilibrium vapour pressure equal to that of the pure liquid at that temperature is
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- Bound moisture
- Unbound moisture
- Critical moisture
- Equilibrium moisture
The Correct Option is B
Solution and Explanation
When a solid contains moisture, this moisture can exist in different forms and exhibit different vapor pressure characteristics. Key classifications include: Bound moisture: This is moisture held within the solid by physical or chemical forces, such as adsorption, capillary condensation in fine pores, or chemical hydration. Bound moisture exerts a vapor pressure lower than that of the pure liquid at the same temperature. The removal of bound moisture requires more energy than the latent heat of vaporization due to these binding forces. Unbound moisture: This is moisture held in the larger pores of a solid and behaves essentially like the pure liquid at the prevailing temperature. It exerts its full vapor pressure, equal to the saturation pressure of the pure liquid at that temperature. Equilibrium moisture: This is the moisture content of a solid when it is in equilibrium with the surrounding air at a specific temperature and humidity. At equilibrium, there is no net transfer of moisture between the solid and the air. The equilibrium moisture content depends on the material and the conditions of the air. Critical moisture content: This is a specific moisture content during drying. It marks the transition from the constant-rate drying period to the falling-rate drying period. Above the critical moisture content, the surface of the solid is considered to be saturated with moisture, and drying occurs at a constant rate similar to the evaporation from a free liquid surface. Below the critical moisture content, the rate of drying decreases as the moisture is removed from within the solid, and the surface is no longer saturated. Step 2: Relate the vapor pressure of moisture in the solid to pure liquid vapor pressure.
The question specifically describes moisture in a solid that exerts an equilibrium vapor pressure equal to that of the pure liquid at the same temperature. Bound moisture, by definition, exerts a lower vapor pressure due to the binding forces.
Equilibrium moisture is defined by equilibrium with the surrounding air, not necessarily equal vapor pressure to the pure liquid within the solid itself.
Critical moisture content is a point in the drying process and doesn't inherently define a vapor pressure equal to that of the pure liquid for all moisture at that content.
Unbound moisture, as defined, behaves like pure liquid within the solid's pores and thus exerts the vapor pressure of the pure liquid at that temperature.
Step 3: Match the description to the correct type of moisture.
The description provided in the question directly corresponds to the definition of unbound moisture.
Top Questions on Mass Transfer
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