- Marks Questions:
1. Define the term (a) Latent heat of fusion (b) Latent heat of vaporization
2.
State the effect of (i) surface area (ii) nature of the liquid on the rate of evaporation.
3.
Liquids generally have lower density as compared to solids. But you must hac
observed that ice floats on water. Why?
What is the physical state of water at 250°C, 100°C, 0°C?
5. Give reasons :i) A sponge can be pressed easily; still it is called a solid.ii) Water
vapours have more energy than water at same temperature.
6. What are intermolecular forces ? How are these related to the three states of matter?
Is it possible to liquify atmospheric gases? If yes, suggest a method.
4.
7.
Answers
Answer:
The latent heat of fusion or melting of solid is the quantity of heat in joules required to convert 1 kg of solid to liquid,without any change in temperature
1 (i) LATENT HEAT OF FUSION-The amount of heat required to convert one unit amount of substance from the solid phase to the liquid phase — leaving the temperature of the system unaltered — is known as the latent heat of fusion. ... It is also equal to the enthalpy difference between the solid and liquid phases, ΔHSL.
(ii) LATENT HEAT OF VAPORIZATION-The enthalpy of vaporization, also known as the heat of vaporization or heat of evaporation, is the amount of energy that must be added to a liquid substance to transform a quantity of that substance into a gas. The enthalpy of vaporization is a function of the pressure at which that transformation takes place
2 (i) SURFACE AREA-The rate of a chemical reaction can be raised by increasing the surface area of a solid reactant. This is done by cutting the substance into small pieces, or by grinding it into a powder.
(ii) NATURE OF THE LIQUID ON THE RATE OF EVAPORATION-Rate of evaporation increases with the increase in surface area of the liquid since evaporation is a surface phenomenon. Nature of liquid-More volatile liquid evaporates faster than the less volatile liquid