CHANGE OF STATES

CHANGE OF STATE

Evaporation:
Evaporation is the process where a liquid turns automatically into vapour below its boiling point. Evaporation takes place at all temperatures.
Factors That Affect Evaporation:
The ate of evaporation is affected by the following factors:
I. Nature of e liquid: High volatile liquids have high rate of evaporation while liquids that have low volatility have low rate of evaporation.
II. Temperature of the surrounding: Rate of Evaporation will be high if the temperature of the surrounding is high. Rate of evaporation will be low if temperature of the surrounding is low.
III. Surface area of the liquid that is exposed: The rate of evaporation of a liquid depends on the area of the liquid surface that is exposed. The rate of evaporation will be increase if the area of the liquid surface that is exposed is increased. It will decrease if the area of the liquid surface that is reduced.
IV. Amount of pressure on the surface of the liquid: The amount of pressure on the liquid surface determine the rate of evaporation. The rate of evaporation will reduced if the amount of pressure on the liquid surface is increased. It will increase if the amount of pressure on the liquid surface is reduced.
V. Humidity: The rate of evaporation will reduced if the relative humidity of the environment is high. It will increase if the relative humidity of the environment is low.
VI. The presence of wind: The presence of wind gives room for evaporation by getting rid of saturated air and allow room for more liquid to evaporate.
VII. Dryness of air: The rate of evaporation will increase if the air is very dry. It will decrease if he air is moist.
Molecular Explanation Of Evaporation:
According to kinetic theory of matter, liquid as a matter is made of molecules. The molecules are in state of constant random motion with certain amount of velocity and possess kinetic energy. When the temperature of the molecules is increased, the kinetic energy of the molecules is increase. This enable the molecules at the surface of the liquid to brake away from the intermolecular force of attraction from molecules below and exist as vapour. The presence of wind sweep the vapour away and create room for more vapour.
Cooling Effect of Evaporation:
When ever methylated spirit or petrol is spilled any part of the body,  The most important effect of evaporation is cooling the body. When the body perspire during exercises, evaporation of the sweat cools the temperature of the body.
Explanation Of Cooling Effect Of Evaporation Using Kinetic Molecular Theory:
The sweat or the methylated spirit acquired its latent heat of vaporization from the body and change to vapour or vaporized. This acquisition of latent heat of vaporization by the sweat, from the body, reduces the temperature of the body which causes cooling of the body.
Working Principle of Refrigerator:
The working principle of a refrigerator is based on the cooling effect of evaporation.
Explanation of Working Principle of Refrigerator:
A volatile liquid called refrigerant or liquefied gas is used. The refrigerant is contained in a copper pipes which surround the freezing chamber of the refrigerator. As the refrigerant evaporates, it absorbs latent heat of vaporization from the surrounding and therefore cool the inside of the refrigerator and its contents. A compressor at the back of the refrigerator removes the vapour, compresses it and pumps it into condenser fixed with metal cooling fins that are attached at the back of the refrigerator. The compressed vapour condenses and give out the latent heat it absorbed initially, to the surrounding by convection and radiation. The condensed vapour goes back into the freezing chamber and the process repeats itself again and again.
BOILING
Boiling is the change of  state of a substance from liquid to vapour when its surrounding vapour pressure is equal to the atmospheric pressure. Boiling can also be defined as the vaporization of liquid molecules throughout the entire liquid. The temperature at which the liquid boils to change to vapour is called saturated temperature. The temperature at which the liquid boils is called boiling point.
Factors That Affect Boiling: The following factors affect boiling of a substance:
I. Impurities: The presence of impurities in a substance  ( liquid ) increases the boiling point of the liquid. A pure liquid boils at its exert boiling point.
II. Pressure: Increase in pressure increases the boiling point of a liquid while a decrease in pressure reduces the boiling point of a liquid. Decrease in pressure is the basics behind water boiling at a temperature below its boiling point at the top of a mountain.
III. Mass of the liquid:                                               IV. Nature of the liquid:
Similarities Between Boiling And Evaporation:
            Boiling.                                                               Evaporation
• Does not cause cooling.                                It causes cooling
• It occurs in every part of the liquid.          It occurs at the surface.
• It is affected by the mass of e liquid.         It is not affected by mass of the            .                                                                                                                                     Liquid
• It depend on the nature of the                    it does not depends on nature of                    

   container because it absorbs its                 Container
 own heat.                            
• It occurs at a specific temperature.           It occurs at all temperature.      
• Wind do not assist boiling.                          Wind assist evaporation
• Temperature remains constant.                 Temperature is not remain constant
Similarities between boiling and evaporation:
1.  Escape of molecules is involved in both cases.                   2. Both of them depend on the nature of the liquid.
3. They are both affected by pressure.   4. They are both affected by impurities      5. Acquisition of energy is involved in both case

Relative Humility is the ratio of the mass of water vapour present in a certain volume of air to the mass of water vapour required to separate the same volume of air at the same temperature.

Relative humidity =  x 100%

Dew Point is the temperature at which the water vapour present in the air is just sufficient to saturate it. Dew point is dependent upon prevalent atmospheric conditions like temperature, wind and the amount of water vapour in the atmosphere.

When moist air near the surface of the land cools until it reaches dew point, water vapour originally present in the air begins to condense around tiny suspended dust particles in the air. They form suspended water droplets in the atmosphere. A collection of these suspended water droplets constitute a mist. In severe mist situation, we have a fog.

A thick mist when formed high up in the atmosphere is known as a cloud. Instability in the condition of the cloud may cause rain to fall. 

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