Matter In our surroundings (Part –IV)

Matter In our surroundings (Part –IV) 

Evaporation: The process of conversion of a substance from the liquid state to the gaseous state at any temperature below its boiling point is called evaporation or vaporization. 

How does Evaporation occur? 

• Particles of matter are always moving and are never at rest. 
• At a given temperature in any gas, liquid or solid, there are particles with different amounts of kinetic energy. 
• In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour. 
• This phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation. 

Factors Affecting Evaporation 

• Surface area: The rate of evaporation increases with an increase of surface area. 
• Temperature: With the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state. 
• Humidity: It is the amount of water vapour present in air. The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in air is already high, the rate of evaporation decreases. 
• Wind speed: The higher the wind speed, the more evaporation. 

Evaporation Vs Boiling 

Evaporation causes cooling: 

During the process of evaporation, the particles of liquid absorb energy or latent heat of vaporisation from the surrounding to get converted to gaseous state. This absorption of energy from the surroundings makes the surroundings cold. 

For example: 

• · The perspiration or sweating in our body keep the body temperature constant by taking away the extra heat from body as the latent heat of vaporisation. 
• · Our palm feels cold when we pour some acetone (nail polish remover) on it because the particles of acetone gain energy from your palm or surroundings and evaporate causing the palm to feel cool. 
• · After a hot sunny day, people sprinkle water on the roof or open ground because the large latent het of vaporisation of water helps to cool the hot surface.