Matter In Our Surroundings
Process of change of states of matter:
The process of change of water into vapor is called vaporization. When water is heated after reaching at 1000C water starts boiling. At this temperature water turns into vapor.
Since, water boils at 1000C, hence 1000C is called the boiling point of water.
Boiling Point: The common definition of boiling point is, the temperature at which a liquid boils is called its boiling point. Different liquid boils at different temperatures.
The change of vapor into water because of decrease in temperature is called condensation. Condensation is the reverse process of vaporization.
When the temperature of vapor decreases it changes into water, this process is known as condensation.
Distilled water is manufactured by the condensation of vapor. The process of making of distilled water is known as distillation. In distillation first water is boiled to vaporize and the vapor is cooled, i.e. condensed to get distilled water.
The change of liquid into solid because of decrease in temperature is called freezing. Water change into ice because of decrease in temperature, in other words water freezes into ice because of decrease in temperature. Water freezes at 00C.
The change of solid into liquid due to increase in temperature is known as melting. Ice, which is a solid melts, i.e. changes into water at 00C.
When water is heated up-to 1000C it starts boiling and changes into vapor. But we see that even after continuous supply of heat temperature does not rise above the 100C while boiling of water.
Temperature supplied after 100C to boiling water is used to change the water into vapor and temperature of water does not rise.
On the other hand we see that when heat is supplied to ice, temperature does not rise above the 00C, until all ice melts. In this process also the heat supplied to ice after 00C is used to change of ice into water and temperature of ice does not rise.
Heat is used in these processes without rise in temperature is known as Latent Heat.
The latent heat is used in change of states of matter, such as from solid to liquid or from liquid to gas without rising in temperature.
Hence, Latent heat is the heat released or absorbed by a body during the process without change in temperature of the system. This happens while change of state of matter meaning a phase transition. Example: Melting of ice, boiling of water.
The particles of solid and liquid are bonded together with great force of attraction, because of which a matter exists in a particular state. When we supply heat to a solid or liquid, the heat is supplied without come in notice is used to break the force of attraction between particles and this heat is not used to increase the kinetic energy of particles. Since, kinetic energy of particles do not increase we do not see any rise in temperature of the system.
The word "latent" is derived from the Latin word "Latere" which means "to lie hidden". Joseph Black introduced the term Latent heat around 1762.
Types of Latent Heat:
- Latent heat of fusion
- Latent heat of vaporization
Latent Heat of Fusion:
When solid changes into liquid, the head required changing the state without rising in temperature is called the Latent Heat of Fusion.
The change of solid to liquid state is an endothermic reaction as heat is required in it. The reaction in which heat is supplied or used is called endothermic reaction or process.
Let us take the example of melting of ice.
When heat is supplied to melt ice, temperature does not rise from 00C even after continuous supply of heat till all ice melts. After melting of all ice temperature starts rising. The additional heat is required to melt the ice without coming into notice is the latent heat of fusion.
The latent heat of fusion of ice is the energy which is used to change the state of ice (solid) to water (liquid).
The quantity of heat required to convert I kilogram of solid to liquid without any change in temperature is called Latent Heat of fusion.
The heat required is measured in joules (J).
3.34 x 105 joules of heat is required to convert 1 kilogram of ice into water at its melting point. Thus, the heat of fusion of ice at its melting point = 3.34 x 105 joules.
Latent Heat of Vaporization:
When liquid changes into gas because of rise in temperature, the heat required changing the state without rising in temperature is called the Latent Heat of vaporization.
The change of liquid to gaseous state is an endothermic reaction as heat is required in it.
Let us take the example of boiling of water.
Water boils at 1000C. When heat is supplied to water temperature does not rise after 1000C even after continuous supply of heat. The heat supplied at this stage is used to change water into vapor and hence does not come into notice. The additional heat is required to change the water into vapor without coming into notice is the latent heat of vaporization.
The latent heat of vaporization of water is the energy which is used to change the state of water (liquid) to vapor (gas).
22.5 x 105 J energy is required to convert 1 kilogram of water into vapor. Hence, the latent heat of water is equal to 22.5 x 105 J per kilogram or it is written as 22.5 x 105 J/kg.
Different liquid has different latent heat of vaporization.
The process in which a solid changes into vapor without changing into liquid and from vapor changes into solid without changing into liquid is known as sublimation.
Generally solid first changes into liquid and then changes into gas because of rise in temperature. But there are many substances, which change into gas without changing into liquid and changes into solid from gas without changing into liquid. Such substances, which go under sublimation, are known as sublime.
For example; camphor, naphthalene balls, ammonium chloride, iodine, dry ice, etc.
The solid obtained after cooling of the gas of sublime is called Sublimate. The process of cooling of vapor of sublime to get sublimate is also known as ‘sublimation’ although it is also known as deposition.
When camphor is heated it changes into vapor without changing into liquid. When the vapor of camphor is cooled it changes into solid without changing into liquid.