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Matter - Introduction



Anything that has both mass and volume is called matter. For example – me, you, chair, table, computer, mouse, keyboard, dog, cat, cow, ram, pen, pencil, tree, plant, building, stone, brick, mountain, river, etc.
Early Indian philosopher categorized matter in five types and called them panch-tatwa (Five-elements) - Vayu (Air), Jal (Water), Agni (Fire), Prithvi (Earth) and Aakash (Sky).
According to science matters are divided according to their physical and chemical properties.

Physical Nature of Matter
• Matters are made of particles.
• The particles of matters are very small.
• The particles of matter are moving continuously.
• Particles of matter have space between them.
• Particles of matter attract each other because of force of attraction.

Matter is made of particles –
All matters are made of particles. These particles are very small and cannot be seen by naked eyes. For example a drop of water contains about 1021 particles of water.

Particles of matter are very small –
Particles of matters are very small. They cannot even seen using a simple microscope.
When a tea spoon of salt is dissolved in one or two litre of water, every drops of that water taste salty.
When few drops of dettol are mixed in water, whole water gives the smell of dettol. Even after diluting this dettol mixed water, it gives the smell of dettol.
This proves that particles of matter are very small.

Particles of matter are moving continuously –.
This can be proved by putting a small crystal of potassium permanganate in water. When you will put a small crystal of potassium permanganate in water in a transparent glass, you will see that the purple thread like structures start mixing with water and after some time all water becomes purple. The thread like structures is the particles of potassium permanganate, which start mixing with water because of the motion of particles of water. Because of continuous motion, all particles start colliding and finally potassium permanganate is mixed with water.
When you put a spoon of salt or sugar in a glass of water, it dissolved in water after some-times. This happens because of the motion of particles of sugar, salt and water.
Mixing of gases in nature is also the evidence of motion of particles. We get the scent of our favourite food sitting in the drawing room while food is being cooked in the kitchen. This happens because vapor coming out from the hot food mixes with air comes to your nostril because of the motion of their particles.
This proves that particles of matter are in motion continuously.

Brownian Motion - Mr. Robert Brown, a Scottish botanist observed the random movement of pollen grains in water in 1827, it is called Brownian motion.
When pollen grains are kept in water, they start giggling rapidly in random order. This is also an evident of motion of particles of matter. Pollen grains moves randomly in water because the particles of water hit the pollen grains from all sides in a random manner.
Pollen grains move faster in warm water, because particles of warm water move more rapidly.
Brownian motion can be observed in the mixing of two gases also having different colors. You can observe the dancing particle of dust in the beam of sunlight which is coming through a slit in the room. The particles of dust appear dancing because of its continuous motion along with the particles of air.
Brownian motion proves that matters are made of very small particles and they are moving continuously.
Particles of matter have space between them – Gas can be compressed a lot because of the space between their particles.
When sugar is dissolved in water, the particles of sugar disappear in water. This happens because particles of sugar get adjusted in the spaces between the particles of water. Additionally you will notice that there is no rise of water level takes place when one or two teaspoon of sugar is added in a glass of water, this is because sugar particles get adjusted in the space between the particles of water and no rise in the water level comes in result.

Particles of matter attract each other because of force of attraction.
Force of attraction between particles of matter keeps the particles bonded together. The force of attraction between particles of solid is greatest, between particles of liquid is moderate and between particles of gas is lowest.
Because of the lowest force of attraction between the particles of gas we can move our hand through air easily. To move our hand in liquid, such as water, we have to apply some force, but from a solid such as wood, we cannot move our hand. This is because the force of attraction between particles of gas is almost negligible, in liquid the forces of attraction is moderate but it is greatest in solid.
The force of attraction between particles of solid, liquid and gas can be arranged in decreasing order as follows:

Solid > Liquid > Gas

States of Matter
There are three states of matter – solid, liquid and gas.

Solids – Matters which have fixed volume and shape are called solids. For example - stone, wood, brick, ice, sugar, salt, coal, etc.
All metals are solid except mercury and gallium.

Properties of solids –
• Solid has fixed volume.
• Solid has fixed shape.
• Solid has high density.
• Solids are heavy.
• Solid does not flow.

Liquid – Matters which have fixed volume but indefinite shape are called liquids. For example - milk, water, petrol, kerosene, alcohol, oil, etc.
Since liquid can flow, it is also called fluid.

Properties of liquid –
• Liquid has definite volume.
• Liquid has no definite shape.
• Liquid gets the shape of container in which it is kept.
• Liquid cannot be compressed much.
• Liquid has less density compare to solid.
• Liquid is lighter than solid.
• Liquid flows and hence is called fluid.

Gas – Matters which have indefinite shape and volume are called solids. For example - air, oxygen, hydrogen, nitrogen, carbon-dioxide, etc.

Properties of gas –
• Gas has indefinite shape
• Gas has no fixed volume.
• Gas gets the shape and volume of container.
• Gas fills the container completely.
• Gas has very low density.
• Because of low density gas are light.
• Gas can flow easily and hence are called fluid.
Cause of different physical states of matters
The physical states of matter depend upon three main factors:-
• The force of attraction between particles.
• The space between the particles.
• The kinetic energy of particles.

Solid:-
• The force of attraction between the particles of solids is very strong.
• There are minimum spaces between the particles of solids.
• The particles of solids have minimum kinetic energy.
Because of great force of attraction particles of solids are closely packed together. This makes the space between particles of solids almost negligible. The lowest kinetic energy of particles does not able to move the particles of solids.
Hence, the great force of attraction and least space between particles of solids and lowest kinetic energy of particles keep the particles at fixed places. Because of the combination of these characters matter exists in solid state.

Liquid:-
• The force of attraction between particles of solid is strong but less strong than solids.
• The space between particles is more than that of solid but not too more.
• The kinetic energy of particles is greater than solid.
Strong force of attraction keeps the particles of liquids packed together. But the force of attraction between particles of solids is less strong than that of solid. Because of this particles of liquids are loosely packed compared to solid. The kinetic energy of particles of liquids is greater than that of solids.
Because of more space between particles and more kinetic energy than solids the particles of liquids slide over one another. These characters make a matter to exist in liquid state.
Because of slide of particle over one another liquid can flow.

Gas
• The force of attraction between particles of gas is almost negligible.
• The space between particles of solid is greatest.
• The particles of gases have greatest kinetic energy.

Because of negligible force of attraction the particles of gases are loosely packed consequently there are lots of spaces between their particles. Because of greatest kinetic energy the particles of gas move with high speed.
Because of negligible force of attraction between particles and greatest kinetic energy the particles of gas have always tendency to escape out.
Because of these characters a matter exists in gaseous state.
Thus, these can be concluded that:

• A matter exists in solid state because of greatest force of attraction between its particles which makes the particles closely packed.
• A matter exists in liquid state because of less force of attraction between its particles than a solid, which makes the particles closely packed but allow to slide over one another.
• A matter exists in gaseous state because of almost negligible force of attraction between its particles, which is unable to keep the particles bonded together.

Other states of matter – Plasma and Bose-Einstein Condensate(BEC) - fourth and fifth sate of matter
Plasma and BEC (Bose-Einstein Condensate) are considered as states of matter other than solid, liquid and gas. These are known as fourth and fifth states of matter.

Plasma – It is considered as the fourth state of matter. Plasma is similar to the gas. Particles of plasma are made of free electrons and ions.
Plasma does not have a definite shape or a definite volume unless enclosed in a container.
Plasma may be defined as an electrically neutral medium of positive and negative particles.
Plasma is one of the most commonly occurring states of matter in universe. Plasma occurs naturally in the stars. All stars are made of plasma. Because of the presence of plasma stars glow. Plasma is formed because of nuclear fusion in stars. Our sun glows because of presence of plasma.
Plasma TV got its name because of presence of plasma in it. Plasma is also found in fluorescent light or neon sign. Plasma is formed when electricity is passed in a fluorescent tube or neon sign, which makes them glow.

Bose-Einstein Condensate (BEC) – It may be considered as fifth state of matter. Satyendra Nath Bose and Albert Einstein were predicted about this state of matters, that’s why it got its name as Bose-Einstein Condensate (BEC).
Plasma and BEC are has opposite characters. Plasma is a super hot and super excited atom while Condensate has super cool and super unexcited atoms.
BEC has been obtained by cooling the vapor of rubidium-87 at super low temperature by Eric Cornell and Carl Wieman on June 5 1995. After sometimes Wolfgang Ketterle also obtained BEC from sodium-23 at MIT, USA. Cornell, Wieman and Ketterle got Nobel Prize in Physics for this achievement in 2001.

Change of States of Matter
Matters can be changed from one state to another state. A solid can be changed into liquid and a liquid can be changed into gas. Most of the metals, which are solid, turn into liquid on heating and turn into vapor on further heating.
The change of state of matters depends upon mainly two factors:
• Temperature
• Pressure

Effect of temperature on states of matter:
Solids change into liquid with increase in temperature.
A liquid changes into gas by increase in temperature.

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Gas changes into liquid by decrease in temperature.
liquid changes into solid by decrease in temperature.
Example - Ice is solid, water is liquid and vapour is gas.
On increase in temperature ice changes into water. On further increase in temperature water changes into vapor.

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On decrease in temperature vapor changes into water. On further decrease in temperature water changes into ice.
On heating the particles of a solid get more kinetic energy and they start moving rapidly. On the other hand heating increases the space between the particles. When the kinetic energy of particles and space between them become similar to the liquid, the matter fulfills the condition of arrangement of particles. In this condition a solid changes into liquid.
On heating the particles of a liquid gets more kinetic energy and they start moving more rapidly. The increase in temperature increases the kinetic energy of particles and inter-space between them increases. The increase in kinetic energy and space between the particles the force of attraction between particles decreases. When the kinetic energy of particles of liquid and space between the particles increases and force of attraction between them decreases enough, the particles of liquid start moving with great speed. In this condition the particles of liquid attain the arrangement similar to gas and liquid changes into gas.
Water (a liquid) changes into ice (a solid) at 00C. Water changes into vapour (a gas) at 1000C.
The change of solid to liquid is called melting. The change of liquid to gas is called the vaporization. This happens because of increase in temperature.

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The change of gas into liquid is called condensation. The change of liquid into solid is called freezing. These takes place because of decrease in temperature.

Effect of pressure:

Solid –There is no effect of pressure on solids.
Solids are non compressible, i.e. solids cannot be compressed as there is no space between their particles which could allow compression.
When the pressure is increased on a solid, it is deformed and finally broken.

Liquid – There is no effect on pressure on liquid.
Liquids are non compressible, i.e. liquids cannot be compressed since there is not enough space between their particles to get compressed.

Gas – The volume of gas decreases with increase in pressure.
Since there is lot of space between the particles, gas is highly compressible. Large volume of gas can be compressed to a small volume. Because of this nature high compressibility, gas is transported easily after compressed to a small volume in cylinders.
Natural gas is compressed to small volume and packed in cylinders. It is used widely as fuel to running vehicles. Because of compression it is called Compressed Natural Gas or simply known by CNG (Compressed Natural Gas).
Oxygen is compressed and packed in small cylinders, which is used to save life in hospitals.
On increasing more pressure gas turns into liquid.

The liquefaction of gas by increasing of pressure:
In general condition, the particles of gas are far from each other. They move independently and rapidly in all directions. There is lot of space between the particles of gas. The force of attraction is negligible between the particles of gas. Because of these characters gas can be compressed a lot.
When pressure is applied on the gas, its particles come closer to each other. After applying high pressure, the particles of gas come very close to each other that they start attracting each other. The space between the particles of gas also decreases with increase in pressure. While applying high pressure a lot of heat is evolved, which was using by the particles of gas in movement. So, while applying high pressure to compress the gas, temperature is keeping low to overcome with the heat released. As they come closer, they lose kinetic energy. Finally they get closely packed at a certain high pressure, at this stage they get bonded with each other and turned into liquid.
This process is called liquidation or liquefaction of gas.
Petroleum Gas is compressed to small volumes. At more pressure it turns into liquid, after that it is packed into cylinders. This is used widely as fuel to cook food in households. Compressed petroleum gas is commonly known as LPG (Liquefied Petroleum Gas) since it turns into liquid form.
Oxygen, hydrogen, nitrogen, helium, etc. are compressed to liquefy and used for many purposes. Liquefied oxygen is used as propellant in spacecraft rockets. Liquefied oxygen is used for industrial and medical purposes also. Liquefied oxygen is of blue color.
On further increase in pressure, gas turns into solid.
Carbon dioxide is gas turns into solid on high pressure. Solid carbon dioxide is known as dry-ice. It is also known as ‘Cardice’ or ‘Card ice’.
Dry ice is used in the storage of food.
On decrease in pressure liquefied gas turns into gas. Solid carbon dioxide (dry ice) turns into gas without changing into liquid on decrease in pressure and increase of temperature.

Unit of Temperature:
Temperature is measured in Degree Celcius, Fahrenheit and Kelvin.

Fahrenheit: Before the end of 20th century Fahrenheit was used as unit to measure the temperature. The scale of Fahrenheit was named after, the physicist Daniel Gabriel Fahrenheit. Fahrenheit is written as “0F” and read as degree Fahrenheit.
320F (Thrity two degree Fahernheit) has been defined for the freezing point of water.
2120F (Two hundred tweleve degree Fahrenheit) has been defined for the boiling point of water. Fahrenheit was replaced by Celsius.

Degree Celsius: The unit of Celsius is named after the Swedish Astronomer Anders Celsius, who developed a similar scale. Untill 1948 Celsius was known as Centigrade. The word centigrade comes after the Latin word ‘Centum’.
Degree Celsius is written as “0C” and read as degree Celsius.
00C (zero degree Celsius) has been defined for the freezing point of water.
1000C (hundred degree Celsius) has been defined for the boiling point of water.
Degree Celsius is replaced by Kelvin. Moreover, it is used widely even today in clinical as well as laboratory thermometer.

Kelvin: Kelvin is the SI unit of temperature. The symbol of Kelvin is ‘K’. The Kelvin scale is named after the physicist William Thomson, 1st Baron Kelvin.
The scale of Kelvin is used widely because of its many advantages over degree Celsius. In Kelvin temperatures are written in positive usually.
273 K is defined as the freezing or melting point of ice.
373 K is defined as the boiling point of water.
At Kelvin scale -273 K is considered as the absolute zero temperature.
Degree Celsius - Degree Fahrenheit - Kelvin

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Process of change of states of matter:
• Vaporization
• Condensation
• Freezing
• Melting
• Sublimation
• Evaporation

Vaporization: (Change of liquid into gas): 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 points – 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.

Condensation: – (Change of gas into liquid) - 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.

Freezing: – (Change of liquid into solid) - 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 zero degree C.

Melting – (Change of solid into liquid) - 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 zero degree C.

Latent Heat
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 (Melting or Freezing): 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 105joules.

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.

Sublimation: 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.

Sublimation in everyday life:
The dry ice (solid carbon dioxide) turns into vapor without changing into liquid and is considered as sublime. Because of this property dry ice is used to give the illusion of smoke or cloud on the stage in movies and stage shows.
Naphthalene balls are kept with cloths and documents to protect them from insects. Since naphthalene balls go under sublimation, hence it changes into vapor without changing into liquid and its vapor prevent the insects to come or stay in cloths or documents. This protects the documents and cloths to get destroyed.
We usually see that the size of naphthalene balls decrease gradually and finally disappeared when they are kept in open. This happens because of sublimation of naphthalene.
Naphthalene balls are used in toilets also as disinfectant and air freshener.

EVAPORATION
The change of liquid into vapor without reaching at its boiling point is called Evaporation.
Evaporation takes place only at the surface of liquid while vaporization takes place on the whole mass of liquid.
Evaporation takes place even at room temperature also. Evaporation speeds up with rise in temperature.
When water or other liquid is left in open, gradually its volume decreases. If you left some water in a pot in open, after two or three days water disappears. If the water left in garden or in a open balcony, it disappears quickly than kept in a room. This happens because of evaporation.
Process of Evaporation - Molecules at the surface of water, when exposed some temperature, their kinetic energy increases. Because of increase in kinetic energy those molecules become able to overcome the force of attraction between the particles of liquid. After getting required kinetic energy and decrease in force of attraction, they escape in the air in the form of vapor. Additionally those kinetic energy get some of the required kinetic energy from their neighboring molecules also because of which the temperature of the adjacent molecules decrease, which finally result in decrease of the temperature of surface of liquid.

Factors affecting the Evaporation:-
• Temperature
• Pressure
• Surface area
• Humidity in air
• Wind speed

Temperature:- Evaporation increases with increase in temperature and decreases with decrease in temperature. This means rate of evaporation is directly proportional to the temperature.
With increase in temperature the particles of liquid at surface get required kinetic energy to overcome the force of attraction and escape in air quickly. Hence, the increase in temperature increases the rate of evaporation.

Pressure:- Evaporation decreases with increase in pressure and increases with decrease in pressure. This means the rate of evaporation is indirectly proportional to the pressure.
Particles at the surface of liquid require more kinetic energy to escape in air when there is more pressure over it and hence rate of evaporation will decrease. While if there is less pressure over the surface of liquid, the particles would require less kinetic energy to escape in air and hence rate of evaporation will increase. Therefore, increase in pressure slows down the rate of evaporation and decrease in pressure speeds up the rate of evaporation.

Surface Area: Evaporation increases with increase in surface area and decreases with decrease in surface area.
Since evaporation takes place at the surface of liquid only, hence if the more surface of liquid is exposed to atmosphere more particles will receive the required temperature to get the required kinetic energy to escape in air. Therefore, evaporation takes place more rapidly with larger surface area. This means rate of evaporation increases with increase in surface area and decreases with decrease in surface area.
After rain roads are dried up quickly than pot holes. This happens because of increase in surface area of water. On roads water is spread over a large area, because of that large area of water exposed to atmosphere, and evaporation of water takes place quickly resulting in quickly drying of the roads. While in pot holes less water surface is exposed to air because of that less water area could come in contact with air and receives less temperature, resulting in delayed evaporation. That’s why water dried from road quickly than in pot holes.
Wet clothes are spread up over the laundry line to get them dried up quickly. More surface area of water exposes to the air because of spreading of clothes this speeds up the rate of evaporation and clothes are dried up quickly. On the other hand if wet clothes are left even in the sun without spreading, they take more time to get dried because of less surface area exposed to air. That’s why wet clothes are kept spread over laundry line to get dried up quickly.
Water kept in a plate evaporates quickly than water kept in a tumbler (glass). This happens because in plate more surface area of water exposed to atmosphere which receives more heat and evaporates quickly. While in a glass less surface area of water exposed to atmosphere because of that less molecules of water receives heat from the atmosphere and evaporates slowly compare to the water exposed with large surface area.
Hence, rate of evaporation increases with increase in surface area and decreases with decrease the surface area.

Humidity in air: Evaporation decreases with increase in humidity and increases with decrease in humidity present in air. This means rate of evaporation is indirectly proportional to the humidity present in air.
Humidity is the amount of water vapor present in air. In weather reports, which are published in news paper or given on the TVs channels, the humidity percent is given, which shows the percent of water vapor present in air.
Because of more water vapor present in air the water holding capacity of atmosphere decreases which decrease the rate of evaporation. If air is dry then it can holds more water and thus in dry air rate of evaporation increases.
This is the cause that our cloths get dried up quickly in summer and winter than in rainy season. Because in rainy season there is more water vapor present in air, which decrease the water holding capacity of atmosphere resulting in decrease the rate of evaporation and our cloths do not dry up quickly in the rainy season.
Our sweat does not dry up quickly in rainy season. Because of that we feel uneasiness because of damp. This is because of higher percent of humidity present in air decreases the rate of evaporation in rainy season and our sweat does not evaporate quickly and we feel uneasy because of damp.

Wind Speed: Evaporation increases with the increase in wind speed and decreases with decrease in wind speed. This means rate of evaporation is directly proportional to the speed of wind.
Speedy wind propelled away some of the particles of water with it which speeds up the rate of evaporation. That’s why speedy wind speeds up the rate of evaporation.
We see that wet cloth is dried up quickly in a windy day since the wind speeds up the rate of evaporation.
The wet clothes are given jerks before hanging them on laundry line because by giving jerks some of the water droplets propelled out. This reduces the presence of water in the wet cloths and they dried up quickly.

Evaporation in everyday life:
(a) Water from the surface of oceans, seas and other large water bodies evaporate continuously as they are exposed to atmosphere. The water vapor because of evaporation rises up in air and cumulates in the form of cloud, which makes the rain. Hence, evaporation is one of the essential parts of water cycle. Thus we can say that evaporation is one of the most natural phenomena for us.
(b) In summer days sweats come out to regulate the temperature of our body. The sweat evaporates because of increase in surface area and getting the temperature from atmosphere. This is resulting in decrease in temperature of skin and finally our body, which gives relief to us in hot days. Sweating is a natural mechanism to keep cool the surface of our body in hot days. This is the cause that with increase in temperature our body sweats a lot especially in hot summer days.
(c) Water is kept in earthen pots to keep them cool. Earthen pot has lot of pores. Water kept in earthen pots evaporates from the pores of pots, which cools the neighboring molecules of water. This process continues and whole of the water kept in the earthen pots become cooler. Hence, water is kept in the earthen pot to keep them cool for drinking purpose.
(d) Wet clothes on the laundry lines are dried up because of evaporation.
(e) Sea water has lot of salt. Sea water is left in shallow pond. The water evaporates gradually because of heat of sun leaving the salt in the shallow pond. These salts are collected and used for with food after purification.
(f) Evaporative coolers are widely used in hot summer days. In evaporative coolers, dry air is blow over husk saturated of water. From the surface of husk water is evaporated resulted in cooling of husk. The water particles at the surface of wet husk evaporate and cool the rest portion of wet husk. Air blown from the cool husk is sent in the room, which cools the room.

Diffusion in Matters

Diffusion: The phenomenon of mixing of particles of different substances together is known as diffusion. Diffusion takes place because of the movement of particles of matters.
Diffusion is a natural process. The mixing of different gases in air is a natural process that takes place continuously.
Diffusion takes place from higher concentration to lower concentration.
Diffusion comes from Latin word ‘diffundere’. The meaning of ‘diffundere’ is ‘to spread out’.
It was Robert Brown who discovered the random moment of particles of matter. Albert Einstein developed the theory of Brownian motion based on the discovery of Robert Brown.
Diffusion takes place in solid, liquid and gases.

Diffusion in gas:
Diffusion takes place most rapidly in gasses.
The particles of gas have more kinetic energy due to that they move with high speed. Because of the movement of particles with high speed gas diffuses most rapidly.
Example – Mixing of gases in air.
Smoke coming out of factories is seen only near the mouth of chimneys. After rising high it mixes up with air and vanishes out. This happens because of diffusion of gases.

Diffusion in liquid:
Diffusion takes place in liquids. The rate of diffusion is less in liquid than that of gases.
The particles of liquid have enough movement because of kinetic energy for diffusion. When two liquids are kept together they are mixed because of the diffusion.
For example – When salt solution is kept in water this makes whole the solution salty after some time. This happens because of diffusion in liquids.

Diffusion in solid:
Diffusion takes place with slowest rate in the case of solids. The rate of diffusion is almost negligible in solids.
Since the particles of solid have lowest kinetic energy so they do not move. Hence, diffusion takes a long time in the case of solid.
Example – Some time we observe that the marks of chalk on the black board could not be wiped out easily after a long time. This happens because of the diffusion of particles of chalks with the particles of black-board and marks of chalk could not be wiped out.
Alloys are the mixture of two or more than two metals. Alloys are possible to get prepared because of the diffusion of solid into solid. Bronze, steel, brass are the examples of alloy.

Diffusion in everyday life:
(a) We get the smell of our favourite food sitting in the drawing room even when the food is being cooked in kitchen.
The vapor coming out from the food reaches to us because of diffusion in air and we get the smell of food.
(b) We get the smell of burning incense stick sitting far from it. When an incense stick is burnt, the incense present in it vaporizes because of heat. The vapor coming out from the incense stick mixes with air and reaches to us.
In similar way we sense the good or bad smell from a distance.
(c) When sugar is added in water, it is mixed because of the diffusion. The particles of sugar collide with the particles of water because of their continuous movement. And finally they are mixed together because of diffusion.
(d) Carbonated drinks are prepared by the diffusion of gas in water. We notice a hiss sound when the cap of bottle of a carbonated drink is open, the hiss sound comes because of the diffused gas coming out of water. Soda, Soft drinks (coca-cola) etc. are the carbonated drinks and prepared mainly because of the diffusion of carbon dioxide in water.
(e) Aquatic animals take dissolved oxygen in water while breathing. Aquatic plants synthesize their food under water because of the dissolved carbon dioxide in water. These gases dissolved in water because of the diffusion.

Temperature and Rate of Diffusion:
The rate of diffusion increases with increase in temperature and decreases with decrease in temperature.
Diffusion takes place because of the movements of particles of matters. The increase in temperature increases the kinetic energy, which increase the speed of movement of particles of matter. The increase in the speed of movement increases the rate of diffusion.

Example - We do not get the smell of cold food from a distance while we get the smell of hot food from a distance. Because smell coming out from the cold food in the form of gas do not have enough kinetic energy to cover more distance. But when food is hot the vapor coming out from it moves more rapidly because of more kinetic energy and reaches to us even if we are at a distance from it. This shows that temperature increases the rate of diffusion.

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