Matter in Our Surroundings

"Everything in this universe can be organised around two concepts, matter and energy."

1.0Introduction

The air we breathe, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand, everything is matter. We can also see, as we look around that all the things mentioned above occupy space and have mass. In other words, they have both mass and volume.

Early Indian philosophers classified matter in the form of five basic elements "Panch Tatva"

air, earth, fire, sky and water.

Ancient Greek philosophers also classified matter in similar manner.

Definition

Matter: Anything which occupies space (or have volume) and has mass is called matter. Some examples of matter are water, air, metals, plants, animals, etc. The perception of joy, love, hate, thought, cold, hot, pain is not considered as matter.

2.0Physical nature of matter

From a long time, there were two views about the physical nature of matter (i) Continuous nature, like a block of wood or a sheet of glass. (ii) Particulate nature, that matter is made up of particles like sand. Matter is made up of particles (Particulate nature) The particle nature of matter can be demonstrated by a simple activity.

3.0Characteristics of particles of matter

(i) Particles of matter have space between them

When sugar is dissolved in water, the volume of the liquid remains unchanged because during dissolution, the particles of sugar get into the spaces between the particles of water. As a result, they get evenly distributed and there is no noticeable change in volume. Similarly, when

Gas

Matter have spaces between the particles potassium permanganate is dissolved in water, its particles get evenly distributed throughout the bulk of water. This is indicated by uniform colour of the solution. This indicates that there are spaces between particles of matter. The particles of potassium permanganate get uniformly distributed in the spaces between water molecules. Similarly, when we prepare tea, coffee or lemonade (nimbu pani) we observe that particles of one type of matter get into the spaces between particles of other.

(ii) Particles of matter are continuously moving

We have so far concluded from our discussion that matter is made up of very small particles and these are separated from one another by empty spaces or voids also called interparticle spaces. A question will immediately come to our mind. Are these particles stationary or in a state of motion? The following activity will illustrate that particles are continuously moving. These are not stationary.

Some important characteristics of particles of matter-

4.0States of matter

Matter around us exists in three different states: (i) solids (ii) liquids (iii) gases

These states of matter arise due to the variation in the characteristics of the particles of matter. Now, let us study about the properties of these three states of matter in detail.

The Solid State

Solids are known for their hardness and rigid nature.

Characteristics of the solid state

(1) Solids have fixed shapes. (2) Some solids can change their shape. (3) Solids keep their volume. (4) Solids can be hardly compressed on applying pressure. (5) Solids have negligible kinetic energy of the particles. (6) Solids do not have the property of diffusion.

Different shapes of solids

Q. Why a wooden block should be called a solid? Explanation A wooden block has a fixed shape and is rigid and follows all properties of a solid. Hence, it should be called a solid.
Wooden block, a solid has fixed shape
Q. A rubber band undergoes a change in shape on stretching, still we call it a solid. Why? Explanation A rubber band is called a solid because although it undergoes a change in shape on stretching yet it regains the same shape when the force is removed.

The Liquid State

The liquids have fluidity and the molecular motion is comparatively more than solids. Both these characteristics in the liquid state are because of the presence of weaker interparticle forces.

Characteristics of the liquid state

(1) Liquids do not have fixed shapes. (2) Liquids occupy definite volume or keep their volume. (3) Liquids have fluidity and not rigidity. (4) Liquids have lesser density as compared to solids. (5) The kinetic energy of the particles in the liquid state is more than in the solid state. (6) Particles in the liquid state can easily diffuse.

The Gaseous State

Out of the three states of matter, the interparticle spaces are the maximum in the gaseous state. The interparticle forces which hold the different particles in the gaseous state together are the minimum. As a result, rigidity is the minimum while fluidity is the maximum. Characteristics of gaseous state (1) Gases do not have fixed shape. (2) Gases have maximum fluidity and least rigidity. (3) Gases do not have fixed volume and are highly compressible. (4) Density of gases is very less. (5) The kinetic energy of the particles in the gaseous state is very high. (6) Gases exert pressure. (7) Gases diffuse very rapidly.

Same gas has acquired different shapes depending on the shape of balloon.

Please note that even the heavier gases can rise upwards and lighter gases can move downwards. This means that the diffusion of the gases is not influenced by gravity. For example, invert a cylinder containing hydrogen gas (colourless) over a cylinder containing nitrogen dioxide (reddish brown) and separate the two cylinders by a lid.

Now, remove the lid. What will you observe? Both the cylinders will acquire the same colour i.e., light brown. This means that hydrogen gas has moved downwards and nitrogen dioxide upwards. Both the cylinders contain a uniform mixture of these two gases and are light brown in colour.

For example, Air is the common example of the gaseous state. It is a mixture of number of gases like nitrogen, oxygen, carbon dioxide, inert gases, etc. A few other examples are hydrogen, ammonia, sulphur dioxide, chlorine, etc.

More examples

(i) CNG (Compressed natural gas) is used as fuel in internal combustion engines. (ii) Oxygen in compressed form is supplied to hospitals for serious patients in cylinders. (iii) LPG (Liquefied petroleum gas) which is used in home for cooking. (iv) Cooking gas (LPG) is obtained by compressing petroleum gas into cylinders. Its major constituent is butane

(C_{4} H_{10})

Comparison of characteristic properties of solids, liquids and gases

Property	Solids	Liquids	Gases
Shape	Definite	Not Definite. Take the shape of the container, but do not necessarily occupy all of it	Not Definite. Take the shape of the container by occupying whole of the space available to them.
Volume	Definite	Definite	Not Definite. Takes the volume of the container.
Compressibility	Almost nil	Very very less	Very large
Fluidity or Rigidity	Rigid	Fluid	Fluid
Density	High	Low	Very low
Diffusion	Generally, do not diffuse	Diffuse slowly	Diffuse rapidly
Intermolecular	Negligible	More than solids	Maximum
space	Maximum	Less than solids	Minimum
Intermolecular force	Minetic energy of	Negligible	More than solids

5.0Can matter change its state?

We all know from our observation that water can exist in three states of matter: solid as ice, liquid as the familiar water and gas as water vapour. A substance may exist in three states of matter i.e. solid, liquid or gas, depending upon the conditions of temperature and pressure. By changing the conditions of temperature and pressure, all three states could be obtained (solid, liquid, gas). On heating, a solid change into a liquid which on further heating changes into gas.

Change in three states of matter

If a solid is to be converted into liquid, the interparticle spaces have to be increased. Similarly, if a liquid is to be converted into gas, these spaces must be further increased. In other words, we can say that one state of a substance can be converted into another by changing interparticle spaces and interparticle forces of attraction. Please note that the process can be reversed also under suitable conditions. This is known as interconversion of states of matter and this can be brought about by two ways (i) By changing the temperature (ii) By changing the pressure

Effect of change of temperature

The effect of temperature on three states of matter could be seen by performing the following activity.

Explanation about interconversion of different states of matter

(i) Change of state from solid to liquid - Melting

Ice is a solid. In solids, the particles are tightly packed together. When we heat a solid, its particles become more energetic and kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating more strongly with greater speed. The energy supplied by heat overcomes the intermolecular forces of attraction between the particles. As a result, the particles leave their mean position and break away from each other. After this, solid melts and a liquid is formed. "The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point". The melting point of ice is $0^{\circ} C$ . It may also be written as 273.15 K or 273 K . $^{\circ} C + 273 = K$

Conversion of temperature on Celsius scale to Kelvin scale For example, $0^{\circ} C = 0 + 273 = 273 K$ $10 0^{\circ} C = 100 + 273 = 373 K$

Conversion of temperature on Kelvin scale to Celsius scale For example, $373 K = 373 - 273 = 10 0^{\circ} C$ $273 K = (273 - 273) = 0^{\circ} C$

In Kelvin temperature, the symbol $(^{\circ})$ is not used.
Temperature conversion formulas- (i) The temperature conversion formula from Celsius to Kelvin is: $K = C + 273.15$ (ii) The temperature conversion formula from Kelvin to Celsius is: $C = K - 273.15$ (iii) The temperature conversion formula from Fahrenheit to Celsius is: $9/5 (^{\circ} C) =^{\circ} F - 32$

Convert the following temperatures to the Celsius scale. (a) 300 K (b) 573 K Ans. (a) $(300 - 273) = 2 7^{\circ} C$ . (b) $(573 - 273) = 30 0^{\circ} C$ .
Convert the following temperature to the Kelvin scale. (a) $2 7^{\circ} C$ (b) $37 8^{\circ} C$ Ans. (a) $27 + 273 = 300 K$ (b) $378 + 273 = 651 K$

Latent heat (hidden heat)

It is observed that the temperature of the system does not change after melting point is achieved till all the ice melts, though we continue to heat the beaker. This happens because the heat supplied is used up in changing the state by breaking the intermolecular forces of attraction which hold them in solid state. As a result, there is no change in temperature till all the ice melts. This energy required to change solid into liquid is called "latent heat". The word "latent" means "hidden" because this energy is hidden into the contents of the beaker.

Latent heat is of two types (a) Latent heat of fusion (b) Latent heat of vaporization
Latent heat of fusion Latent heat of fusion is defined as the amount of heat energy required to change 1 kg of a solid into a liquid at atmospheric pressure without any change in temperature at its melting point. The latent heat of fusion of ice is $3.34 \times 1 0^{5} J / kg$ .

(ii) Change of state from liquid to solid - Freezing

When the temperature of a solid is raised, it melts to form a liquid. Conversely, if the temperature of a liquid is lowered the reverse process takes place. The kinetic energy of the particles decreases and the particles start moving slowly. As the temperature is further lowered, the attractive forces pull the particles close together and the substance freezes i.e. the liquid changes into solid. Thus, the temperature at which a liquid freezes to become a solid at atmospheric pressure is called the freezing point.

(iii) Change of state from liquid to gas - Boiling

In a liquid most of the particles are close together. When we supply heat energy to the liquid, the particles of water start vibrating even faster. Some of the particles become so energetic that they can overcome the attractive forces of the particles around them. Therefore, they become free to move and escape from the liquid. Thus, the liquid evaporates i.e. starts changing into gas. "The temperature at which a liquid changes into a gas or vapour at the atmospheric pressure is called its boiling point." For example, the boiling point of water is

10 0^{\circ} C

or 373 K .

6.0Latent heat of vaporization

The latent heat of vaporization of a liquid is the quantity of heat in joules required to convert 1 kilogram of the liquid (at its boiling point) to vapour or gas, without any change in temperature. The latent heat of vaporization of water is $22.5 \times 1 0^{5}$ joules per kilogram (or $22.5 \times 1 0^{5} J / kg$ ).

Q. Why it takes much longer to cook food in the hills (mountains) than in the plains (Sea level)? Explanation The boiling point of a liquid depends upon the pressure acting on it. It increases, if the pressure is increased or decreases if the pressure acting on it is decreased. For example, water boils at 373 K at sea level where the pressure is 1 atmosphere. However, on mountains, it boils at a lower temperature where the pressure is less than 1 atmosphere. Because water boils at a lower temperature at hills food will cook at a lower temperature and it will take longer to get enough heat for cooking. It is because of this reason that cooking of food takes longer time on mountains and lesser time in plains.

(iv) Change of state from gas to liquid - Condensation

When a gas or vapour is cooled by lowering its temperature, the kinetic energy of their constituent particles decreases. Due to decrease in the kinetic energy, the particles start moving slowly. As the temperature is further lowered, the attractive forces pull the particles close together and the gas or vapour condenses i.e. gas or vapour changes into liquid. Thus, the process of changing a gas (or vapour) to liquid by cooling is called condensation. For example, We see water droplets on the outer surface of a glass containing ice-cold water. Take some ice-cold water in a glass. Soon we will see water droplets on the outer surface of the glass. The water vapour

Droplets formed on the outer surface of the glass containing ice cold water. present in air, on coming in contact with the cold glass of water loses energy and gets converted to liquid state, which we see as water droplets.

(v) Sublimation

The process of conversion of a solid into gas without undergoing into liquid state is known as sublimation. The process of conversion of a gas into solid state is known as deposition or desublimation. For example, Ammonium chloride, camphor, iodine, naphthalene, solid carbon dioxide (dry ice), anthracene undergoes sublimation. Sublimation can be represented as

Sublime: A gaseous form, directly formed from a solid on heating, is known as sublime.
Sublimate: A solid state of matter formed directly from its gaseous state on cooling, is called sublimate.
More examples of sublimation (i) In very cold places, the snow does not melt but sublimes directly to vapours. (ii) In frost-free refrigerators, ice on the walls of the freezer sublimes when warm air is circulated through the compartment during the defrost cycle.

Effect of change of pressure

To convert a gas into a liquid or to convert a liquid into a solid, the interparticle distances must by decreased and the interparticle forces of attraction must be made stronger. This can be done in the following ways (i) By applying pressure (ii) By lowering temperature or (iii) By combination of both the factors discussed above.

(i) By applying pressure

Gases are compressible because on applying pressure, the spaces between the gaseous particles decrease. Therefore, gases can be compressed readily.

By applying pressure particles of gas can be brought close together.

(ii) By lowering temperature

If we cool the gas, the kinetic energy decreases and the particles slow down. As a result, interparticle distances decrease and interparticle forces of attraction increase which pull the gas particles close to form a liquid.

(iii) By combination of both the factors discussed above

From the above discussion, it is evident that a gas can be liquefied either by increasing the pressure or by lowering the temperature. However, in most of cases, a combination of both these factors is used to liquefy the gases. If the pressure on the liquefied gas is further increased and the temperature further lowered, the liquefied gas may change into the solid state.

Interchange between different states -

Q. Why solid $CO_{2}$ is also known as dry ice? Explanation If carbon dioxide is cooled under high pressure, it can be directly converted into solid carbon dioxide called dry ice. If the pressure on dry ice is decreased to one atmosphere, it sublimes i.e. it directly gets converted into the gaseous state (i.e. carbon dioxide gas) without passing through the intervening liquid state. As a result, unlike ordinary ice, dry ice does not wet the surface on which it is kept. It is because of this reason that solid carbon dioxide is called dry ice. It is used as a refrigerant under the name dricold.
Solid $CO_{2}$

Three conditions of temperature and pressure which decide the state of matter.

If the melting point of a substance is above the room temperature at the atmospheric pressure, it is classified as solid.
If the boiling point of a substance is above room temperature under atmospheric pressure, it is classified as liquid.
If the boiling point of the substance is below the room temperature at the atmospheric pressure, it is classified as gas.

7.0Evaporation

"The process of a liquid changing into vapour (or gas) at any temperature below its boiling point is called evaporation." Whatever be the temperature at which evaporation takes place, the latent heat of vaporization must be supplied whenever a liquid changes into vapour (or gas). For example, (i) Water in ponds changes from liquid to vapour without reaching the boiling point. (ii) Water when left uncovered slowly changes into vapour. (iii) When we put wet clothes for drying, the water from the clothes goes to the atmosphere.

Differences between Evaporation and Boiling

	Evaporation	Boiling
$1$	Evaporation process takes place spontaneously at all temperatures.	Boiling takes place only at definite temperature (boiling point) at which the vapour pressure of the liquid is equal to atmospheric pressure.
$2$	Evaporation takes place only at the surface of the liquid. Evaporation is a surface phenomenon.	Boiling takes place even below the surface of the liquid in the form of bubbles. Boiling is a bulk phenomenon.
$3$	It always causes cooling.	It does not cause cooling.

Factors which affects the rate of evaporation.

(i) Nature of liquid

Different liquids have different rates of evaporation. A liquid having weaker interparticle attractive forces evaporates at faster rate because less energy is required to overcome the attractive forces. For example, Acetone evaporates faster than water.

(ii) Surface area of the liquid

The evaporation depends upon the surface area. If the surface area is increased, the rate of evaporation increases because the high energy particles from liquid can go into gas phase only through surface. For example,

Well spread clothes dry faster (a) The rate of evaporation increases when we put kerosene or petrol in an open china dish than in a test tube. (b) Clothes dry faster when they are well spread because the surface area for evaporation increases.

(iii) Temperature

Rate of evaporation increases with increase in temperature. This is because with the increase in temperature more number of particles get enough kinetic energy to go into the vapour state (or gaseous state). For example, Clothes dry faster in summers than in winters.

(iv) Humidity in the air

The air around us contains water vapour or moisture. The amount of water present in the air is referred as humidity. The air cannot hold more than a definite amount of water vapour at a given temperature. If the humidity is more, the rate of evaporation decreases. The rate of evaporation is more if the air is dry. For example, clothes do not dry easily during rainy season because the rate of evaporation is less due to high moisture content(humidity) in the air.

(v) Wind speed

The rate of evaporation also increases with increase in speed of the wind. This is because with increase in speed of wind, the particles of water vapour move away with wind, resulting in decrease in the amount of vapour in the atmosphere. For example, (a) Clothes dry faster on a windy day. (b) In a desert cooler, an exhaust fan sucks the moist air from the cooler chamber which results in greater rate of evaporation of water and hence greater cooling.

Factors affecting evaporation -

Q. Why evaporation causes cooling? Explanation: During evaporation, cooling is always caused. This is because evaporation is a phenomenon in which only the high energy particles leave the liquid surface. As a result, the particles having low energy are left behind. Therefore, the average molecular energy of the remaining particles left in the liquid state is lowered. As a result, there is decrease in temperature on the part of the liquid that is left. Thus, evaporation causes cooling.

For example, (a) When we pour some acetone (nail polish remover) on our palm, we feel cold. This is because the particles gain energy from our palm or surroundings and leave the palm feeling cool. (b) We sprinkle water on the roof or open ground after a sunny hot day. This cools the roof or open ground. This is because the large latent heat of vaporization of water helps to cool the hot surface.

Some other examples of evaporation

(i) We should wear cotton clothes in hot summer days to keep us cool and comfortable.

We get a lot of sweat on our body in hot summer days. Cotton is a good absorber of water, so it absorbs the sweat from our body and exposes it to the air for evaporation. The evaporation of this sweat cools our body. The synthetic clothes (made of polyester, etc) do not absorb much of sweat, so they fail to keep our body cool in summer.

(ii) Water stays cool in the earthen pot(matki) during summer.

When the water oozes out of the pores of an earthen pot, during hot summer, it evaporates rapidly. As the cooling is caused by evaporation, therefore, the temperature of water within the pot falls and hence it becomes cool.

(iii) Rapid cooling of hot tea.

If tea is too hot to sip, we pour it in the saucer. In doing so, we increase the surface area and the rate of evaporation increases. This, in turn, causes cooling and the tea attains a desired temperature for sipping.

(iv) A wet handkerchief is placed on the forehead of a person suffering from high fever.

The logic behind placing wet cloth is that as the water from the wet cloth evaporates, it takes heat from the forehead. This, in turn, lowers the temperature of head and protects brain from any damage due to high temperature.

(v) We often sprinkle water on the road in summer.

The water evaporates rapidly from the hot surface of the road, there by taking heat away from it. Thus, the road becomes cool.

8.0Plasma

Definition: Plasma is the fourth phase of matter, apart from the traditional solids, liquids, and gases. It is a most common state of matter made from a gas that has lost its electrons due to heat.

Plasma was first identified as "radiant matter" by Sir William Crookes in 1879. Irving Langmuir assigned the term "Plasma" in 1928. Composition: Plasma may be formed by heating and ionizing a gas. It is a collection of charged particles that respond strongly and collectively to electromagnetic fields, taking the form of gas like clouds or ion beams.

Plasma is distinct from a gas because it possesses unique properties.
Plasma has neither a definite volume nor a definite shape.
Free electrical charges (not bound to atoms or ions) cause plasma to be electrically conductive.

For example, Flame, interstellar nebulae, aurora borealis, lightning stars, and even the empty vastness of space are all examples of the plasma state of matter. You can find plasma inside fluorescent lights and neon signs.

Since the particles in plasma are electrically charged (generally by being stripped of electrons), it is frequently described as an "ionized gas".

9.0Bose-Einstein condensate-BEC ( 5^{\text {th }} state of matter)

A Bose-Einstein condensate is a gaseous superfluid phase formed by atoms cooled to temperature very near to absolute zero.

Satyendra Bose and Albert Einstein, had predicted it in the 1920. They didn't have the equipment and facilities to make it happen in the 20s.

The first such condensate was produced by Eric Cornell, Ketterle and Carl Wieman in 1995, using a gas of rubidium atoms cooled at 170 nanokelvins ( nK ). As in plasma, atoms are super-hot and super excited, the atoms in a Bose Einstein condensate (BEC) are total opposites. They are super-unexcited and super-cold atoms. The BEC forms at super low temperatures. At zero Kelvin, all molecular motion stops. When you get to a temperature near absolute zero, atoms begin to clump. The result of this clumping is the BEC. A group of atoms takes up the same place, creating a "super atom". There are no longer thousands of separate atoms. They all take on the same qualities and become one blob.

Some important quantities and the units

Quantity	Unit	Symbol
Mass	Kilogram	kg
Length	Meter	m
Temperature	Kelvin	K
Weight/Force	Newton	N
Volume	Cubic meter	$m^{3}$
Density	Kilogram /Cubic meter	$kg / m^{3}$
Pressure	Pascal	Pa

10.0Some Important Relations

1 kg = 1000 g

1 m = 100 cm

1 m^{3} = 1 0^{6} cm^{3}

1 0^{3} L

(litre)

1 0^{3} cm^{3} = 1 L

11.0Basic terminology

Fluidity - Property to flow.
Rigidity - Inflexibility, opposite of fluidity.
Compressibility - Property to be compressed.
Volatility - Property of forming vapours.
Humidity - Amount of water vapour in air.
Diffuse - To spread.
Interparticle - Between two particles.
Thermometer- Device used to measure temperature
Incense stick - Agarbatti
Dilution - Addition of water to a liquid.
Viscous - Thick and sticky.
Density- Mass per volume.
Constituent particles - Particle that cannot be broken into smaller pieces.

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