Matter in Our Surroundings

Heat (energy) absorbed or released by a substance during the change in its phase (physical state) without changing in its temperature is called LATENT HEAT.

The 'Latent` is a Latin word comes from 'LATERE' which means 'to lie hidden'. Thus, LATENT HEAT means internal heat.

In other words, the heat required to covert a solid into liquid or a liquid into solid without change in temperature is called LATENT HEAT.

It can be observed while supplying heat to ice, that the temperature of the system does not change after the melting point is reached unless all the ice melts. This happens even though continue to heat the beaker, that is, we continue to supply heat. This heat gets used up in changing the state by overcoming the force of attraction between particles. As this heat energy is absorbed by ice without showing any rise in temperature, it is considered that it gets hidden into the contents of the beaker and this heat is known as LATENT HEAT.

Heat of Fusion

The amount of heat energy that is required to change 1 kg of solid into liquid at atmospheric pressure at its melting point is known as the LATENT HEAT OF FUSION.

Since, heat absorbed is laid hidden in water, thus at `O^o\ C` (273 K) water have more energy as compared to particles in ice at the same temperature.

Changing of water into vapour

Water gets converted into vapour when required heat is supplied to it.

When heat energy is supplied to water, particles of water start moving even faster. At a certain temperature, a point is reached when the particles have enough energy to break free from the forces of attraction of each other. At this temperature the liquid starts changing into gas.

Boiling Point

The temperature at which a liquid starts boiling at the atmospheric pressure is known as its BOILING POINT. Boiling is a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to change into vapour sate.

Boiling point of water is 373 K (`100^o\ C`).

Latent Heat of Vapourisation

The amount of heat energy that is required to change 1 kg of liquid into vapour at atmospheric pressure at its boiling point is known as the LATENT HEAT OF VAPOURISATION.

While supplying heat to the system to vapourise the liquid, the temperature of the system does not change even after reaching of boiling point, i.e. liquid starts boiling, till all the liquid changes into vapour. This happens even though continue supplying of heat to the beaker (system). This heat gets used up in changing the state by overcoming the forces of attraction.

Why steam, i.e. water vapour has more heat energy than water at same temperature?

Particles in steam, that is, water vapour at 373 K (`100^o\ C`) have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vapourisation.

Sublimation

A change of state directly from solid to gas without changing into liquid state and from gas to solid without changing into liquid is called SUBLIMATION.

Matters change their state from solid to liquid and from liquid to gas on application of heat. But there are some substances which changes directly from solid to gas on application of heat. This phenomenon is known as Sublimation.

Example: Camphor or aluminium chloride, when heated, it changes from solid to gas without changing into liquid and from gas to solid without changing into liquid.

Thus, Camphor or aluminium chloride goes under sublimation.

Effect of Pressure

By applying pressure and reducing temperature, gases can be liquefied, that is gases can be changed into liquid.

Carbon dioxide (`CO_2`) gas is solidified by applying high pressure. Solid Carbon dioxide (`CO_2`) is known as dry ice.

On the other hand solid Carbon dioxide (`CO_2`) gets converted directly to gaseous state on decrease of pressure to 1 atmosphere without coming into liquid state.

Solid Carbon dioxide (`CO_2`) is used to create smoke effect in cinemas.

Thus, we can say that pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas.

Evaporation

The phenomenon of change of a liquid into vapour at any temperature below its boiling point is called EVAPORATION.

Example:

Uncovered water slowly changes into vapour because of evaporation.

Drying up of wet clothes happens because of evaporation.

Particles of matter are always moving and are never at rest. At 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, phenomenon of which is known as EVAPORATION>

Factors Affecting Evaporation

Surface area, temperature, humidity and wind speed affect the phenomenon of Evaporation. This means that evaporation depends on surface area, temperature, humidity and wind speed.

Surface area

Increase in surface area increases the rate of Evaporation. For example clothes are spread up before putting them for drying up.

Evaporation is a surface phenomenon, that is, evaporation takes place because of particles of liquid at the surface of liquid. This happens because with increase in surface area more particles of liquid are at the surface area which increases the rate of evaporation.

If clothes are put for drying up without spreading them, it takes more time in drying up those clothes.

Temperature

Evaporation increases with increase in temperature decrease in temperature decreases the rate of evaporation.

With increase in temperature more number of particles get enough kinetic energy to go into the vapour state, resulting in increase in rate of evaporation.

Humidity

Rate of evaporation increases with decrease in humidity and decreases with increase in humidity.

The amount of water vapour present in air is known as humidity. 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, i.e. humidity is already high, this decreases the rate of evaporation.

Wind speed

With increase in wind speed, the rate of evaporation increases and decrease in wind speed, the rate of evaporation decreases.

Because more wind speed the particles of water vapour move away with the wind which decreases the water vapour in the surrounding, that is decrease the humidity, because of this rate of evaporation increases.

How Does Evaporation Cause Cooling?

In an open vessel, the liquid keeps on evaporation. The particles of liquid absorb energy from the surrounding to regain energy lost during evaporation. The absorption of energy from surroundings make the surrounding cool.

What happens when one pour some acetone (nail polish remover) on his palm?

The particles gain energy from palm or surroundings and evaporate which causes palm of the person to feel cool.

Whey people sprinkle water on the roof or open ground in hot sunny days?

After a hot sunny day, people sprinkle water on the roof or open ground because, the large latent heat of vapourisation of water helps to cool the hot surface.

Why should we wear cotton clothes in summer?

During summer, we perspire (sweating) more than other days. Perspiration is a mechanism of body which keeps our outer surface cool while hot days.

During the evaporation, the particles at the surface of the liquid gain energy from the surroundings of body surface and change into vapour. The heat energy equal to the latent heat of vaporization is absorbed from the body leaving body cool.

Cotton, which is a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation, which keep us more cool.

Thus, in summer we should wear cotton clothes.

Other two States of Matter

In modern days, science considered two more states of matter, other than solid, liquid and gas. These two states of matter are: Plasma and Bose-Einstein Condensate (BEC).

Thus, as per modern science, there are total five states of Matter.

Plasma

Plasma is fourth fundamental states of matter. Plasma does not naturally exist on the earth under normal surface conditions. But plasma can be artificially generated from neutral gases.

Plasma consists of super energetic and super excited particles found in the form of ionized gases. The fluorescent tube and neon sign bulbs.

In fluorescent tube and neon sign bulb inert gas, such as helium, neon, etc. are filled up. When electric current is flown thorough fluorescent tube or neon sign bulb, gas filled in it gets ionized, i.e. gets charged. This charging up creates a plasma glowing inside the tube or bulb. The particles of plasma glow inside the tube or bulb.

Plasma is produced artificially on earth. Plasma is found in plasma displays, including TV screens, rocket exhaust and ion thrusters, electric arc in arc lamp, arc welder or plasma torch.

In universe plasma is found in sun and other stars, in solar wind, etc.

Bose-Einstein Condensate

Bose-Einstein Condensate is considered as fifth states of matter. Bose-Einstein Condensate is known BEC or BE condensate in short. The BEC is formed by cooling a gas of extremely low density to super low temperatures.

Bose-Einstein condensate got its name in the honour of Satyendra Narayan Bose (an Indian scientist) and Albert Einstein.