PHYSICAL STATES OF MATTER

Introduction:

As we know that matter is physical material of universe. It is defined as anything which has mass and occupy space. States of matter differ in some observable properties. A gas has no fixed volume or shape it can easily be compressed and expanded. A liquid state has no fixed shape but has fixed volume it cannot be compressed easily. A solid has a definite shape and volume, it cannot be compressed easily. In addition to the above three states, there are two more states of matter named as plasma state and Bose Einstein condensate. The different physical states of matter are due to arrangement of molecules and intermolecular forces. 

Gaseous State:

The gaseous state molecules are lying away from one another, this assumption was proposed by Boltzmann, Maxwell, Kelvin. They explain the behavior of gases according to their kinetic molecular theory. Gaseous state shows following characteristics

The molecules in gases are widely separated from each other.

The molecules have negligible volume.

The gas molecules are in constant random motion.

The gas molecules moves in straight line until they collide with each other or wall of container.

On collision molecules do not lose energy because their collision is perfectly elastic.

Pressure Produced when molecules collide with the wall of container.

There are no attractive and repulsive forces between molecules.

PROPERTIES OF GASES 

The kinetic molecular theory explains the behavior of gases such as Diffusion, Effusion, Pressure, compressibility, Mobility and Density which are defined below: 

Diffusion: 

The Diffusion is defined as spontaneous mixing of molecules by random motion and collision to form a homogenous mixture. Gases are rapidly diffusible and depend upon the molecular mass of the gases. Lighter gases diffuse rapidly than heavier gases. as H2 diffuses four times more than O2.

Gharam’s Law of diffusion

Diffusion is movement of particles from an area of higher concentration to lower concentration. The rate of this movement depends upon temperature, viscosity of the medium and the size or mass of the particles. Diffusion results in the gradual mixing of materials, and eventually it forms a homogeneous mixture.

For Examples:

• You can smell perfume because it diffuses into the air and makes its way into your nose.
• Smoke diffuses into the air.
• Flower smell, garbage stink or body odor.

Effusion:

The Effusion is escaping of gas molecules through a tiny hole into a space with lesser pressure. Effusion depends upon molecular masses of gases .Lighter gases effuses rapidly than heavier gases. For process of effusion the diameter of hole must be smaller than the molecule's mean free path.

For Examples:

• Leakage of air through tyre pin hole.
• Leakage of helium through gas balloons

Pressure:

The force exerted by gaseous particles per unit area is called gas pressure. It can be expressed mathematically as.

Pressure = Force/Area or P = F/A = N/m² 

The S.I unit of force is Newton (N) and unit of area is m² , hence pressure has S.I unit of Nm-². It is also known as Pascal (Pa). 1 Pascal=1Nm-²

The molecules of gases are in continuous motion,

But the pressure is developed by the collisions of molecules of gas with the walls of container. Barometer is used to measure the atmospheric pressure and manometer is used to measure the pressure of gases in the laboratory.

Compressibility:

The capacity of something to be flattened or reduced in size by pressure is called compressibility. The gases are highly compressible due to larger spaces between their molecules. When gases are compressed, the molecules come closer to one another and occupy less volume as compared to the volume of uncompressed state

Mobility:

The ability to move freely is known as mobility. As the gas molecules are in continuous motion they can move fast due to high kinetic energy. The molecules move freely in the empty space .This mobility is responsible to produce a homogenous mixture of gases.

Density:

The Density is degree of compactness or closeness of a molecules. Gases have low density because of light mass and more volume occupied by the gas molecules. Gas density is expressed in grams per dm'. Gases are less denser than liquids. The density of gases can be increased by cooling

LAWS RELATED TO GASES:

The properties of gases are governed by the following laws. 

Boyle's Law:

Robert Boyle

In 1662 Robert Boyle proposed gaseous law about the relationship between volume and pressure of gas at constant temperature, Boyles law states that "The volume of a given mass of a gas is inversely proportional to applied pressure, at constant temperature"

Mathematical Representation of Boyle's Law:

According to Boyle's law the volume (V) of a given mass of a gas decreases with the increase of pressure (P) at constant temperature.

V∝1/P  Or V=K/P  where K= is the constant

PV = K

The product of pressure and volume of a fixed mass of a gas is constant at a constant temperature.

If ____ P₁ V₁ = K   ____ Then. _____ V₂ P₂  = K 

Where P₁= initial pressure  P₂= final pressure

V₁ = initial volume V₂= final volume

As the both equations have same constant therefore their variable are also equal to each so other P₁ V₁ = V₂ P₂

This equation establish a relationship between pressure and volume.Where given mass of a gas at constant temperature shows increase in volume by decrease in pressure. On the other hand increase in pressure decreases volume. But the product of pressure and volume is constant in both cases.

Charles' Law:

Jacques Charles

In 1787 French scientist J.Charles proposed his law to explain the relationship between volume and temperature keeping the pressure constant. He states that "the volume of a given mass of a gas is directly proportional to the absolute temperature if the pressure is kept constant".

Mathematical Representation of Charles' Law:

According to Charles law if temperature of a gas is increased, its volume will also increase.

Mathematically it is represented a

V ∞ T

Or

V = KT

V/T = K

Where K is proportionality constant. Then when temperature increases the volume also increases.

For example, if we double the temperature from 300 K to 600 K, at constant pressure, the volume of a fixed mass of the gas will become double. 

Imagine a gas at a certain temperature (T₁) and volume (V₁). If change in the temperature (T₁) to a new value (T₁), occur then volume (V₁) changes to a new value (V₁). We can use Charles's law to describe both sets of conditions:

T₁  / V₁ = K 

V₂  /  T₂= K

The constant, k, is the same in both cases, therefore

V₁ / T₁  = V₂ / T₂

LIQUID STATE:

The liquid state is the intermediate between gaseous and solid states. According to their kinetic molecular theory liquid state shows following chractarstics.

• The molecules of a liquid are randomly arranged like gases.
• The molecules of liquids have less kinetic energy than gases
• The molecules of liquids are fairly free to move.
• The Liquids has no definite shape but assumes the shape of container.
• The Boiling point of liquids depends on the external atmospheric pressure.
• The Liquids are denser and not compressible like gasses.

Properties of Liquids:

Evaporation

The process by which a liquid changes to a gas phase is called evaporation) Evaporation is endothermic reaction in which heat is absorbed.

For example clothes dry under the sun due to evaporation, in this process water is converted from liquid state into vapours by acquiring Heat. 

Water (Liquid)→Vapour (gas)

The molecules of liquids are in continuous motion they collide with each other but all the molecules do not have same kinetic energy. Majority of the molecules have average kinetic energy and few have more than average kinetic energy. The molecules having more average kinetic energy overcome the attractive forces among the molecules and escape from the surface by evaporation. It is directly proportional to temperature and increase with the increase in temperature.

The evaporation is also considered as cooling process because when high kinetic energy molecules escape in the air in the form of vapours by taking energy from lower molecules as a result the energy of remaining molecules falls down. To compensate this deficiency of energy molecules absorb energy from the surrounding, due to which temperature of surrounding decreases and cooling occurs

Factors Affecting Evaporation:

1. Surface Area: The evaporation is a surface based process. Greater the surface area greater is evaporation. For example water left in bowl evaporate slowly then water left in a large tub. A saucer is used to cool the tea quickly than tea cup.
2. Temperature: The rate of evaporation increases with the increase in temperature. Because temperature increases the kinetic molecular energy which overcome the intermolecular forces and makes evaporation rapidly. For example clothes dry quickly in a sunny day than in a cloudy day.
3. Intermolecular Forces: The rate of evaporation increases with weak intermolecular forces .If intermolecular forces are stronger evaporation is lesser. For example perfume have weak intermolecular forces than water therefore it evaporates quickly.

Vapour pressure The pressure exerted by vapours at equilibrium on its pure liquid state at a particular temperature is called Vapour Pressure. The equilibrium is a state when rate of evaporation is equal to rate of condensation but in opposite directions.

Condensation

 Liquid ⇋ Vapours

Vaporize

Vapour pressure takes place in a closed system on heating because in open system or open surface liquid molecule evaporates and mix-up with air

When a liquid is heated in a closed container evaporated molecules start gathering over the liquid surface. Initially the vapours condense slowly to liquid After sometimes condensation process increases and a stage reaches when the rate of evaporation become equal to rate of condensation. At that stage, the number of molecules evaporate will be equal to the number of molecules condensate (coming back) to liquid. At this point, pressure exerted by the vapours on liquid is called vapour pressure. The unit of pressure is expressed in mm of Hg, atmosphere, torr or newton 

Factors Affecting Vapour Pressure:

1. Nature of Liquid: The vapour pressure depends upon the nature of liquids. Polar liquids have low vapour pressure than nonpolar liquids at the same temperature. It is because of strong intermolecular forces of molecules and high boiling point of polar liquids. For example water (polar liquid) has less vapour pressure than alcohol (non polar liquid).
2. Size of Molecules: The vapour pressure is more in small size molecules because small sized molecules evaporate easily and exert more vapour pressure. For example hexane (C6H14) has small sized molecules as compared to decane (C10H22), due to this hexane evaporate rapidly and exert more pressure. 
3. Temperature: The vapour pressure increases with raise in temperature. The average kinetic energy of molecules increases with temperature which causes increase in vapour pressure. For example vapour pressure of water at 0° is 4.58 mm Hg while at 100°C it increases up to 760mm Hg. 

Boiling Point :

The temperature at which vapour pressure of a liquid become equal to atmospheric pressure is called boiling point of that liquid. When the liquid is heated, bubbles begin to form throughout its volume. The bubbles (contain vapour pressure) which being lighter than the liquid, rise to surface and burst. The vapour pressure in bubble is equal to atmospheric pressure. All bubbles containing vapours will rise to the surface of the liquid and burst into air. It appears that water is boiling. The boiling point varies with the atmospheric pressure.

Factors Affecting Boiling Point:

1. Atmospheric Pressure: The boiling point is directly proportional to atmospheric pressure. Boiling point can be increased by increasing atmospheric pressure. For example working of pressure cooker
2. ii. Nature of Liquid: The boiling point depends upon the nature of liquid as polar liquids have high boiling point than nonpolar liquids, because polar liquids have stronger intermolecular forces than nonpolar liquids. Boiling points of few liquids are given in table 
   
   
   
   
   
3. Intermolecular forces: The intermolecular forces play very important role in the boiling points of liquids. Substances having stronger intermolecular forces have highboiling points, because such liquids attain a level of vapour pressure equal to external pressure at high temperature.

Freezing Point:

The temperature at which the vapour pressure of a liquid state becomes equal to the vapour pressure of its solid state is known as Freezing Point of a liquid. At this temperature liquid and solid coexist in dynamic equilibrium

Factors Affecting Freezing Point:

The freezing point depends upon the temperature and intermolecular forces. Molecules with stronger intermolecular forces are pulled together to form a solid at higher temperature. Due to this they show high freezing point. Molecules with lower intermolecular forces solidify on more lower temperature.

Freezing points of few liquids are given in table

Diffusion:

The diffusion is defined as spreading out of the molecules throughout the vessel. The liquids diffuse less rapidly than gases.

As the molecule of liquid are in cluster and bounded with strong intermolecular binding forces, the liquid molecules roll over one another and are in continuous motion. They move from higher concentration to lower concentration and mix up with molecules of others liquids and may form homogenous mixture.

For example when few drops of ink are dropped in water filled flask, the molecules of ink move around and after a while spread in whole of flask, thus diffusion takes place as shown in picture 

Factors Affecting Diffusion:

1. Inter molecular forces: liquids have weaker intermolecular forces than solid due to this they diffuses faster than solid but less rapidly than gases.
2. Size of Molecules: Diffusion depends upon size of molecules small size of molecules diffuses rapidly than bigger one. For example diffusion is slow in water than alcohol.
3. Shape of molecules: Molecules with irregular shape diffuses slowly while regular shaped molecules diffuses faster because they can easily slip over and move faster.
4. Temperature: Diffusion increases by increasing temperature because at high temperature intermolecular forces becomes weak due to high kinetic energy of the molecules.

Mobility: The mobility is ability to move freely. The molecules in a liquid move freely, due to free movement they can adjust their shape in a container. Due to this reason liquids can flow.

Factors Affecting Mobility:

1. Temperature: Mobility increases by increasing the temperature. When temperature increases in a liquid movement of molecules increases accordingly.
2. Inter molecular forces: Mobility increases by decrease in intermolecular forces. The liquids which have strong intermolecular forces show less mobility