There are five main states of matter. Solids, liquids, gases, plasmas, and Bose-Einstein condensates (BEC) are all different states of matter. Each of these states is also known as a phase. Elements and compounds can move from one phase to another when specific physical conditions are present. One example is temperature. When the temperature of a system goes up, the matter in the system becomes more excited and active. Scientists say that it moves to a higher energy state. Generally, as the temperature rises, matter moves to a more active state.
A "phase" describes a physical state of matter. The key word to notice is physical. Things only move from one phase to another by physical means. If energy is added (like increasing the temperature) or if energy is taken away (like freezing something), you have created a physical change. 

Gases, liquids and solids are all made up of microscopic particles, but the behaviors of these particles differ in the three phases. The following figure illustrates the microscopic differences.


Microscopic view of a gas   Microscopic view of a liquid   Microscopic view of a solid

Phase Transitions:

A state change of any material due to temperature or pressure change is a phase transition. A phase transition is a physical change (or reaction).

The following diagram illustrates the key phase transitions: You should know the names of the process for these phase transitions.

                     sublimation                      deposition
   SOLID  ============>  GAS    ==============> SOLID
                         melting                           freezing
   SOLID  ============>  LIQUID  =============>  SOLID
              condensation                    vaporization
   GAS  =============>   LIQUID  =============> GAS

 The following table summarizes properties of gases, liquids, and solids and identifies the microscopic behavior responsible for each property.

Some Characteristics of Gases, Liquids and Solids and the Microscopic Explanation for the Behavior
assumes the shape and volume of its container 
particles can move past one another
assumes the shape of the part of the container which it occupies 
particles can move/slide past one another
retains a fixed volume and shape 
rigid - particles locked into place
lots of free space between particles
not easily compressible 
little free space between particles
not easily compressible 
little free space between particles
flows easily 
particles can move past one another
flows easily 
particles can move/slide past one another
does not flow easily 
rigid - particles cannot move/slide past one another

• Matter is made up of small particles.

• The matter around us exists in three states— solid, liquid and gas.

• The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases.

• The spaces in between the constituent particles and kinetic energy of the particles are minimum in the case of solids, intermediate in liquids and maximum in gases.

• The arrangement of particles is most ordered in the case of solids, in the case of liquids layers of particles can slip and slide over each other while for gases, there is no order, particles just move about randomly.

• The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure.

• Sublimation is the change of gaseous state directly to solid state without going through liquid state, and vice versa.

• Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.

• Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapour state.

• The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed.

• Evaporation causes cooling.

• Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.

• Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.

• Some measurable quantities and their units to remember:

quantities and units

Note: Kelvin is the SI unit of temperature, 00 C =273.16 K. we take 00 C = 273 K. To change a temperature on the Kelvin scale to the Celsius scale we have to subtract 273 from the given temperature, and to convert a temperature on the Celsius scale to the Kelvin scale we have to add 273 to the given temperature.

Atmosphere (atm) is a unit of measuring pressure exerted by a gas. The unit of pressure is Pascal (Pa):

1 atmosphere = 1.01 × (10 to the power 5) Pa. The pressure of air in atmosphere is called atmospheric pressure. The atmospheric pressure at sea level is 1 atmosphere, and is taken as the normal atmospheric pressure.

                       In this page we are going to discuss about physical and Chemical changes in matter concept . Matter undergoes certain changes as a result of the application of energy. Water from saltpans on the seacoast dry up, leaving behind salt; water from the sea evaporates to from water vapour, which convert into clouds and then condense to form rain. Glaciers melt in summer and rivers freeze in winter. A candle upon burning gives light, heat, water vapour and carbon dioxide. Hydrogen burns in air to form the water molecule H2O.

The different changes that matter undergoes, may be broadly classified into'physical' and 'chemical' changes.

Physical changes  


When the shape, size, appearance or state, of a substance is altered, but its chemical composition remains same a physical

change of matter takes place. No new substance is formed. It is usually a change, which is reversible, that is, by reversing the

process, the original substance can be obtained.

By using a piece of gold, a goldsmith can make a gold chain and can later alter it to make a gold bracelet, ring or a pair of

earings. All of them consist of the same substance, namely gold. This is an example of a physical change. A more common

everyday example is that of water, which can be converted into solid ice, liquid water, and gaseous water vapour. It can be

reconverted to its previous state by various methods. Yet, in all the three forms, the chemical composition of water is not altered.

No new substance with new chemical properties is formed. In all these, water consists of two atoms of hydrogen and one atom

of oxygen.

different states of matter

Thus, a Physical change is a change in which the chemical composition of the substance is not affected, i.e., no new substance is formed.

Examples of Physical Changes

(a) Dissolving of sugar in water 

  When crystalline sugar is dissolved in water, it seems to disappear completely, and not even a very powerful microscope can show us the molecules of sugar in water. The solution obtained is uniformly sweet. By evaporating the water the sugar can be recovered in a crystalline form.


physical change found in sugar solvent


(b) Magnetising an iron rod

An iron rod can be converted into a magnet by passing an electric current through an insulated coil wound around it. When the current flows, the iron bar gets magnetised. One end becomes North Pole and the other the South Pole. If the direction of the current is reversed, the North Pole changes to South Pole and the South Pole changes to North Pole.


magnetising an iron rod


(c) Glowing of an electric bulb 

When an electric current is passed through the filament of a bulb, the filament starts glowing and the glow stops as soon as the current is cut off. The chemical composition of the filament does not alter in either state.


glowing of an electric bulb


Chemical Change


A change in which the composition of a substance is altered is called as chemical change of matter. As a result, the original

properties get changed and one or more new substances are formed.


Iron is greyish white metal and conducts electricity. It is attracted by a magnet, and reacts with dilute acids to yield hydrogen.

Sulphur is a non-metal, and is yellow in colour. It dissolves in carbon disulphide. When powdered iron and sulphur are heated

together, a completely new substance, iron sulphide is formed. The properties of iron sulphide are entirely different from those of

iron and sulphur. It is black in colour, does not get attracted by a magnet and does not allow electric current to pass through it.

It reacts with dilute acids to from hydrogen sulphide gas. In short, the properties of neither iron nor sulphur are exhibited by iron



Conditions For Chemical Change


The criterion for a chemical change is the production of one or more new substances. Therefore, certain conditions should be

met in order to bring about a chemical change. The necessary conditions are:

1.A minimum amount of energy needed to initiate a reaction, called the activation energy, should be supplied in the form of heat,

light or electric current. In a chemical change the reactants combine to form new products. For this process it is necessary to

break the old bonds of the reactants and forms fresh bonds in order to give new products. This requires a certain amount of



2. For the occurrence of any reaction, the molecules or atoms of the reactants must collide with one another, in order to break

old bonds and form new bonds.


3. The speed with which the chemical reaction takes place is called the rate of the chemical reaction. This should be

appreciable, to bring about the change.

4. The rate of a reaction depends on following factors:

  • Temperature
  • Presence of light
  • Presence of catalyst
  • Electricity
  • Pressure.



  • Temperature : Certain chemical reactions do not take place at room temperature but occur readily at a higher temperature. Accordingly, heat is required to start the reaction e.g. fuels like coal and wood only start burning when heated to a certain temperature called its ignition temperature.

  • Presence of Light : Some reactions take place only in light and do not take place in dark e.g. photosynthesis in green plants or reaction between H2 and Cl2 to form HCl.
  • Presence of a Catalyst : A catalyst is a substance that increases the rate of chemical reaction without itself undergoing any change.Example: Hydrogenation of oils to form fats takes place faster, in presence of nickel.
  • Electricity : Certain reactions take place with the help of an electric current.Example: Decomposition of acidulated water to give hydrogen and oxygen gas

  • Pressure : Some chemical reactions need very high pressure to proceed. For e.g., in the commercial manufacture of ammonia from nitrogen and hydrogen by Haber's process, a pressure of over 200 atmosphere is required, in presence of a catalyst iron and a temperature of 450oC to 500oC.


Examples of Chemical Changes

Below are the examples on chemical changes - 

(a) Effect of heat on lead nitrate : Lead nitrate is a white, crystalline solid. When heated, it starts decomposing with a

crackling sound, producing a reddish brown gas called nitrogen dioxide, and a colourless gas, oxygen. A yellow residue of lead

monoxide is left behind in the test tube.

(b) Action of concentrated sulphuric acid on sugar :When concentrated sulphuric acid is added to sugar, it becomes a

black mass of sugar charcoal. The acid removes all the water from the sugar, that is, hydrogen and oxygen and absorbs it

leaving a residue of spongy carbon.


action of concentric H2SO4 on sugar


(c) Action of sodium on cold water :


When a small piece (pea size) of sodium is placed in cold water, it darts about on the water with a hissing sound and produces hydrogen. The water left behind, acquires the property of turning red litmus blue. This shows the presence of a basic substance, which is sodium hydroxide



action of sodium reaction on cold water




 Physical Change Chemical Change
 No new or different substance is formed. The composition of the substance, that undergoes the change, remains unchanged Results in the formation of at least one new substance. The constituent particles of the new substance are different from the constituent particles of the original substance
 It is temporary change and in most cases it can be reversed by the reversal of conditions It is permanent change and cannot be reversed by mere reversal of conditions
 No change occurs in the mass of the substances undergoing the change Mass of the individual substances that undergoes the change, always, either increases or decreases. However, the total mass of all the reactants is equal to the total mass of all the products