Class IX

Chapter – 1(Chemistry)
Interconversion of states of matter
The phenomenon of change of matter form one state to another state and back to original
state, by changing the conditions of temperature and pressure, is called interconversion of
matter.
The various states of matter can be interchanged into one another by
(a) By changing the temperature
(b) By changing the pressure.

By changing the temperature:

(a) Interconversion of solid into liquid state and vice versa :
The solids can be converted into liquids by heating them. Similarly liquids can be cooled to
form solids.
e.g. : Ice at 0oC changes into water at 0oC, when heat energy is supplied to it. The water at
0oC changes into ice at 0oC on freezing.

 Melting or Fusion : The process due to which a solid changes into liquid state by
absorbing heat energy is called melting or fusion.
 Freezing or Solidification : The process due to which a liquid changes into solid
state by giving out heat energy is called freezing or solidification.
 Melting Point : The minimum temperature at which a solid changes into liquid state
at normal atmospheric pressure is called it melting point.
 Freezing Point : The minimum temperature at which a liquid changes into solid state
at normal atmospheric pressure is called freezing point.

The numerical value of freezing point and melting point is same.

Melting point of ice = Freezing point of water = 0oC (273.16 K).
Ice starts melting and water starts freezing at same temperature of 0°C.

Explanation: On increasing the temperature of solids, the kinetic energy (K.E.) of particles
increases. Due to increases in K.E., the particles start vibrating with greater speed. The
energy supplied overcomes the force of attraction between the particles. Then, the particles
leave their fixed positions and start moving freely and thus solid melts.

LATENT HEAT
Latent heat: The amount of heat required to change the state of matter from one state to
another without any change in temperature is known as latent heat of that substance.
The function of the latent heat is to break the force of attraction between the particles and
convert one state to another state.it does not increase the kinetic energy of the particles and
hence no change in temperature, rather it gets hidden within the force of attraction to change
the state of matter. Hence, it is also called hidden heat.
 Latent heat of fusion: The amount of heat required to convert 1kg of solid liquid at
its melting point and at normal atmospheric pressure is known as latent heat of fusion.
 Latent heat of fusion of water is 334kJ/Kg

Ice at 273 K will be more effective than water at same temperature for cooling
because ice will absorb more heat than water from the substance to overcome the
latent heat of fusion and thus providing a more effective cooling effect. Water
however does not absorb any extra heat from the substance.

(b) Interconversion of liquid into gaseous state and vice versa :

Liquids can be converted into gases by heating them. Similarly, gases can be converted into
liquids by cooling them.
e.g. Water at normal pressure changes into gas (steam) at 100 oC by absorbing heat. Steam at
100oC changes into water by giving out energy.
 Boiling or Vaporisation: The process due to which a liquid changes into gaseous
state by absorbing heat energy is called boiling.
 Condensation or Liquefaction: The process due to which a gas changes into liquid
state by giving out heat energy is called condensation.
 Boiling point: The constant temperature at which a liquid rapidly changes into
gaseous state by absorbing heat energy at normal atmospheric pressure is called
boiling point.
The numerical value of condensation point and boiling point is same.
Condensation point of vapour (water) = Boiling point of water = 100oC (373 K).
Explanation: When heat is supplied to water, particles start moving faster. At a certain
temperature, a point is reached when the particles have enough energy to break the forces of
attraction between the particles. At this temperature the liquid starts changing into gas.

Latent heat of vaporisation: The amount of heat which is required to convert 1 kg of the
liquid (at its boiling point) to vapour or gas without any change in temperature under normal
atmospheric pressure.

Latent heat of vaporisation of water = 22.5 × 105 J/kg.

Particles in steam, that is water vapour at 373 K or at 100°C have more energy than water at
the same temperature. Because the particles of steam have absorbed extra energy in the form
of latent heat of vaporisation. That is why steam causes more severe burn than boiling water
at same temperature.

SUBLIMATION AND DEPOSITION:

Sublimation

 Definition: The process where a solid changes directly into a gas without becoming
a liquid first.
 Example:
o Dry ice (solid CO₂) turns directly into carbon dioxide gas.
o Naphthalene balls (used in closets) slowly disappear as they sublimate.

Deposition (Vice Versa of Sublimation)

 Definition: The process where a gas changes directly into a solid, skipping the liquid
phase.
 Example: Frost formation: Water vapor in the air turns directly into ice on cold
surfaces.

SUBLIMATION

Sublimation is the process of conversion of a solid directly into a gas without changing into
liquid state. Substances that show sublimation are called sublime products .e.g. Ammonium
chloride, Camphor, Naphthalene balls, iodine, solid CO2 (dry Ice).

Experiment to demonstrate sublimation: Take some ammonium chloride (NH4Cl) in a

china dish, and cover it with an inverted funnel as shown in figure. Plug the stem of funnel
with cotton. Now heat slowly.

Observation and Discussion: Ammonium chloride, will convert into vapours which will
deposit on the inner side of the funnel as sublimate. The vapours in turn, condense on the
cooler portions of the funnel to give pure NH4Cl.
Precaution: Cover the top of the funnel with a cotton plug so that, vapours should not go out.

Conclusion: A change of state directly from solid to gas without changing into liquid (or
vice-versa) is called sublimation.

# The separation of ammonium chloride and sodium chloride:

Ammonium chloride sublimates, but sodium chloride does not.

 Ammonium chloride → Sublimes (solid → gas directly on heating).

 Sodium chloride → Does not sublime (remains solid on heating).

EFFECT OF CHANGE OF PRESSURE

The effect of pressure on the states of matter can be discussed by the following experiment:

Experiment: Take a gas in a cylinder and apply pressure by pushing the piston down as
shown in figure.
By applying pressure, particles of a gas come close together.

Observation: A gas can be first liquified and then converted into solid.

# To convert one state of matter into another, temperature and pressure work together. We
can liquefy a gas by

(a) Increasing the pressure

(b) Decreasing the temperature

Cooking on mountains is more difficult than on plains because atmospheric pressure

decreases with altitude, causing water to boil at a lower temperature. This lower boiling point
results in less heat being transferred to the food, requiring a longer cooking time to reach the
desired level of doneness.

GRAPH on INTERCONVERSION OF THE STATES OF MATTER