Change in
states of matter
Matter
exists in three different forms: solid, liquid and gaseous state. These forms
are interchangeable, i.e. we can change a substance from solid state to liquid
state or from liquid state to gaseous state and similarly the reverse from
gaseous to liquid state and from liquid to solid state. For example, ice melts
to from water and when water is heated it evaporates to form water vapour which
is in gaseous state. Likewise when water vapour condenses it forms water and
water freeze it converts to ice.
The physical
state of matter can be change using two techniques:
1. Changing the temperature
2. Changing the pressure
Effect of
change of temperature:
The state of
matter can be changed by changing the temperature, either by heating or by
cooling.
When
temperature is increased the kinetic energy of particles increases causing more
vibration in particles, this leads to decrease in inter particle attraction.
Similarly when temperature is decreased the kinetic energy of particles decreases
causing vibration of particles to reduce, this leads to increase in inter
particle attraction.
1. Solid to liquid (Melting):
The process in which a solid substance changes into liquid on heating is
called melting. Ice melts to form water.
The temperature at which solid substance melts and changes into liquid
form at atmospheric pressure is called the melting point of substance. . Ice
melts to form water at 0o C, so 0o C is the melting point
of ice
Melting point of substance is the measurement force of attraction between
the particles of the substance. The greater the force of attraction greater
will be the melting point. Melting point of ice is 0o C and that of
wax is 63o C. this means the intermolecular force of attraction
between wax particles is greater than that of ice.
Causes of conversion: when a solid substance is heated, the heat energy
make the particles vibrate vigorously. At melting point the solid particles
have sufficient kinetic energy to overcome the strong force of attraction which
holds the particles of solid in fixed position. This kinetic energy break the
particles in smaller units and thus the solid melts to form liquid.
2. Liquid to gas (boiling or vaporisation):
The process in which a liquid substance changes into gas on heating is
called boiling. Water boils to form water vapour.
The temperature at which liquid substance evaporates and changes into
gaseous form at atmospheric pressure is called the boiling point of substance. Water
evaporates to form water vapour at 100o C, so 100o C is
the boiling point of water.
Melting point of substance is the measurement force of attraction between
the particles of the substance. The greater the force of attraction greater
will be the boiling point. Boiling point of water is 100o C and that
of alcohol is 78o C. this means the intermolecular force of
attraction between water particles is greater than that of alcohol.
Causes of conversion: when a liquid substance is heated, the heat energy
make the particles vibrate vigorously. At boiling point the particles have
sufficient kinetic energy to overcome the strong force of attraction which holds
the particles of liquid together. This kinetic energy breaks the particles in
individual units and thus the liquid evaporates to form gas.
3. Liquid to solid (freezing):
The process in which a liquid substance changes into solid on decreasing
the temperature is called freezing. Water freezes to form ice.
The temperature at which liquid substance freezes and changes into solid
form at atmospheric pressure is called the freezing point of substance. Water freezes
to form ice at 0o C, so 0o C is the freezing point of
water.
Causes of conversion: when a liquid substance is cooled by lowering the
temperature, the particles lose energy due to which they start moving slowly. When
liquid is cooled enough till its freezing point, its each particle stop moving
and vibrate about a fixed point. This is the point when liquid change and
become solid.
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