Kinetic Theory of Particles:
Kinetic particle theory explains
the behavior of the particles of solids, liquids and gases. This theory also
explains the interconversion of states with application or removal of heat.
Kinetic Particle theory: Melting and Boiling.
In solids, particles are held
together by strong inter-particular forces of attraction and can only vibrate
about their fixed positions. As heat is applied to the solid, the Kinetic
energy of the particles near the hot end increases, and as a result, they begin
to vibrate more vigorously. This vibration of the particles transfer heat to
all the adjacent particles and all the particles begin to vibrate with more
Kinetic energy. The temperature of the solid increases and these vibrations
increase and become more vigorous with increase in temperature, until the
melting point of the solid is reached.
Melting Point:
Melting point of a solid is
defined as the fixed temperature of a solid at which it changes its state to
liquid, at atmospheric pressure, without a change in its temperature.
Heat applied to the solid at its
melting point does not show a change on the temperature scale, instead it is
being used up by the solid particles to increase their K.E and overcoming the
inter-particular forces of attraction. Once, these forces are overcome, the
solid melts to form a liquid.
In liquids, the particles are
clumped together in variable clumps of variable sizes which can move around
freely, within the volume of the liquid. Heat applied to the melted liquid
increases the K.E of the particles of the liquid and they begin to move with
greater speeds. The temperature of the liquid increases with the increase in
the K.E of its particles, until its boiling point is reached.
Boiling Point:
Boiling point of a liquid is
defined as the fixed temperature of a liquid at which the liquid boils to
become a gas, at atmospheric pressure, without a change in its temperature.
At the boiling point of a liquid,
the thermometer reading becomes constant in spite of the constant application
of heat. The heat supplied is being used up in overcoming the inter-particular
forces of attraction and break their clumps and increase their K.E to boil off
from the surface of the liquid, as gas.
Note:
It is important to note here,
that the applied heat can either change/increase the temperature of the matter
or change its state. It CANNOT do both.
Figure 5a: Graph of temperature
vs time for melting and boiling of water
