2. Matter exist in three different states- solid, liquid, gas.
According to kinetic molecular theory, all forms of matter are
composed of small, rapidly moving particles. The same substance
can exist in three different states.
Ice Water Water vapour
Solids are rigids and have definite shape & volume.
Intermolecular force of attraction is strong and K.E of particles is
very small.
Liquids have no definite shape but have definite volume. The
particles are loosely bound, hence intermolecular force of attraction
is smaller than solids.
Gases have on definite shape nor definite volume, they take the
shape of the container. Particles are far apart form one another.
Thus intermolecular force is weaker and K.E is very large than other
two states.
3. The word ‘gas’ , introduced in 1620 by van Helmont, is used to refer
substances which exist in gaseous states at ordinary temperatures
and pressures. Changing these variables any substances can exist as
gas, a liquid or a solid.
The important measurable properties of gases are mass, volume,
pressure and temperature.
GAS LAWS
The quantitative relationships connecting the measurable
properties such as pressure, volume, temperature and mass of a gas
are called gas laws. They are,
Boyles Law
Charles Law
Avogadro law
4. In 1662, Robert Boyle studied the relation between the pressure and
volume of a gas and formulated the result in the form of a law
known as Boyle’s Law.
It states that,
At constant temperature the volume of a given
mass of a gas is inversely proportional to its
pressure.
Mathematically ,
v α 1/p
ie., v = constant/p
vp = constant.
Let the volumes occupied by a given mass of a gas at a constant
temperature T be v1 and v2 at pressures p1 and p2 respectively. Then,
p1v1 = p2v2
5. A quantitative relationship between the volume of a gas and its
temperature was given by French Chemist Jacques Charles(1787) in
the form of a law known as Charle’s Law.
It states that,
At constant pressure, the volume of a given
mass of a gas is directly proportional to its
absolute temperature.
Mathematically,
V α T , where T = (t°c+273)
v = constant x T
V/T = constant
If V1 is the volume at temperature T1 and V2 is the volume at
temperature T2 at the same pressure. Then,
V1/T1 = V2/T2
6. The Boyle’s law, Charles law can be combined to get the combined
effect of pressure and temperature on the volume of a gas.
This gives a more general equation, relating the variables V, P and T,
called combined gas equation.
Derivation.
According to Boyle’s law, Vα 1/P (T constant)
According to Charles law, Vα T (P constant )
Combining these laws , we get
V αT/P
Vα 1/P x T
V = a constant x 1/P x T
PV∕T = a constant.
7. This law relates the volume of a gas to the number of molecules
at constant temperature and pressure. It was suggested by
Amedeo Avogadro in 1811.
It states that ,
“Equal volumes of all gas under the same
conditions of temperature and pressure
contains the same number of molecules”.
It follows that the volume V of a given mass of a gas is
directly proportional to the number of moles n,
V α n , at constant pressure and
temperature.
8. All of these gas laws are based on ideal gases.
Most gases found in nature do not meet all these properties for
ideal gas .
They follow the rule of the gas laws closely enough that we can
use the equation of gas laws.
Also it will not present a significant difference from what occurs
in nature.
