Introduction
If the thermal energy is greater than the forces of attraction, then we have matter in its
Gaseous state.
Molecules in the gaseous state move with very large speeds and the forces of attraction amongst them are not sufficient to bind the molecules at
one place, with the result that the molecules move practically independent of one another because of this feature, gases are characterized by marked sensitivity of volume
change with change of Temperature & Pressure.
There exists no boundary surface and, therefore, gas tends to fill completely any available space, i.e., they do not possess a fixed volume.
A Gas is said to be
Ideal if it follows Following Laws : -
- Boyle's law
- Charles law
- Avogadro's law
- Daltons law
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In the mid 1600's,
Robert Boyle studied the relationship between the
pressure p
and the
volume V of a confined gas held at a
constant temperature.
Boyle observed
that the product of the pressure and volume are observed to be nearly constant.
The product of pressure and volume is exactly a constant for an ideal gas.
p * V = Constant
Thus, the law states that pressure(p) is inversely proportional to volume(V) or vice-versa.
This relationship between pressure and volume is called
Boyle's Law in his honor.
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The relationship between
temperature and volume, at a
constant number of moles and
pressure,
is called
Charles and Gay-Lussac's Law in honor of the two French scientists who first
investigated this relationship.
Charles did the original work, which was verified by Gay-Lussac.
They observed that if the pressure is held constant, the volume V is equal to a constant times the
temperature T.
V = constant * T
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Avogadro's Law (Avogadro's theory; Avogadro's hypothesis) is a principle stated in 1811
by the Italian chemist
Amedeo Avogadro (1776-1856) that
"Equal volumes of gases at the same temperature and pressure contain the same number of molecules regardless of their
chemical nature and physical properties".
This number (Avogadro's number) is
6.022 X 1023.
It is the number of molecules of any gas present in a volume of
22.41 L and is the same
for the lightest gas (hydrogen) as for a heavy gas such as carbon dioxide or bromine.
The law can be stated mathematically
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The equation which gives the simultaneous effect of pressure and temperature on the
volume of a gas is known as an ideal gas equation or an equation of state for an ideal gas.
It can be derived by combining Boyle’s law, Charles’ law and Avogadro’s hypothesis as shown below:
where,
n = number of moles
R = universal gas constant = 8.3145 J/mol K
N = number of molecules
k = Boltzmann constant = 1.38066 x 10
-23 J/K = 8.617385 x 10
-5 eV/K
k = R/N
A
NA = Avogadro's number = 6.0221 x 10
23 /mol
Implications of Ideal Gas Law
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