GAS LAWS
The gas laws only hold true for ideal gases.
Certain postulates have to be understood before studying gas laws. The kinetic theory of gases
states the following assumptions for ideal gases:
Gases consist of a large number atoms and molecules. These particles are extremely tiny
in comparison to the distance between the particles. The size of the individual particle is
considered negligible. Therefore, the volume occupied by the gas is also considered
negligible.
These molecules are in constant random motion. This results in collision with each other
and with the walls of the container. During this, they impart momentum to the walls
which results in the production of a measurable force. Force divided by area gives
pressure. The pressure of the gas is proportional to the number of particles colliding
(frequency of collisions) in unit time per unit area on the wall of the container.
The aforementioned collisions between the molecules and the walls are perfectly elastic
in nature. This means that they do not lose kinetic energy and the energy before and after
the collision is same.
The average kinetic energy of the gas particles changes with temperature i.e. the higher
the temperature, the higher the average kinetic energy of the gas.
The molecules do not exert any force of attraction or repulsion on one another except
during collisions.
BOYLE’S LAW- Boyle’s law states that the pressure of a given mass of an ideal gas is
inversely proportional to its volume, at a constant temperature.
This means that on increasing pressure, volume would decrease and vice versa.
P∝1/V,
P=k/V,
PV=k (where k is a constant, P=pressure, V=volume)
, P1V1=P2V2=P3V3=...P∞V∞=k
The PV graph obtained is a rectangular hyperbola. This implies that the product of pressure and
volume (for all values of P and V) is constant throughout the process.
Note- Boyle’s law equation can be used only when values of mass of the gas (m) or number of
moles (n= m/M) and temperature are fixed.
(n= number of moles, m=mass taken and M= molecular mass)
CHARLES’S LAW- The law states that the volume of a given mass of an ideal gas is
directly proportional to its absolute temperature, at a constant pressure.
This means that there would be an increase in temperature if we increase the volume and vice
versa.
V∝T,
V= kT, (where k is a constant, V= volume, T= absolute temperature)
V/T= k or,
The gas laws only hold true for ideal gases.
Certain postulates have to be understood before studying gas laws. The kinetic theory of gases
states the following assumptions for ideal gases:
Gases consist of a large number atoms and molecules. These particles are extremely tiny
in comparison to the distance between the particles. The size of the individual particle is
considered negligible. Therefore, the volume occupied by the gas is also considered
negligible.
These molecules are in constant random motion. This results in collision with each other
and with the walls of the container. During this, they impart momentum to the walls
which results in the production of a measurable force. Force divided by area gives
pressure. The pressure of the gas is proportional to the number of particles colliding
(frequency of collisions) in unit time per unit area on the wall of the container.
The aforementioned collisions between the molecules and the walls are perfectly elastic
in nature. This means that they do not lose kinetic energy and the energy before and after
the collision is same.
The average kinetic energy of the gas particles changes with temperature i.e. the higher
the temperature, the higher the average kinetic energy of the gas.
The molecules do not exert any force of attraction or repulsion on one another except
during collisions.
BOYLE’S LAW- Boyle’s law states that the pressure of a given mass of an ideal gas is
inversely proportional to its volume, at a constant temperature.
This means that on increasing pressure, volume would decrease and vice versa.
P∝1/V,
P=k/V,
PV=k (where k is a constant, P=pressure, V=volume)
, P1V1=P2V2=P3V3=...P∞V∞=k
The PV graph obtained is a rectangular hyperbola. This implies that the product of pressure and
volume (for all values of P and V) is constant throughout the process.
Note- Boyle’s law equation can be used only when values of mass of the gas (m) or number of
moles (n= m/M) and temperature are fixed.
(n= number of moles, m=mass taken and M= molecular mass)
CHARLES’S LAW- The law states that the volume of a given mass of an ideal gas is
directly proportional to its absolute temperature, at a constant pressure.
This means that there would be an increase in temperature if we increase the volume and vice
versa.
V∝T,
V= kT, (where k is a constant, V= volume, T= absolute temperature)
V/T= k or,
