Gases do not have definite shape or volume. In case of gases The distance between the molecules is very large. The force of attraction between the molecules is negligible. Molecules of gas move in straight lines
And occupy the whole space available in a container. Impact of gas molecules with high velocity on the walls of the container causes the pressure to be exerted on the walls.
On an average the same number of molecules strike a given area on the wall in unit time, hence the pressure is equal, uniform and exert in all directions.
Gases have low density. Gas molecules have the tendency to mix with other gases.
Temperature of a gas is the average kinetic energy possessed by a molecule. Kinetic energy increases with increase in temperature.
Pressure of a gas is the average force exerted by the bombardment of gas molecules on the walls of a container per unit area of the container.
Volume of the gas Practically all gases liquefy or solidify before reaching this temperature. is the space occupied by the fixed mass of the gas.
By keeping the temperature of a fixed mass of a gas constant, if the pressure is increased the volume correspondingly decreases.
By keeping the temperature of a fixed mass of a gas constant if the pressure is increased the volume decreases.
Behaviour of real gases: deviation from ideal gas behaviour:The above concept was generalized by Robert Boyle
Boyle's law
temperature remaining constant the volume of a given mass of a gas is inversely proportional to its pressure.
V is inversely proportional to 1/P
V = K X 1/P
Charles' law
Pressure remaining constant, the volume of a given mass of a dry gas increases or decreases by 1/273 of its original volume at 0degree Celsius for each degree centigrade rise or fall in temperature.
Consider a known mass of a gas of volume 273 cc. at temperature 0degree Celsius
At -1degree Celsius the volume will be 272cc.At -2degree Celsius the volume will be 271cc
At -273degree Celsius the volume will be zero.
The temperature -273degree Celsius is called absolute zero.
Reduction of volume of a gas to 0cc. is theoretical concept. practically all gases liquefy or solidify before reaching this temperature.
Absolute scale of temperature
The new temperature scale with its zero at -273degree Celsius and each degree equal to one degree on the Celsius scale is called Kelvin or absolute scale of temperature.
Based on the above scale Charles' states Pressure remaining constant the volume of a given mass of a gas is directly proportional to its absolute (Kelvin) temperature
V is proportional to T
Gas equation
According to Boyle's law at constant temperature
V Is proportional to 1/ P
Charles' law
V is proportional to T
On combining these two laws
V is proportional to T/P
V= K. T/P
On rearranging the above equation
PV/T = K
P1V1/ T1 = P2V2/T2
This is the required gas equation.
Behaviour of real gases: deviation from ideal gas behaviour:Some laws:-
Gaylussacs' Law
It states that when gases react they do so in volumes which bear a simple whole number ratio to one another and to the volumes of the products, if gaseous, provided the temperature and pressure of the reacting gases and their products remain constant.
Avogadro's Law
Equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules.
Graham's Law
The rate at which the gas molecules diffuse is inversely proportional to the square root of its density.
Dalton's Law of partial pressure
The pressure of a mixture of gases is the sum of the partial pressures of the individual components.
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