Ideal gas and Laws
Ideal gas :- it is that gas which obeys the gas laws and obey ideal gas equation.
Characteristics of ideal gas :-
- The size of the molecule of a gas is zero.
- There is no force of attraction or repulsion among the molecules of the gas.
- There is no ideal gas; however at low press use & high temperature, some real gas like H2, O2, He etc obeys the ideal gas behavior.
- At low pressure & high gas obeys the relation :-
PV = KT
& K is a constant i.e.
N number of molecules of the gas KB botzmann constant = 1.38 x 10-23 J/K So
For two gases
So if P,V,T are same then N is same for all the gases.
Avagadro’s Hypothesis :- equal volume of all gases contains equal number of molecules under same temperature and pressure.
NA => Avagadro’s number = 6.02 x 1023
Use of Avagardro’s number
- To calculate number of atom :- No of atoms in m gram =
- To calculate number of molecules :- Number of molecules =
- To calculate number of molecules in a given Volume of gas :- =
- R = 8.314 J mol-1 or R = 0.0821 atm L mol-1 K-1
( at constant temp ) or PV = constant
Charle’s law :- for a given mass of a gas; volume of a gas is directly proportional to temperature at constant pressure.
P α V ( at constant temperature.)
Dalton’s law of partial pressure :- according to this law when two or more than two non-reacting gases combine with each other than the total pressure is given by the sum of the partial pressure of the gases.
P = P1 + P2 + P3.
Postulates of KINETIC THEORY OF GAS :-
- Gases are made up of large number of particles called molecules which are vey small in size.
- All gas molecules have same mass and they are in random motion.
- Volume occupied by the gas molecules is negligible as compared to total volume occupied by the gas.
- There is no inter molecular force of attraction between the gas molecules.
- There is a collision between the gas molecules & the collision is elastic.
- Pressure exerted by a gas is due to bombardment of gas molecules on the wall of container.
- The kinetic energy of gas molecules is directly proportional to the temperature.