“If we assume that the last breath of, say, Julius Caesar has by now become thoroughly scattered through the atmosphere, then the chances are that each of us inhales one molecule of it with every breath we take.”
― James Jeans, An Introduction To The Kinetic Theory Of Gases
Kinetic Molecular Theory of Gases - Law explained:
This law defines the behaviour of gases and it consist of various assumptions are-
- This state of matter contains a large number of gaseous particles that can move in any direction.
- These particles move in a straight line that collide with one another or with the walls and total no. of collisions are elastic in nature
- These particles are much smaller than the distance between particles.
- There is no force of attraction between gas particles
- The average kinetic energy of molecules depends on the temperature
2. Derived Average Kinetic Energy-
It is defined for the energy produced from the motion of the particles which is proportional to the absolute temperature of the gas.
It depends on quantity like Temperature , mass of a gas molecule . average velocity and other certain conditions.
3. Relationship Between P and N-
P – pressure as force exerted on the walls of the container during collision
N – No. of the particles
When the number of particles increases, The frequency of collisions with the walls also increases.
Hence, pressure increases with increase in gas molecules.
3. Ideal Gas-
The kinetic molecular theory of gas followed by the laws are defined for the ideal gas , whose molecules have no interionic interactions.
PV=nRT , R is a gas constant
4. Laws Explained by Kinetic Molecular Theory of Gas-
CHARLES LAW (V,T)
Keeping constant the pressure of a gas , the volume becomes proportional to the temperature of the gas. This is based on the fact that as mass of the particles is constant , this thereby increases and balances the pressure applied by the gas particles on the surface of the wall . Hence , the volume of gas becomes larger as temperature increases.
5. Boyle Law (P=1/v)-
Keeping temperature constant, The pressure applied by the gas molecules is inversely proportional to the volume.
I based on the constant Temperature conditions , which results in the same kinetic energy. Hence during collisions of high number , pressure of the gas also increases , but the volume decreases because now frequency of collision is high.
6. Avogadro Hypothesis (V-N)-
Keeping temperature and pressure, The volume of the gas is proportional to the number of gas molecules.
7. Dalton Law of Partial Pressures-
This law states that the total pressure of a mixture of gases must be the sum of partial pressure of each gas present in the mixture. These gases must be non-reactive with each other.
8. Gay-Lussac Law (P-T)-
By joseph Louis GAY-LUSSAC
It is based on the assumption that keeping constant the volume and temperature of the gas.
The pressure applied is proportional to the temperature.
9. Absolute Zero-
The 0K or -273.15°C is called absolute zero temperature. It can be represented in the V/T curve after extra plotting of the curve to zero. At this temperature, all molecular motions would cease.
10. Real Gases –
The behaviour of real gases behaves differently as of ideal gases and deviates the laws because-
Real gas molecules both attract and repel due to interionic force of interaction.
True gas molecules have an infinite volume
But at high temperature and low pressure all the real gases behave ideally.
Questions:
Q 1. In a closed vessel , If total pressure is 6Atm by the mixtures of gases consisting of Hydrogen , oxygen and nitrogen with the partial pressure of 3atm , 2.5 . Then what will be the partial pressure exerted by nitrogen gas ?
Solution:
Total pressure = 6 atm
Applying DALTON LAW
Total pressure = PH2 + PO2 + PN2
6= 3+ 2.5 + PN2
0.5 atm = PN2
Answer: PN2 = 0.5 atm
Q 2. Which law obeys only at constant volume conditions?
Boyle law
Charles law
Gay lussac law
Dalton theory of partial pressure
Ans: Boyle law
Q3 Which of the conditions are necessarily for Real gas to behave ideally?
Constant Temperature and pressure
High pressure and low temperature
Low pressure and high temperature
Low pressure and low temperature
Ans: Low pressure and high temperature
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Frequently Asked Questions
How does the kinetic molecular theory apply to gases?
Gas laws (Boyle’s law, Avogadro’s law, Dalton’s law and Charles’s law) can be explained using kinetic molecular theory. The increase in pressure of a gas on decreasing the surface area of a container is due to increased molecular strikes per unit of time. Volume must be increased to keep the pressure constant. Increase in temperature of gas results in increased kinetic energy of the molecules. The gas expands to keep the pressure constant.
What is most important about kinetic molecular theory?
Kinetic molecular theory explains different properties of gases and different gas laws. Boyle’s law can be explained by kinetic molecular theory. The pressure of a gas depends on the number of times the molecules strike the surface of the container. On compressing the gas to a smaller volume, the surface area is smaller but the number of molecules is the same. In other words the number of molecules striking against the surface is now more. Hence, pressure will increase. To keep the pressure constant, the volume must increase, which explains Avogadro's law.
Charles’s law can also be explained using kinetic molecular theory. According to kinetic molecular theory the increase in temperature increases average kinetic energy of the molecules. If the molecules are moving with more speed but the pressure remains the same, then the molecules must stay apart, so that the increase in the rate of molecular collisions with the surface of the container is compensated for by the increased surface area.
What are the 3 main points of the kinetic molecular theory of gases?
- The molecules of gas are constantly moving randomly and the combined volume of these molecules is negligible.
- The molecules exert no force on each other, the collisions between them are completely elastic.
- The average kinetic energy of the molecules is directly proportional to the temperature.
What is the concept of kinetic theory of gases?
- The kinetic theory of gases is based on five postulates-
- The molecules of gas are in constant random motion
- The combined volume of the gas molecules is negligible compared to the volume of gas.
- The molecules exert no force on each other.
- The collision between the molecules is completely elastic.
- The average kinetic energy of the molecules is directly proportional to the temperature.
Why is kinetic molecular theory important to humans?
Kinetic molecular theory is very useful in understanding both microscopic and macroscopic properties of gases. All gas laws including Boyle’s law, Avogadro's law, Charles’s law can be explained using kinetic molecular theory of gases.
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