Content Curator
Behaviour of Gas Molecules refers to the way the gas molecules behave in a given circumstance and it is determined by the properties and laws that the molecules of the gas obey. The distribution of molecules in a gas differs dramatically from that of molecules in liquids and solids. The behaviour of gas molecules is governed by five characteristics and five gas laws. The properties of gases are simpler to comprehend than those of solids and liquids. This is due to the fact that molecules in a gas are apart from one another and their mutual interactions are minimal unless two molecules collide.
Read Also: Pressure of an Ideal Gas
Key Terms: Gas Molecules, Kinetic Theory of Gases, Gas, Kinetic Energy, Temperature, Pressure, Mass, Volume
Kinetic Theory of Gases
[Click Here for Sample Questions]
The kinetic theory of gases is typically used to explain the behaviour of gas molecules. At the macroscopic level, it is mainly the study of gas molecules. The five postulates of the kinetic theory of gases are as follows:
- Gas is made up of a large number of molecules that are constantly moving randomly.
- Since the distance between gas molecules is usually greater than the size of the molecules, the volume of the molecules is negligible.
- Intermolecular interactions are negligible.
- Molecules collide with each other and the container's walls are always elastic.
- The temperature can affect the average kinetic energy of all the molecules.
Factors Affecting Behaviour of Gases
[Click Here for Sample Questions]
Factors affecting the behaviour of gases are as follows:
- Temperature (T): As the temperature rises, so does the pressure of the gas molecules.
- Volume (V): When a container's volume is reduced, the gas molecules have less room to travel about. As a result, they will strike the container's walls more frequently, increasing the pressure.
- Pressure (P): As the gas's pressure will increase at any given constant temperature, the volume of the gas will decrease.
- Quantity (n): Pressure rises as the quantity of gas molecules in a given volume container increases.
Also Read:
| Related Topics | |
|---|---|
| Gas Constant | Stefan Boltzmann constant |
| Properties of gases | Kinetic Theory |
Gas Laws
[Click Here for Sample Questions]
The gas laws are as follows:
Boyle’s Law
According to Boyle’s law, the volume of the gas is inversely proportional to the pressure at a constant temperature.
It is represented mathematically as:
P α 1/v
PV = constant
P1V1 = P2V2
Where, P = pressure of gas
V = volume of gas
Boyle’s Law
Charles Law
According to Charles’s law, the temperature is directly proportional to the volume of a gas with a fixed mass.
V α T
Where,
- T = temperature of gas
- V = volume of gas
Read More: Charles Law
Gay-Lussac’s Law
According to Gay-Lussac’s law, the pressure of a given mass of gas is directly proportional with the absolute temperature of the gas when the volume of the gas is constant.
It is represented mathematically as:
P1/T1 = P2/T2
Where,
- T1 = initial temperature
- P1 = initial pressure
- T2 = final temperature
- P2 = final pressure
Gay Lussac’s Law
Avogadro’s Law
According to Avogadro’s law, When the pressure and temperature of a gas remain constant, the number of moles and the gas's volume are proportional.
V α n
Or V/n = k
Where,
- V = volume of the gas
- n = number of moles
- k = proportionality constant
Read More: Ideal Gas Equation
Ideal Gas Law
According to Ideal gas law, the product of pressure and volume of one gram molecule of an ideal gas is equivalent to the product of a number of moles of the gas, universal gas constant and the absolute temperature.
PV = nRT = NkT
Where,
- P = pressure of gas
- V = volume of gas
- n = number of moles
- R = universal gas constant = 8.3145 J.mol-1.K-1
- T = temperature of gas
- k = proportionality constant
- N = Avogadro’s number, NA = 6.0221×1023
Ideal Gas Law
Read Also: Specific Heat Capacity of Water
Things to Remember
- The volume of the gas increases as the temperature increases due to the expansion of gas molecules.
- As the temperature decreases, the volume of the gas reduces as well due to the contraction of gas molecules.
- As the temperature rises, the pressure of the gas rises as well due to an expansion of gas molecules.
- As the temp decreases, the pressure of the gas decreases as well due to the contraction of gas molecules.
- The temperature of the gas must be very low or the pressure of the gas must be very high to transform gas into solid or liquid.
- When the quantity reduces, the pressure decreases, and when the quantity increases, the pressure increases.
- The volume and quantity of the gas should be reduced to decrease pressure.
- To increase pressure, the volume and amount of the gas must be increased.
Sample Questions
Ques. What happens to the pressure of a closed gaseous system when the temperature increases two-fold? (1 Mark)
Ans. From Gay-lussac’s law,
P1/T1 = P2/T2
According to the question,
T2 = 2 T1
Thus, P1/T1 = P2/2 × T1
P2 = 2P1
Therefore, the pressure becomes double.
Ques. A gas has a volume of 10 L at 0 degrees Celsius. What is the final temperature of the gas if its volume is increased to 29 L? Assume that the amount of the gas and its pressure does not change. (2 Marks)
Ans. Given,
Initial temperature T1 = 0?C = 273K
Initial Volume V1 =10L
Final Volume V2 = 29L
Applying Charles' Law,
V1/T1 =V2/T2
T2 =V2×T1/V1 =29×273/10=791.7
Therefore, the final temperature is 791.7 K
Ques. 2.0mol of an ideal gas are contained in a 3.0L container at a temperature of 25C. The gas exerts a pressure of 16atm on the container. If pressure is kept constant, what is the final volume of the gas if the temperature of the container is increased to 200C? (2 Marks)
Ans. Given,
T1 = 25°C = 298K
T2 = 200°C = 473K
V1 = 3L
V1/T1 = V2/T2
3/298 = V/573
V = 4.8L
Ques. An ideal gas exerts a pressure of 3atm in a 3L container. The container is at a temperature of 298K. What will be the final pressure if the volume of the container changes to 2L? (2 Marks)
Ans. Given,
P1 = 3 atm
V1= 3L
V2 = 2L
Applying Boyles’s law,
P1 V1 = P2 V2
3 × 3 = P × 2
P = 4.5 atm
Ques. 50g of nitrogen gas are contained in a 3.0L container. The gas exerts a pressure of 3atm on the container. If pressure is kept constant, what is the final molar amount of gas present in the container if gas is added until the volume has increased to 5.0L? (3 Marks)
Ans. Given,
V1 = 3L
V2 = 5L
Since nitrogen is diatomic,
n1 = 50/28 = 1.79mol
Applying Avogadro’s law,
n1/V1 = n2/V2
1.79/3 = n/5
n = 3.0 mol
Ques. A 4.5L container of gas has a pressure of 3.0atm at a temperature of 100oC. The container is expanded to 6L, and the temperature is increased to 200oC. What is the final pressure of the container? (3 Marks)
Ans. Given,
T1 = 100+273 = 373K
T2 = 200+272 + 473K
P1 = 3atm
V1 = 4.5L
V2 = 6L
P1V1/T1 = P2V2/T2
3 × 4.5/373 = P × 6/473
P = 2.9atm
Ques. A sample of chlorine gas fills a vessel at a temperature of 37oC. The vessel has a volume of 3L and it experiences a pressure of 3atm. What is the mass of the chlorine gas in the vessel? (5 Marks)
Ans. Given,
T = 310K
P = 3atm
V = 3L
R = 0.08206
As we know,
PV = nRT
And n = mass/molar mass = m/M
PV = mRT/M
m = PVM/RT
As we know chlorine is diatomic, therefore its molecular mass would be double the atomic mass.
M = 2 × 35.5
M = 7 g/mol
Putting the values,
m = 3 × 3 × 71/ 0.08206 × 310
m = 25.1g
Ques. At STP, an unknown gas has a density of 1.7gL. Based on this information provided and the periodic table, what is the gas in the container? (3 Marks)
Ans. From ideal gas law,
PV = nRT
We know that Density has units of mass over volume, and moles are equal to mass divided by molar mass.
So, PV = mRT/MM
m/V = PMM/RT
STP means that pressure is 1 atm, temperature is 273K, Solving for molar mass:
1.7 = 1 × MM/ 0.08206 × 273
MM = 38.1 g/mol
Fluorine gas has a molar mass of 38g/mol. Thus, the unknown gas is fluorine.
Check-Out:
Comments