Unit 3: Gases

What are Gases in Chemistry?

The “Gases” unit in Chemistry explores the properties and behavior of gaseous substances. This unit covers the fundamental concepts related to gases, including their physical properties, the laws governing their behavior, and their role in chemical reactions. Understanding gases is crucial for grasping various chemical phenomena and applications, from industrial processes to natural atmospheric conditions.

Key Topics in Gases:

• Properties of Gases: Examining the characteristics of gases, including their expansion, compression, and low density.
• Gas Laws: Understanding the fundamental laws that describe the behavior of gases, such as Boyle’s Law, Charles’s Law, and Avogadro’s Law.
• Ideal Gas Law: Exploring the relationship between pressure, volume, temperature, and the number of moles of a gas using the ideal gas law equation (PV=nRT).
• Real Gases: Investigating the deviations from ideal behavior and understanding the factors that affect real gases, such as intermolecular forces and molecular size.

Benefits of Studying Gases:

• Fundamental Knowledge: Provides essential insights into the behavior of gases, which is crucial for understanding broader chemical principles and processes.
• Practical Applications: Helps in applying gas laws to real-world scenarios, such as predicting the behavior of gases in different conditions and industrial processes.
• Scientific Understanding: Enhances comprehension of how gases interact with other substances and their role in various chemical reactions and environmental phenomena.

Mastering the “Gases” unit is vital for building a strong foundation in Chemistry, as it provides key insights into the behavior of gaseous substances and their impact on chemical and physical processes. This knowledge is essential for both academic success and practical applications in science and industry.

1. Pressure remaining constant, at which temperature the volume of a gas will become twice of what it is at 0^oC

a. 546oC
b. 200oC
c. 546K
d. 273K

2. Number of molecules in one dm3 of water is close to

a. 6.022*10²³/22.4
b. 12.04*10²³/22.4
c. 18*10²³/22.4
d. 55.6 * 6.022*10²³

3. Which of the following will have the same number of molecules at STP?

a. 280cm3 of CO2 and 280cm3 of N2O
b. 11.2dm3 of O2 and 32g of O2
c. 44g of N2 and 11.2 dm3 of CO
d. 28g of N2 and 5.6 dm3 of oxygen

4. If absolute temperature of a gas is doubled and pressure is reduced to one half, the volume of the gas will be

a. remain unchanged
b. increases four times
c. reduce to 1/4
d. doubled

5. How should the conditions be changed to prevent the volume of a given gas from expanding when its mass is increased

a. temperature is lowered and pressure is increased
b. temperature is increased and pressure is lowered
c. temperature is lowered and pressure is lowered
d. temperature is increased and pressure is increased

6. The molar volume of CO2 is maximum at

a. STP, 127^oC and 1atm
b. 127^oC and 1atm
c. 0^oC and 2atm
d. 237^oC and 2atm

7. The order of the rate of diffusion of gases NH3,SO2,Cl2 and CO2 is

a. NH3>SO2>Cl2>CO2
b. NH3>CO2>SO2>Cl2
c. Cl2>SO2>CO2>NH3
d. NH3>CO2>Cl2>SO2

8. Equal masses of methane and oxygen are mixed in an empty container at 25oC. The fraction of total pressure exerted by oxygen is

a. 1/3
b. 8/9
c. 1/9
d. 16/17

9. Gases deviate from ideal behaviour at high pressure.Which one of following is correct for non-ideality

a. At high pressure, gas molecules move in one direction only
b. At high pressure, the collision between gas molecules are increased manifold
c. At high pressure,, the volume of the gas become insignificant
d. At high pressure, the intermolecular attractions become significant.

10. The deviation of a gas from ideal behaviour is maximum at

a. -10^oC and 5atm
b. -10^oC and 2 atm
c. 100^oC and 5atm
d. 0^oC and 2atm