PIEAS Entry Test Chemistry Gases — Set 2

1. Question 1

   Q1. A gas occupies 2 L at 1 atm. What is its volume at 4 atm, assuming constant temperature?

   • A) 0.5 L
   • B) 1 L
   • C) 2 L
   • D) 4 L

   Answer: 0.5 L

   Explanation: Using Boyle's Law: P1V1 = P2V2, we get 1*2 = 4*V2, so V2 = 0.5 L.

2. Question 2

   Q2. The volume of 1 mole of an ideal gas at STP is:

   • A) 11.2 L
   • B) 22.4 L
   • C) 33.6 L
   • D) 44.8 L

   Answer: 22.4 L

   Explanation: At STP, 1 mole of an ideal gas occupies 22.4 L, as per Avogadro's hypothesis.

3. Question 3

   Q3. The ratio of specific heats (Cp / Cv) for a monatomic gas is:

   • A) 1.33
   • B) 1.4
   • C) 1.67
   • D) 1.29

   Answer: 1.67

   Explanation: For monatomic gases, Cp / Cv = (5/2)R / (3/2)R = 5/3 = 1.67.

4. Question 4

   Q4. The pressure exerted by a gas is due to:

   • A) Collisions with container walls
   • B) Intermolecular forces
   • C) Gravity
   • D) Viscosity

   Answer: Collisions with container walls

   Explanation: The kinetic molecular theory states that gas pressure is due to collisions with container walls.

5. Question 5

   Q5. The partial pressure of a gas in a mixture is proportional to its:

   • A) Mole fraction
   • B) Mass fraction
   • C) Volume fraction
   • D) Density

   Answer: Mole fraction

   Explanation: Dalton's Law states that partial pressure = mole fraction * total pressure.

6. Question 6

   Q6. A gas deviates from ideal behavior at:

   • A) High temperature and low pressure
   • B) Low temperature and high pressure
   • C) High temperature and high pressure
   • D) Low temperature and low pressure

   Answer: Low temperature and high pressure

   Explanation: At low T and high P, intermolecular forces become significant, causing deviation from ideal behavior.

7. Question 7

   Q7. The van der Waals equation for real gases corrects for:

   • A) Only intermolecular forces
   • B) Only molecular volume
   • C) Both intermolecular forces and molecular volume
   • D) Neither

   Answer: Both intermolecular forces and molecular volume

   Explanation: The van der Waals equation includes 'a' for intermolecular forces and 'b' for molecular volume.

8. Question 8

   Q8. The critical temperature of a gas is the temperature above which it:

   • A) Cannot be liquefied
   • B) Can be liquefied
   • C) Behaves ideally
   • D) Diffuses rapidly

   Answer: Cannot be liquefied

   Explanation: Above the critical temperature, a gas cannot be liquefied, no matter the pressure.

9. Question 9

   Q9. The ratio of the rates of diffusion of two gases is 2 : 1. The ratio of their molecular masses is:

   • A) 1 : 4
   • B) 4 : 1
   • C) 1 : 2
   • D) 2 : 1

   Answer: 1 : 4

   Explanation: According to Graham's Law, the ratio of rates of diffusion ∝ √(M2/M1), so M1/M2 = (1/2)² = 1/4.

10. Question 10

    Q10. The density of a gas is directly proportional to its:

    • A) Molecular mass
    • B) Pressure
    • C) Temperature
    • D) Both A and B

    Answer: Both A and B

    Explanation: Density = PM/RT, so it is directly proportional to both P and M.

11. Question 11

    Q11. The behavior of real gases is closer to ideal gases at:

    • A) High pressure and low temperature
    • B) Low pressure and high temperature
    • C) High pressure and high temperature
    • D) Low pressure and low temperature

    Answer: Low pressure and high temperature

    Explanation: At low P and high T, real gases behave more ideally due to negligible intermolecular forces.

12. Question 12

    Q12. The unit of the gas constant R is:

    • A) J/mol
    • B) J/(mol*K)
    • C) L*atm/(mol*K)
    • D) Both B and C

    Answer: Both B and C

    Explanation: R can be expressed in different units, including J/(mol*K) and L*atm/(mol*K).

13. Question 13

    Q13. The ratio of rates of diffusion of gases A and B is 1 : 2. If the ratio of their masses present in the mixture is 2 : 3, what is the ratio of their mole fractions?

    • A) 1 : 4
    • B) 4 : 1
    • C) 2 : 3
    • D) 3 : 2

    Answer: 1 : 4

    Explanation: Use Graham's law of diffusion: r1/r2 = √(M2/M1). Then, relate mole fractions to mass ratio and molar masses.

14. Question 14

    Q14. A gas occupies 1 L at 1 atm. What is its volume at 2 atm, if temperature remains constant?

    • A) 0.5 L
    • B) 1 L
    • C) 2 L
    • D) 4 L

    Answer: 0.5 L

    Explanation: Apply Boyle's law: P1V1 = P2V2, so V2 = P1V1 / P2 = 1 * 1 / 2 = 0.5 L.

15. Question 15

    Q15. At what temperature will the volume of a gas be doubled if the initial temperature is 27°C?

    • A) 327°C
    • B) 54°C
    • C) 600°C
    • D) 300°C

    Answer: 327°C

    Explanation: Use Charles' law: V1 / T1 = V2 / T2. For V2 = 2V1, T2 = 2T1 = 2 * (27 + 273) = 600 K, or 327°C.

16. Question 16

    Q16. The density of a gas at 1 atm and 0°C is 1.5 g/L. What is its molecular weight?

    • A) 33.6
    • B) 22.4
    • C) 44.8
    • D) 67.2

    Answer: 33.6

    Explanation: Use the ideal gas law to find M: d = PM / RT, so M = dRT / P = 1.5 * 0.0821 * 273 / 1 = 33.6 g/mol.

17. Question 17

    Q17. A mixture of N2 and O2 has a total pressure of 1 atm. If the partial pressure of N2 is 0.8 atm, what is the mole fraction of O2?

    • A) 0.2
    • B) 0.8
    • C) 0.5
    • D) 0.1

    Answer: 0.2

    Explanation: Use Dalton's law of partial pressures: P_total = P_N2 + P_O2. So, P_O2 = 1 - 0.8 = 0.2 atm, and X_O2 = P_O2 / P_total = 0.2.

18. Question 18

    Q18. For a given mass of an ideal gas, the volume is directly proportional to

    • A) pressure
    • B) temperature in Celsius
    • C) temperature in Kelvin
    • D) 1 / pressure

    Answer: temperature in Kelvin

    Explanation: Charles' law states that V ∝ T (in Kelvin) at constant P.

19. Question 19

    Q19. The average kinetic energy of the molecules of a gas is proportional to

    • A) T
    • B) T²
    • C) √T
    • D) 1 / T

    Answer: T

    Explanation: The average kinetic energy is directly proportional to the temperature in Kelvin.

20. Question 20

    Q20. The root mean square speed of the molecules of a gas is

    • A) √(3RT/M)
    • B) √(2RT/M)
    • C) √(RT/M)
    • D) √(8RT/πM)

    Answer: √(3RT/M)

    Explanation: The RMS speed is given by √(3RT/M), where M is the molar mass.