This set of Basic Chemical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Modeling and Predicting Vapor Pressure”.

1. What is the pressure of a gas at T = 227^{o}C, it is given that A = 5, B = 4 X 104 and C = 0 if T is in kelvin and p in mm Hg?

a) 0.024 mm Hg

b) 0.049 mm Hg

c) 0.075 mm Hg

d) 0.096 mm Hg

View answer

Explanation: ln p* = A – B/(C + T), => ln p = 5 – 4 X 10

^{3}/(273 +227) = -3, => p = 0.049 mm Hg.

2. A material’s mass is given by the equation, m = 32P^{0.02}/T^{0.5}, where T is in Kelvin, m is in Kg and P is in mm Hg, what is the mass of material at 127^{o}C, use A = 10, B = 6 X 10^{3} and C = 0?

a) 1.44 Kg

b) 1.69 Kg

c) 1.96 Kg

d) 2.25 Kg

View answer

Explanation: ln p* = A – B/(C + T) = 10 – 6 X 10

^{3}/(400) = -5, => p = 0.0067 mm Hg, => m = 32*(0.0067)

^{0.02}/400

^{0.5}= 1.44 Kg.

3. If the pressure of a gas at 27^{o}C is 15 mm Hg, what will be its pressure at 127^{o}C, use B = 5 X 10^{3}, C = 0, T is in kelvin and P is in mm Hg?

a) 579 mm Hg

b) 775 mm Hg

c) 961 mm Hg

d) 999 mm Hg

View answer

Explanation: ln P

_{1}/P

_{2}= B (1/T

_{2}– 1/T

_{1}), => ln 15/P

_{2}= 5 X 10

^{3}(1/400 – 1/300), P

_{2}= 961 mm Hg.

4. Pressure of a gas at 127^{o}C is 10 mm Hg and the pressure at 527^{o}C is 20 Pa, what is the value of B?

a) 225.1

b) 365.5

c) 499.2

d) 554.5

View answer

Explanation: ln 10/20 = B (1/800 – 1/400), => B = 554.5.

5. Pressure of a gas at temperature T is P, What is the pressure of the gas at 2T, use B = 1?

a) Pe^{1/T}

b) Pe^{1/2T}

c) Pe^{1/3T}

d) Pe^{1/4T}

View answer

Explanation: ln P/P

_{2}= 1*(1/2T – 1/T), => P

_{2}= Pe

^{1/2T}.

6. What is the pressure of CO_{2} at 325 K, if it is given that pressure at 330 K is 6 Pa, and pressure at 320 K is 4 Pa?

a) 4.5 Pa

b) 5 Pa

c) 5.5 Pa

d) 6 Pa

View answer

Explanation: Using linear interpolation, P

_{325K}= 4 + (325 – 320)*(6 – 4)/(330 – 320) = 4 + 5*2/10 = 5 Pa.

7. Temperature of SO_{2} at 5 Pa is 395 K and at 10 Pa temperature is 420 K, what is the temperature at 6 Pa?

a) 400 K

b) 405 K

c) 410 K

d) 415 K

View answer

Explanation: Using linear interpolation, T

_{6Pa}= 395 + (6 – 5)*(420 – 395)/(10 – 5) = 395 + 5 = 400 K.

8. At which of the following values of pressure a solid melts first?

a) 5 atm

b) 720 mm Hg

c) 500 KPa

d) 40 Torr

View answer

Explanation: A solid melts first at the highest pressure which is 5 atm.

9. A liquid evaporates first at which of the following conditions?

a) High attraction forces

b) Low attraction forces

c) Low vapor pressure

d) High boiling point

View answer

Explanation: A liquid evaporates first at low attraction forces.

10. At triple point, vapor pressure of ice is given by ln p* = 18 – 2560/T, and vapor pressure of water is given by ln p* = 28 – 5120/T, what is the temperature at triple point?

a) 225 K

b) 256 K

c) 320 K

d) 400 K

View answer

Explanation: At triple point pressure and temperature of all the phases becomes same, => 18 – 2560/T = 28 – 5120/T, => 10 = 2560/T, => T = 256 K.

11. The vapor pressure of liquid benzene is given by ln p* = 15 – 1280/T, and that of vapor benzene is given by ln p* = 23 – 2560/T, what is the boiling point of benzene?

a) 160 K

b) 200 K

c) 240 K

d) 300 K

View answer

Explanation: At boiling point pressure and temperature of both the phases will be same, => 23 – 2560/T = 15 – 1280/T, => 8 = 1280/T, => T = 160K.

12. The vapor pressure of a compound in a liquid phase is given by ln p* = 21 – 2800/T, and in solid phase it is given by ln p* = 28 – 3500/T, what is the sublimation temperature of the compound?

a) 100 K

b) 120 K

c) 150 K

d) 200 K

View answer

Explanation: At sublimation point pressure and temperature of both the phases will be same, => 21 – 2800/T = 28 – 3500/T, => T = 100 K.

13. For CaOCl_{2}, the rate of evaporation is given by W = 325p^{0.5}M/T^{1.5} g/liter, where T is in K, p in mm Hg, and M is molecular weight, if its pressure is given by ln p* = 25 – 2700/T, what is the evaporation rate at T = 150 K?

a) 256 g/liter

b) 499 g/liter

c) 571 g/liter

d) 744 g/liter

View answer

Explanation: ln p* = 25 – 2700/150 = 7, => p = 1096.6 mm Hg, => W = 325(1096.6)

^{0.5}*127/150

^{1.5}= 744 g/liter.

14. What is the vapor pressure of ammonia at 305 K, if it is given that the vapor pressure of ammonia at 315 K is 5 mm Hg and at 325 K it is 6 mm Hg?

a) 1 mm Hg

b) 2 mm Hg

c) 3 mm Hg

d) 4 mm Hg

View answer

Explanation: p305K = 5 – (315 – 305)*(6 – 5)/(325 – 315) = 5 – 1 = 4 mm Hg.

15. The pressure of a compound at 200 K is 10 mm Hg and at 400 K it is 50 mm Hg, what is the pressure at T = 250 K?

a) 18.1 mm Hg

b) 24.2 mm Hg

c) 36.3 mm Hg

d) 48.4 mm Hg

View answer

Explanation: Let the pressure of the compound is given by ln p* = a + b/T, => ln 10 = a + b/200, ln 50 = a + b/400, => ln 5 = -b/400, => b = -643.7, => a = 5.5, => At T = 250 K, ln p* = 5.5 – 643.7/250 = 2.9, p = 18.1 mm Hg.

**Sanfoundry Global Education & Learning Series – Basic Chemical Engineering.**

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