250+ TOP MCQs on Vaporization and Energy Balances for Open, Unsteady-State Systems and Answers

Chemical Engineering Questions & Answers for entrance exams on “Vaporization and Energy Balances for Open, Unsteady-State Systems”.

1. For an open unsteady state system, 5 J of heat was supplied and 10 J of work was done on the system, what is the value of a change in enthalpy?
a) 5 J
b) 10 J
c) 15 J
d) 20 J

Answer: c
Clarification: ∆H = 5 + 10 = 15 J.

2. For an open unsteady state system, 10 J of heat was supplied and 10 J of work was done by the system, what is the value of a change in enthalpy?
a) 0
b) 10 J
c) 20 J
d) – 20 J

Answer: a
Clarification: ∆H = 10 – 10 = 0.

3. For an open unsteady state system, 5 J of heat was supplied and 10 J of work was done by the system, what is the value of a change in enthalpy?
a) – 5 J
b) 5 J
c) 10 J
d) 15 J

Answer: a
Clarification: ∆H = 5 – 10 = – 5 J.

4. For an open unsteady state system, 15 J of heat was taken off and 10 J of work was done by the system, what is the value of a change in enthalpy?
a) – 5 J
b) 5 J
c) 25 J
d) – 25 J

Answer: a
Clarification: ∆H = 10 – 15 = – 5 J.

5. For an open unsteady state system, 15 J of heat was supplied and -5 J of work was done on the system, what is the value of a change in enthalpy?
a) 10 J
b) – 15 J
c) 20 J
d) – 25 J

Answer: a
Clarification: ∆H = 15 – 5 = 10 J.

6. Which of the following represents vaporization?
a) Change of vapor to liquid
b) Change of vapor to solid
c) Change of solid to vapor
d) Change of liquid to vapor

Answer: d
Clarification: Vaporization is the reverse of condensation which is a change of liquid to vapor.

7. Which of the following can definitely cause vaporization?
a) Heating a liquid
b) Heating a liquid at constant pressure
c) Cooling a liquid
d) Cooling a liquid at constant volume

Answer: b
Clarification: Vaporization is caused by heating a liquid at constant pressure.

8. Vaporization starts at which point?
a) Dew point
b) Bubble point
c) Triple point
d) None of the mentioned

Answer: b
Clarification: Bubble point is the point at which liquid starts evaporating which is the point at which vaporization starts.

9. What is the vaporization temperature of water at standard conditions?
a) 100^oF
b) 212^oF
c) 345^oF
d) 432^oF

Answer: b
Clarification: Vaporization temperature of water at standard conditions is 100^oC = 212^oF.

10. What is the point of saturation of a condensable vapor?
a) Bubble point
b) Boiling point
c) Triple point
d) Dew point

Answer: d
Clarification: Condensation of gas starts at its dew point.