Basic Chemical Engineering Multiple Choice Questions & Answers (MCQs) on “Phase Transitions”.
1. Which of the following is heat required in phase transitions?
a) Latent Heat
b) Sensible Heat
c) Depends on type of phase transition
d) None of the mentioned
Answer: a
Clarification: Heat required for phase transitions is latent heat.
2. What is the latent heat for melting?
a) Heat of vaporization
b) Heat of fusion
c) Heat of Solidification
d) None of the mentioned
Answer: b
Clarification: Latent heat for melting is called heat of vaporization.
3. 15 J is the latent heat for melting of ice, what is the heat of transition from 0oC ice to 15oC water if heat of transition from 0oC water to 15oC water is 10 J?
a) 10 J
b) 15 J
c) 25 J
d) 40 J
Answer: c
Clarification: H = 15 + 10 = 25 J.
4. 5 J is the latent heat for melting of ice, what is the heat of transition from 0oC ice to 15oC water if heat of transition from 0oC water to 15oC water is 12 J?
a) 5 J
b) 12 J
c) 15 J
d) 17 J
Answer: d
Clarification: H = 5 + 12 = 17 J.
5. 150 J is the latent heat for vaporization of water, what is the heat of transition from 50oC water to 100oC steam if heat of transition from 50oC water to 100oC water is 12 J?
a) 12 J
b) 152 J
c) 162 J
d) 200 J
Answer: c
Clarification: H = 150 + 12 = 162 J.
6. Heat of fusion of benzene is 10 J at 0oC, if Cp of solid benzene is 10 J/oC, and that of liquid benzene is 5 J/oC what is the enthalpy change of benzene from – 10oC to 10oC?
a) 160 J
b) 200 J
c) 240 J
d) 300 J
Answer: a
Clarification: ∆H = -10∫010.dT + 10 + 0∫105.dT = 10*10 + 10 + 5*10 = 160 J.
7. If Cp of liquid water is 10 J/oC, what is the enthalpy change of water at standard conditions from – 10oC to 0oC?
a) 10 J
b) 50 J
c) 100 J
d) Cannot be determined
Answer: d
Clarification: Since the phase of water from – 10oC to 0oC is solid ice, but Cp of liquid water is given, so it cannot be determined.
8. If Cp of liquid benzene is 15 J/oC, what is the enthalpy change of water from 5oC to 10oC?
a) 15 J
b) 50 J
c) 75 J
d) 90 J
Answer: c
Clarification: ∆H = 5∫1015.dT = 75 J.
9. If Cp of solid benzene is 10 J/oC, what is the enthalpy change of water from 5oC to 75oC?
a) 5 J
b) 10 J
c) 75 J
d) 700 J
Answer: d
Clarification: ∆H = 5∫7510.dT = 700 J.
10. If Cp of steam is 105 J/oC, what is the enthalpy change of steam from 106oC to 118oC?
a) 420 J
b) 640 J
c) 890 J
d) 1260 J
Answer: d
Clarification: ∆H = 106∫118105.dT = 1260 J.
11. If Cp of water is (23 + T) J/oC, what is the enthalpy change of water from 3oC to 5oC?
a) 54 J
b) 96 J
c) 140 J
d) 196 J
Answer: a
Clarification: ∆H = 3∫5(23 + T).dT = 23(5 – 3) + (52 – 32)/2 = 54 J.
12. If Cp of water is 45T J/oC, what is the enthalpy change of water from 6oC to 8oC?
a) 7 J
b) 14 J
c) 28 J
d) 56 J
Answer: b
Clarification: ∆H = 6∫8T.dT = (82 – 62)/2 = 14 J.
13. Cp of ice is 25 J/oC and that of water is 30 J/oC, what is the enthalpy change of water from – 10oC to 35oC at standard conditions, if the later heat of fusion of water is 110 J?
a) 250 J
b) 595 J
c) 960 J
d) 1410 J
Answer: d
Clarification: ∆H = -10∫025.dT + 110 + 0∫3530.dT = 25*10 + 110 + 35*30 = 1410 J.
14. Cp of ice is 10 J/oC and that of water is 15 J/oC, what is the enthalpy change of water from – 15oC to 0oC at standard conditions, if the later heat of fusion of water is 110 J?
a) 150 J
b) 315 J
c) 485 J
d) 560 J
Answer: c
Clarification: ∆H = -15∫025.dT + 110 = 25*15 + 110 = 485 J.
15. Cp of water is 10 J/oC and that of steam is 15 J/oC, what is the enthalpy change of water from 75oC to 110oC at standard conditions, if the later heat of vaporization of water is 245 J?
a) 395 J
b) 645 J
c) 840 J
d) 999 J
Answer: b
Clarification: ∆H = 75∫10010.dT + 245 + 100∫11015.dT = 25*10 + 245 + 15*10 = 645 J.