# Chemical Engineering Questions and Answers – Energy Balances for Closed, Unsteady-State Systems

This set of Chemical Engineering online quiz focuses on “Energy Balances for Closed, Unsteady-State Systems”.

1. 10 J of heat and 5 J of work are supplied to the system, what is the change in internal energy?
a) 5 J
b) 10 J
c) 15 J
d) 20 J

Explanation: ∆U = 5 + 10 = 15 J.

2. 15 J of heat is supplied to a system and system does 5 J of work, what is the change in internal energy?
a) 5 J
b) 10 J
c) 15 J
d) 20 J

Explanation: ∆U = 15 – 5 = 10 J.

3. 5 J of heat is taken out of the system and 20 J of work is done on the system, what is the change in internal energy of the system?
a) 5 J
b) 10 J
c) 15 J
d) 20 J

Explanation: ∆U = 20 – 5 = 15 J.

4. 10 J of heat is supplied and 3 J is taken out, if the change in internal energy of the system is 5 J, what is the work done on the system?
a) 2 J
b) – 2 J
c) 5 J
d) – 5 J

Explanation: 5 = 10 – 3 + W, => W = – 2 J.

5. 5 J of work is done by the system, if the change in internal energy of the system is 10 J, what is the heat supplied to the system?
a) – 5 J
b) 5 J
c) – 15 J
d) 15 J

Explanation: 10 = – 5 + Q, => Q = 15 J.
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6. 2 Kg of steam is enclosed in a container with internal energy = 5 J/Kg, then 5 J of heat is supplied to the system, what is the final internal energy?
a) 7.5 J/ Kg
b) 15 J/Kg
c) 22.5 J/Kg
d) 30 J/Kg

Explanation: 5 = 2(U – 5), => U = 7.5 J/Kg.

7. 5 Kg of steam is enclosed in a container with internal energy = 10 J/Kg, then 25 J of heat is supplied to the system, what is the final internal energy?
a) 5 J/Kg
b) 10 J/Kg
c) 15 J/Kg
d) 20 J/Kg

Explanation: 25 = 5(U – 10), => U = 15 J/Kg.

8. In a 2 stage process Q1 = 5 J, Q2 = 10 J, if the change in internal energy in first stage is 10 J and the total change in internal energy is 20 J, what is the work do done in second stage?
a) 0
b) 5 J
c) 10 J
d) – 5 J

Explanation: Change in internal energy in second stage = 20 – 10 =10 J, Work done in second stage = 10 – 10 = 0.

9. In a 3 stage process Q1 = 10 J, Q2= – 15 J, Q3 = 25 J, if ∆E1 = 15J and ∆E3 = 10 J, what is the work done in second stage, if the total ∆E is 30 J?
a) 5 J
b) 10 J
c) 15 J
d) 20 J

Explanation: ∆E2 = 5 J, => W2 = 5 + 15 = 20 J.

10. What is the heat transferred to 2 Kg and 5 m3 of a rigid system, with change in enthalpy 5 J/Kg?
a) 5 J
b) 10 J
c) 15 J
d) 20 J

Explanation: Since the system is rigid, ∆V = 0, => Q = ∆H = 5*2 = 10 J.

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