This set of Chemical Engineering Problems focuses on “Application of the Energy Balance to Open Systems”.
1. What is the energy balance to open system?
a) Energy in the system is constant
b) Matter in the system is constant
c) Matter is constant energy is variable
d) Both matter and energy are variable
View answer
Explanation: Both matter and energy are variable in an open system.
2. 5 Kg of water is pumped to a height of 5 m, the enthalpy is changed by 10 J/Kg, and work done by the motor is 100 J/Kg, assuming system is insulated what is the change in internal energy of water?
a) 50 J
b) 100 J
c) 150 J
d) 200 J
View answer
Explanation: ∆U = Q + W – m (∆H + ∆PE + ∆KE), => ∆U = 0 + 100*5 – 5 (10 + 10*5) = 500 – 50 – 250 = 200 J.
3. 10 Kg of water is pumped to a height of 2 m, the enthalpy is changed by 15 J/Kg, and work done by the motor is 50 J/Kg, assuming system is insulated what is the change in internal energy of water?
a) 50 J
b) 100 J
c) 150 J
d) 200 J
View answer
Explanation: ∆U = Q + W – m (∆H + ∆PE + ∆KE), => ∆U = 0 + 50*10 – 10*(15 + 10*2) = 500 – 350 = 150 J.
4. 1 Kg of water is pumped to a height of 1 m, the enthalpy is changed by 5 J/Kg, and work done by the motor is 25 J/Kg, assuming a system is insulated what is the change in internal energy of water?
a) 10 J
b) 25 J
c) 35 J
d) 50 J
View answer
Explanation: ∆U = Q + W – m (∆H + ∆PE + ∆KE), => ∆U = 0 + 25*1 – 1*(5 + 10*1) = 25 – 15 = 10 J.
5. 1 Kg of water is pumped to a height of 10 m, the enthalpy is changed by 50 J/Kg, and work done by the motor is 300 J/Kg, assuming a system is insulated what is the change in internal energy of water?
a) 100 J
b) 150 J
c) 200 J
d) 300 J
View answer
Explanation: ∆U = 0 + 300*1 – 1*(50 + 10*10) = 150 J.
6. 2 Kg of water (CP = 0.15 J/KgoC) is pumped to a height of 0.1 m, work done by the motor is 10 J/Kg, and heat liberated by it is 5 J/Kg, what is the final temperature of water if the initial temperature was 27oC?
a) 10oC
b) 19oC
c) 27oC
d) 37oC
View answer
Explanation: ∆U = Q + W – m (∆H + ∆PE + ∆KE), => 0 = – 5 + 10 – 2(∆H + 10*0.1), => ∆H = 1.5 J/Kg, => 1.5 = 0.15(T – 27), => T = 37oC.
7. 1 Kg of water (CP = 0.5 J/KgoC) is pumped to a height of 0.5 m, work done by the motor is 40 J/Kg, and heat liberated by it is 10 J/Kg, what is the final temperature of water if the initial temperature was 10oC?
a) 10oC
b) 30oC
c) 40oC
d) 60oC
View answer
Explanation: ∆U = Q + W – m (∆H + ∆PE + ∆KE), => 0 = – 10 + 40 – 1*(∆H + 10*0.4), => ∆H = 25 J/Kg, => 25 = 0.5(T – 10), => T = 60oC.
8. 1 Kg of water (CP = 0.5 J/KgoC) is pumped to a height of 1 m, work done by the motor is 20 J/Kg, and heat liberated by it is 5 J/Kg, what is the final temperature of water if the initial temperature was 20oC?
a) 20oC
b) 30oC
c) 40oC
d) 50oC
View answer
Explanation: ∆U = Q + W – m (∆H + ∆PE + ∆KE), => 0 = – 5 + 20 – 1*(∆H + 10*1), => ∆H = 5 J/Kg, => 5 = 0.5(T – 20), => T = 30oC.
9. 1 Kg of water (CP = 0.4 J/KgoC) is pumped to a height of 2 m, work done by the motor is 50 J/Kg, and heat liberated by it is 10 J/Kg, what is the final temperature of water if the initial temperature was 25oC?
a) 25oC
b) 45oC
c) 60oC
d) 75oC
View answer
Explanation: ∆U = Q + W – m (∆H + ∆PE + ∆KE), => 0 = – 10 + 50 – 1*(∆H + 10*2), => ∆H = 20 J/Kg, => 20 = 0.4(T – 20), => T = 75oC.
10. 5 Kg of water (CP = 1 J/KgoC) is pumped to a height of 0.5 m, work done by the motor is 50 J/Kg, and heat liberated by it is 5 J/Kg, what is the final temperature of water if the initial temperature was 0oC?
a) 2oC
b) 4oC
c) 6oC
d) 8oC
View answer
Explanation: ∆U = Q + W – m (∆H + ∆PE + ∆KE), => 0 = – 5 + 50 – 5*(∆H + 10*0.5), => ∆H = 6 J/Kg, => 6 = 1*(T – 0), => T = 6oC.
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