This set of Basic Chemical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Steady-State and Unsteady-State Systems”.

1. Which of the following remains constant in the steady state system?

a) Mass

b) Energy

c) Momentum

d) Density

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Explanation: In a steady state system what amount of material goes in the same amount comes out, so the overall mass remains constant.

2. A reaction occurs in a vessel such that its mass does not change but its temperature is increased, then the system is which of the following?

a) Steady-state

b) Unsteady-state

c) Cannot say

d) None of the mentioned

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Explanation: For a steady-state system all the properties temperature, pressure, mass should remain constant with respect to time, so it is an unsteady-state process.

3. A fluid enters a vessel at the rate of 10 liters/s, and leaves in two pathways one with 7 liters/s and other with 3 liters/s, then what type of flow it is?

a) Steady-state

b) Unsteady-state

c) Cannot say

d) None of the mentioned

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Explanation: Since the flow in rate and flow out rate of the fluid are equal, the system is in steady-state.

4. A fluid enters a vessel at the rate of 10 liters/s, and leaves in two pathways one with 5 liters/s and other with 3 liters/s, then what type of flow it is?

a) Steady-state

b) Unsteady-state

c) Cannot say

d) None of the mentioned

View answer

Explanation: Since the flow in rate and flow out rate of the fluid are unequal, the system is in unsteady-state.

5. The rate flow in and flow out in an unsteady state process are now increased by 10 Kg/s, which will be the change in accumulation?

a) 0

b) 5 Kg/s

c) 10 Kg/s

d) 20 Kg/s

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Explanation: Initial accumulation = rate of flow out – rate of flow in, => Final accumulation = (rate of flow out + 10) – (rate of flow in + 10) = Initial accumulation, => Change in accumulation = 0.

6. An unsteady-state system, with 10 liters as initial amount of water in the vessel, water flow in rate is 8 liters/ s and flow out rate is 5 liters/s, what will be the amount of water in the vessel after 10 seconds?

a) 10 liters

b) 20 liters

c) 30 liters

d) 40 liters

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Explanation: Amount of water added to the vessel in 10 seconds = (8 – 5)*10 = 30 liters, => Final amount of water = 10 + 30 = 40 liters.

7. An unsteady-state system, with 6 liters as initial amount of water in the vessel, water flow in rate is 2 liters/ s and flow out rate is 4 liters/s, what will be the amount of water in the vessel after 1 second?

a) 2 liters

b) 4 liters

c) 6 liters

d) 8 liters

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Explanation: Total amount of water reduced from the vessel in 1 second = (4 – 2)*1 = 2 liters, => Final amount of water = 6 – 2 = 4 liters.

8. What is the final amount of fluid in the vessel if the system is in steady state?

a) Same as the initial amount

b) Twice the initial amount

c) Zero

d) None of the mentioned

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Explanation: Since in steady-state the rate of flow in is equal to the rate of flow out, so final amount of fluid in the vessel is same as the initial amount.

9. In what ratio 57 octane and 63 octane should be mixed to obtain 59 octane?

a) 1:1

b) 2:1

c) 3:1

d) 4:1

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Explanation: 59*1 = 63*x + 57*(1 – x), => x= 1/3, => 1 – x = 2/3, => ratio of 57 octane: 63 octane = 2/3:1/3 = 2:1.

10. What amount of 57 octane should be mixed with 3 liters of 63 octane to obtain 4 liters of 59 octane?

a) 1 liter

b) 2 liters

c) 2.5 liters

d) 4.5 liters

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Explanation: 59*1 = 63*x + 57*(1 – x), => x = 1/3, now 4 = (1/3)*3 + (2/3)*w, => w = 4.5 liters.

11. An unsteady state system, the flow in rate of A is 10 mole/s, what is the flow out rate of B if the accumulation was 10 mole in 2 seconds?

a) 5 mole/s

b) 10 mole/s

c) 15 mole/s

d) 20 mole/s

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Explanation: Flow rate of B = 10 – 10/2 = 5 mole/s.

12. An unsteady state system, the flow in the rate of A is 12 mole/s, what is the flow out rate of B if the accumulation was 18 mole in 3 seconds?

a) 4 mole/s

b) 6 mole/s

c) 8 mole/s

d) 9 mole/s

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Explanation: Flow rate of B = 12 – 18/3 = 6 mole/s.

13. An unsteady state system, the flow in rate of A is 5 mole/s, what is the flow out rate of B if the accumulation was 10 mole in 5 seconds?

a) 1 mole/s

b) 2 mole/s

c) 3 mole/s

d) 5 mole/s

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Explanation: Flow rate of B = 5 – 10/5 = 3 mole/s.

14. An unsteady state system, the flow in rate of A is 8 mole/s, what is the flow out rate of B if the accumulation was 6 mole in 2 seconds?

a) 1 mole/s

b) 2 mole/s

c) 3 mole/s

d) 5 mole/s

View answer

Explanation: Flow rate of B = 8 – 6/2 = 5 mole/s.

15. An unsteady state system, the flow in the rate of A is 6 mole/s, what is the flow out rate of B if the accumulation was 18 mole in 9 seconds?

a) 1 mole/s

b) 2 mole/s

c) 3 mole/s

d) 4 mole/s

View answer

Explanation: Flow rate of B = 6 – 18/9 = 4 mole/s.

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