Laws of Thermodynamics
Exam Duration: 45 Mins Total Questions : 40
Which of the following are intensive properties?
1. Kinetic energy
2. Specific enthalpy
3. Pressure
4. Entropy
Select the correct answer using the codes given below.
- (a)
1 and 3
- (b)
2 and 3
- (c)
1, 3 and 4
- (d)
2 and 4
Consider the following properties:
1. Entropy
2. Viscosity
3. Temperature
4. Specific heat at constant volume
Which of the above properties of a system is/are extensive?
- (a)
Only 1
- (b)
1 and 2
- (c)
2,3 and 4
- (d)
1, 2 and 4
A reversible heat engine rejects 50 % of the heat supplied during a cycle of operation. If this, engine is reversed and operates as a heat pump, then what is its coefficient of performance?
- (a)
1.0
- (b)
1.5
- (c)
2.0
- (d)
2.5
A balloon which is initially collapsed and flat is slowly filled with a gas at 100 kPa, so as to form it into a sphere of 1 m radius. The work done by the gas in the balloon during the filling process is
- (a)
428.9 kJ
- (b)
418.9 kJ
- (c)
420.9 kJ
- (d)
416.9 kJ
Which one of the following statements applicable to a perfect gas will also be true for an irreversible process? (Symbol have the usual meanings)
- (a)
dQ = dU + pdV
- (b)
dQ = TdS
- (c)
TdS = dU + pdV
- (d)
None of these
Which one of the following temperature entropy diagrams of steam shows the reversible and irreversible processes correctly?
- (a)
- (b)
- (c)
- (d)
Consider the following statements: When a perfect gas enclosed in a cylinder piston device executes a reversible adiabatic expansion process
1. its entropy will increase.
2. its entropy change will be zero.
3. the entropy change of the surroundings will be zero.
Which of these statements is/are correct?
- (a)
1 and 3
- (b)
Only 2
- (c)
2 and 3
- (d)
Only 1
When a system undergoes a process such that \(\int \frac{dQ}{T}=0\) and \(\Delta S\)= 0,the process is
- (a)
irreversible adiabatic
- (b)
reversible adiabatic
- (c)
isothermal
- (d)
isobaric
The throttling process undergone by a gas across an orifice is shown by its states in the following figure.
It can be represented on the diagram as
- (a)
- (b)
- (c)
- (d)
Consider the following statements:
1. Availability is generally conserved.
2. Availability can either be negative or positive.
3. Availability is the maximum theoretical work obtainable.
4. Availability can be destroyed in irreversibilities.
Which of these statements are correct?
- (a)
3 and 4
- (b)
1 and 2
- (c)
1 and 3
- (d)
2 and 4
A system of 100 kg mass undergoes a process in which its specific entropy increases from 0.3 kJ/kg-K to 0.4 kJ/kg-K. At the same time, the entropy of the surroundings decreases from 80 kJ/K to 75 kJ/K.The process is
- (a)
reversible and isothermal
- (b)
irreversible
- (c)
reversible
- (d)
impossible
10 kg of water is heated from 300 K to 350 K in an insulated tank due to churning action by a stirrer. The ambient temperature is 300 K. In this context, match List I with List II and select the correct answer using the codes given below the lists.
| List I | List II | ||
|---|---|---|---|
| P. | Enthalpy change | 1. | 12.2 kJ/kg |
| Q. | Entropy change/kg | 2. | 1968 kJ |
| R. | Availability/kg | 3. | 2090 kJ |
| S. | Loss of availability | 4. | 656 J/kg-K |
- (a)
Codes P Q R S 3 1 4 2 - (b)
Codes P Q R S 2 4 1 3 - (c)
Codes P Q R S 3 4 1 2 - (d)
Codes P Q R S 2 1 4 3
A system comprising of a pure substance executes reversibly a cycle 1-2-3-4-1 consisting of two isentropic
and two isochoric processes as shown in the figure below.
Which one of the following is the correct representation of this cycle on the temperature-entropy coordinates?
- (a)
- (b)
- (c)
- (d)
Consider the following statements regarding the throttling process of wet steam:
1. The steam pressure and temperature decreases but enthalpy remains constant.
2. The steam pressure decreases, the temperature increases but enthalpy remains constant.
3. The entropy, specific volume and dryness fraction increases.
4. The entropy increases but the volume and dryness fraction decreases.
Which of these statements are correct?
- (a)
1 and 4
- (b)
2 and 3
- (c)
1 and 3
- (d)
2 and 4
A reversible engine operates between temperatures T1 and T2. The energy rejected by this engine is received by a second reversible engine at temperature T2 and rejected to a reservoir at temperature T3. If the efficiencies of the engines are same then, the relationship between T1,T2 and T3 is given by
- (a)
\(T_{2}=\frac{T_{1}+T_{3}}{2}\)
- (b)
\(T_{2}=\sqrt{T^{2}_{1}+T^{2}_{2}}\)
- (c)
\(T_{2}=\sqrt{T_{1}T_{3}}\)
- (d)
\(T_{2}=\frac{T_{1}+2T_{3}}{2}\)
1 kg of air is subjected to the following processes:
1. Air expands isothermally from 6 bar to 3 bar.
2. Air is compressed to half the volume at constant pressure.
3. Heat is supplied to air at constant volume till the pressure becomes three fold.
In which of the above processes, the change in entropy will be positive?
- (a)
1 and 2
- (b)
2 and 3
- (c)
1 and 3
- (d)
1, 2 and 3
An inventor claims to have developed an engine that takes in 105 MJ at a temperature of 400 K, rejects 42 MJ at a temperature of 200 K and delivers 15 kW -h of mechanical work. Which statement is correct?
- (a)
Engine is economical
- (b)
Inventor claim is not possible
- (c)
Engine violates the law of conservation of energy
- (d)
Both (b) and (c)
An electric motor of 1 kW rating is used for driving heat pump which supplies heat to a building for maintaining at 260C. Heat loss from building to the surrounding due to temperature difference is 6 MJ/h when the surroundings temperature is 3 0C, then select the false statement.
- (a)
This motor is sufficient to maintain the desired
temperature - (b)
Theoretical input power of motor is 0.145 kW
- (c)
If motor efficiency is 80%, then it is unable to maintain the desired temperature
- (d)
None of the above
A refrigerator is maintained at a temperature of 2 0C. Every time the door is opened, warm material is placed inside introducing an average of 420 kJ, but making only a small change in the temperature of the refrigerator. The door is opened 20 times a day and the refrigerator operates at 15% of the ideal COP. If atmospheric temperature is 30 0C then power input to refrigerator is
- (a)
1.58 kW-h/day
- (b)
5701.87 kW-h/day
- (c)
2950 kJ/day
- (d)
3.16 kW-h/day
A heat engine is used to drive a heat pump. The heat transfers from the heat engine and from the heat pump are used to heat the water circulating through the radiators of a building. The efficiency of the engine is 27% and the COP of the pump is 4. The ratio of the heat transfer to the circulating water to the heat transfer to the heat engine.
- (a)
2.70
- (b)
3.29
- (c)
1.81
- (d)
4.21
A heat pump takes in heat from a reservoir at 5°C and delivers heat to a reservoir at 60OC. The heat pump is driven by a reversible heat engine which takes in heat from a reservoir at 840 OCand rejects heat to a reservoir at 60 OC. This heat engine also drives a machine that absorbs 30 kW. If the heat pump extracts 17 kJ/s from the 5 OC reservoir.
The rate of heat supply from the 8400C source is
- (a)
27.53 kW
- (b)
47.61 kW
- (c)
51.09 kW
- (d)
23.54 kW
A heat pump takes in heat from a reservoir at 5°C and delivers heat to a reservoir at 60OC. The heat pump is driven by a reversible heat engine which takes in heat from a reservoir at 840 OCand rejects heat to a reservoir at 60 OC. This heat engine also drives a machine that absorbs 30 kW. If the heat pump extracts 17 kJ/s from the 5 OC reservoir.
The rate of heat rejection to the 60 OCsink is
- (a)
37.53 kW
- (b)
47.61 kW
- (c)
27.09 kW
- (d)
34.61 kW
Two Carnot engines works in series between the source and sink temperatures of 550 K and 350 K. If both engines develop equal power then, intermediate temperature is
- (a)
350 K
- (b)
400 K
- (c)
450 K
- (d)
500 K
In a power plant cycle as shown in figure.
Given, h2 = 687 kJ/kg, h3 = 2760 kJ/kg
h4 = 2160 kJ/kg, h1 = 209 kJ/kg
Which is correct for this process?
- (a)
Reversible process
- (b)
Irreversible process
- (c)
Impossible process
- (d)
None of these
In given cycle Carnot engine runs the Carnot refrigerator.
(I) If Q1 = Q2 then T3 = ?
- (a)
200 K
- (b)
300 K
- (c)
400 K
- (d)
500 K
In given cycle Carnot engine runs the Carnot refrigerator.
Efficiency of Carnot engine
- (a)
43%
- (b)
33%
- (c)
28%
- (d)
37%
In given cycle Carnot engine runs the Carnot refrigerator.
COP of refrigerator
- (a)
1
- (b)
2
- (c)
3
- (d)
0.5
The latent heat of fusion of water at O°C is 335 kJ/kg. How much does the entropy of 1 kg of ice change as it melts into water, if heat is supplied reversibly to a mixture of ice and water at 0OC?
- (a)
(ΔS)ice = -1.227 kJ/K
- (b)
(ΔS)ice = 1.227 kJ/K
- (c)
(ΔS)ice =0
- (d)
Data is insufficient
10 g of water at 20 OCis converted into ice at constant atmospheric pressure. Assume that the specific heat of liquid water to remain constant at 4.2 J/g-K and that of ice to be half to this value and taking the latent heat of fusion of ice at 0OCto be 335 J/g, the total entropy change of the system
- (a)
-12.271 J/K
- (b)
-15.63 J/K
- (c)
15.63 J/K
- (d)
12.271 J/K
A reversible engine as shown in figure during a cycle of operations draws 5 MJ from the 400 K reservoir and does 840 kJ of work. Select the correct option.
- (a)
Q2 = 4980 kJ, Q3 = 820 kJ
- (b)
Q2 = - 4980 kJ, Q3 = 820 kJ
- (c)
Q2 = 4980 kJ, Q3 = - 820 kJ
- (d)
Q2 = - 4980 kJ, Q3 = - 820 kJ
2 kg of water at 80 OCare mixed adiabatically with 3 kg of water at 300C in a constant pressure process of 1 atm. The increase in the entropy of the total mass of water due to the mixing process (Cp of water = 4.187 kJ/kg-K) is
- (a)
- 0.05915 kJ/K
- (b)
0.05915 kJ/K
- (c)
zero
- (d)
None of these
0.1 m3 of hydrogen initially at 1.2 MPa, 200 OCundergoes a reversible isothermal expansion to 0.1 MPa. The change in entropy of the gas is (\(\gamma\)= 1.4)
- (a)
-0.4886 kJ/kg-K
- (b)
0.4886 kJ/kg-K
- (c)
-0.6294 kJ/kg-K
- (d)
0.6294 kJ/kg-K
An ideal gas of molecular weight 30 and g = 1.3 occupies a volume of 1.5 m3 at 100 kPa and 350 K. The gas is compressed according to the law pV1.25 = constant, to a pressure of 3 MPa.
Change of entropy of gas is
- (a)
0.97 kJ/K
- (b)
-0.97 kJ/K
- (c)
0.19 kJ/K
- (d)
-0.19 kJ/K
An ideal gas of molecular weight 30 and g = 1.3 occupies a volume of 1.5 m3 at 100 kPa and 350 K. The gas is compressed according to the law pV1.25 = constant, to a pressure of 3 MPa.
Work done by the gas
- (a)
-584.64 kJ
- (b)
584.64 kJ
- (c)
0.97 kJ
- (d)
-0.97 kJ
An ideal gas of molecular weight 30 and g = 1.3 occupies a volume of 1.5 m3 at 100 kPa and 350 K. The gas is compressed according to the law pV1.25 = constant, to a pressure of 3 MPa.
Heat transfer is
- (a)
-97.5 kJ
- (b)
97.5 kJ
- (c)
584.64 kJ
- (d)
-584.64 kJ
In the given figure, a reversible engine is shown in a cyclic process.
If W = 20.0. kJ/min and Q1 = 150.0. kJ/min then Q2 and Q3 will be respectively as
- (a)
1600 kJ/min, 300 kJ/min
- (b)
1600 kJ/min, -300 kJ/min
- (c)
-1600 kJ/min, 300 kJ/min
- (d)
-1600 kJ/min, -300 kJ/min
In the given figure, a reversible engine is shown in a cyclic process.
If W = 20.0. kJ/min and Q1 = 150.0. kJ/min then Total entropy change is
- (a)
zero
- (b)
-3 kJ/K
- (c)
4 kJ/K
- (d)
-1 kJ/K
80 kg of water at 100 0C are mixed with 50. kg of water at 600C while the temperature of the surroundings is 15 0C. Determine the decrease in availableenergy due to mixing.
- (a)
234.8 kJ
- (b)
130.04 kJ
- (c)
307.25 kJ
- (d)
406.09 kJ
A heat engine receives reversibly 420 kJ/cycie of heat from a source at 3270C and rejects heat reversibly to a sink at 270C. In which case, process will be irreversible?
- (a)
If 210 kJ/cycle rejected
- (b)
If 105 kJ/cycle rejected
- (c)
If 315 kJ/cycle rejected
- (d)
None of the above
For a steady flow process from state 1 to 2, enthalpy changes from h1 = 40.0. kJ/kg to h2 = 100.kJ/kg and entropy changes from S1 = 1.1 kJ/kg-K to $2 = 0..7 kJ/kg-K. Surrounding environmentaltemperature is 300 K. Neglect changes in kinetic and potential energy. The change in availability of the system is
- (a)
420 kJ/kg
- (b)
300 kJ/kg
- (c)
180 kJ/kg
- (d)
90 kJ/kg
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