Thermodynamics NEET MCQs

In following figures (a) to (d), variation of volume by change of pressure is shown in figure. The gas is taken along the path ABCDA. Change in internal energy of the gas will be (a) (b) P (c) (d) B B →V V

1. (1) Positive in all cases from (a) to (d)
2. (2) Positive in cases (a), (b) and (c) but zero in case (d)
3. (3) Negative in cases (a), (b) and (c) but zero in case (d)
4. (4) Zero in all the four cases

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Select the correct statement for work, heat and change in internal energy.

1. (1) Heat supplied and work done depend on initial and final states
2. (2) Change in internal energy depends on the initial and final states only
3. (3) Heat and work depend on the path between the two points
4. (4) All of these

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In a thermodynamic process pressure of a fixed mass of a gas is changed in such a manner that the gas releases 20 J of heat when 8 J of work was done on the gas. If the initial internal energy of the gas was 30 J, then the final internal energy will be

1. (1) 2 J 18 J
2. (3) 42 J
3. (4) 58 J

A perfect gas goes from state A to state B by absorbing 8 × 10⁵ joule and doing 6.5 × 10⁵ joule of external work. If it is taken from same initial state A to final state B in another process in which it absorbs 10⁵ J of heat, then in the second process work done

1. (1) On gas is 10⁵ J
2. (2) On gas is 0.5 × 10⁵ J
3. (3) By gas is 10⁵ J
4. (4) By gas is 0.5 × 10⁵ J

A certain amount of an ideal monatomic gas needs 20 J of heat energy to raise its temperature by 10°C at constant pressure. The heat needed for the same temperature rise at constant volume will be

1. (1) 30 J
2. (2) 12 J
3. (3) 200 J
4. (4) 215.3 J

If during an adiabatic process the pressure of mixture of gases is found to be proportional to square of its absolute temperature. The ratio of C_p/C, for mixture of gases is

1. (1) 2
2. (2) 1.5
3. (3) 1.67
4. (4) 2.1

For a certain process, pressure of diatomic gas varies according to the relation P = aV2, where a is constant. What is the molar heat capacity of the gas for this process? 17R 6R 13R 16R

1. (1)
2. (2)
3. (3)
4. (4) 6 17 6 7

Following figure shows P-T graph for four processes A, B, C and D. Select the correct alternative. (0, 0)

1. (1) A - Isobaric process
2. (2) B - Adiabatic process
3. (3) C - Isochoric process
4. (4) D - Isothermal process

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An ideal gas with adiabatic exponent y is heated at constant pressure. It absorbs Q amount of heat. Fraction of heat absorbed in increasing the temperature is 1

1. (1) Y
2. (2)
3. (3)
4. (4) 2Y Y

Two cylinders contain same amount of ideal monatomic gas. Same amount of heat is given to two cylinders. If temperature rise in cylinder A is To then temperature rise in cylinder B will be Free piston Fixed piston Tạạạnn Heat Heat To

1. (1) 3T0
2. (2) 2To
3. (3)
4. (4) 3T0 2

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A mass of dry air at N.T.P. is compressed to 32 th of its original volume suddenly. If y = 1.4, the final pressure would be 1

1. (1) 32 atm
2. (2) 128 atm
3. (3) - atm
4. (4) 150 atm 32

A mixture of gases at NTP for which y = 1.5 is suddenly compressed to - th of its original volume. The final temperature of mixture is

1. (1) 300°C
2. (2) 546°C
3. (3) 420°C
4. (4) 872°C

In which process P-V diagram is a straight line parallel to the volume axis?

1. (1) Isochoric Isobaric
2. (3) Isothermal
3. (4) Adiabatic

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The pressure and volume of a gas are changed as shown in the P-V diagram in this figure. The temperature of the gas will B D → V

1. (1) Increase as it goes from A to B
2. (2) Increase as it goes from B to C
3. (3) Remain constant during these changes
4. (4) Decrease as it goes from D to A

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The figure shows P-V diagram of a thermodynamic cycle. Which corresponding curve is correct? (0, 0) >V ALe B B

1. (1)
2. (2)
3. (3) B
4. (4) 7

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During the thermodynamic process shown in figure for an ideal gas PA → V

1. (1) ΔT = 0
2. (2) ΔQ = 0
3. (3) W< 0
4. (4) ΔU > 0

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For P-V diagram of a thermodynamic cycle as shown in figure, process BC and DA are isothermal. Which of the corresponding graphs is correct? D • V

1. (1)
2. (2)
3. (3)
4. (4) D (0,0)" (0,0) (0,0) (0,0)'

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Work done for the process shown in the figure is B(30 kPa, 25 cc) A(10 kPа, 10 cc) →

1. (1) 1 J
2. (2) 1.5 J
3. (3) 4.5 J
4. (4) 0.3 J

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During which of the following thermodynamic process represented by PV diagram the heat energy absorbed by system may be equal to area under PV graph? P4 P4

1. (1)
2. (2)
3. (3)
4. (4) All of these B • V B.v

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In a thermodynamic process two moles of a monatomic ideal gas obeys p o V-2 . If temperature of the gas increases from 300 K to 400 K, then find work done by the gas (where R = universal gas constant).

1. (1) 200 R -200 R
2. (3) -10⁰ R
3. (4) -400 R

A Carnot engine working between 300 K and 600 K has a work output of 800 J per cycle. The amount of heat energy supplied to engine from the source in each cycle is

1. (1) 800 J 1600 J
2. (3) 3200 J
3. (4) 6400 J

The maximum possible efficiency of a heat engine is

1. (1) 10⁰% T,
2. (2)
3. (3) T₁ + 1 T₂
4. (4) Dependent upon the temperature of source (T,) and sink (T,) and is equal to (1-7?)

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Which of the following can be coefficient of performance of refrigerator?

1. (1) 1
2. (2) 0.5
3. (3) 9
4. (4) All of these

The temperature inside and outside a refrigerator are 273 K and 300 K respectively. Assuming that the refrigerator cycle is reversible, for every joule of work done, the heat delivered to the surrounding will be nearly

1. (1) 11 J 22 J
2. (3) 33 J
3. (4) 50 J

By opening the door of a refrigerator placed inside a room you

1. (1) Can cool the room to certain degree
2. (2) Can cool it to the temperature inside the refrigerator
3. (3) Ultimately warm the room slightly
4. (4) Can neither cool nor warm the room

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A Carnot engine whose sink is at 300 K has an efficiency of 40%. By how much should the temperature of source be increased to as to increase its efficiency by 50% of original efficiency?

1. (1) 150 K 250 K
2. (3) 300 K
3. (4) 450 K

Entropy of a system decreases

1. (1) When heat is supplied to a system at constant temperature
2. (2) When heat is taken out from the system at constant temperature
3. (3) At equilibrium
4. (4) In any spontaneous process

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A container is filled with 20 moles of an ideal diatomic gas at absolute temperature T. When heat is supplied to gas temperature remains constant but 8 moles dissociate into atoms. Heat energy given to gas is

1. (1) 4RT
2. (2) 6RT
3. (3) 3RT
4. (4) 5RT

A triatomic, diatomic and monatomic gas is supplied same amount of heat at constant pressure, then

1. (1) Fractional energy used to change internal energy is maximum in monatomic gas
2. (2) Fractional energy used to change internal energy is maximum in diatomic gas
3. (3) Fractional energy used to change internal energy is maximum in triatomic gases
4. (4) Fractional eneray used to change internal enerav is same in all the three gases

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If a gas is taken from A to C through B then heat absorbed by the gas is 8 J. Heat absorbed by the gas in taking it from A to C directly is P (kPа) 20 10 200 400 → V(cc)

1. (1) 8J
2. (2) 9 J
3. (3) 11 J
4. (4) 12 J

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Liquid oxygen at 50 K is heated to 300 K at constant pressure of 1 atm. The rate of heating is constant. Which one of the following graphs represents the variation of temperature with time? Temperature Temperature Temperature

1. (3) Time Time Time Time

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10⁵ calories of heat is required to raise the temperature of 3 moles of an ideal gas at constant pressure from 30°C to 35°C. The amount of heat required in calories to raise the temperature of the gas through the range (60°C to 65°C) at constant volume is Y= G,=14)

1. (1) 50 cal N 75 cal
2. (3) 70 cal
3. (4) 90 cal

A gas may expand either adiabatically or isothermally. A number of P-V curves are drawn for the two processes over different range of pressure and volume. It will be found that

1. (1) An adiabatic curve and an isothermal curve may intersect
2. (2) Two adiabatic curves do not intersect
3. (3) Two isothermal curves do not intersect
4. (4) All of these

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A hydrogen cylinder is designed to withstand an internal pressure of 10⁰ atm. At 27°C, hydrogen is pumped into the cylinder which exerts a pressure of 20 atm. At what temperature does the danger of explosion first sets in?

1. (1) 500 K 1500 K
2. (3) 10⁰⁰ K
3. (4) 2000 K

The variation of pressure P with volume V for an ideal diatomic gas is parabolic as shown in the figure. The molar specific heat of the gas during this process is →V

1. (1) 9R 17R 3R 8R
2. (2)
3. (3)
4. (4) 6 4 5

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When 1 kg of ice at 0°C melts to water at 0° C, the resulting change in its entropy, taking latent heat of ice to be 80 cal/°C is

1. (1) 293 cal/K
2. (2) 273 cal/K
3. (3) 8 × 10⁴ cal/K
4. (4) 80 cal/K

Two moles of a gas at temperature T and volume V are heated to twice its volume at constant pressure. If C_p=y then increase in internal energy of the gas is RT 2RT 2RT 2T

1. (1)
2. (2)
3. (3) 3(y-1)
4. (4) y-1 y-1 y-1

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To an ideal triatomic gas 800 cal heat energy is given at constant pressure. If vibrational mode is neglected, then energy used by gas in work done against surroundings is

1. (1) 200 cal
2. (2) 300 cal
3. (3) 400 cal
4. (4) 60 cal

A closed cylindrical vessel contains N moles of an ideal diatomic gas at a temperature T. On supplying heat, temperature remains same, but n moles get dissociated into atoms. The heat supplied is E(N-n)RT

1. (2)
2. (3)
3. (4) 2nRT 2nRT =nRT

An ideal monatomic gas at 300 K expands adiabatically to 8 times its volume. What is the final temperature?

1. (1) 75 K
2. (2) 300 K
3. (3) 560 K
4. (4) 340 K

Figure shows, the adiabatic curve on a log T and log V scale performed on ideal gas. The gas is 2- 1 23 45> 109V

1. (1) Monatomic
2. (2) Diatomic
3. (3) Polyatomic
4. (4) Mixture of monatomic and diatomic

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A diatomic gas undergoes a process represented by PV1.3 = constant. Choose the incorrect statement

1. (1) The gas expands by absorbing heat from the surroundings
2. (2) The gas cools down during expansion
3. (3) The work done by surroundings during expansion of the gas is negative
4. (4) None of these

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The process CD is shown in the diagram. As system is taken from C to D, what happens to the temperature of the system? P 3p..c Po. Vo 3Vo

1. (1) Temperature first decreases and then increases
2. (2) Temperature first increases and then decreases
3. (3) Temperature decreases continuously
4. (4) Temperature increases continuously

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A P-T graph is shown for a cyclic process. Select correct statement regarding this B/ D →T

1. (1) During process CD, work done by gas is negative
2. (2) During process AB, work done by the gas is positive
3. (3) During process BC internal energy of system increases
4. (4) Durina process BC internal eneray of the system decreases

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An ideal gas of volume V and pressure P expands isothermally to volume 16 V and then compressed adiabatically to volume V. The final pressure of gas is [y = 1.5]

1. (1) P 2 ЗP
2. (3) 4P
3. (4) 6P

The pressure P of an ideal diatomic gas varies with its absolute temperature T as shown in figure. The molar heat capacity of gas during this process is [R is gas constant] P. / →T

1. (1) 1.7 R
2. (2) 3.25 R
3. (3) 2.5 R
4. (4) 4.2 R

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An ideal gas expands according to the law PZV = constant. The internal energy of the gas

1. (1) Increases continuously
2. (2) Decreases continuously
3. (3) Remain constant
4. (4) First increases and then decreases

Neon gas of a given mass expands isothermally to double volume. What should be the further fractional decrease in pressure, so that the gas when adiabatically compressed from that state, reaches the original state?

1. (1) 1 -2-213 1 - 31/3
2. (3) 21/3
3. (4) 32/3

A heat engine rejects 600 cal to the sink at 27°C. Amount of work done by the engine will be (Temperature of source is 227°C & J = 4.2 J/cal)

1. (1) 1680 J 2 840 J
2. (3) 2520 J
3. (4) None of these

The volume (V) of a monatomic gas varies with its temperature (T), as shown in the graph. The ratio of work done by the gas, to the heat absorbed by it, when it undergoes a change from state A to state B, is [NEET-2018]

1. (1)
2. (2)
3. (3)
4. (4)

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The efficiency of an ideal heat engine working between the freezing point and boiling point of water, is [NEET-2018]

1. (1) 26.8%
2. (2) 20%
3. (3) 12.5%
4. (4) 6.25%

Muaseigme naung an eniciency of 10 as heat engine, is used as a refrigrator. If the work done on the system is 10 J, the amount of energy absorbed from the reservoir at lower temperature is [NEET-2017]

1. (1) 1J
2. (2) 90 J
3. (3) 99 J
4. (4) 10⁰ J

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Thermodynamic processes are indicated in the following diagram. P. •500 K 1700 K *300 Kv Match the following Column-l Column-Il P. Process I a. Adiabatic Q. Process II b. Isobaric R. Process IIII c. Isochoric S. Process IV d. Isothermal [NEET-2017]

1. (1) P → a, Q →C, R → d, S → b
2. (2) P → c, Q → a, R → d, S → b
3. (3) P → c. Q → d. R → b. S → a
4. (4) P → d. Q → b. R → a, S → c

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One mole of an ideal monatomic gas undergoes a process described by the equation PV3 = constant. The heat capacity of the gas during this process is [NEET (Phase-2)-2016]

1. (1)
2. (2)
3. (3) 2R
4. (4) R

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The temperature inside a refrigerator is tz°C and the room temperature is t,°C. The amount of heat delivered to the room for each joule of electrical energy consumed ideally will be INEET (Phase-2) - 2016] 4, +273

1. (1)
2. (2) 1 -12 4-12 t2 + 273 t1 + t2
3. (3)
4. (4) t1-t2 ty + 273

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A refrigerator works between 4°C and 30°C. It is required to remove 600 calories of heat every second in order to keep the temperature of the refrigerated space constant. The power required is [Take 1 cal = 4.2 J) [NEET-2016]

1. (1) 2365 W
2. (2) 2.365 W
3. (3) 23.65 W
4. (4) 236.5 W

A gas is compressed isothermally to half its initial volume. The same gas is compressed separately through an adiabatic process until its volume is again reduced to half. Then [NEET-2016]

1. (1) Which of the case (whether compression through isothermal or through adiabatic process) requires more work will depend upon the atomicity of the gas
2. (2) Compressing the gas isothermally will require more work to be done
3. (3) Compressing the gas through adiabatic process will require more work to be done
4. (4) Compressing the gas isothermally or adiabatically will require the same amount of work

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One mole of an ideal diatomic gas undergoes a transition from A to B along a path AB as shown in the figure P (in kPa) 4 5 2---- 4 6 V (in m') The change in internal energy of the gas during the transition is [AIPMT-2015]

1. (1) -12 kJ
2. (2) 20 kJ
3. (3) -20 kJ
4. (4) 20 J

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A Carnot engine, having an efficiency of n = To as heat engine, is used as a refrigerator. If the work done on the system is 10 J, the amount of energy absorbed from the reservoir at lower temperature is [AIPMT-2015]

1. (1) 1J
2. (2) 10⁰ J
3. (3) 99 J
4. (4) 90 J

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A a voarom loas the Tinal pres sure of nge gas is: (Vexpa S/sothermally to a volume 2V and the ApiaT-2014) to a volume 16V. the final pressure of the gas is: (take y = 5/3)

1. (1) 64P
2. (2) 32P
3. (3) P/64
4. (4) 16P

The molar specific heats of an ideal gas at constant pressure and volume are denoted by C, and C, respectively. If Y = and R is the universal gas constant, then C, is equal to [NEET-2013] R (Y -1) i+Y

1. (1)
2. (2)
3. (3) yR
4. (4) (v - 1) R 1-Y

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During an adiabatic process, the pressure of a gas is found to be proportional to the cube of its temperature. The ratio of - for the gas is: [NEET-2013] 5 3 4

1. (1) 2
2. (2)
3. (3)
4. (4) 3 2 3

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One mole of an ideal gas goes from an initial state A to final state B via two processes: It first undergoes isothermal expansion from volume V to 3V and then its volume is reduced from 3V to V at constant pressure. The correct P-V diagram representing the two processes is [AIPMT (Prelims)-2012] A 1 1

1. (1) P
2. (2)
3. (3) P
4. (4) P B B A B V 3V 3V V 3V V 3V →V »V

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A thermodynamic system is taken through the cycle ABCD as shown in figure. Heat rejected by the gas during the cycle is [AIPMT (Prelims)-2012] -2PD Pressure -P 4 V 3V Volume

1. (1) 1PV
2. (2) PV
3. (3) 2 PV
4. (4) 4 PV

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During an isothermal expansion, a confined ideal gas does -150 J of work against its surroundings. This implies that [AIPMT (Prelims)-2011]

1. (1) 150 J of heat has been added to the gas
2. (2) 150 J of heat has been removed from the gas
3. (3) 300 J of heat has been added to the gas
4. (4) No heat is transferred because the process is isothermal

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A mass of diatomic gas (y = 1.4) at a pressure of 2 atmospheres is compressed adiabatically so that its temperature rises from 27°C to 927°C. The pressure of the gas in the final state is [AIPMT (Mains)-2011]

1. (1) 256 atm
2. (2) 8 atm
3. (3) 28 atm
4. (4) 68.7 atm

In thermodynamic processes which of the following statements is not true? [AIPMT (Prelims)-2009]

1. (1) In an isochoric process pressure remains constant
2. (2) In an isothermal process the temperature remains constant
3. (3) In an adiabatic process PVY = constant
4. (4) In an adiabatic process the system is insulated from the surroundings

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At 10°C the value of the density of a fixed mass of an ideal gas divided by its pressure is x. At 110°C this ratio is [AIPMT (Prelims)-2008] 283 383 10

1. (1) 202x
2. (2)
3. (3) 502Х
4. (4)

An engine has an efficiency of 1/6. When the temperature of sink is reduced by 62°C, its efficiency is doubled. Temperature of the source is [AIPMT (Prelims)-2007]

1. (1) 99°C
2. (2) 124°C
3. (3) 37°C
4. (4) 62°C

A Carnot engine whose sink is at 300 K has an efficiency of 40%. By how much should the temperature of source be increased so as to increase its efficiency by 50% of original efficiency? [AIPMT (Prelims)-2006]

1. (1) 275 K
2. (2) 325 K
3. (3) 250 K
4. (4) 380 K

The molar specific heat at constant pressure of an ideal gas is -R. The ratio of specific heat at constant pressure to that at constant volume is : [AIPMT (Prelims)-2006]

1. (1) 5
2. (2) 5
3. (3)
4. (4) 7

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A system is taken from state a to state c by two paths adc and abc as shown in the figure. The internal energy at a is Ua = 10 J. Along the path adc the amount of heat absorbed SQ, = 50 J and the work obtained oW, = 20 J whereas along the path abc the heat absorbed 8Q2 = 36 J. The amount of work along the path abc is d 1 a b V →

1. (1) 6 J
2. (2) 10 J
3. (3) 12 J
4. (4) 36 J

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Consider two insulated chambers (A, B) of same volume connected by a closed knob, S. 1 mole of perfect gas is confined in chamber A. What is the change in entropy of gas when knob S is opened? R = 8.31 J mol-'K-1. B

1. (1) 1.46 J/K
2. (2) 3.46 J/K
3. (3) 5.46 J/K
4. (4) 7.46 J/K

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A Carnot engine has efficiency 25%. It operates between reservoirs of constant temperatures with temperature difference of 80°C. What is the temperature of the low-temperature reservoir?

1. (1) -25°C 25°C
2. (3) -33°C
3. (4) 33°C

In an adiabatic change, the pressure and temperature of a monatomic gas are related as Poc T°, where c equals 2 5

1. (1)
2. (2)
3. (3)
4. (4) 5 5

An ideal Carnot engine, whose efficiency is 40%, receives heat at 500 K. If its efficiency is 50%, then the intake temperature for the same exhaust temperature is

1. (1) 800 K
2. (2) 900 K
3. (3) 600 K
4. (4) 700 K

A monatomic gas initially at 18°C is compressed adiabatically to one eighth of its original volume. The temperature after compression will be

1. (1) 1164 K
2. (2) 144 K
3. (3) 18 K
4. (4) 887.4 K

The efficiency of a Carnot engine operating with reservoir temperature of 10⁰°C and - 23°C will be 373 + 250 373 - 250 10⁰ + 23 10⁰ - 23

1. (1)
2. (2)
3. (3)
4. (4) 373 373 10⁰ 10⁰

An ideal gas at 27°C is compressed adiabatically to 8/27 of its original volume. The rise in temperature is (Take v = 5/3)

1. (1) 275 K
2. (2) 375 K
3. (3) 475 K
4. (4) 175 K

Two Carnot engines A and B are operated in series. The engine A receives heat from the source at temperature T, and rejects the heat to the sink at temperature T. The second engine B receives the heat at temperature T and rejects to its sink at temperature T₂. For what value of T the efficiencies of the two engines are equal? T, + T₂

1. (1)
2. (2) T,-Tг
3. (3) T,T₂
4. (4) ST,T₂ 2

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The (W/Q) of a Carnot engine is 1/6. Now the temperature of sink is reduced by 62°C, then this ratio becomes twice, therefore the initial temperature of the sink and source are respectively

1. (1) 33°C, 67°C
2. (2) 37°C, 99°C
3. (3) 67°C, 33°C
4. (4) 97K, 37K

One mole of an ideal gas at an initial temperature of T K does 6R joules of work adiabatically. If the ratio of specific heats of this gas at constant pressure and at constant volume is 5/3, the final temperature of gas will be

1. (1) (T + 2.4) K
2. (2) (T - 2.4) K
3. (3) (T + 4) K
4. (4) (T-4) K

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In a vessel, the gas is at a pressure P. If the mass of all the molecules is halved and their speed is doubled, then the resultant pressure will be

1. (1) 4P
2. (2) 2P
3. (3)
4. (4) PI2

The value of critical temperature in terms of van der Waals' constants a and b is given by 8a 27a

1. (1) Tc =
2. (2) To = 27Rb 8Rb a
3. (3) Tc =
4. (4) To = 27Rb 2Rb

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A : Work done by a gas in isothermal expansion is more than the work done by the gas in the same expansion adiabatically. R : Temperature remains constant in isothermal expansion and not in adiabatic expansion.

A : Coefficient of performance of a refrigerator is always greater than 1. R : Efficiency of heat engine is greater than 1.

A : During a cyclic process work done by the system is zero. R : Heat supplied to a svstem in the cyclic process converts into internal eneray of the svstem.