(a) Zero
(b) 30 J
(c) −90 J
(d) −60 J
Ans: (a)
Path bc is an isochoric process.
∴ Work done by gas along path bc is zero.
Q2: Which amongst the following options is the correct relation between change in enthalpy and change in internal energy? [NEET 2023]
(a)
(b)
(c)
(d)
Ans: (a)
Q3: The temperature of a gas is −50^{∘}C. To what temperature the gas should be heated so that the rms speed is increased by 3 times?
(a) 3295^{∘}C
(b) 3097 K
(c) 223 K
(d) 669^{∘}C [NEET 2023]
Ans: (a)
Q4: A Carnot engine has an efficiency of 50% when its source is at a temperature 327^{∘}C. The temperature of the sink is :
(a) 15^{∘}C
(b) 100^{∘}C
(c) 200^{∘}C
(d) 27^{∘}C [NEET 2023]
Ans: (d)
Efficiency of carnot engine
Q1: Which of the following pV curve represents maximum work done? [NEET 2022 Phase 1]
(a)
(b)
(c)
(d)
Ans: (b)
Work done under any thermodynamic process can be determined by area under the 'pV' graph. As it can be observed maximum area is covered in option '2'.
Q2: One mole of an ideal gas at 300 K is expanded isothermally from 1 L to 10 L volume. ΔU for this process is :
(Use R = 8.314 J k^{−1} mol^{−1}) [NEET 2022 Phase 2]
(a) 0 J
(b) 1260 J
(c) 2520 J
(d) 5040 J
Ans: (a)
For isothermal condition; ΔT = 0
ΔU = 0
Q3: A vessel contains 3.2 g of dioxygen gas at STP (273.15 K and 1 atm pressure). The gas is now transferred to another vessel at constant temperature, where pressure becomes one third of the original pressure. The volume of new vessel in L is : (Given : molar volume at STP is 22.4 L) [NEET 2022 Phase 2]
(a) 67.2
(b) 6.72
(c) 2.24
(d) 22.4
Ans: (b)
At constant temperature and amount
Q1: Which one among the following is the correct option for right relationship between C_{p} and C_{V} for one mole of ideal gas ? [NEET 2021]
(a) C_{P} = RC_{V}
(b) C_{P} = RC_{V}
(c) C_{P} + C_{V} = R
(d) C_{P}  C_{V} = R
Ans: (d)
Hint: C_{P}  C_{V} is equal to gas constant
The relation between C_{p} and C_{V} for an ideal gas is as follows:
C_{P}  C_{V} = R
Here, C_{V} is heat capacity at constant volume and C_{P} is heat capacity at constant pressure.
Q2: For irreversible expansion of an ideal gas under isothermal condition, the correct option is : [NEET 2021]
(a) ΔU = 0, Δ S_{total} ≠ 0
(b) ∆U ≠ 0, ∆ S_{total} = 0
(c) ∆U = 0, ∆ S_{total} = 0
(d) ∆U ≠ 0, ∆ S_{total} ≠ 0
Ans: (a)
Hint: ∆U = _{n}C_{V}∆T
In the case of isothermal process, ΔT is zero. The value of ΔU is also zero from the relation, ∆U=_{n}C_{V}∆T.
Thus, for reversible and irreversible expansion for an ideal gas, under isothermal conditions, ∆U = 0. But the value ∆S for irreversible expansion of an ideal gas under isothermal conditions is not equal to zero.
The total entropy change ( ∆S total) for the system and surroundings of a spontaneous process is given by
Q1: For the reaction, 2Cl(g) → Cl_{2}(g), the correct option is: [NEET 2020]
(a) Δ_{r}H < 0 and Δ_{r}S > 0
(b) Δ_{r}H < 0 and Δ_{r}S < 0
(c) Δ_{r}H > 0 and Δ_{r}S > 0
(d) Δ_{r}H > 0 and Δ_{r}S < 0
Ans: b
2Cl(g) → Cl_{2}(g) + Heat
Due to bond formation stability increases which results in release of heat.
∴ ΔH_{r} = ve or exothermic process
ΔH_{r} < O
& ΔS < O, because number of Cl atoms decreases in the formation of Cl_{2}(g)
Q2: The correct option for free expansion of an ideal gas under adiabatic condition is : [NEET 2020]
(a) q = 0, Δ T < 0 and w > 0
(b) q < 0, Δ T = 0 and w = 0
(c) q > 0, Δ T > 0 and w > 0
(d) q = 0, Δ T = 0 and w = 0
Ans: (d)
Free expansion, so p_{ex} = 0
So, w = − p_{ex}Δ V = 0
Since, adiabatic process, so q = 0
Since both q and w are equal to zero. Then according to first law of thermodynamics Δ E = q + w
Δ U = 0
Hence, Δ T = 0
Q1: In which case change in entropy is negative? [NEET 2019]
(a) Sublimation of solid to gas
(b) 2H(g)
(c) Evaporation of water
(d) Expansion of a gas at temperature
Ans: (b)
2H(g) → H2(g)
Due to bond formation, entropy decreases.
Q2: Under isothermal condition, a gas at 300 K expands from 0.1 L to 0.25 L against a constant external pressure of 2 bar. The work done by the gas is [Given that 1 L bar = 100 J] [NEET 2019]
(a) 25 J
(b) 30 J
(c) 30 J
(d) 5 KJ
Ans: (b)
W = –P_{ext} (V_{2}–V_{1})
P_{ext} = 2 bar
V_{1} = 0.1 L
V_{2} = 0.25 L
W = –2 bar[0.25 – 0.1] L
W = –2 × 0.15 bar L
W = –0.30 bar L
W = (–0.30) × 100 = –30 J
Q1: The bond dissociation energies of X_{2} , Y_{2} and XY are in the ratio of 1 : 0.5 : 1.
(a) 800 kJ mol^{–1}
(b) 200 kJ mol^{–1}
(c) 400 kJ mol^{–1}
(d) 100 kJ mol^{–1}
Ans: (a)
Let bond dissociation energies of X_{2} , Y_{2} and XY are x kJ mol^{–1} , 0.5x kJ mol^{–1} and x kJ mol^{–1} respectively.
Q1: A gas is allowed to expand in a well insulated container against a constant external pressure of 2.5 atm from an initial volume of 2.50 L to a final volume of 4.50 L. The change in internal energy ΔU of the gas in joules will be [NEET 2017]
(a) 500 J
(b) 505 J
(c) +505 J
(d) 1136.25 J
Ans: (b)
w =  P_{ext}ΔV = 2.5(4.50  2.50)
ΔU = q + w
As, the container is insulted, thus q = 0
Hence, ΔU = w = 506.625 J
Q2: For a given reaction, ΔH = 35.5 kJ mol^{$$1} and ΔS = 83.6 J K^{$$1} mol^{$$1}. The reaction is spontaneous at (Assume that ΔH and ΔS do not vary with temperature.) [NEET 2017]
(a) T > 425 K
(b) Ball temperatures
(c) T > 298 K
(d) T < 425 K
Ans: (a)
For a spontaneous reaction,
Q1: For a sample of perfect gas when its pressure is changed isothermally from pi to pf, the entropy change is given by [NEET 2016]
(a)
(b)
(c)
(d)
Ans: (b)
For an ideal gas undergoing reversible expansion, when temperature changes from T_{i} to T_{f} and pressure changes from P_{i} to P_{f}.
Then amount of heat released on formation of 44 g CO_{2} = 393.5 kJ
∴ Amount of heat released on formation of
During adsorption of a gas, entropy decreases i.e, ΔS < 0
For spontaneous adsorption, ΔG should be negative, which is possible when ΔH is highly negative.
102 videos411 docs121 tests

1. What is the first law of thermodynamics? 
2. How is heat transfer related to thermodynamics? 
3. What is the difference between endothermic and exothermic reactions in thermodynamics? 
4. How do thermodynamic processes affect the efficiency of engines? 
5. What is entropy in thermodynamics and how does it relate to the second law of thermodynamics? 

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