Integer Answer Type Questions for JEE: Thermodynamics | Chapter-wise Tests for JEE Main & Advanced PDF Download

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Q.1. One mole of an ideal gas is allowed to expand reversibly and adiabatically from a temperature of 27°C. If the work done during the process is 3 kJ, the final temperature will be equal to (C_v = 20 JK^–1)

Ans.  150 K
dW = dU
nC_VΔT = 3
1 × 20 × ΔT = 3 × 10³
(Since after expansion the temperature will be lowered)

Q.2. Enthalpy change for the transition of liquid water to steam is 41 kJ mol^–1 at 100ºC. The entropy change for the above process is

Ans. 110

= 110 J K^–1 mol^–1

Q.3. 1m³ of neon gas initially at 273.2 K and 10 atm undergoes expansion isothermally and reversibly to final pressure of 1 atm. The work done by the gas is

Ans. –2332 kJ
Work done in isothermal reversible process is

So, to apply the above equation first we calculate ‘n’ by using PV= nRT
So,

W = –2332 kJ

Q.3. A piston exerting a pressure of 1 bar rests on the surface of water at 100ºC. The pressure is reduced to a small extent and as a result 10 g of water evaporates and absorb 20.0 kJ of heat. The value of ΔH_vap. of water is

Ans. 36 kJ mol^–1
Heat absorbed by 10 g of water = 20.0 kJ
Heat absorbed by 18 g of water = 20.0 × 18/10 = 36 kJ
∴ ΔH_vap of water = 36 kJ mol^-1.

Q.4. The dissociation energy of CH₄ is 360 kcal/mol and of ethane is 620 kcal/mol. Calculate C-C bond energy.

Ans. 80 kcal
Given, CH₄ → C + 4H ;
∴ Bond energy of 4(C-H) bond = 360 kcal
∴ Bond energy of C-H bond = 360/4 =  90 kcal
In C₂H₆ → 2C + 6H
Bond energy of C₂H₆ = 1(C-C) + 6(C-H)
∴ 620= 1(C-C) + 6 × 90= 80 kcal
Bond energy of C-C = 80 kcal.

Q.5. Compute the magnitude of heat of formation of liquid methyl alcohol in kilo joule per mol using the following data. Heat of vaporisation of liquid methyl alcohol = 38 kJ/mol. Heat of formation of gaseous atoms from the elements in their standard states: H, 218 kJ/mol; C, 715 kJ/mol ; O, 249 kJ/mol.
Average bond energies: C-H, 415 kJ/mol C-O, 356 kJ/mol O-H, 463 kJ/mol.

Ans. -266 kJ mol^-1
C(s) + 2H₂(g) + ½O₂(g) → CH₃OH(l) ; ΔH = ?
ΔH = Bond energy data for formation + bond energy data for dissociation +  energy released during liquefaction
= -[3C-H + 1C-O + 1O-H] + [C_{s → g} + 2H-H + ½O-O]
- [CH₃OH(g) → CH₃OH(l)]
= -[3 × 415 + 356 + 463] + [715 + 2 × 436 + ½ × 249] - 38
= -266 kJ mol^-1.