NEET Thermodynamics — Set 8

Question 1

For a reversible isothermal expansion of an ideal gas, the work done is given by:

Accepted Answer

For reversible isothermal expansion, $w = -nRT \ln(V_2/V_1)$, where $V_2 > V_1$.

Question 2

Calculate $ \Delta S_{sys} $ for the condensation of 1 mol of ethanol at 351 K. ($ \Delta H_{vap} = 38.6 \, \text{kJ/mol} $)

Accepted Answer

For $ C_2H_5OH(g) \rightarrow C_2H_5OH(l) $, $ \Delta S_{sys} = -\frac{\Delta H_{vap}}{T} = -\frac{38.6 \times 10^3}{351} \approx -110.0 \, \text{J/K·mol} $, as condensation decreases entropy.

Question 3

For an ideal gas undergoing adiabatic expansion from 2 L to 4 L at 400 K ($ \gamma = 1.67 $), what is the final temperature?

Accepted Answer

For adiabatic process, $ T_2 = T_1 (V_1/V_2)^{\gamma-1} = 400 \times (2/4)^{0.67} \approx 400 \times 0.62996 = 252.0 \, \text{K} $.

NEET Chemistry: Thermodynamics — Practice Set 8

Q1. For a reversible isothermal expansion of an ideal gas, the work done is given by:

Q2. Calculate \( \Delta S_{sys} \) for the condensation of 1 mol of ethanol at 351 K. (\( \Delta H_{vap} = 38.6 \, \text{kJ/mol} \))

Q3. For an ideal gas undergoing adiabatic expansion from 2 L to 4 L at 400 K (\( \gamma = 1.67 \)), what is the final temperature?

Q4. Using bond enthalpies (\(C-H = 413 \, \text{kJ/mol}\), \(Cl-Cl = 243 \, \text{kJ/mol}\), \(C-Cl = 328 \, \text{kJ/mol}\), \(H-Cl = 431 \, \text{kJ/mol}\)), calculate \(\Delta H\) for \(CH_4(g) + Cl_2(g) \rightarrow CH_3Cl(g) + HCl(g)\).

Q5. Calculate the work done when 1 mol of an ideal gas (\( \gamma = 1.67 \)) is compressed adiabatically from 20 L to 4 L at 300 K. (\( R = 8.314 \, \text{J/mol·K} \))

Q6. Calculate \(\Delta S_{surr}\) when 1 mol of a substance melts at 300 K with \(\Delta H_{fus} = 9 \, \text{kJ/mol}\).

Q7. Calculate \(\Delta H\) for \(C_2H_5OH(l) \rightarrow C_2H_4(g) + H_2O(l)\) using: \(\Delta H_f^\circ (C_2H_5OH,l) = -277.7 \, \text{kJ/mol}\), \(\Delta H_f^\circ (C_2H_4,g) = 52.3 \, \text{kJ/mol}\), \(\Delta H_f^\circ (H_2O,l) = -285.8 \, \text{kJ/mol}\).

Q8. Calculate \(\Delta S_{surr}\) when 1 mol of \(H_2O(l)\) forms under standard conditions at 298 K, given \(\Delta_f H^\circ = -286 \, \text{kJ/mol}\).

Q9. Calculate the heat absorbed when 32 g of sulfur is heated from 30°C to 130°C at constant pressure. (\(C_p = 22.7 \, \text{J/mol·K}\), molar mass = 32 g/mol)

Q10. For which process does entropy decrease?