NEET Thermodynamics — Set 23

Question 1

A system in a cyclic process performs $ 300 \, \text{J} $ of work and rejects $ 200 \, \text{J} $ of heat. What is the heat absorbed?

Accepted Answer

For cyclic: $ \Delta U = 0 $, $ Q_{\text{net}} = W $. $ Q_{\text{absorb}} - Q_{\text{reject}} = W $. $ Q_{\text{absorb}} - 200 = 300 \Rightarrow Q_{\text{absorb}} = 500 \, \text{J} $.

Question 2

Which variable is classified as an extensive thermodynamic state variable?

Accepted Answer

Extensive variables depend on the size or amount of the system and scale with it (e.g., halve when the system is halved). Volume ($ V $) is extensive, while pressure ($ P $) and temperature ($ T $) are intensive, not dependent on size.

Question 3

A gas undergoes an isothermal compression from $ 8 \, \text{L} $ to $ 2 \, \text{L} $ at $ 350 \, \text{K} $ with $ 0.2 \, \text{moles} $. What is the heat released? ($ R = 8.3 \, \text{J mol}^{-1} \text{K}^{-1} $)

Accepted Answer

For isothermal: $ W = \mu R T \ln\left(\frac{V_2}{V_1}\right) $, $ \Delta U = 0 $, $ Q = W $. $ W = 0.2 \times 8.3 \times 350 \times \ln\left(\frac{2}{8}\right) = 581 \times \ln(0.25) $. $ \ln(0.25) = -\ln(4) \approx -1.386 $. $ W = 581 \times (-1.386) \approx -805 \, \text{J} $. $ Q = -805 \, \text{J} $ (negative implies heat released).

NEET Physics: Thermodynamics — Practice Set 23

Q1. A system in a cyclic process performs \( 300 \, \text{J} \) of work and rejects \( 200 \, \text{J} \) of heat. What is the heat absorbed?

Q2. Which variable is classified as an extensive thermodynamic state variable?

Q3. A gas undergoes an isothermal compression from \( 8 \, \text{L} \) to \( 2 \, \text{L} \) at \( 350 \, \text{K} \) with \( 0.2 \, \text{moles} \). What is the heat released? (\( R = 8.3 \, \text{J mol}^{-1} \text{K}^{-1} \))

Q4. What is the molar specific heat capacity at constant volume for a diatomic gas if \( R = 8.3 \, \text{J mol}^{-1} \text{K}^{-1} \)?

Q5. Which factor primarily causes irreversibility in a process involving friction?

Q6. How much heat is required to raise the temperature of \( 0.25 \, \text{kg} \) of tungsten from \( 15^\circ \text{C} \) to \( 45^\circ \text{C} \)? (Specific heat of tungsten = \( 134.4 \, \text{J kg}^{-1} \text{K}^{-1} \))

Q7. How many joules are equivalent to \( 350 \, \text{cal} \) of heat? (1 cal = \( 4.186 \, \text{J} \))

Q8. A monatomic gas undergoes an adiabatic expansion from \( 720 \, \text{K} \) to \( 360 \, \text{K} \) with \( 1.5 \, \text{moles} \). What is the work done? (\( R = 8.3 \, \text{J mol}^{-1} \text{K}^{-1} \), \( \gamma = 1.67 \))

Q9. Which of the following statements is incorrect about isothermal processes?

Q10. A gas is compressed adiabatically from \( 20 \, \text{L} \) to \( 5 \, \text{L} \), increasing its pressure from \( 3 \, \text{atm} \) to \( 12 \, \text{atm} \). What is \( \gamma \)?