NEET Thermodynamics — Set 2

Question 1

Which of the following statements correctly describes the First Law of Thermodynamics?

Accepted Answer

The First Law ($ \Delta Q = \Delta U + \Delta W $) is a conservation principle, stating heat added equals internal energy increase plus work done. Option D is correct.

Question 2

A gas is compressed adiabatically from $ 8 \, \text{L} $ to $ 2 \, \text{L} $. If the initial pressure is $ 1 \, \text{atm} $ and $ \gamma = 1.4 $, what is the final pressure?

Accepted Answer

$ P_1 V_1^\gamma = P_2 V_2^\gamma $. $ P_1 = 1 \, \text{atm} $, $ V_1 = 8 \, \text{L} $, $ V_2 = 2 \, \text{L} $, $ \gamma = 1.4 $. $ 1 \times 8^{1.4} = P_2 \times 2^{1.4} $. $ P_2 = \frac{8^{1.4}}{2^{1.4}} = \left(\frac{8}{2}\right)^{1.4} = 4^{1.4} $. $ 4^{1.4} = (2^2)^{1.4} = 2^{2.8} \approx 6.96 \, \text{atm} $.

Question 3

Why is the specific heat capacity of a substance temperature-dependent?

Accepted Answer

Specific heat capacity varies with temperature because the energy required to raise the temperature of a substance depends on molecular interactions and vibrational modes, which change with temperature (e.g., water’s variation in Fig. 11.5).

NEET Physics: Thermodynamics — Practice Set 2

Q1. Which of the following statements correctly describes the First Law of Thermodynamics?

Q2. A gas is compressed adiabatically from \( 8 \, \text{L} \) to \( 2 \, \text{L} \). If the initial pressure is \( 1 \, \text{atm} \) and \( \gamma = 1.4 \), what is the final pressure?

Q3. Why is the specific heat capacity of a substance temperature-dependent?

Q4. An ideal gas expands isothermally at \( 420 \, \text{K} \) from \( 7 \, \text{L} \) to \( 21 \, \text{L} \) with \( 0.4 \, \text{moles} \). What is the work done by the gas? (\( R = 8.3 \, \text{J mol}^{-1} \text{K}^{-1} \))

Q5. Why is the Zeroth Law fundamental to the measurement of temperature?

Q6. In an isobaric process, \( 0.8 \, \text{moles} \) of an ideal gas expand from \( 6 \, \text{L} \) to \( 12 \, \text{L} \) at \( 350 \, \text{K} \). What is the work done by the gas? (\( R = 8.3 \, \text{J mol}^{-1} \text{K}^{-1} \))

Q7. A gas expands isothermally at \( 400 \, \text{K} \) absorbing \( 800 \, \text{J} \) of heat. What is the change in its internal energy?

Q8. In an isochoric process, what happens to the work done by the gas?

Q9. Why does the specific heat capacity of a solid generally agree with \( 3R \) at ordinary temperatures?

Q10. Why can’t a heat engine operate with a single reservoir according to the Second Law?

Q11. Which of the following statements is incorrect regarding the First Law of Thermodynamics?

Q12. In an isobaric process, \( 0.8 \, \text{moles} \) of gas expand from \( 330 \, \text{K} \) to \( 410 \, \text{K} \). What is the heat supplied if \( C_p = 29.1 \, \text{J mol}^{-1} \text{K}^{-1} \)?

Q13. What is the change in internal energy when \( 0.1 \, \text{kg} \) of lead is heated from \( 20^\circ \text{C} \) to \( 40^\circ \text{C} \)? (Specific heat of lead = \( 127.7 \, \text{J kg}^{-1} \text{K}^{-1} \))

Q14. A system absorbs \( 700 \, \text{J} \) of heat while \( 300 \, \text{J} \) of work is done on it. What is the change in internal energy?

Q15. How much heat is required to vaporize \( 1.4 \, \text{g} \) of water at \( 100^\circ \text{C} \) and \( 1 \, \text{atm} \)? (Latent heat = \( 2256 \, \text{J/g} \))