NEET Thermodynamics — Set 6

Question 1

How much heat is required to vaporize $ 0.7 \, \text{g} $ of water at $ 100^\circ \text{C} $ and $ 1 \, \text{atm} $? (Latent heat = $ 2256 \, \text{J/g} $)

Accepted Answer

$ \Delta Q = m L $. $ m = 0.7 $, $ L = 2256 $. $ \Delta Q = 0.7 \times 2256 = 1579.2 \, \text{J} \approx 1579 \, \text{J} $.

Question 2

A gas undergoes an isothermal expansion at $ 300 \, \text{K} $ from a volume of $ 2 \, \text{L} $ to $ 6 \, \text{L} $. If the number of moles of the gas is $ 0.1 $, what is the work done by the gas? (Take $ R = 8.3 \, \text{J mol}^{-1} \text{K}^{-1} $)

Accepted Answer

For an isothermal process, $ W = \mu R T \ln\left(\frac{V_2}{V_1}\right) $. Substitute: $ \mu = 0.1 $, $ R = 8.3 $, $ T = 300 $, $ V_2 = 6 $, $ V_1 = 2 $. $ W = 0.1 \times 8.3 \times 300 \times \ln\left(\frac{6}{2}\right) = 249 \times \ln(3) $. $ \ln(3) \approx 1.0986 $, so $ W \approx 249 \times 1.0986 \approx 273.55 \, \text{J} $. Rounded: $ W \approx 274 \, \text{J} $.

Question 3

How much heat is required to raise the temperature of $ 0.25 \, \text{kg} $ of tungsten from $ 25^\circ \text{C} $ to $ 55^\circ \text{C} $? (Specific heat of tungsten = $ 134.4 \, \text{J kg}^{-1} \text{K}^{-1} $)

Accepted Answer

$ \Delta Q = m s \Delta T $. $ m = 0.25 $, $ s = 134.4 $, $ \Delta T = 55 - 25 = 30 $. $ \Delta Q = 0.25 \times 134.4 \times 30 = 1008 \, \text{J} $.

NEET Physics: Thermodynamics — Practice Set 6

Q1. How much heat is required to vaporize \( 0.7 \, \text{g} \) of water at \( 100^\circ \text{C} \) and \( 1 \, \text{atm} \)? (Latent heat = \( 2256 \, \text{J/g} \))

Q2. A gas undergoes an isothermal expansion at \( 300 \, \text{K} \) from a volume of \( 2 \, \text{L} \) to \( 6 \, \text{L} \). If the number of moles of the gas is \( 0.1 \), what is the work done by the gas? (Take \( R = 8.3 \, \text{J mol}^{-1} \text{K}^{-1} \))

Q3. How much heat is required to raise the temperature of \( 0.25 \, \text{kg} \) of tungsten from \( 25^\circ \text{C} \) to \( 55^\circ \text{C} \)? (Specific heat of tungsten = \( 134.4 \, \text{J kg}^{-1} \text{K}^{-1} \))

Q4. A system absorbs \( 690 \, \text{J} \) of heat and has \( 210 \, \text{J} \) of work done on it. What is the change in internal energy?

Q5. How many calories are equivalent to \( 836 \, \text{J} \) of heat? (1 cal = \( 4.186 \, \text{J} \))

Q6. 0.2 moles of an ideal gas expand isothermally at 350 K from 4 L to 10 L. What is the heat absorbed? (\( R = 8.3 \, \text{J mol}^{-1} \text{K}^{-1} \))

Q7. How much heat is required to raise the temperature of \( 0.3 \, \text{kg} \) of silver from \( 35^\circ \text{C} \) to \( 65^\circ \text{C} \)? (Specific heat of silver = \( 236.1 \, \text{J kg}^{-1} \text{K}^{-1} \))

Q8. An ideal gas expands isothermally at \( 380 \, \text{K} \) from \( 5 \, \text{L} \) to \( 15 \, \text{L} \) with \( 0.25 \, \text{moles} \). What is the work done by the gas? (\( R = 8.3 \, \text{J mol}^{-1} \text{K}^{-1} \))

Q9. Which of the following statements is correct about the Second Law of Thermodynamics?

Q10. How many joules are equivalent to \( 300 \, \text{cal} \) of heat? (1 cal = \( 4.186 \, \text{J} \))