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25 grams of water vaporises at 373 K against a constant external pressure of 1 atm. The molar enthalpy of vaporisation is 9.72 kcal/mol. If steam obeys perfect gas laws, then work done against the atmosphere and change of internal energy in the above process, respectively, are
  • a)
    -1036.194 cal and 12,464.886 cal
  • b)
    921.4 cal and 11,074 cal
  • c)
    1029.4 cal and 12,470.6 cal
  • d)
    1129.3 cal and 10,207 cal
Correct answer is option 'A'. Can you explain this answer?
Most Upvoted Answer
25 grams of water vaporises at 373 K against a constant external press...
Given data:
- Mass of water vapor = 25 grams
- Temperature = 373 K
- External pressure = 1 atm
- Molar enthalpy of vaporisation = 9.72 kcal/mol

Calculations:
1. Calculate the number of moles of water vapor:
Number of moles = Mass / Molar mass
Molar mass of water = 18 g/mol
Number of moles = 25 g / 18 g/mol = 1.389 moles
2. Calculate the work done against the atmosphere:
Work done = -PΔV
ΔV = nRT/P (from ideal gas law)
ΔV = 1.389 * 0.0821 * 373 / 1 = 43.96 L
Work done = -1 atm * 43.96 L = -43.96 L.atm
Convert work to calories: 1 L.atm = 101.3 J = 0.241 cal
Work done = -43.96 * 0.241 cal = -10.6 cal
3. Calculate the change in internal energy:
Change in internal energy = q + w
q = nΔH
q = 1.389 * 9.72 kcal = 13.494 kcal
Change in internal energy = 13.494 - 10.6 = 2.894 kcal = 2894 cal

Final answer:
- Work done against the atmosphere = -10.6 cal = -1036.194 cal (rounded off)
- Change in internal energy = 2894 cal
Therefore, option 'A' is the correct answer.
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25 grams of water vaporises at 373 K against a constant external pressure of 1 atm. The molar enthalpy of vaporisation is 9.72 kcal/mol. If steam obeys perfect gas laws, then work done against the atmosphere and change of internal energy in the above process, respectively, area)-1036.194 cal and 12,464.886 calb)921.4 cal and 11,074 calc)1029.4 cal and 12,470.6 cald)1129.3 cal and 10,207 calCorrect answer is option 'A'. Can you explain this answer?
Question Description
25 grams of water vaporises at 373 K against a constant external pressure of 1 atm. The molar enthalpy of vaporisation is 9.72 kcal/mol. If steam obeys perfect gas laws, then work done against the atmosphere and change of internal energy in the above process, respectively, area)-1036.194 cal and 12,464.886 calb)921.4 cal and 11,074 calc)1029.4 cal and 12,470.6 cald)1129.3 cal and 10,207 calCorrect answer is option 'A'. Can you explain this answer? for JEE 2024 is part of JEE preparation. The Question and answers have been prepared according to the JEE exam syllabus. Information about 25 grams of water vaporises at 373 K against a constant external pressure of 1 atm. The molar enthalpy of vaporisation is 9.72 kcal/mol. If steam obeys perfect gas laws, then work done against the atmosphere and change of internal energy in the above process, respectively, area)-1036.194 cal and 12,464.886 calb)921.4 cal and 11,074 calc)1029.4 cal and 12,470.6 cald)1129.3 cal and 10,207 calCorrect answer is option 'A'. Can you explain this answer? covers all topics & solutions for JEE 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for 25 grams of water vaporises at 373 K against a constant external pressure of 1 atm. The molar enthalpy of vaporisation is 9.72 kcal/mol. If steam obeys perfect gas laws, then work done against the atmosphere and change of internal energy in the above process, respectively, area)-1036.194 cal and 12,464.886 calb)921.4 cal and 11,074 calc)1029.4 cal and 12,470.6 cald)1129.3 cal and 10,207 calCorrect answer is option 'A'. Can you explain this answer?.
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