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JEE Main20199 Jan 2019Evening ShiftChemistryThermodynamics (C)Actual

The entropy change associated with the conversion of 1 k g of ice at 273 K to water vapours at 383 K is: (Specific heat of water liquid and water vapour are 4.2 k J K - and 2.0 k J K - 1 k g - 1 ; heat of liquid fusion and vaporization of water are 334 k J k g - 1 and 2491 k J k g - 1 , respectively). ( l o g 273 = 2.436 , log ⁡ 373 = 2.572 , log ⁡ 383 = 2.583 )

Options

  1. A9.26 k J k g - 1 K - 1
  2. B2.64 k J k g - 1 K - 1
  3. C8.49 k J k g - 1 K - 1
  4. D7.90 k J k g - 1 K - 1

Correct answer

A. 9.26 k J k g - 1 K - 1

Step-by-step solution

( i ) Phase change H 2 O ( l ) → H 2 O ( s ) So ( i i ) Temperature change phase same (fusion) H 2 O ( l ) → Δ S 2 Δ H 2 O ( l ) Δ S 2 =  mS  ln   T 2 T 1 = 1 × 4 .2   ln   373 273 = 1 .31 ( i i i ) Phase change (vapourisation) Δ S 3 = Δ H v a p 373 = 2491 373 = 6.67 ( i v ) Temperature change phase same H 2 O ( g ) 373   K → Δ S 4 H 2 O ( g ) 383   K Δ S 4 = 2   l n 383 373 = 0.0529 Δ S    tot

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