ForExam4-erratum

# ForExam4-erratum - (a Calculate q for this heating and...

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Calculate the change in entropy when 2.00 mol of water is heated from 50 o C to 150 o C at 1 atm pressure. The molar heat capacities are: H 2 O(l) = 75.3 J/(K mol) H 2 O(g)= 36.4 J/(K mol) and the enthalpy of vaporization for water is 40.7 kJ/mol at 100 o C . Carry out calculations in 3 reversible steps: 1. D S(l) 50 o C 100 o C (heat the liquid) 2. D S(l g) at 100 o C (change the liquid to a gas) 3. D S(g) 100 o C 150 o C (heat the gas) 1. 2. 3. 4. K J T T nc S p / 7 . 21 323 373 ln 3 . 75 00 . 2 ln ) 1 ( 1 2 D K J T H n S bp v / 10 18 . 2 373 10 07 . 4 00 . 2 ) 2 ( 2 4 D D K J T T nc S p / 16 . 9 373 423 ln 4 . 36 00 . 2 ln ) 3 ( 1 2 D K J S S S S / 249 16 . 9 218 7 . 21 ) 3 ( ) 2 ( ) 1 ( D D D D

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One mole of water initially at 30 ° C is heated to 140 ° C at constant pressure of 1 atm. The molar heat capacities ( C P ) for liquid and gaseous water are: C P ( l ) = 75.3 J K -1 mol -1 and C P ( g ) = 36.4 J K -1 mol -1 , and are assumed to be temperature independent. The enthalpy of vaporization is 40.7 kJ mol -1 . Ideal gas behavior is assumed.
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Unformatted text preview: (a) Calculate q for this heating and boiling process Heating 30-100 o C: q 1 =nc p (l) D T=1x75.3x70=5.27 kJ [use definition of heat capacity: c=q/ D T] Boiling at p=const: q 2 = D H=40,700= 40.70 kJ [at p=const, D H=q= D U + p D V] Heating 100-140 o C: q 3 =nc p (g) D T=1x36.4x40=1.46 kJ q=q 1 +q 2 +q 3 (b) Calculate D H for this heating and boiling process At p=const, D H=q (c) Calculate D S for this heating and boiling process (as the previous problem) Heating 30-100 o C: D S 1 =nc p (l)ln(T 2 /T 1 )=1x75.3xln(373/303)=15.65 J/K Boiling: D S 2 = D H/T b =40,700/373=109.12 J/ K Heating 100-140 o C: D S 3 =nc p (g)ln(T 2 /T 1 )=1x36.4xln(413/373)=3.71 J/K Total D S=128.48 J/K If asked to compute changes in the internal energy U, use D H= D (U+PV). For this calculation, you will need to know how to evaluate the PV term....
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## This note was uploaded on 07/22/2008 for the course CHEM 115b taught by Professor Reisler during the Spring '08 term at USC.

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ForExam4-erratum - (a Calculate q for this heating and...

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