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# Solved Example Problem: Second Law of thermodynamics

Chemistry : Thermodynamics: Second Law of thermodynamics : Solved Example Problem

### Problem: 7.10

If an automobile engine burns petrol at a temperature of 816o C and if the surrounding temperature is 21o C, calculate its maximum possible efficiency.

### Solution: Here

Th = 816+273= 1089 K;

Tc= 21+273= 294K

%Efficiency=( 1089-294 / 1089) x100

%Efficiency=73%

### Problem: 7.6

Calculate the standard entropy change for the following reaction( ŌłåS0f ), given the standard entropies of CO2(g), C(s),O2(g) as 213.6 , 5.740 and 205 JKŌłÆ1 respectively.

C(g) + O2(g) ŌåÆCO2(g)

S0r = Ōłæ S0products ŌłÆ Ōłæ Sreac0 tan ts

S0r = {S0CO 2 } ŌłÆ {SC0 + S0O2 }

S0r = 213.6 ŌłÆ [5.74 + 205]

S0r = 213.6 ŌłÆ[210.74]

S0r = 2.86 JKŌłÆ1

### Problem: 7.7

Calculate the entropy change during the melting of one mole of ice into water at 00 C and 1 atm pressure. Enthalpy of fusion of ice is 6008 J mol-1

### Given:

ŌłåHfusion = 6008 JmolŌłÆ1

Tf = 0 0

C = 273 K

2O(S) --273 KŌåÆ H 2O ( l) fusion = 22 .007 J K ŌłÆ1 moleŌłÆ1

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11th Chemistry : UNIT 7 : Thermodynamics : Solved Example Problem: Second Law of thermodynamics |