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posted by  Mr. Eko on 11/3/2009 12:29:47 PM  |  status: Closed  |  Earned Karma: 25

Thermodynamic Question - Enthalpy/Entropy (Equilibrium Temp)

Course Textbook Chapter Problem Needs by
Thermodynamics N/A N/A N/A 11/5/2009 at 9:00:00 PM
Question Details:
One kilogram of ice at 0?C is added to 7 kg of water at 30?C and 1 bar. The enthalpy of
melting for ice is 335 kJ/kg. Consider that the process is adiabatic.

(a) What is the final equilibrium temperature (?C)?
(b) Calculate the entropy production (kJ/K) during this process.
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posted by kwyjibo on 11/3/2009 10:12:06 PM  |  status: Live
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Response Details:
a)

1 kg ice *(334e3 J/kg)  + 1000g* 4.18 J/g/C*(Tfinal - 0 C)= 7kg*(4.18 J/g/C)*(30 C - Tfinal)
334e3 J + 4180 J*Tfinal = 877800 J - 29260J*Tfinal

Tfinal*(4180 J + 29260 J) = 877800 J - 334e3 J
Tfinal = 16.2619617 = 16 Celsius

b)

ΔS = ΔH/T_melt + m_meltedice*Cp*ln[T2/T1] + m_cooled water*Cp*ln[T4/T3]
ΔS = 334 kJ/273 K  + 1 kg*(4.18 kJ/kg/K)*ln([16 + 273]/[0 + 273]) + 7 kg*(4.18 kJ/kg/K)*ln([16+273]/[30+273])
ΔS = 0.0773376808 kJ/K
ΔS = 7.73 e-2 kJ/K
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