Calculate the value of S for the conversion of n = 1 molof liquid water at 100C

Question

Calculate the value of S for the conversion of n = 1 molof liquid water at 100C and 1 bar pressure into vapor at the sametermperature and a pressure of 0.01 bar. Assume idealbehavior for vapor. The molar enthalpy of vaporization ofwater at 100C and 1 bar is 40.0 kJ/mol. Please help with this problem. Have an exam this weekand would like to see how this is solved. Thanks alot. Calculate the value of S for the conversion of n = 1 molof liquid water at 100C and 1 bar pressure into vapor at the sametermperature and a pressure of 0.01 bar. Assume idealbehavior for vapor. The molar enthalpy of vaporization ofwater at 100C and 1 bar is 40.0 kJ/mol. Please help with this problem. Have an exam this weekand would like to see how this is solved. Thanks alot.

Explanation / Answer

we know that from second law of thermo dynamics entropy change = S = Q/T where Q is the heat exchanged also we know that Q = U + W                                   = U -PV and H = U + PV + VP so H = Q + VP now Q = H - VP                = 40*1000 -( 22.4*(1-0.01)*105)                = -2177600 J now T = 100 degrees C            =100+ 273.15 K            =373.15 K so S = Q/T            = -2177600/373.15            = -5835.7229 J/K/mol (ans)

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