Exercise 17.36 The enthalpy change associated with the vaporization of ethanol i

Question

Exercise 17.36

The enthalpy change associated with the vaporization of ethanol is 38.6 kJmol1 at its boiling point of 78 C.

Part A

Determine the change in entropy for the vaporization of ethanol.

Express your answer using three significant figures and include the appropriate units.

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Part B

Compare the change in entropy for the vaporization of ethanol to that computed for water (Hvap = 40.7 kJmol1)

Compare the change in entropy for the vaporization of ethanol to that computed for water ( = 40.7 )

Explanation / Answer

The entropy change associated with the vapourization of ethanol can be found out by using the simple relation:

Delta Svap = DeltaHvap/Boiling point

As, delta G = 0 for any phase change

And deltaG = delta H - TdeltaS

DeltaG = 0

DeltaH = TdeltaS

S = deltaH/T

Now deltaHvap =38.6kJ/mol

T = 78C = 78+273K = 351K

DeltaSvap = 38.6kJ/mol / 351K = 0.10997kJ/molK = 109.97J/molK = 110J/molK

Change in entropy for vapourization of water:

DeltaHvap = 40.7kJ/mol

Boiling point = 100C = 373K

DeltaSvap = 40.7kJ/mol /373K = 109.11J/molK = 109J/molK

Thus,the values of entropy change for vapourization of ethanol and water are about the same.

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