(a) Trouton’s rule states that the ratio of the molar heat of vaporization of a liquid (ΔHvap) to its boiling point in kelvins is approximately 90 J/K · mol. Use the following data to show that this is the case and explain why Trouton’s rule holds true.
(b) Use the values in Table 12.5 to calculate the same ratio for ethanol and water. Explain why Trouton’s rule does not apply to these two substances as well as it does to other liquids.
(a)
Interpretation:
To verify Trouton's rule for the given set of substances.
Concept Introduction:
According to Trouton's rule for, various liquids attheir boiling point the change in entropy value will be the same. The ratio of enthalpy of vaporization and boiling temperature of various liquids has the same value.
Where,
Answer to Problem 14.47QP
Trouton's rule is verified for benzene, hexane, mercury and toluene. All the four substances have
Explanation of Solution
To record the given data
To verify Trouton's rule for benzene
Trouton's rule can be verified by plugging in the values of
Since the value is approximately equal to
To verify Trouton's rule for hexane
Trouton's rule can be verified by plugging in the values of
Since the value is approximately equal to
To verify Trouton's rule for mercury
Trouton's rule can be verified by plugging in the values of
Since the value is approximately equal to
To verify Trouton's rule for Toluene
Trouton's rule can be verified by plugging in the values of
Since the value is approximately equal to
(b)
Interpretation:
To verify Trouton's rule for the given set of substances.
Concept Introduction:
According to Trouton's rule for, various liquids attheir boiling point the change in entropy value will be the same. The ratio of enthalpy of vaporization and boiling temperature of various liquids has the same value.
Where,
Answer to Problem 14.47QP
Trouton's rule is not obeyed by water and ethanol due to the high entropy of vaporization.
Explanation of Solution
To record the given data
To verify Trouton's rule for ethanol
Trouton's rule can be verified by plugging in the values of
Since, the value is greater than
To verify Trouton's rule for water
Trouton's rule can be verified by plugging in the values of
Since the value is greater than
To explain the reason for the deviation from hydrogen bond in case of water and ethanol.
For water and ethanol there exist strong hydrogen bonding attraction in the liquid state. Hydrogen bonding interaction decreases the entropy in the system. In gaseous state the hydrogen bonding interaction becomes weaker and the molecules will have more randomness in the system. The entropy of vaporization will be high. This is the reason why water and ethanol is showing larger deviation from Trouton's rule.
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Chapter 14 Solutions
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