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### Self-Test 9.7A

Posted: **Tue Feb 06, 2018 1:39 pm**

by **Lily Guo 1D**

I'm a little confused about how to apply Trouton's Law. For example, self-test 9.7A says "Use Troutonâ€™s rule to estimate the standard enthalpy of vaporization of liquid bromine, which boils at 59 C." I thought that Trouton's Law said that most liquids have a standard enthalpy of vaporization of 85 J/K mol, but the answer to this was 28 kJ/mol. How do you get that answer?

### Re: Self-Test 9.7A

Posted: **Wed Feb 07, 2018 3:57 pm**

by **Dylan Davisson 2B**

Trouton's law says that the standard entropy of vaporization are commonly 85 J/(K*mol). It talks about entropy, not enthalpy. The question, on the other hand, asks you to solve for the enthalpy of vaporization of bromine liquid.

The question asks you to apply the assumption that the entropy of vaporization (S) for the liquid bromine is 85 J/(K*mol) in the entropy of vaporization equation: deltaS=(deltaH)/(Tb). Once the entropy of vaporization and the boiling temperature (Tb=332K) are put into the equation, you can solve for the standard enthalpy of the vaporization of liquid bromine, which is approximately 28kJ/mol.

### Re: Self-Test 9.7A

Posted: **Thu Feb 08, 2018 2:42 pm**

by **Lily Guo 1D**

Dylan Davisson 2B wrote:Trouton's law says that the standard entropy of vaporization are commonly 85 J/(K*mol). It talks about entropy, not enthalpy. The question, on the other hand, asks you to solve for the enthalpy of vaporization of bromine liquid.

The question asks you to apply the assumption that the entropy of vaporization (S) for the liquid bromine is 85 J/(K*mol) in the entropy of vaporization equation: deltaS=(deltaH)/(Tb). Once the entropy of vaporization and the boiling temperature (Tb=332K) are put into the equation, you can solve for the standard enthalpy of the vaporization of liquid bromine, which is approximately 28kJ/mol.

Thank you so much! This was super helpful :)