### 8.37

Posted:

**Tue Jan 16, 2018 10:24 am**How do you know how to find the enthalpy? I don't understand how they derived the answer in the solutions manual.

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=75&t=25607

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Posted: **Tue Jan 16, 2018 10:24 am**

How do you know how to find the enthalpy? I don't understand how they derived the answer in the solutions manual.

Posted: **Tue Jan 16, 2018 11:30 am**

For part a, you know that the vaporization of 0.579 moles of Ch4 requires 4.76 kJ of heat, so all you have to do is divide the amount of heat by the moles to find the enthalpy (kJ/mol).

4.76 kJ/0.579 mol=8.22 kJ/mol

For part b it is very similar but instead of being given moles, you are given grams. In this problem, you must first convert grams to moles using the molar mass. The molar mass of C2H5OH is 46.07 g/mol. To get moles, divide 22.45 grams by 46.07 g/mol to get 0.4873 moles. Now you can do the same thing you did in part a. Divide the amount of heat required in the reaction by the amount of moles to find the enthalpy.

21.2kJ/0.487 mol=43.5 kJ/mol

Hope this helps!

4.76 kJ/0.579 mol=8.22 kJ/mol

For part b it is very similar but instead of being given moles, you are given grams. In this problem, you must first convert grams to moles using the molar mass. The molar mass of C2H5OH is 46.07 g/mol. To get moles, divide 22.45 grams by 46.07 g/mol to get 0.4873 moles. Now you can do the same thing you did in part a. Divide the amount of heat required in the reaction by the amount of moles to find the enthalpy.

21.2kJ/0.487 mol=43.5 kJ/mol

Hope this helps!

Posted: **Tue Jan 16, 2018 2:11 pm**

nevermind I understand now

Posted: **Tue Jan 16, 2018 2:12 pm**

Shoot just saw this. Thank you Kelly!