Midterm Review Question

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Chem_Mod
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Midterm Review Question

Postby Chem_Mod » Tue Feb 12, 2019 4:06 pm

Hey Everyone!

I have put together a worksheet with a couple of practice questions for tomorrow's midterm. I would also post the solution later in this discussion. Let me know if there is any questions.

Good luck studying! Y'all got this!

Best,
Cindy
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Chem 14B Midterm Review Practice Problem.docx
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Emmaraf 1K
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Re: Midterm Review Question

Postby Emmaraf 1K » Tue Feb 12, 2019 6:46 pm

I am completely lost on #12. How would you even start?

Jim Brown 14B Lec1
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Re: Midterm Review Question

Postby Jim Brown 14B Lec1 » Tue Feb 12, 2019 7:16 pm

I think you need the bond enthalpy for ethane, then use it to heat water to 100º C and to reach its ∆Hvap

Jim Brown 14B Lec1
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Re: Midterm Review Question

Postby Jim Brown 14B Lec1 » Tue Feb 12, 2019 7:18 pm

Jim Brown 14B Lec1 wrote:I think you need the bond enthalpy for ethane, then use it to heat water to 100º C and to reach its ∆Hvap

Enthalpy of combustion*

Emmaraf 1K
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Re: Midterm Review Question

Postby Emmaraf 1K » Tue Feb 12, 2019 7:28 pm

Jim Brown 14B Lec1 wrote:
Jim Brown 14B Lec1 wrote:I think you need the bond enthalpy for ethane, then use it to heat water to 100º C and to reach its ∆Hvap

Enthalpy of combustion*


Okay that makes 10x more sense . Thanks!

Jim Brown 14B Lec1
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Re: Midterm Review Question

Postby Jim Brown 14B Lec1 » Tue Feb 12, 2019 7:34 pm

Jim Brown 14B Lec1 wrote:
Jim Brown 14B Lec1 wrote:I think you need the bond enthalpy for ethane, then use it to heat water to 100º C and to reach its ∆Hvap

Enthalpy of combustion*

nvm this [censored] is rough idk how to do it :'(

Chem_Mod
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Re: Midterm Review Question

Postby Chem_Mod » Wed Feb 13, 2019 1:27 am

Here is the answer key to the work sheet
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Chem 14B Midterm Review Practice Problem Key.docx
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Chem_Mod
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Re: Midterm Review Question

Postby Chem_Mod » Wed Feb 13, 2019 1:31 am

With regard to number 12:

you first find the number of moles for ethane using n=PV/RT
n=0.95×6.70.08314×298
n=0.2569mol

Then you calculate total enthalpy released is q=(-1437.17kJ/mol)×0.2569mol=-369.21kJ

Finally, assume all the heat is absorbed by the water to bring it to a boil: 369210=(m)(4.184)(373−298)
M=1176.58 g = 1.177 L

Hope this helps!

AdityaGuru1H
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Re: Midterm Review Question

Postby AdityaGuru1H » Wed Feb 13, 2019 11:13 am

Could someone please explain what we are supposed to do for #14 because I feel like i don't have enough information to do anything

Esther Lee 4H
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Re: Midterm Review Question

Postby Esther Lee 4H » Wed Feb 13, 2019 12:54 pm

im also struggling on 14 if anyone could help out

Emmaraf 1K
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Re: Midterm Review Question

Postby Emmaraf 1K » Wed Feb 13, 2019 3:33 pm

Can you post the explanation to 14. I feel like you need the enthalpy of CH4? Would you calculate it by finding the change in entropy associated with the loss of CH4 and O2 by calculating their entropies/mol (step 1), then finding the change in entropy as the reaction proceeds by doing delta H of the reaction divided by T (step 2), and then finally finding the change in entropy with the creation of CO2 and H2O by calculating their entropies/mol (step 3) and then adding the entropies of step 1, step 2, and step 3?


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