Winter 2015 Midterm 2a

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204635822
Posts: 25
Joined: Fri Sep 25, 2015 3:00 am

Winter 2015 Midterm 2a

Postby 204635822 » Tue Feb 09, 2016 12:43 pm

On question 2a on the winter 2015 midterm,the question says "the reaction between gaseous iodoethane and water vapor generates ethanol and HI. Assume the rxn happens under constant pressure, 1atm, and 25 C. 36 g of h2o is converted to ethanol and HI gas. V1=20L. internal energy = 84KJ"

I dont understand why you cant use pv=nrt to find pv and then multiply it by -1 since w=-pv. Why is work =0? Why does having a gas make volume change 0?

Emma Edmond 3E
Posts: 29
Joined: Fri Sep 25, 2015 3:00 am

Re: Winter 2015 Midterm 2a

Postby Emma Edmond 3E » Tue Feb 09, 2016 5:03 pm

When you calculate work for this problem you need w=-PDeltaV. We don't have the information for Delta V, so we can use the equation w=-DeltanRT. The change in moles is 0 because you have the same number of moles on each side of the equation, therefore work is 0. In addition, because this reaction is happening under constant pressure DeltaU=DeltaH, which means DeltaH=84.00kJ.

204635822
Posts: 25
Joined: Fri Sep 25, 2015 3:00 am

Re: Winter 2015 Midterm 2a

Postby 204635822 » Tue Feb 09, 2016 5:14 pm

Thank you so much. I was trying to calculate nrt, not the change of each


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