8.57 Clarification

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Ranger Saldivar 2D
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Joined: Fri Sep 25, 2015 3:00 am

8.57 Clarification

Postby Ranger Saldivar 2D » Sat Jan 23, 2016 6:14 pm

In 8.57, in the textbook, to find the reaction enthalpy when given the final reaction, in this case the hydrogention of ethyne to ethane, how do we know how to get to that reaction with the use of other reactions. Do we always take the reactants and producta and combust them with O2?

ConnieDo3I
Posts: 31
Joined: Fri Sep 25, 2015 3:00 am

Re: 8.57 Clarification

Postby ConnieDo3I » Sat Jan 23, 2016 6:38 pm

For this problem, they give you the ∆H°c for each of the compounds involved in the final equation. This means that they gave you the enthalpy of combustion for each compound, which means the heat released when the compound undergoes combustion.

To get the reaction that the book gives you, you have to write out the combustion reactions (reacting with O2 and producing CO2 and H2O) for each of the compounds.

Then you use Hess's Law to combine the equations you wrote out (don't forget to switch the signs of the ∆H°c if you switch around an equation and multiply by any scalars you use), canceling out compounds not present in the final equation that you should get (which is the one the book gives you).

Hope this helps!

Ranger Saldivar 2D
Posts: 28
Joined: Fri Sep 25, 2015 3:00 am

Re: 8.57 Clarification

Postby Ranger Saldivar 2D » Sat Jan 23, 2016 6:41 pm

Thanks I didn't see the c so I did not know it meant combustion.


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