Homework problem 8.65

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Miya Eberlein 1J
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Homework problem 8.65

Postby Miya Eberlein 1J » Tue Jan 26, 2016 9:21 pm

Can someone help clarify #65 for me? We're trying to get to the equation N2 + 5/2 O2 --> N205
but at the end of the problem the solution is to subtract twice the enthalpy of NO from the formation of N205 because we don't need it... but we don't have N2 in the equation. Do we not need it because we wouldn't factor it in anyways, as that's its natural state? and does it not matter that taking away the NO would mean we only have 3 O2 molecules on the left side, even though we need 5 on the right?
thank you!

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Re: Homework problem 8.65

Postby Chem_Mod » Thu Jan 28, 2016 7:59 am

Always post the entire question so that Chemistry Community posts are self-sufficient.

In this problem, we are asked to find the enthalpy of formation of dinitrogen pentoxide from two given reactions ( and ) and the entropy of formation of NO.

By adding the first reaction to 1/2 the second reaction, we get the reaction . The enthalpy of this reaction is equal to .

Therefore, to find , we simply need to subtract .

Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

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