8.65

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Michelle Dong 1F
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8.65

Postby Michelle Dong 1F » Mon Jan 22, 2018 10:07 am

65. Calculate the standard enthalpy of formation from dinitrogen pentoxide form the following data,
2NO (g) + O2 (g) --> 2NO2 (g) delta h = -114.1 kJ
4NO2 (g) + O2 (g) --> 2N2O5 (g) delta h = -110.2 kJ
and from the standard enthalpy of formation of nitric oxide, NO.

How do you go about solving this?

Chem_Mod
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Re: 8.65

Postby Chem_Mod » Mon Jan 22, 2018 11:50 am

the standard enthalpy of formation of nitric oxide means the enthalpy change of following reaction under standard condition:
N2 (g) + O2 (g) --> 2NO (g)
And the next step is to use Hess's Law. For further clarification, please clearly state the point that you are unsure of.

Hannah Chew 2A
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Re: 8.65

Postby Hannah Chew 2A » Mon Jan 22, 2018 11:53 am

To start off, you should write the reaction for the formation of N2O5, where N2O5 is on the right hand side with a coefficient of 1. Using the other reactions they give you, you want to rearrange the equations so that the sum of the 2 reactions would give you the overall reaction above. Using Hess's Law, you can also find delta H for the overall reaction (should be-169.2kJ). Lastly, you can solve for the enthalpy of formation of N2O5 with this equation: -169.2kJ = enthalpy of formation of N2O5 - 2 (enthalpy of formation of NO). Using simple algebra, you can solve the problem.

Cassandra Mullen 1E
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Re: 8.65

Postby Cassandra Mullen 1E » Fri Jan 26, 2018 8:06 am

To write the formation equation for dinitrogen pentoxide, you want 1 mol of N2O5 to form from its elements in standard state. After writing down the proper elements, don't forget to balance! :)


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