The heat of formation of N2O from N2 and O2 is 68 kJ. The heat of formation of NO2 from NO and O2 is -131 kJ. What is the heat of formation of NO from N2 and O2

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justaguide | College Teacher | (Level 2) Distinguished Educator

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In the problem, the following information is provided: The heat of formation of `NO_2` from `N_2` and `O_2` is 68 kJ. The heat of formation of `NO_2` from NO and `O_2` is -131 kJ. The heat of formation or standard enthalpy of formation is the change in enthalpy when the final products are created from the reactants.

The chemical reaction of nitrogen and oxygen combining to form nitrogen dioxide (`NO_2` ) is:

`N_2 + 2O_2 -> NO_2`, `Delta H` ` `=  68 kJ

The chemical reaction of nitrogen monoxide and oxygen to form nitrogen dioxide is:

`2NO + O_2 -> 2NO_2` , `Delta H` = -131 kJ

To determine the enthalpy of formation of NO from nitrogen and oxygen, the enthalpy of the following reaction has to be determined: `N_2 + O_2 -> 2NO`

`N_2 + O_2 -> 2NO`

=> `NO_2 -> O_2 + 2NO` ,  `DeltaH` = 131 kJ

+    `N_2 + 2O_2 -> NO_2` , `DeltaH` = 68 kJ

Adding the two equations gives:

`N_2 + O_2 -> 2NO`

Using Hess's Law, the enthalpy of formation of the two reactions can be added to give 131 + 68 = 199 KJ

From the given information, the enthalpy of formation of NO from `N_2` and `O_2` is 199 kJ

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