Given the following dаta:

2O3 - > 3O2 (enthalpy = - 427 kJ)

O2 - > 2O (enthalpy = + 495 kJ)

NO + O3 - > NO2 + O2 (enthalpy = - 199 kJ)

Calculate the enthalpy for the reaction

NO + O - > NO2 using Hess's Law ...?

Just try to find how you will get the reaction by adding the other reactions. Reverse the second eq as O is in reactant side and half it ...

Now in the final reaction there is neither ozone nor oxygen so now you have oxygen on the products side after adding reversed

2 and 3, O - >1/2 O2

adding this to the third eq you get,

NO+O + O3 - > NO2 + 3/2 O2

Now you need to remove O3 and O2 using the first equation,

So reverse the first one, half it and add, 3/2O2-> O3 adding it removes O3 and O2 you get the requires equation,

NO + O->NO2 you can do the calculation bit yourself when you add reactions Enthalpy is also added by Hess law so yeah that part should be pretty simple.