Calculate the enthalpy change for the reaction no(g) + o(g) → no2(g) from the following data: no(g) + o3(g) → no2(g) + o2(g) δh = –198.9 kj o3(g) → 1.5o2(g) δh = –142.3 kj o2(g) → 2o(g) δh = 495.0 kj

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Solution:- The enthalpy changed asked to calculate for the reaction,

It is based on Hess's law where we use the given equations to make the desired equation and calculate it's enthalpy change.

For our equation we need one NO(g) on reactant side and it is present in first equation so let's write this as such.

Now we need O(g) on reactant side which is present in third equation. Third equation has two O on product side so we need to divide it by 2 and also reverse it so that we could get one O on reactant side. When an equation is reversed then sign of delta H also gets changed.

To cancel ozone, we need to reverse second equation.

Let's add all these three equations now:

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So, the enthalpy change for the given equation asked to calculate is -304.1 kJ.

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