  Use Hess's law to calculate ΔG°rxn using the following information.             NO(g) + O(g) → NO2(g)                             ΔG°rxn = ?              2 O3(g) → 3 O2(g)                                       ΔG°rxn = +489.6 kJ            O2(g) → 2 O(g)                                            ΔG°rxn = +463.4 kJ            NO(g) + O3(g) → NO2(g) + O2(g)             ΔG°rxn = -199.5 kJ

Question

Use Hess's law to calculate ΔG°rxn using the following information.

NO(g) + O(g) → NO2(g)                             ΔG°rxn = ?

2 O3(g) → 3 O2(g)                                       ΔG°rxn = +489.6 kJ

O2(g) → 2 O(g)                                            ΔG°rxn = +463.4 kJ

NO(g) + O3(g) → NO2(g) + O2(g)             ΔG°rxn = -199.5 kJ

Step 1

The first thing to do is to change the bottom three reactions to make it look like the top reaction.  Then add them all again.

Step 2

Only the bottom reaction stays the while the other you have to now change the sign of the Delta Grxn.

Now divide or multiply when necessary to cancel out any unwanted molecules, but remember whether you multiply or divide, be sure to do the same with the Delta Grxn of each. Like so:

Step 3

Then all you get left over is (When combinin...

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