Practice Problem 3

Use the Lewis structures of NO2 and N2O4 and the stoichiometry of the following reaction to decide whether delta H and delta S favor the reactants or products of this reaction:

2 NO2(g) equilibr.gif (63 bytes) N2O4(g)


NO2 has an unpaired electron in its Lewis structure:

ex21_3a.gif (1739 bytes)


When two NO2 molecules collide in the proper orientation, a covalent bond can form between the nbitrogen atoms to produce the dimer, N2O4:

ex21_3b.gif (1962 bytes)

Because it forms a new bond, this reaction should be exothermic.  delta H for this reaction therefore favors the products.  The reaction leads to a decrease in the entropy of the system because the system becomes less disordered when two molecules come together to form a larger molecule  delta S for this reaction therefore favors the reactants.

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