Practice Problem 3

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

2 NO₂(g) N₂O₄(g)

Solution

NO₂ has an unpaired electron in its Lewis structure:

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

Because it forms a new bond, this reaction should be exothermic.  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  S for this reaction therefore favors the reactants.