- E The activation energy of forward and reverse reactions is always
characterized by the “hump” that you see in pictures of this kind. It’s the
energy necessary to get the reaction going. The reactants of the reverse
reaction have energy that is expressed by the flat portion of the curve to
the right of the hump. For a reaction to occur, these reactants must gain
an energy equal to that represented by the top of the hump. This energy
that must be acquired is represented by (E). Remember that catalysts
reduce activation energy and the rate of the reaction.
- B The enthalpy change of a reaction is the amount of heat the reaction
absorbs or gives off. In this case, the reactants begin at one energy level
(represented by the flat portion of the curve to the left of the hump), and
the products are associated with another (represented by the flat portion
of the curve to the right of the hump). The difference represents the
enthalpy change of the reaction (which, in this case, is negative—the
reaction liberates heat; it’s exothermic).
- A Recall that the activated complex represents the highest energy state
reactants achieve as they are transformed into new substances. So the
energy of the activated complex is measured from the very bottom of the
diagram to the top of the activation energy barrier. This distance is
represented by (A).
- B BaI 2 is composed of a metal (Ba) and nonmetal (I) bonded together. This
is an ionic compound that held together by—surprise—ionic bonding.
- C You may be tempted to go with “ionic bonding” here, but resist that
impulse. The ions in an ionic solid are too restricted in their movement to
conduct a charge, so (B) is incorrect. Now think: What solids conduct
electricity? Metals, of course. And why can copper wire be used to
conduct electricity? Because the metallic bonds that hold a sample of
copper together do so through the motion of many free electrons, which
can conduct electricity as they move.
- D Don’t be fooled by (A). Hydrogen bonds occur between, not within
molecules. A hydrogen molecule consists of nonmetal hydrogen atoms in
a bond. Nonmetals form covalent bonds, and identical nonmetal atoms
form nonpolar covalent bonds.
