116 . F, T
Catalysts increase the rate of a reaction by decreasing the activation energy.
117. Part C
25 . B
Percent of sulfur: (32/98) × 100% = 33%
26 . D
To answer this question, you should know that when hydrochloric acid, a very strong acid, is
added to a solution, it will dissociate completely into hydrogen ions and chloride ions. This
increases the concentration of chloride ions already in the solution from the barium chloride.
According to Le Châtelier’s principle, if the concentration of one reaction species is increased,
the reaction will be driven in the opposite direction. For this example and the dissociation
reaction of barium chloride, if you increase the concentration of chloride ion, you will drive the
reaction in the direction of reassociation of barium chloride. Therefore, barium chloride will
precipitate out of the solution.
27 . C
Percent of aluminum: (54/342) × 100% = 15.8%
28 . C
Light is considered in a class by itself, but the different behaviors of light can be explained by
thinking of it as either a particle or a wave. The ability of light to show interference is a wave
property, while the photoelectric effect is a property best described through a particle model.
29 . D
