3.27 Chemical Reaction Rate
collide with greater force. For example, food spoils because of chemical reactions, and these reactions occur faster
at higher temperatures (see the bread on the left in theFigure3.40). This is why we store foods in the refrigerator
or freezer (like the bread on the right in theFigure3.40). The lower temperature slows the rate of spoilage.
FIGURE 3.40
Left image: Bread after 1 month on a
warm countertop. Right image: Bread
after 1 month in a cold refrigerator.Concentration of Reactants
Concentrationis the number of particles of a substance in a given volume. When the concentration of reactants is
higher, the reaction rate is faster. At higher concentrations, particles of reactants are crowded closer together, so they
are more likely to collide and react. Did you ever see a sign like the one in theFigure3.41? You might see it where
someone is using a tank of pure oxygen for a breathing problem. Combustion, or burning, is a chemical reaction in
which oxygen is a reactant. A greater concentration of oxygen in the air makes combustion more rapid if a fire starts
burning.
FIGURE 3.41
Q:It is dangerous to smoke or use open flames when oxygen is in use. Can you explain why?
A:Because of the higher-than-normal concentration of oxygen, the flame of a match, lighter, or cigarette could
spread quickly to other materials or even cause an explosion.