212 DIY Science: Illustrated Guide to Home Chemistry Experiments
EvdRE y Ay CHEmICAL kINETICS
We make use of the principles of chemical kinetics in many aspects of everyday life. Here are just a few examples:- Cooking is actually an application of the effect of temperature on reaction rates. When we cook food, the higher
temperature causes many chemical reactions to occur quickly within the food; primarily, the denaturation of proteins.
For example, when you hard-boil an egg, the liquid albumin protein is denatured to a different chemical compound. This
conversion of proteins during cooking is important not only for palatability, but because the denatured forms of proteins
are often more easily metabolized than the natural forms. - Sterilization and disinfection by heat is another application of chemical kinetics. When we heat an object to sterilize it,
the heat increases the rate of various reactions among the chemical compounds present in microbes, converting those
compounds to useless forms. - Chemical kinetics processes in the form of catalysis are used to minimize the amount of air pollution produced by
automobile exhausts (via catalytic converters) and factory smokestacks (via catalytic scrubbers). - Catalysts are essential for the production of many important industrial chemicals, including mineral acids, fertilizers, and
many other compounds. - Catalytic cracking is used to produce gasoline and other short-chain hydrocarbon fuels from the heavy, long-chain
hydrocarbons present in crude petroleum.
LABORATORY 12.1:
dETERmINE THE EffECT of TEmpERATURE oN REACTIoN RATE
Reactions proceed faster at higher tempera-
tures because increasing the temperature
also increases the average kinetic energy
of the reactant molecules, making it more
likely that a collision between two reactant
molecules will have sufficient energy to initiate
the reaction. An old rule of thumb states that
increasing the temperature by 10°C doubles
the rate of reaction. (So, of course, reducing the
temperature by 10°C halves the reaction rate.)
RIREEqU d EqUIpmENT ANd SUppLIES£ goggles, gloves, and protective clothing£ balance and weighing papers£ thermometer£ timer£ foam cup£ Alka-Seltzer tablets (3)£ water (hot and cold tap water)We’ll test that rule of thumb in this lab by reacting Alka-Seltzer
tablets with water at different temperatures. When an Alka-Seltzer
tablet is dropped into water, it emits carbon dioxide as it dissolves
and its components react. We could get basic data about the
reaction rate simply by determining how long it takes a tablet to
dissolve completely in water at various temperatures. But using
that method gives us data only about the starting and ending
points. It doesn’t tell us, other than in the most general terms,
whether the reaction rate is linear or if it changes over time.
We know that this reaction evolves gaseous carbon dioxide, which
means that the mass of the reaction vessel and contents decreases
as the reaction proceeds. By recording the mass of the reaction
vessel and its contents periodically as the reaction progresses, we
can gather the data needed to determine whether the reaction rate
is linear and whether reaction temperature affects the linearity of
the reaction rate.