Chemicals interact with each other in chemical reactions. Chemical reactions break
existing chemical bonds and form new ones. The reaction is represented symbolically by an
arrow. Consider the following chemical reaction: 2H2 + O2 –>
2H2O. In this reaction two molecules of hydrogen combine with one molecule of
oxygen to yield two molecules of water (figure 6.11).
The second law determines whether or not this reaction will happen. Let
the chemicals be the system. The electrons in water have less energy than those in
hydrogen and oxygen. This decrease in electron energy releases heat as the reaction takes
place. This heat increases the entropy of the surroundings, figure 6.12. This heat drives
the reaction forward because it ensures that the entropy of the universe increases. Thus,
this chemical reaction is said to be spontaneous. This means that given time, the reaction
will happen. It does not mean that the reaction will happen quickly.
Figure 6.11: A Simple Chemical Reaction
Figure 6.12: System Diagram for Above Reaction
Notice that the entropy decreases for the isolated system because when the system exists
as oxygen and hydrogen more micro-states are available than when the system exists as
water, but just like the bicycle example, the heat released increases the entropy of the
surroundings. This allows the entropy of the universe to increase. Therefore, the reaction
is spontaneous.
next: Chemical Kinetics
home: Intelligent Design and the origin of life |
