11.1. Chemical Equations http://www.ck12.org
The modern day formulation of gun powder is called black powder. It is still commonly used today. Its formulation
is still quite similar to what was used in 9thcentury China. Black powder is considered a low explosive. It is a
mixture that burns quickly, but the resulting shock wave travels at subsonic speeds. The speed at which it burns is
dependent on the accessibility of oxygen atoms to the carbon source. In contrast, high explosives like nitroglycerin
detonate instead of burning, creating shock waves that are supersonic (faster than the speed of sound).
The Chemical Equation
Chemical equations describe the changes in composition that take place during a chemical reaction. Along with
the identities of the starting reactants and the final products, chemical equations show the ratios in which these
substances are consumed and produced. The reaction of iron with oxygen to form iron(III) oxide is shown in the
Figure11.5.
FIGURE 11.5
The sparks from a steel grinder are
molten iron. The iron reacts with oxygen
to form iron(III) oxide.We can describe this reaction with a chemical equation:
4Fe(s)+3O 2 (g)→2Fe 2 O 3 (s)
This equation is said to be balanced, because the amount of each element expressed on the reactants side is equal to
the amounts expressed on the products side. This is shown more explicitly in the followingTable11.1.
TABLE11.1: 4Fe
Reactants Products
Fe 4 4
O 6 6Often times, the processes described by chemical equations do not represent a single reaction. For example, the
following equation shows the starting materials and the products for photosynthesis:
6CO 2 (g)+6H 2 O(l)
light
→C 6 H 12 O 6 (s)+6O 2 (g)
This process does not occur in a single step. A sequence of many individual reactions is required to make glucose
and oxygen gas out of carbon dioxide and water. Chemical equations can be used to represent individual reactions