The 5 branches are organic, inorganic, biochemistry, analytical, and physical. There are different branches because they each apply to different parts of chemistry. For example organic chemistry is the study of carbon compounds and inorganic chemistry is the study of non carbon compounds. You can't just have one type of chemistry because these are very different.
Cars, aeroplanes, factories etc
The rate of a chemical reaction can be raised by increasing the surface area of a solid reactant. This is done by cutting the substance into small pieces, or by grinding it into a powder.
Enzymes in our body increases the speed of chemical digestion.
