It is learnt that when atoms unite to form compounds, the atoms themselves achieve stability. It might be concluded from this that, when a compound is former, it is stable and nonreactive. However, this is not necessarily the case.

Under certain conditions of temperature, pressure, pH, or other factors, compounds. This involves breaking existing bonds and the formation of new ones. We have already seen how this may occur whenever acids or bases react with buffering systems, or even with one another.

However, let us now look more closely at chemical reactions-the breaking of old bonds and the formation of new ones. By way of analogy, let us consider atoms as letters, molecules as words, and a chemical reaction as sentence imparting a though. Just as there are ways to classify sentences, so we may deal with chemical reactions listed below are fundamental ones.

Synthetic Reactions. As the name implies, something is made in a reaction abstractly as follows:

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H2 + CL, -» 2HC1

Since two substances react to form a third, we might represent this reaction abstractly as: A + B -> C. Synthetic reactions are quite common in living systems. For example, many of the reactions involved in growth, where new substances are being formed constantly, are synthetic in nature.

Decomposition reactions. This typed of reaction is the reverse of a synthetic reaction. To illustrate, 2HC1 -> H +

As we would suppose, a decomposition reaction may be represented symbolically as: C -» A + B. and respiration, where complex molecules are broken down into smaller molecules.

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Displacement, or exchange, reactions Displacement reactions involve the replacement of an atom or a group of atoms by another atom or another group. Let us consider the following typical reaction: Zn + 2HC1 -> ZnCl2 + H2

This type of reaction may be generalized as: A + BC -» AC + B

Displacement reactions are very important to living systems. For example, in the body fluids of higher animals, various ions and molecules constantly displace each other as they are transported to and from tissues by certain compounds. Double displacement reactions these reactions involve a mutual exchange between compounds. For instance, NaOH+ HC1 -> NaCl + H20

This reaction may be symbolized as: AB+CD -> AD+BC

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Double displacement reactions are quite common in living systems. Buffering reactions are included in this type. Rearrangement reactions these reactions simply involve a change in the bonding pattern within a molecule where there is no change in the number or kinds of atoms.