Chapter Summary

• A complete chemical equation represents the reactants, products and their physical states symbolically.
•  A chemical equation is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation. Equations must always be balanced.
• In a combination reaction two or more substances combine to form a new single substance.
• Decomposition reactions are opposite to combination reactions. In a decomposition reaction, a single substance decomposes to give two or more substances.
• Reactions in which heat is given out along with the products are called exothermic reactions.
•  Reactions in which energy is absorbed are known as endothermic reactions.
• When an element displaces another element from its compound, a displacement reaction occurs.
• Two different atoms or groups of atoms (ions) are exchanged in double displacement reactions.
• Precipitation reactions produce insoluble salts.
•  Reactions also involve the gain or loss of oxygen or hydrogen by substances.
• Oxidation is the gain of oxygen or loss of hydrogen. Reduction is the loss of oxygen or gain of hydrogen.

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