Chemistry Concepts

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Avogadro’s number

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Chemical equation

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A symbolic representation of a chemical reaction. Reactants are shown on the left, and products are shown on the right. In a balanced equation, there are the same numbers of each type of atom on each side.

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Chemical formula

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A symbolic representation of an element or compound. Uses subscripts and parentheses to denote the number of atoms in a molecule. Examples include NaCl, H_{2}O, and Ca(OH)_{2}.

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Chemical reaction

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A process in which one or more substances are transformed into others. Bonds are broken and new bonds are formed, joining atoms into different combinations. No atoms are created or destroyed.

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Coefficient

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A number that multiplies a term in an equation. Indicates the number of each type of molecule. For example, 6H_{2}O means there are six water molecules.

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Combination reaction

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A chemical reaction in which two or more reactants form a single product. Also called synthesis reactions. Example: hydrogen (H_{2}) combines with oxygen (O_{2}) to form water (H_{2}O).

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Combustion

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A chemical reaction in which a fuel is burned. Involves the burning of a hydrocarbon in oxygen, producing water and carbon dioxide. Example: methane burns in oxygen to form water and carbon dioxide.

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Conservation of matter

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A scientific law stating that the total amount of matter in a closed system remains constant. A chemical equation satisfies conservation of matter if it is balanced.

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Decomposition

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A chemical reaction in which a single substance is broken down into two or more products. Example: NaCl decomposes into Na and Cl₂.

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Double replacement

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A chemical reaction where two compounds exchange elements or molecules. Example: Na₂S and HCl react to form NaCl and H₂S.