Chemical Reactions and Balancing Equations

In a chemical reaction, bonds between atoms

are broken and new bonds are formed, joining atoms into different combinations.

A chemical equation satisfies

conservation of matter if it is balanced.

No atoms are

created or destroyed in a chemical reaction.

In a chemical equation,

reactants are shown on the left, and products are shown on the right.

For example, the subscript "2" in H2O indicates

that there are two hydrogen atoms in a water molecule.

synthesis

The combination of parts to make a whole A+B=AB

Subscript

a number in a chemical formula representing the number of atoms of a particular element in one molecule of the compound.

Coefficient

a number that multiplies a term in an equation.

Chemical reaction

a process in which one or more substances are transformed into others.

single displacement (replacement)

a reaction in which one element or radical takes the place of another element or radical in a compound A + BC → AC + B

Conservation of matter

a scientific law that states that the total amount of matter in a closed system remains constant.

Product

a substance that is formed in a chemical reaction.

Reactant

a substance that takes part in a chemical reaction.

Chemical equation

a symbolic representation of a chemical reaction.

For example

the chemical equation Na + Cl2 → NaCl describes the reaction of sodium (Na) and chlorine gas (Cl2) to form table salt.

double displacement (replacement)

the positive ion of one compound replaces the positive ion of the other to form two new compounds AB + CD → AD + CB

In a balanced chemical equation

there are the same numbers of each type of atom on each side of the equation: 2Na + Cl2 → 2NaCl is balanced because there are two sodium atoms and two chlorine atoms on each side of the equation.

Chemical formulas use subscripts and parentheses

to denote the number of atoms in a molecule of the substance.

A water molecule (H2O) is made of

two hydrogen atoms and one oxygen atom.

Examples of chemical formulas include

NaCl (table salt), H2O (water), and Ca(OH)2 (calcium hydroxide).

In a chemical equation, the coefficients indicate the number of each type of molecule. For example,

6H2O means that there are six water molecules.

decomposition

A chemical reaction that breaks down compounds into simpler products. AB=A+B