Balancing Equations
When balancing chemical equations, it is important to remember that no matter is created or
destroyed.
Chemical equations are written with the reactants on the left side of the equation (reaction arrow) and
products on the right side of the equation (reaction arrow).
HCl +KOH H
2
O + KCl
Reactant: A substance that undergoes change in a chemical reaction and is written on the left side of
the reaction arrow in a chemical equation.
Product: A substance that is formed in a chemical reaction and is written on the right side of the
reaction arrow in a chemical equation.
The bonds between atoms in the reactants are rearranged to form new compounds in chemical
reactions, but none of the atoms disappear and no new ones are formed. As a consequence, chemical
equations must be balanced, meaning that the number and kinds of atoms must be the same on both
sides of the reaction arrow.
The numbers placed in front of formulas to balance equations are called coefficients, and they multiply
all the atoms in a formula. Thus, the symbol “2 NaHCO
3
” indicates two units of sodium bicarbonate,
which contain 2 Na atoms, 2 H atoms, 2 C atoms, and 6 O atoms (2 X 3= 6, the coefficient times the
subscript for O). Count the numbers of atoms on the right side of the equation to convince yourself that
it is indeed balanced.
2 NaHCO
3
Na
2
CO
3
+ H
2
O + CO
2
Balanced Equation: A chemical equation in which the numbers and kinds of atoms are the same on
both sides of the reaction arrow.
Coefficient: A number placed in front of a formula to balance a chemical equation.
The Four Steps of Balancing Equations:
1. Write an unbalanced equation, using the correct formulas for all reactants and products.
Remember that the scripts in chemical formulas cannot be changed in balancing an equation
because doing so would change the identity of the substances in the reaction.
2. Add appropriate coefficients to balance the number of atoms of each element.
3. Check the equation to make sure the numbers and kinds of atoms on both sides of the
equation are the same.
4. Make sure the coefficients are reduced to their lowest whole-number values
2 H
2
SO
4
+ 4 NaOH 2Na
2
SO
4
+ 4 H
2
O reduces to H
2
SO
4
+ 2 NaOH Na
2
SO
4
+ 2 H
2
O
Law of conservation of mass: Matter is neither created nor destroyed in chemical reactions