Download What is the Law of Conservation of Mass?

TEKS 8.5F: Recognize whether a chemical equation containing coefficients is balanced or not and how
that relates to the law of conservation of mass.
What is the Law of Conservation
of Mass?
• The law of conservation of mass states that during a chemical
reaction, matter is neither created nor destroyed. In any
chemical reaction, the total mass of the reactants must equal the
total mass of the products.
• According to the law of conservation of mass, atoms are not
created or destroyed in a chemical reaction. However, they may
be rearranged, forming new substances.
1. Define In your own words, write a definition of the law of conservation of
mass.
TEKS 8.5F: Recognize whether a chemical equation containing coefficients is balanced or not and how
that relates to the law of conservation of mass.
What Does a Balanced Chemical
Equation Tell You?
• A chemical equation uses formulas and other symbols to
represent a chemical reaction. For example, the following
equation tells you that hydrogen (H) reacts with oxygen (O),
forming water (H2O).
H2 + O2  H2O
• Look at the diagram below that shows the molecules in this
reaction.
2. Interpret What does the number 2 in the formula H2 tell you?
(contd.)
TEKS 8.5F: Recognize whether a chemical equation containing coefficients is balanced or not and how
that relates to the law of conservation of mass.
• Atoms help explain the law of conservation of mass. The total
number of atoms of each element in the reactants is equal to the
total number of atoms of each element in the products.
• A balanced chemical equation uses coefficients—numbers
written in front of a chemical formula—to make the number of
atoms of each element equal on both sides of the equation.
• Look again at the equation for the reaction of hydrogen and
oxygen, forming water. This equation is balanced because it has
four atoms of hydrogen and two atoms of oxygen on both sides
of the equation.
2 H2 + O2  2 H2O
3. Recognize Tell whether or not the following chemical equation
containing coefficients is balanced. Explain your answer.
2 Fe2O3 + 3 C  4 Fe + 3 CO2
(contd.)
TEKS 8.5F: Recognize whether a chemical equation containing coefficients is balanced or not and how
that relates to the law of conservation of mass.
• The diagram below shows the molecules represented by the
balanced equation of the reaction of hydrogen and oxygen that
forms water. Notice that the number of hydrogen atoms is the
same on both sides of the arrow. The same is true for the
oxygen atoms.
2 H2 + O2  2 H2O