Page 21 - Science Course 3 (Book 2)

Mo8-L2b: Why is Mass Conserved in a Chemical Reaction?

Law of Conservation of Mass A subscript describes the number of atoms of an
element in a compound.
law that states that the total mass of the reactants
before a chemical reaction is the same as the total If an element’s symbol does not have a subscript, the
mass of the products after the chemical reaction. compound contains only one atom of that element.

Symbols and Formulas of Some Elements and
Compounds

Let’s Begin 2

Chemical Equations

A chemical equation is a description of a reaction
using element symbols and chemical formulas. A chemical equation includes both the substances
that react and the substances that are formed in a
chemical reaction.

The starting substances in a chemical reaction are
reactants.
The substances produced by the chemical reaction
are products.

The reactants are written to the left of the arrow.

The products are written to the right of the arrow.

C H CH + H C H + CH
In chemical equations, element symbols represent 6 5 3 2 6 6 4
elements and chemical formulas represent
compounds. The general structure for a chemical equation is:

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