Writing Chemical Equations

Numbers written before a molecular formula mean the number of ————— of that substance

molecules

e.g.

2NaCl means 2 molecules of sodium chloride

Numbers written as a lowercase after an atomic symbol mean the number of ———— of that element within a single molecule of that substance

atoms

e.g.

H2O means that in a single molecule of water, there are 2 hydrogen atoms and a single oxygen atom

2H2O means ….

there are two water molecules, each with 2 hydrogen atoms and a single oxygen atom for a total of 4 hydrogens and 2 oxygens

what is a word equation

Provides a simple way to describe chemical reactions by stating the reactants and products.
e.g

Solid sodium Metal reacts with Oxygen in the atmosphere to form sodium oxide solid. 

what is a chemical equation

Chemical equations describe a chemical reaction, with the reactants to the left of the arrow and products to the right.

• Formulae are used to represent the chemicals involved.

• The physical states of the chemicals are often included.

• Numbers are written in front of the formulae in order to balance the numbers of atoms on each side of the equation.

e.g.

2Na(s) + O ₂(g) → 2Na ₂O(s)

what are the reactants

the substances that enter a chemical reaction

what are products

are formed as the result of reactants reaction