Chemistry

Chemical Reactions – Rearranging Atoms

Particle Model of Matter

All matter is made up of tiny particles that are constantly in motion

The smallest particle of matter is the atom Many chemical and physical properties of

matter can be described using the particle model

Solid Liquid Gas

Chemical Reactions

Two or more substances chemically combine to form a new substance

The substances (particles) entering the reaction are called reactants

The substances (particles) produced as a result of the reaction are called the products

The atoms of the reactants “rearrange” to form the products

Conservation of mass

Hydrogen gas (H2) combines with oxygen gas (O2) to produce water (H2O)

The mass of the reactants (H2 and O2) must equal the mass of the product (H2O)

This means the number of hydrogen and oxygen atoms in the reactants have to equal the number of hydrogen and oxygen atoms in the product

Conservation of Mass

A particle diagram can be used to “balance” the number of atoms of the reactants and products

Notice that it takes 2 molecules of H2 plus 1 molecule of O2 to produce 2 molecules of H2O

H2O2

H2O

Chemical Equations

Shorthand representation of a chemical reaction using chemical formula and coefficients

The subscript in a chemical formula describes the number of atoms of each element in the compound

The coefficient in front of the chemical formula describes the number of particles needed for the reaction to be “balanced”

Chemical Equations

H2O2

H2O

2H2O2 2H2O