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 SolidLiquidGas

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 (H 2 ) combines with oxygen gas (O 2 ) to produce water (H 2 O) The mass of the reactants (H 2 and O 2 ) must equal the mass of the product (H 2 O) 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 H 2 plus 1 molecule of O 2 to produce 2 molecules of H 2 O H2H2 O2O2 H2OH2O

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 H2H2 O2O2 H2OH2O 2H 2 O2O2 2H 2 O