Chemical Reactions:

a well defined example of a chemical change. Chemical reaction: a well defined example of a chemical change.

The substances that are about to react. Reactants: The substances that are about to react.

The new substances produced. Products: The new substances produced.

Law of Conservation of Mass: In a chemical reaction, matter is not created or destroyed but is conserved.

Writing equations: A variety of symbols are used when writing equations: Chemical symbols, other symbols, subscripts, and coefficients.

Coefficient: Represents the number of units of each substance taking part in a reaction.

Subscripts The little numbers in a chemical equation on the right side of elements which tells you the number of element atoms are present

A balanced chemical equation: Has the same number of atoms on each side of the equation.

Steps for balancing an equation:

Step 1: Write a chemical equation for the reaction. H2(g) + O2(g) --> H2 O(l)

Step 2: H2(g) + O2(g) --> H2 O(l) Check equation for atom balance. H = 2 H = 2 O =2 O = 1

Step 3: If there is atom balance, then you are done. If there is not atom balance, you must choose coefficients.(This is a trial & error procedure. It gets easier with practice.)

Choosing coefficients 2H2(g) + O2(g) -->2 H2 O(l) H = 4 H = 4 O = 2 O = 2

This procedure will get easier as you practice!

Symbols in Chemical Equations Chart

Energy in Chemical Reactions

Exothermic Reactions: Some form of energy is given off by the reaction. (heat, light)

Endothermic Reaction: Some form of energy must be added for the reaction to take place. (heat, light)

A substance added to speed up a chemical reaction. Catalyst: A substance added to speed up a chemical reaction.

Used to prevent chemical reactions from occurring. Inhibitors: Used to prevent chemical reactions from occurring.