1. Describing Chemical Reactions
The process by which one or more substances change into one or more new substances.

2. Reactant – the original substance/s
substance/s that undergo a change
found on the left side of chemical equation
Product – the substance/s created
found on the right side of chemical equations

3. Evidence of a Chemical Change
Change in energy
Release of energy as heat or light
Production of sound
Reduction or increase of temperature
Absorption or release of electrical energy
Formation of gas
change in odor
bubbling or fizzing
Change in color
Formation of a precipitate
An insoluble solid

4. Exothermic and Endothermic Reactions
Exothermic reactions – energy is released
Energy can be thought of as a product
Endothermic reactions – energy is absorbed
Energy can be thought of as a reactant

5. Constructing a Chemical Equation
A correctly written chemical equation shows the chemical formulas and relative amounts of all reactants and products.
The first step in writing a chemical equation is to write a word equation.
A word equation consists of the names of reactants and products separated by the yield sign, an arrow, which means produces or forms.

6. Formula Equations
The next step is to change a word equation into a formula equation.
Replace the names of substances with their formulas.
This kind of formula does not give any quantitative information.

7. Equations and Reactions Information
Equations give information about the amounts of each substance in the reaction
Information about specific conditions and that are needed for the reaction to take place can also be included in the equation.
This information is written over or under the yield sign.
350 C, kPa
N2(g) + 3H2(g)   2NH3(g)
catalyst

8. Symbols Represent States of Matter
(g) gas
(s) solid
(l) liquid
(aq) aqueous (dissolved in water)
 yields or produces
 reversible reaction in which product
can reform into reactants, results in a
mixture of products and reactants
heat conditions can be placed over or under the arrow to show conditions necessary for the reaction to take place