1. Intro to Chemical Equations
Chapter 8 Sections 1 & 2

2. Vocabulary
Chemical Reaction – process by which one or more substances change to produce one or more different substances
Evidence of a chemical reaction
Formation of a gas
Formation of a precipitate (solid)
Change in color, odor
Change in energy (exothermic, endothermic, light)

3. Vocabulary Physical Changes -
Change in physical state (melting, vaporization)

4. Vocabulary
Endergonic – a chemical reaction that must absorb energy to occur

5. Vocabulary
Exergonic – a chemical reaction that releases energy as the products are produced

6. Vocabulary
Chemical Equation – a representation of a chemical reaction that uses symbols to show the relationship between the reactants and products

7. How to Write a Chemical Reaction
Step 1. Start with Word Equations
Write down the reactant names separated with a + sign.
Use an arrow to point from reactants to the products
Write products to the right of the arrow, also separated by + signs.

8. Word Equation Example
When a solid aluminum oxide and hydrogen gas are heated, molten aluminum and water vapor will form
Aluminum oxide + hydrogen  Aluminum + H2O

9. Formula Equation
Step 2
Substitute correct chemical formulas for the names in the word equation
Aluminum oxide + hydrogen  Aluminum + H2O
Al2O3 + H2  Al + H2O

10. State Symbols and Reaction Conditions p. 265
Meaning
(s)
Solid state
(l)
Liquid state
(g)
Gaseous state
(aq)
Aqueous solution – dissolved in water 
“produces” or “yields” 
Reversible reaction
Δ or heat
Reactants are heated Pd
Name or formula of catalyst that speeds up the reaction → → →
Let’s go back and add the proper symbols to our example!

11. The Seven Diatomic Gases
Learn the seven diatomic gases, sometimes called diatomic elements. They are:
Names hydrogen oxygen nitrogen chlorine bromine iodine fluorine
Formulas H2 O2 N2 Cl2 Br I F2
ClIF H BrON

12. Sample Problems
Write the word equation for the electrolysis of water into its two gas elements.