Intro to Chemical Equations Chapter 8 Sections 1 & 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)

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

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

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

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

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.

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

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

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!

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 Br2 I2 F2 ClIF H BrON

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