Chemical Equations and Reactions

Describing Chemical Reactions

Example: (NH₄)₂Cr₂O₇ → N₂(g) + Cr₂0₃(s) + 4H₂O(g)

Four Indications of a Chemical Reaction

• Release of energy as heat or light
• Production of a gas, typically in gas bubbles
• Formation of a precipitate
• Color change

3 Characteristics of Chemical Equations

• All reactants and products must be identified, through chemical analysis or from sources that give the results of the experiment
• The equation must contain the correct formulas for the reactants and products, determined through oxidation numbers.
• There should be the same number of atoms for each element should be there onboth sides of the chemical equation

A word equation is when the products are described using words instead of chemical formulas.
Example of formula equation: CH₄ + O₂ → CO₂ + H₂ 0.
Example of word equation: methane+ oxygen → carbon dioxide + water

There are five types of chemical equations: Synthesis Reactions, Decomposition Reactions, Single-Displacement Reactions, Double-Displacement Reactions, and Combustion Reactions

Synthesis Reactions

• In a synthesis reaction, two or more substances combine to form a new compound. Example: A + B → AB

Reactions of Elements with Oxygen and Sulfur

• One type of synthesis reaction is the combination of an element with oxygen to create an oxide of the specific element. Example: 2Mg(s) + O₂ → 2MgO
• Other Group 2 elements react very similiarly
• Group 1 elements need 2 metals atoms for every oxygen atom(Ex. Li₂O)
• Elements react react with sulfur similiarly to how they do with oxygen. These reactions produce sulfides(Ex. Li₂S