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
- 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