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31 terms

Unit #2- Writing and Balancing Chemical Equations

STUDY
PLAY
Reactants
Substances which enter into the chemical reaction/change
Products
Substances which are produced by the chemical reaction
Chemical Equation
Condensed statement which indicates what has happened during a chemical reaction
What are the two types of double replacements?
1. Precipitation Double Replacement
2. Acid-Based Double Replacement
Precipitation Double Replacement
-The reactants are both ionic compounds
-Occurs in aqueous solution
-Insoluble product = precipitate (solid)
-Can write molecular, ionic, and net ionic equations
Acid-Base Double Replacement
-Reactants must be an acid or base
-Acid: substance which releases hydrogen ions into solution
-Base: substance which releases hydroxide ions into solution
-Can write molecular, ionic, and net ionic equations
Hydrochloric Acid
HCl(aq)
Sulfuric Acid
H2SO4(aq)
Nitric Acid
HNO3(aq)
Writing Molecular Equations
-All substances are represented by element symbols/ compound formulas and phase symbols
-Must be balanced
Writing Ionic Equations
-Dissociate the aqueous compounds into their ions
-Ions are represented by element symbol, phase symbol, charge, and number of atoms
Writing Net Ionic Equations
-Remove spectator ions (ions that appear in identical form on both sides of the equation) from the ionic equation
Solubility Rules (1-3)
Compound is SOLUBLE if it contains:
1. Group 1 ions
2. Ammonium ions
3. Nitrate ions
What are the two types of single replacements?
1. Metal/Hydrogen SIngle Replacement
2. Halogen Single Replacement
Metal/Hydrogen Single Replacement
-Metallic element (or hydrogen gas) reacting with an ionic compound (or an acid)
-Will only occur if the metal is higher in the activity series than the cation in the compound
-Can write molecular, ionic, and net ionic equations
Halogen Single Replacement
-Halogen element is reacting with an ionic compound
-Halogen MUST be higher than the anion in order for a reaction to occur (period table = activity series)
-Can write molecular, ionic, and net ionic equations
What are the three types of non-aqueous reactions?
1. Synthesis
2. Decomposition
3. Hydrocarbon combustion
Synthesis
-Reactants are individual elements
-Product is always a single compound
-Only molecular equations are written
-Most are exothermic-energy is written on the right side
Decomposition
-Reactant is always a single compound
-Assume products are individual elements
-Only molecular equations are written
-All are endothermic-energy is written on the right side
Hydrocarbon Combustion
-Hydrocarbon: compound that contains hydrogen, carbon, and sometimes oxygen
-Requires oxygen as a reactant
-Products are carbon dioxide gas and gaseous water
-Only molecular equations are written
-All are exothermic-energy is written on the right side
What are the two types of energy changes in chemical reactions?
1. Endothermic Reactions
2. Exothermic Reactions
Endothermic Reaction
-Energy (usually heat) is absorbed from surroundings
-Occurs when reactant(s) are continually heated OR when the reaction vessel becomes cooler as the reaction proceeds
-Breaking chemical bonds requires energy --> decomposition = endothermic
-"Energy" is written on left side of the equation
Exothermic Reaction
-Energy (usually heat) is released into the surroundings
-Reaction vessel becomes warmer as the reaction proceeds
-Formation of chemical bonds between atoms releases energy --> most synthesis + all combustions = exothermic
-"Energy" is written on right side on the equation
Oxidation and Reduction Mnemonic
OIL RIG
Oxidation
-Loss of electrons (electrons are added to the right side)
-Use element name or symbol
Reduction
-Gain of electrons (electrons are added to the left side)
-Use element name or symbol
Oxidizing Agent
-Substance that is reduced
-Use exact name or formula
Reducing Agent
-Substance that is oxidized
-Use exact name or formula
Redox Reactions
-Involve the exchange of electrons between two reactions
Balancing Non-Trivial Redox Reactions
1. Write two half-reactions
2. Balance atoms except oxygen and hydrogen
3. (if needed) Balance oxygen by adding H2O
4. (if needed) Balance hydrogen by adding H+
5. Balance net electrical charge
6. Equalize electrons
7. Combine and simplify
Assigning Oxidation Numbers
1. Free Elements = 0
2. Monatomic Ions = Charge on the ion
3. Oxygen in most compounds = -2
4. Hydrogen in most compounds = +1
5. Neutral molecules sum of numbers = 0
6. Polyatomic ion sum of numbers = charge on that ion