Chemical Reactions and Aqueous Solutions

8.1: Chemical Equations

What are Reactants?

  • Substances on the left-side of an equation that undergoes change

What are Products?

  • Substances on the right-side of an equation that are the results of reactants

What do Coefficients Mean?

  • They are the #’s in front of a chemical formula that indicate how many mols of that substance is present (ratio)

What does the State Indicate?

  • They indicate the physical matter of a reactant/product and can be considered as: liquid (l), gas (g), solid (s), and aqueous (aq)

What does Aqueous Mean?

  • The mixture of a reactant/product dissolved in water

How to Balance Chemical Equations?

  1. If polyatomic ion is present on both sides, balance them together as a unit

  2. Start by balancing the first element that appears and continued from left to right

  3. Balance any remaining elements

  4. Verify balanced equation:

  • # of each atom is the same reactants and products

  • Coefficients are in the smallest whole-# ratio

8.2: Types of Chemical Reactions

What is the 1st Type of Reaction: Synthesis (Combination)?

  • Simple reactants that combine to form a single product

  • ex: rusting of iron metal (4Fe+3O2→2Fe2O3)

What is the 2nd Type of Reaction: Decomposition?

  • Single reactant breaks down into less complete products

  • ex: water (2H2O→2H2+O2)

What is the 3rd Type Reaction: Single-Replacement?

  • When an element reacts with a compound and displaces one of the elements in that compound, producing a new compound and a new element

  • ex: Zinc with Hydrochloric acid (Zn+HCl→ZCl2+H2)

What is the 4th Type Reaction: Double-Replacement?

  • 2 ionic compounds exchange ions to form 2 new compounds

  • ex: Lead (II) nitrate with potassium iodide (2KI + Pb(NO3)2 → PbI2 + 2KNO3)

What are the 2 Types of Compounds?

  • Acids: type of compound written with H at beginning of formula

  • Bases: type of compound written with OH at end of formula

Why do Chemists Use the term “Salt”?

  • To refer to ionic compounds that don’t contain H+/OH-

What is the 5th Type of Reaction: Combustion?

  • The rapid combustion combination of a substance with oxygen

  • Combustion reaction also involve reaction of oxygen with hydrocarbon fuels

What does Hydrocarbon Mean?

  • Compounds composed of carbon and hydrogen and react with excess oxygen to produce carbon dioxide (CO2) and water (H2O)

  • ex: C3H8 + 5O2→2CO2+4H2O

What are Generic Formulas for Each Type?

  • A+B→C+D (Regular Chemical Equation)

  • A+B→AB (Synthesis)

  • AB→A + B (Decomposition)

  • A+BC→AC+B (Single-Replacement)

  • AB+CD→AD+CB (Double-Replacement)

  • CxHy+O2→CO2+H2O (Combustion)

What does Driving Force Mean?

  • The formation of stable, lower energy products

What are the 3 Driving Forces for Aqueous Solutions?

  1. Precipitation Reaction: double-replacement reactions that result in the formation of a lower energy solid ionic compound

  2. Acid-Base Reaction: an acid (H+) with base (OH-)

  3. Oxidation-Reduction (Redox) Reaction: single-replacement, synthesis, and decomposition reactions involving transfer of electrons to form lower energy products

8.6: Oxidation States and Redox Reactions

What are Oxidation States (#’s)?

  • Used to keep track of the electron transfer in redox reactions

What are the Rules for Assigning Oxidation #’s?

  1. A neutral element that’s not part of a compound has an oxidation state of 0

  2. Monoatomic ions have an oxidation number equal to their ionic charges

  3. Sum of oxidation states in ANY formula equal to overall charge on that formula

  4. Oxygen tends to have oxidation number state of -2 in compounds

  5. Hydrogen tends to have oxidation state of +1 in compounds

What are Redox Reactions?

  • Transfer of electrons; one reactant loses electrons (oxidation), while another gains electrons (reduction)

  • Oxidation occurs when oxidation state of an element increases, while reduction occurs when oxidation state decreases

  • For finding oxidized/reduced, ALWAYS look at reactants

  • Oxidized means reducing agent

  • Reduced means oxidizing agent

  • Typically when oxygen is found in a compound, the oxidation state is -2 (exceptions: fluoride, or if oxygen is represented as peroxide or superoxide)

  • If oxidation state changes, redox reaction occurs

  • All single-replacement reactions are redox

Quick Ways To Tell If Redox:

  • Pure element on one-side to element part of compound on other side

  • Combustion reactions are ALWAYS redox