1. Types of Chemical Reactions

2. How do I tell if a reaction has occurred?
A sign of a chemical must take place
Temperature change
Release of light
Color change
Appearance of precipitates (solids)
Gas/odor released

3. How do I represent a chemical rxn?
Reactant Reactant 2 → Product Product 2
Reactants are starting substances.
Products are substances formed.
Arrow shows direction of progress.
A “+” sign is placed between reactants and products to separate them.
Symbols are used to show physical state of reactants and products – (s) solid, (l) liquid, (g) gas, (aq) dissolved in water.

4. Subscripts and Coefficients
What does a subscript mean in a chemical formula?
Ex. Al2O3, H3PO4, Na2SO4
Number of atoms in a formula
What does a coefficient mean written in front of an element or formula?
How many of the element or compounds/molecules there are present in the reaction

5. Subscripts and Coefficients
Let’s practice counting! Ca3P2 2Mg3(PO4)2

6. Word & Skeletal Equations
A) Word equations:
reaction written with words instead of chemical symbols.
Ex. Magnesium (s) + Oxygen (g) → Magnesium oxide (s)
Magnesium reacts with oxygen to produce magnesium oxide.
B) Skeleton Equations:
Use chemical formulas and symbols instead of words – not balanced.
Ex. Mg(s) + O2(g) → MgO(s)

7. Balancing Chemical Equations
We use coefficients in front of reactants and products – usually whole numbers – and tells you the smallest # of particles involved in the reaction.
Steps:
Write skeleton equation.
Count the # of elements in reaction.
Change the coefficients to make the # of atoms of each element equal on both sides of the equation.
Write the coefficients in their lowest possible ratio.
Check your work.

8. IV. Conservation of Mass
-matter is neither created or destroyed in a chemical reaction.
-number of atoms in reactant equals number of atoms in product.
-sum of mass in reactant equals sum of mass in product.
Ex. 2H2O2 → 2H2O + O2
68.0g g + _?_
68.0g – 32.0g = 36.0 g

9. Practice
_____ H2 + _____O2 → _____H2O
Hydrogen and nitrogen gas react to form nitrogen trihydride.
_____Al2O3 → _____Al + _____O2
_____KClO3 → _____KCl + _____O2
Octasulfide + oxygen gas → sulfur dioxide

10. Dicarbon hexahydride react with oxygen gas to produce carbon dioxide and water.
Aluminum sulfate + calcium hydroxide → aluminum hydroxide + calcium sulfate
­­­­­_____P4 + _____O2 → _____P2O5
_____Ag + _____S8 → _____Ag2S
10. Aluminum and Bromine combine to form Aluminum bromide.

11. Synthesis Special Cases
Non-metal oxide + water → acid
Use oxidation numbers to find the oxidation number of the non-metal.
Use the oxidation number of the non-metal to determine the oxyanion of the acid.
Must balance charges from the ions when you write the formula for the acid.
Example: SO2 + H2O → H2SO3
Non-metal oxide + metal oxide → salt
Use the oxidation number of the non-metal to determine the oxyanion of the salt. The cation is the metal ion.
Must balance charges from the ions when you write the formula for the salt.
Examples:
CO2 + metal oxide → metal carbonate
SO2 + metal oxide → metal sulfite
SO3 + metal oxide → metal sulfate
metal oxide + water → base
The metal is the cation of the base.
The anion is OH-1 (definition of a base).
Must balance charges from the ions when you write the formula for the base.
Example: Al2O3 + H2O → Al(OH)3

12. Decomposition Special cases
acid → Non-metal oxide + water
salt → Non-metal oxide + metal oxide
Uses the oxidation steps from the combination reactions in reverse.
Find the oxidation number of the non-metal in the oxyanion.
Use the oxidation number of the non-metal to determine the formula of the non-metal oxide.
Must balance charges from the ions when you write the formula for the metal oxide. The metal cation is the metal from the salt.
Metal halate → metal halide + oxygen gas
Metal carbonate → metal oxide + carbon dioxide
Metal peroxide → metal oxide + oxygen gas

13. Double Replacement Special cases:
Acid-Base neutralization reactions:
Acid + Base → Salt + water
Acid: Cation = H+
Base: Anion = OH-1
Salt: Anything that can be made from an acid and a base that is not water.
Gas forming reactions:
Acid + metal carbonate → salt + water + carbon dioxide
*Double replacement reaction that produces H2CO3
- H2CO3 breaks down as soon as it forms. Follows the
rules for metal carbonate decomposition.
Acid + metal sulfate → salt + water + sulfur dioxide
-Same type of problem as the acid + metal carbonate.