–Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken

–Chemical reactions involve changes in matter, the making of new materials with new properties, and energy changes.

–Symbols represent elements, formulas describe compounds, chemical equations describe a chemical reaction

Items to the LEFT of the arrow in a chemical equation are called REACTANTS. 2Na + Cl 2 2NaCl

Items to the right of the arrow are called PRODUCTS. Ex: 2Na + Cl 2 2NaCl

Important NOTE: No matter how many reactants and products are involved, all atoms present at the start of a reaction are present at the end.

THE TOTAL MASS OF THE REACTANTS MUST EQUAL THE TOTAL MASS OF PRODUCTS. MATTER IS NEVER CREATED OR DESTROYED.

A number that tells how many molecules of a substance are involved in a chemical reaction. A coefficient of 1 is not written.

Subscripts A subscript indicates how many atoms of an element are in a compound Ex. H 2 SO 4 H= 2 S = 1 O = 4

Subscripts vs. Coefficients

+ -- used to separate two reactants or products. (yields) Separates reactants and products.

Reactions that release heat.

Reactions that absorb heat.

A substance that speeds up chemical reactions.

A substance that slows down a chemical reaction.

Reactions that have hydrocarbons (CH 4 ) and oxygen as reactants, and carbon dioxide and water as products.

Example: C 3 H 8 + 5O 2  3CO 2 + 4H 2 O

2Na + Cl 2 2NaCl Na 2 O + CO 2 Na 2 CO 3

Starts with one reactant and ends with 2 or more products.

2KClO 3 2KCl + 3O 2 2NaCl 2Na + Cl 2

One compound and a free element that recombine to yield a new compound and new free element.

Fe + CuSO 4 Cu + FeSO 4 2Na + 2HCl H 2 + 2NaCl

Starts with 2 compounds as reactants. These recombine to form 2 new compounds as products. + +

NaCl + AgNO 3 NaNO 3 + AgCl KOH + HNO 3 HOH + KNO 3

C + O  CO 2

2NaCl  2Na + Cl 2

FeCl 2 + K 2 S  FeS + 2KCl

C 2 H 4 + 3O 2  2CO 2 + 2H 2 O

2AlCl 3 + 3Na 2 CO 3  Al 2 (CO 3 ) 3 + 6NaCl

CS 2 + 3O 2  CO 2 + 2SO 2

3Fe + 4H 2 O  Fe 3 O 4 + 4H 2

2AlCl 3  2Al + 3Cl 2

2Na + H 2 SO 4 ---> Na 2 SO 4 + H 2

2Cr + 3O 2  2CrO 3