Chemical Reactions

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 + Cl2 2NaCl

Ex: 2Na + Cl2 2NaCl PRODUCTS. Items to the right of the arrow are called PRODUCTS. Ex: 2Na + Cl2 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.

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

A coefficient of 1 is not written. 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. H2SO4 H= 2 S = 1 O = 4

Subscripts vs. Coefficients

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

Reactions that release heat. Exothermic Reactions that release heat.

Reactions that absorb heat. Endothermic Reactions that absorb heat.

A substance that speeds up chemical reactions. Catalyst A substance that speeds up chemical reactions.

A substance that slows down a chemical reaction. Inhibitor A substance that slows down a chemical reaction.

Types of Reactions

Combustion Reactions that have hydrocarbons (CH4) and oxygen as reactants, and carbon dioxide and water as products.

Example: C3H8 + 5O2  3CO2 + 4H2O

Synthesis Reactions

Examples 2Na + Cl2 2NaCl Na2O + CO2 Na2CO3

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

Examples 2KClO3 2KCl + 3O2 2NaCl 2Na + Cl2

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

Examples Fe + CuSO4 Cu + FeSO4 2Na + 2HCl H2 + 2NaCl

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

Examples NaCl + AgNO3 NaNO3 + AgCl KOH + HNO3 HOH + KNO3

Let's Practice!

C + O2 ----- CO2

2NaCl  2Na + Cl2

FeCl2 + K2S  FeS + 2KCl

C2H4 + 3O2  2CO2 + 2H2O

2AlCl3 + 3Na2CO3  Al2(CO3)3 + 6NaCl

CS2 + 3O2  CO2 + 2SO2

3Fe + 4H2O  Fe3O4 + 4H2

2AlCl3  2Al + 3Cl2

2Na + H2SO4 ---> Na2SO4 + H2

2Cr + 3O2  2CrO3