Chemical Reactions

Processes by which one or more substances change to produce one or

more different substances

Chemical bonds are broken & formed

Indicators (clues)• Change in color• Gas formed (bubbles)• Change in temperature (energy taken in

or given off)• Precipitate (solid formed in a solution)• Light is released

*new substance is always formed!!

Language of Chemistry

LettersElement Symbols ex: C

•Chemical Formulas • CO2 Carbon dioxide

• H2O Dihydrogen oxide

• C6H12O6 Sucrose

Chemical Equations

shorthand description of a chemical reaction

2K + Cl2 2KCl

Reactants = starting materials

= yield sign (similar to equal sign)

Products = substances formed

Reads as “Potassium and chlorine react to yield potassium chloride”

IONIC CompoundsBetween a metal & nonmetal

The metal loses electrons, the nonmetal gains electrons

Balance ion charges

Mg 2+ + Cl - = MgCl2

M name 1st then NM with ending changed to “-ide”

Magnesium Chloride

COVALENT Compoundsbetween nonmetalsShare electrons

Use prefixes to tell how many of each element

Ex: CO2 = carbon dioxide

N2O = dinitrogen monoxide

Mono- 1 Hexa- 6

Di- 2 Hepta- 7

Tri- 3 Octa- 8

Tetra- 4 Nona- 9

Penta- 5 Deca- 10

Law of Conservation of Mass• Mass is neither created nor

destroyed

• Mass of the reactants = mass of products

Balancing EquationsUse COEFFICIENTS

- # placed in front of a chemical symbol or formula

Ex: 2 CO2 means 2 molecules of carbon dioxide

Energy & Rate of Chemical Reactions

EVERY reaction involves ENERGY!!

• Energy is USED (absorbed) to break bonds

• Energy is GIVEN OFF as new bonds form

Type of Reaction depends on…Chemical

energy of Reactants

Chemical energy of Products

VS.

Exothermic Reactions“Exo-” = out

“Therm-” = heat

2Na + Cl2 -> 2NaCl + energy

Energy is GIVEN OFF/RELEASEDEx: light, thermal or

electrical energy

Endothermic Reactions“endo-” = in

Energy is ABSORBED

2H2O + energy -> 2H2 +

02

Activation Energy• Smallest amount of energy needed

for substances to react

Factors Affecting Rates of Reaction

TemperatureHigher Temp = faster rate of

reaction

ConcentrationHigher concentration = faster

reaction

Surface Area(amount of exposed surface)

Greater Surface Area = Faster Reaction

Catalyst• Speeds up

reaction without being permanently changed

• Lowers activation energy

Ex: enzymes in body

Inhibitor• Slows down or

stops a chemical reaction

Ex: preservatives in food