chemical reactions processes by which one or more substances change to produce one or more different...

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