Post on 18-Jan-2018
description
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