CHEMICAL REACTIONS
• Chemical reactions: Occur when chemical
bonds break or new bonds form
• Atoms rearrange to form new substances
CHEMICAL REACTIONS
• A chemical reaction has occurred and a new
substance has formed when:
– A gas has formed
– A precipitate (solid) has formed
– Change in temp.
– Change in color
CHEMICAL REACTIONS –
CONTINUED
• Chemical reactions summarize a reaction using
formulas and symbols
• Reactants are the substances at the beginning
of the reaction; left of the arrow
• Products are the substances at the end; right of
the arrow
•  “yields” or “forms”
CHEMICAL REACTIONS –
CONTINUED
• Examples:
• Copper nitrate and zinc yield zinc nitrate
and copper
• Cu(NO3)2 + Zn 
Zn(NO3)2 + Cu
• Reactants = Cu(NO3)2 + Zn
• Products = Zn(NO3)2 + Cu
LAW OF CONSERVATION OF MASS
• Law of Conservation of Mass:
• Mass (or matter) cannot be created or
destroyed during a chemical reaction
LAW OF CONSERVATION OF MASS
• Mass of reactants = mass of products
• All of the atoms present at the beginning of
the reaction are present at the end of the
reaction but they are rearranged
BALANCING EQUATIONS
• Balanced Equations: Equation where the
number of atoms and type of atoms are the
same for reactants and products
• Coefficients: Number before the chemical
formula
BALANCING EQUATIONS
• Element:
# Compounds:
#atoms/compound total # atoms
• 2H2O H=2x2
O=2x1
• 4Cu(NO3)2
Cu=4x1
N=4x1x2
O=4x3x2
Rules for balancing equations:
• Count the number of atoms of each element
on each side of the equation
• Change or add COEFFECIENTS ONLY to
get the number of atoms equal.
Rules for balancing equations:
• Check work by counting atoms of each
element on each side of the equation.
• NEVER CHANGE SUBSCRIPTS!!!!!!!!!!!!
Examples:
• K + Cl2  KCl
• HCl + Mg  MgCl2 + H2
• HgCl2 + H2S  HgS + HCl
O2 + Cl2  Cl2O
K + F2  KF
Types of Reactions:
• Synthesis reactions: 2 or more substances
combine to form another substance
• 2H2 + O2  2H2O
• Decomposition reactions: one substance
breaks down (or decomposes) into 2 or more
simpler substance
• H2CO3  H2O + CO2
Types of Reactions:
• Single Replacement Reactions: one element
replaces another in a compound; 1 element + 1
compound yields 1 element + 1 compound
• Cu + 2AgNO3  Cu(NO3)2 + 2Ag
• Double Replacement Reactions:
• AgNO3 + NaCl  AbCl + NaNO3
Chemical Reactions
• Law of Conservation of Energy:
Energy is never created or destroyed but can
change form
Chemical Reactions
• Exothermic reactions: Some form of energy
is given off
• More energy in the reactants than the
products
• Example: heat pack
Chemical Reactions
Endothermic reactions: Some form of energy
is absorbed
• Less energy in the reactants than the
products
• Heat is absorbed in the chemical bonds
making the substance feel colder
• Example: cold pack
CHARTS
Acids
Bases
Releases H+1 ions when
dissolved in water
Releases OH-1 ions when
dissolved in water
Tastes sour
Tastes bitter
Not slippery
Ph 0-6.9
Slippery
Ph 7.0-14
Begin with H
End in OH
CHARTS
Indicators: change in color when in contact with an acid or base
Indicator
Neutral
Acid
Base
Litmus paper
Blue stays blue
Red stays red
Blue turns red
Red stays red
Blue stays blue
Red turns blue
Phenolphthalein Stays colorless
Stays colorless
Pink
Purple cabbage
water
Stays purple
Pink, red
Green (weak)
Yellow (strong)
Universal
indicator
pH paper
Stays green
Red
Purple
Yellow= 7.0
Red/orange
Green/purple
pH SCALE
•
•
•
•
•
•
pH Scale- Ranges from 0- 14
7.0 is neutral (not acid or base)
0 is strongest acid – lost of H+ ions
6.9 is weakest acid – few H+ ions
14 is strongest base – lots of OH- ions
7.1 is weakest base few OH- ions
Neutralization:
• chemical reaction between an acid and base
to form water and salt
• HCl + NaOH  2H2O + NaCl
• Acid
base
water
salt
Neutralization:
• Salt: formed when negative ions from an
acid combine with positive ions form a base
• Fe(OH)3 + 3HNO3  Fe(NO3)3 + 3H2O
• Base
acid
salt
water
Nuclear Reactions:
• Fission: splitting of nucleus into 2
• Tremendous amount of energy is released;
Atomic bomb, nuclear power plants
Nuclear Reactions:
• Fission  heat energy  heat water 
spin turbines  electricity
• Very difficult to get rid of nuclear waste
Nuclear Reactions:
• Fusion: combining of nuclei
• Takes place in the sun and other stars