Chemical formulas and Equations
Rates of Chemical Reactions
Chemical Formulas and Equations
 Physical Change
 Changes that only affect its physical properties like
size, shape, or whether it is a solid, liquid or gas
 There is no change of material
 You still have the same substance that you began
with
 Ie: crumple paper, cut up wood, changes of water
from ice, to liquid to a gas
Chemical Formulas and
Equations
 Chemical Change
 A change that produces a new substance with
properties different from those of the original
substances
 Things that show that a chemical reaction has
occurred
 Precipitate forms (when 2 liquids combine the new
substance will drop out of solution..is not soluble)
 Odor given off
 Change of color
 Temperature change
Chemical Formulas and
Equations
 Chemical reaction occurs when a chemical change
takes place
 Anytime you have a new substance formed
 Burning paper is a result of a chemical reaction
 Folding paper is a result of a physical change because
you still have paper, only change of shape
Chemical Equations
 Using chemical symbols of elements and chemical
formula you can write a shorthand of a chemical
reaction
 The substances you begin with in a chemical reaction
is called the reactants
 The new substances that are formed is called the
product
 In a chemical reaction you can write the reactants and
resulting products in a chemical equation using arrows
(and is read as produces)
Chemical Equations
 Baking soda + vinegar
 2NaHCO3 + H4C2O2
gas + white solid
2NaH3C2O2 + H2O + CO2
 Sodium hydroxide plus Sulfuric acid produces sodium sulfate and
water
2NaOH + H2SO4
Na2SO4 + H2O
Conservation of Mass
 Antoine Lavoisier: mass of the product must be the
same as the mass of the reactants
 Chemical equations must show that there is the same
kind and number of atoms that you began with as was
formed
 Every atom that appears on the reactant side of the
equation is found on the product side
Balancing Equations
 Chemical equations must show the conservation of
mass by having same kind and same numbers of atoms
on both side of a chemical reaction
 Ag + H2S
Ag2S + H2
 (Silver tarnishes in presence of sulfur)
 Notice that the number of atoms aren’t the same on
both side
 Need to count the atoms… you can’t change the
formula but you can add a coefficient in front of the
formula to balance equations
Balancing Equations
 Ag + H2S
Ag2S + H2
 Notice there is 2 Ag’s on product side and only one on
reactant side…. Add a coefficient of 2 in front of
reactant silver

2Ag +
H2 S
 2 Ag’s, 2 H’s and 1 S
 It is balanced
Ag2S + H2
Balancing Equations
 Al
+ O2
Al2O3
 Aluminum and oxygen produces aluminum oxide
 Not balanced (can only change the coefficient)
 4Al + 3O2
2Al2SO3
Balancing Equations
http://education.jlab.org/elementbalancing/index.html
Energy in
Chemical Reactions
 Energy released
 Heat, light, sound or other energy is given off
 When bonds break in a chemical reaction new bonds
form in the products and energy is given off
 Energy found on product side of chemical reaction
 Called an exothermic reaction
 2H2 + O2
2H2O + energy
Energy in
Chemical Reactions
 Energy is Absorbed
 Energy is required to form new products
 Can absorb light, sound, heat
 Called an endothermic reaction
 Energy is placed on the reactant side of equations
 2H2O + energy
2H2
+
O2
 Ice packs are example of endothermic reactions
Rates of Chemical reaction
 Activation Energy: starting a reaction
 To start a chemical reaction a minimum amount of
energy is required to begin the process
 That energy required is its activation energy
 For gasoline to burn energy needs to be introduced to
begin the chemical reaction…. That energy (match) will
begin the chemical process
Reaction Rate
 Rate refers to a change over time
 Reaction rate refers to the speed at which chemical
reactions takes place over time
 Reactions rates in some industries is important
because the faster the rate, the less the cost
 Some faster reaction rates can hurt industries
 Ripening fruit gives less time from field to markets
 The slower the ripening rate increases the time it can be
on shelves
Reaction Rate
 Temperature changes rate
 Lowering the temperature slows down reaction rates
 Meat in freezers, bacteria grows faster in higher
temperatures, lower movement of molecules, less
chance of causing chemical changes
 Temperature affects Rate
 Most chemical reactions speed up with increase in
temperature because of faster moving molecules
 Lowering temperature usually slows down reaction rate
Reaction Rate
 Concentration Affects Rate
 Closer the reactant atoms and molecules to each other,
the greater the chance of collisions between them and
faster the reaction rate
 Amount of substance present in a certain volume is
called the concentration of that substance
 Increasing the concentrations increases the number of
particles of a substance per unit of volume
Reaction Rate
 Surface Area Affects Rate
 If you increase the surface area you will
increase its chance of reacting with other
substances
 Twigs broken up compared to logs to begin a fire
 Crushing up materials into smaller pieces
increases surface area
Slowing down Reactions
 Inhibitors slow down chemical reactions
 Makes the process of chemical change longer
 BHT on cereal packages slow down the spoilage
of cereal and increase its shelf life
Speeding up Reactions
 Catalysts are substances that speed up a chemical
reaction without entering into the chemical reactions
 It produces the same amount of product faster
 Catalytic Converters utilize metals (platinum) to
produce CO2 and water , which is less harmful in cars
fuel combustion.
 Enzymes are catalysts that are large protein molecules
that speed up reactions needed in cells to work
properly
 They help speed up conversion of food to fuel, build
bone and muscle tissue, and converting energy by fitting
structures together properly so that reactions can occur
faster
Speeding up Reactions
 Proteases is a special type of enzyme
that helps break down large protein
molecules
 Meat tenderizers
 Contact lenses cleaning solutions breaks down
protein from your eyes that collect on your
lenses and cloud your view