2. Recap of Chem vs. Phys
Propeties
Chemical
Properties- The characteristic of
a substance that describes its ability to
change into a new substance
Example: Burning of Magnesium into MgO
Physical
Properties- A characteristic of a
substance that can be observed without
changing the substance into a new
substance
Example: Ice Melting, Cutting a piece of
paper
3. Recap of Chem vs. Phys
Changes
Chemical
changes- a chemical reaction
which results in one or more new
substances being formed
Example: Burning a log in a fireplace
Physical
changes- a change that alters
the form or appearance of something,
but does not create a new substance
Example: Melting metal and reshaping into
a ring
4. Bonding and Chemical
Reactions
In
order for a chemical reaction to have
taken place, bonds must have been
broken and re-created!! Atoms rearrange
to create something totally new.
Bonds can change from one form to
another; covalently bonded atoms can
rearrange to create ionic bonded atoms
(like with the Mg lab)
5. Evidence that a Reaction has
Occured:
Precipitate forms (solid is formed out of liquids
w/o freezing)
Heat is released
Light is released
Energy change (exothermic or endothermic)
Gas is formed (usually in the form of bubbles)
Color change (unexplained, weird)
Rapid temp change (hand warmers, instant
ice pack)
6. Balancing Equations
Reactant + Reactant Product + Product
In a chemical equation, reactants go on the
left, products are always on the right.
7. Conservation of Matter
In 1774, Antoine Lavoisier introduced us to the
idea of the conservation of Matter.
Conservation of Matter tells us that matter is
neither created nor destroyed.
This means that the total mass of the reactants
must equal the total mass of products.
This also means that the number of atoms stays
the same, they are just rearranged when the
bonds are broken and re-created.
8. Open vs. Closed
Remember the difference between open
and closed systems for a chemical reaction?
Open System- the chemical reaction may call
upon the elements around it (like taking
Oxygen from the air)
Closed System- the chemical reaction may
only use what it started with and cannot add
anything new during the change.
9. Factors of a Chem Reaction
Activation
energy- the amount of energy
needed to start a chemical reaction (ALL
chemical reactions require activation
energy)
Surface Area, Concentration,
Temperature and presence of catalysts
and/or inhibitors will have a huge effect
on how quickly a chemical reaction will
occur.
