 Chemical Reaction - Change in which one or
more substances are converted into new
substances
 Reactant - Substances that react
 Products - New substances produced
 Chemical Reaction
 Left side – reactants
 right side - products
  means yields
 Lavoisier’s Contribution
 Scientist who carried out thousands of
experiments to establish what we know as
the Conservation of Mass
 Conservation of Mass - Matter can neither be
created nor destroyed it just changes forms
 Chemical Equation - A way to describe a
chemical reaction using chemical formulas and
other symbols
 Coefficients - Tells the number of units of each
substance taking place in a reaction
 Only way to BALANCE a chemical equation
 Balancing Chemical Equations - Does not change
the substances involved or what happens within a
reaction, it only changes the way the reaction is
REPRESENTED. Has the same number of atoms
on both sides of the equation
 How to Balance Equations
1. Write chemical equation using symbols &
formulas
2. List elements involved
3. List number of atoms for each element
involved on each side
4. Choose coefficients to balance the equation
5. Recheck number of atoms for each element
involved on each side
 Things to remember when balancing equations
 Diatomic Molecules
o Br, O, F, I, N, Cl, H
 Save Oxygen & Hydrogen to last to balance
o Most times they balance themselves
as other elements are balanced
 4 Types of Reactions
 Synthesis, Decomposition, Single Displacement,
Double Displacement
 Synthesis - Two or more substances reacting
(combine) to form a new substance
o A + B  AB
o 2H2 + O2  2H2O
 Decomposition - One substance reacting
(decomposes or breaks down) to form two or
more new substances
o AB  A + B
o 2H2O  2H2 + O2
 Single Displacement - When one element replaces
another element within a compound
o AB + C  AC + B
o AB + C  CB + A
o Cu + 2AgS  CuS2 + 2Ag
 Double Displacement - Positive ion of one
compound replaces the positive ion of the other to
form two new compounds
o AB + CD  AD + CB
o H2O + AgS  H2S + AgO
 Precipitate - An insoluble compound that comes
out of solution during a double displacement
reaction
 Exergonic Reactions - Chemical reactions that
release energy
 Exothermic Reactions - When the energy given
off in a reaction is primarily in the form of heat
 Endergonic Reactions - When a chemical
reactions requires more energy to break bonds
than is released when new ones are formed;
 Energy absorbed can be in the form of light,
heat, or electricity
 Endothermic Reactions - When energy needed is
in the form of heat
 Endothermic refers not just to reactions also
refers to physical changes, Epsom salt
dissolving in water, Ice pack / Cold Pack
 Catalysts - A substance that speeds up a chemical
reaction without being permanently changed itself
 When you add a catalysts the mass of the
product formed remains the same, but it will
form more rapidly
 Inhibitors - Substances that are used to combine
with one of the reactants to prevent certain
reactions from occurring
 Ex. Food preservatives in that they prevent
chemical reactions that would cause the food to
spoil