Chemical Reaction Notes
Chemical Reaction Notes
• We have already discussed the
fact that sometimes individual
atoms (and in the case of
polyatomic ions small groups of
atoms) can join together to form
compounds in order to increase
stability and decrease the total
amount of chemical potential
energy
Chemical Reaction Notes
• Sometimes compounds can come together and
they can become more stable still by
rearranging atoms.
• These changes are called chemical reactions,
and are different from the nuclear reactions we
studied earlier, which are when nuclei come
together (or split apart) and create new atoms
Chemical Reaction Notes
• Chemists represent chemical reactions
with “equations”
Chemical Reaction Notes
• Equations consist of a list of formulas for all of
the reactants (compounds or elements added
together to begin a chemical reaction) on the left
side and a list of all of the products (compounds
or elements which form during a chemical
reaction) on the right side
Chemical Reaction Notes
• Reactants and products are separated by an
arrow
• Reactants are separated from one another by
plus signs (as are products)
Chemical Reaction Notes
• Each formula may be followed by a subscript
(solid, liquid, gas, aqueous) to show what state
each compound is in.
• We may represent energy (heat, light, energy) as
either a product or a reactant by writing it on the
appropriate side of the equation.
Chemical Reaction Notes
• Law of Conservation of Mass: In a
chemical reaction the arrangement of
atoms will change, but the total number of
each type of atom, and therefore the total
mass, will remain constant
http://nanopedia.case.edu/NWPage.php?page=chemical.reactions
Chemical Reaction Notes
• All chemical reactions must obey this law and
therefore all chemical equations must obey it
also.
Chemical Reaction Notes
• In order to ensure that our chemical equations
obey the law of cons. of mass, we balance all of
our equations.
• To do this:
• 1. You must make sure that all of the individual
compound’s formulas are correct.
• (Hydrogen, oxygen, nitrogen, and the halogens
are all diatomic elements, meaning that
whenever they are not found in a compound
they form a molecule with themselves and have
a formula with a subscript 2)
Chemical Reaction Notes
• 2. Pick any element and place a number
(a coefficient) in front of the compound
formula to balance out the amount on both
sides of the equation.
• 3. You should then balance one element
at a time from one side of the equation to
the other by placing coefficients in front of
the remaining formulas
Chemical Reaction Notes
• 4. Multiply coefficients to get rid of fractions if
necessary
• 5. Reduce coefficients if necessary
Chemical Reaction Notes
• Special hints:
• 1. Never change your subscripts
• 2. Balance elements that only appear in one
formula on each side first
• 3. After your first “free choice” of a coefficient,
you must only use coefficients that balance the
elements
• 4. For polyatomic ions, balance them as though
they are single “groups”
• Practice problems p. 287