Law of Conservation of
Matter
Law of ____________ of Matter
and Balancing Equations
Chemical Reactions
■ Chemical reactions occur when bonds
(between the electrons of atoms) are
___________ or ___________
■ Chemical reactions involve ___________ in
the chemical composition of matter - the
making of ___________ materials with
___________ properties
Chemical Equations
■ A chemical equation is written as an
expression similar to a ___________
equation
■ Can be compared to a ___________ that a
chemist follows in order to produce desired
results.
■ What do you need to make a cake? Put those
ingredients together and get a cake.
■ What do you need to make water? Put those
elements together and get water.
■ The Law of Conservation of Matter states that
matter can be neither ___________ nor
___________ in a chemical reaction.
■ What goes in ___________ come out.
■ Elements will be in ___________ compounds
and possibly different ___________ of matter
than when they started, but they will still be
there!
Chemical Equations
■ Chemical ___________ describe a chemical
___________
■ Symbols represent ___________ (O or H)
■ Formulas describe ___________ (H2O)
Chemical Equations
■ All chemical equations have reactants and
products.
■ Reactants: elements or compounds that go
___________ a chemical reaction
■ Products: elements or compounds that come
___________ of a chemical reaction
Chemical Equations
We express a chemical equation as follows:
___________ → ___________
The arrow is equivalent to an “=“ in math. When
we describe the equation we use the word
“___________” or “produces” instead of equals.
Chemical Equations
4 Al(s) + 3 O2 (g) ---> 2 Al2O3 (s)
The numbers in the front are called ___________
If there is no coefficient, it is a ___.
The letters (s), (g), and (l) are the physical
___________ of compounds.
How many of each atom are on each side of this
equation? ___________ the coefficient and the
subscript for each one.
Balancing a Chemical
Equation
■
■
A chemical equation is balanced when the
atoms found on the reactant (left) side of the
equation ___________ those found on the
product (right) side.
Think of an equation like a see-saw. The
___________ can be considered the balance
point.
Chemical Equations
■ Example
C + O2 → CO2
This reads “carbon plus oxygen ___________ to
___________ carbon dioxide”.
Balancing Chemical
Equations
■ Because of the law of the conservation of
matter, an equation ___________ be
balanced.
■ It must have the same ___________ of atoms
of the same kind on both sides.
■ For example, if there are 3 oxygen atoms on
the ___________ side, there must be ___
oxygen atoms on the product side.
Balancing Equations
■ When balancing a chemical equation you may
add ___________ in front of the compounds to
balance the reaction, but you may NOT
change the ___________.
■ Changing the subscripts changes the
___________.
■ The subscripts tell you how many atoms of a
particular element are in a compound. The
coefficient tells you about the quantity, or
number, of molecules of the compound.
Subscripts vs. Coefficients
Chemical Equations
4 Al(s) + 3 O2(g) ---> 2 Al2O3(s)
This equation means
4 Al atoms + 3 O2 molecules
--produces---> 2 molecules of Al2O3
Steps to Balancing Equations
1. Find the ___________ of atoms for each
element on the left side. ___________ those
against the number of the atoms of the
___________ element on the right side.
2. Determine where to place coefficients in
front of formulas so that the left side has
the same number of atoms as the right side
for ___________ element in order to balance
the equation.
Steps to Balancing Equations
Some Suggestions to Help You
3. Check your answer to see if:
■ The ___________ of atoms on both sides
of the equation are now balanced.
■ The coefficients are in the ___________
possible whole number ratios.
(___________)
Helpful hints for balancing equations:
■ Take one element at a time, working left
to right except for H and O. Metals, then
nonmetals are a good way, too. Save __
for next to last, and __ until last.
■ IF everything balances except for O, and
there is no way to balance O with a whole
number, ____________ all the
coefficients and try again. (Because O
is diatomic as an element)
Balancing Equations
___ H2 + ___ O2 ---> ___ H2O
Balance this equation
___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)
Balance this equation!
____ Na + ____ Cl2
___ NaCl