Transcript Balancing Chemical Equations - Center Grove Elementary School

Balancing Chemical Equations
• We’ve done it all – counted atoms,
examined trends, bonded atoms….
• But now, we’re going to string it all
together in a sort of equation.
– Like math…but not math.
• Remember the conservation of mass?
– Matter cannot be created or destroyed.
• CHEMICAL EQUATIONS are
representations of chemical reactions.
– REACTANTS are the chemicals that go into
the reaction.
• These are listed on the left side of the
equation.
– PRODUCTS are the chemicals that come out
of the reaction.
• These are listed on the right side of the
equation.
• Chemical equations are written much like
you would write a math problem.
• You’re basically adding things together to
make a total on the right side.
• But there are some differences, too.
– Instead of a “=“, we use an arrow to show
direction ().
– Sometimes equations aren’t as simple as
adding things up.
• Let’s look at an example.
2H2 + O2  2H2O
• This is the reaction to form water from its
elements.
• What kinds of terms or features do you notice
in this equation?
• What are my reactants? What are my
products?
2H2 + O2  2H2O
• In the formation of water (H2O), we react, or
consume, 2 portions of hydrogen for every 1
portion of oxygen.
• As a result, we produce 2 portions of water.
• Let’s look at the atoms themselves.
– Is this equation BALANCED? Are all the atoms
that start the reaction present at the end?
– 4 hydrogen go in, 4 hydrogen come out
– 2 oxygen go in, 2 oxygen come out
• Try another example:
CH4 + 2O2  CO2 + 2H2O
• This is the reaction for burning methane.
Notice that one of the products is carbon
dioxide, a greenhouse gas.
CH4 + 2O2  CO2 + 2H2O
• How many carbons do we start with?
– How many do we end with?
• How many hydrogens do we start with?
– How many do we end with?
• How many oxygens do we start with?
– How many do we end with?
• This equation has already been balanced for
you. Let’s see if you can balance one on your
own.
___Na + ___H2O  ___NaOH + ___H2
• This is the reaction for sodium metal
with water.
• How can you balance this reaction?
• Now I will provide an equation that is
balanced, but is missing the product’s
formula.
• Can you predict the product of this
reaction?
C6H12O6 + 6 O2  6 CO2 + 6 _______
Predict the product
• Given the reactants, predict the product in
these reactions.
2 Fe + Cl2  _________
2 P + 2 O2  __________
Ca + S  _________
2 C + 2 H2  __________
• Are these products ionic or covalent?
• Can you draw out the product on the fourth
example?
Sodium hydroxide (NaOH) is a potent base that
draws water and carbon dioxide out of the air if
left in the open. It is also a base used to
neutralize certain acids.
___ NaOH + ___ CO2  ___ Na2CO3 + ___ H2O
___ NaOH + ___ HCl  ___ NaCl + ___ H2O
Indiana is well known for its limestone,
harvested around Bloomington. Limestone is a
hard deposit (mostly calcium carbonate) that
was likely deposited by marine life. Limestone is
used in building, but has stopped being used for
monuments in densely-populated areas.
Humans have a large impact on the
environment, with waste producing phenomena
like smog and acid rain.
A reaction for dissolving calcium carbonate is:
___CaCO3 + ___HCl  ___H2O + ___CO2 + ___CaCl2
Why might limestone be a poor building material
choice for densely-populated cities like Los Angeles or
New York City?
Acid rain eats away at the faces of limestone
buildings, eroding the strength of the building.
FYI - The product, calcium chloride (CaCl2), is used as
salt for roads (rock salt) and water hardeners.
Individual/Small group Practice
• Practice with a partner or individually on
balancing some chemical equations. For each
of the problems, find ALL of the coefficients to
balance the equation.
– Aim for 10 basic and 6 advanced @ 100 %
– For extra practice, go for the mastery problems
– I know they won’t all fit on the worksheet. Just fill
in the first 13, then work on scrap paper.
– Write down your problems on the worksheet and
turn it in at the end of class.
• Basic problems
CH4 + O2  CO2 + H2O
KClO3 → KCl + O2
H2 + O2 → H2O
P4 + O2 → P2O5
Al + Br2 → AlBr3
CCl4+O2  CO2+Cl2
C3H8 + O2  CO2 + H2O
SnO2 + H2 → Sn + H2O
C6H6 + O2 → CO2 + H2O
AgI + Na2S → Ag2S + NaI
• Advanced problems
Na + C2Cl6 → NaCl + C2Cl2
C2H6 + O2  CO2 + H2O
C2H3Br3+O2 CO2+HBr
P4 + HCl + O2 → PCl3 + H2O
AlBr3 + Cl2 → AlCl3 + Br2
C6H5F+O2 CO2+H2O+F2
CaCN2+H2O  CaCO3+NH3
TiCl4 + H2O → TiO2 + HCl
C6O6Cr + Cl2 → CrCl3 + CO
• Mastery problems
AlI3 + HgCl2 → AlCl3 + HgI2
HSiCl3 + H2O  H10Si10O15 + HCl
KOH + H3PO4 → K3PO4 + H2O
Ba3N2 + H2O → Ba(OH)2 + NH3
Ca(OH)2 + H3PO4 → Ca3(PO4)2 + H2O
NH3 + CO → CH4 + N2 + O2
AgNO3 + K3PO4 → Ag3PO4 + KNO3
C7H9 + HNO3  C7H6(NO2)3 + H2O