Download Chemical Equations Balancing Chemical Equations Try One…

8/14/2013
Unit #2 – Chemical Equations
To begin our study of equations, we must first
review writing, balancing and naming the
reaction type.
™ In a chemical reaction, only 2 things are
conserved the number of atoms and the
conserved...
number of grams.
™ an arrow
is used to separate reactants
(the starting substances) and the products
(what is made), the arrow is the same as an
“equals sign” (=) in math for the number of
each type of atom must be equal on both sides
(“yields” or “produces”)
™
Balancing Chemical Equations
NH3 (g) +
O2 (g)
NO + H2O(l)
z
This is called the skeleton equation.
Try to read it like a sentence- Gaseous ammonia is
added
dd d to oxygen gas to produce
d
nitrogen
i
monoxide,
id
which is given off as a gas, and water -NOW
BALANCE IT -by adding coefficients-DO NOT
CHANGE SUBSCRIPTS
1. start at the formula with the highest subscript values
2. put a “1” in front, if that doesn’t work try a “2”, etc.
3. go back and forth adding coefficients, until it’s
balanced
z
Try One…
Gaseous Ammonia is combined with Oxygen to
produce Nitrogen Monoxide and Water.
4
5
___NH
3 (g) + ___O2 (g)
____NO
4
6 H2O(l)
+ ___
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Practice Writing/Balancing Equations
Remember the the stoichiometric coeffients
represents the mole ratios!
Octane, C8H18, burns in air to ggive carbon dioxide
(gas) and water.
1. Write the skeleton equation…
16
2
18
___C
__O2(g)
___CO
8H18 + 25
2(g) + ___H
2O(l)
2. Now balance the equation (lowest whole
number ratio)
REACTION TYPES
1. COMBINATION (COMPOSITION)(SYNTHESIS)
REACTIONS:
X + Y
XY
– THESE REACTIONS CAN BE PICKED OUT BECAUSE THEY ONLY HAVE
ONE PRODUCT
2. DECOMPOSITION (ANALYSIS) REACTIONS:
XY
X
+
Y
– THESE ARE NOTICABLE BECAUSE THEY HAVE ONLY ONE REACTANT
(OPPOSITE OF COMBINATION)
3. SINGLE REPLACEMENT OR DISPLACEMENT:
XY + A
XA + Y
OR
XY + B
BY + X
–THESE REACTIONS HAVE AN ELEMENT PLUS A COMPOUND
YIELDING ANOTHER ELEMENT PLUS A COMPOUND
–THESE ARE TRICKY , MAKE SURE YOU RECOMBINE POSITIVE WITH
NEGATIVE (BEWARE OF CATIONS VERSUS ANIONS!!!!!)
4. DOUBLE REPLACEMENT OR DISPLACEMENT:
XY + AB
AY + XB
–THIS TYPE OF REACTION IS LIKE SQUARE-DANCING, EACH ENDS UP
WITH A NEW PARTNER
–MAKE SURE POSITIVE ALWAYS COME FIRST
–WHEN MAKING NEW COMPOUNDS BE SURE TO USE THE CORRECT
SUBSCRIPTS
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Precipitation Reactions are a form of double replacement
The “driving force” is the formation of an insoluble
compound — a precipitate.
----->2
>2 KNO3(aq) + PbI2(s)
Pb(NO3)2(aq) + 2 KI(aq) ----When a precipitation reaction occurs
occurs, you only deal
with the “actual” changeschanges-this is called a “net ionic
equation”--the “spectator ions” are eliminated
equation”
Net ionic equation
---> PbI2(s)
Pb2+(aq) + 2 I-(aq) --->
MORE ABOUT THIS LATER!
Reaction Types, Continued
™
Acid-Base Reactions (also a form of double replacement
reactions)
™ The
“driving
g force” is the formation of water.
NaOH(aq) + HCl(aq) ----->
> NaCl(aq) + H2O(l)
™ Net ionic equation
--->
> H2O(l)
OH- (aq) + H+ (aq) --™ This
applies to ALL reactions of STRONG acids
and bases. Again more,later
Gas-Forming Reactions are another subset
of Double Replacement Reactions
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5. COMBUSTION REACTIONS:
CX H Y
+ O2
CO 2
+
H 2O
–THESE REACTIONS ALWAYS HAVE
OXYGEN AS A REACTANT AND
CARBON DIOXIDE AND WATER AS
PRODUCTS
–EASIEST TO RECOGNIZE, HARDEST
TO BALANCE
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