Transcript CHEMISTRY-1 CHAPTER 8 CHEMICAL REACTIONS

Practice!
• How many atoms are in each of the
following compounds?
– H2SO4 7 atoms!
– Ca(NO3)2 9 atoms!
– (NH4)3PO4 20 atoms!
– C6H12O6 24 atoms!
– 2 H2O 6 atoms!
– 10 CO2 30 atoms!
CHEMICAL
REACTIONS
Chemical reaction• the process by which the
atoms of one or more
substances are rearranged to
form different substances.
Evidence of a chemical reaction:
1. Release of a gas
Zinc is added to hydrochloric acid producing
hydrogen gas and solid zinc chloride.
2. Color changes
two liquids are
mixed
solid and a liquid
mixed
3. Formation of a precipitate
– a precipitate is a solid product formed by the
reaction of two aqueous solutions.
– It is abbreviated ppt.
Aqueous sodium iodide and aqueous lead (II) nitrate
produce solid lead (II) iodide and aqueous sodium nitrate.
4. Changes in heat and light
– all reactions either absorb or release energy
Sodium peroxide (yellow powder) and zinc powder
(gray powder in the bowl) are combined
Water is then squirted in & the mixture ignites
Writing Chemical Equations:
From now on USE PENCIL!!
reactants
yield

products
EXAMPLE:
Na + Cl2  NaCl
Writing Chemical Equations:
• Reactants—the starting substance(s).
• Products—the substance(s) formed during
the reaction.
Possible symbols in chemical equations:
• +
plus
• 
yields
• (s)
solid
• (l)
liquid
• (g)
gas
• (aq)
aqueous
• 
equilibrium
• N.R.
no reaction
• 
light or heat is added
• Catalyst
( & catalysts are written above the yield sign)
Examples: To what is the arrow pointing?
H2 (g) + O2 (g)
MnO2
H2O2 (aq)
CaCO3


H2O (g)
H2O (l) + O2 (g)
CaO (s) + CO2 (g)
Conservation of Mass
Because of the principle of the
conservation of mass,
an equation
must be
balanced.
It must have the same
number of atoms of the
same kind on both sides.
Lavoisier, 1788
Writing and Balancing Chemical
Equations
You must be able to write the symbol
from the words and vice versa.
Example:
Write the equation for the formation of
sodium hydroxide and hydrogen, from the
reaction of sodium with water.
Write the equation for the formation of
sodium hydroxide and hydrogen, from the
reaction of sodium with water.
1. Write the formulas of all reactants to the left of
the arrow and all products to the right of the
arrow.
Sodium + water
sodium hydroxide + hydrogen
Translate the equation and be sure the formulas are
correct.
Na + H2O  NaOH + H2
Write the equation for the formation of
sodium hydroxide and hydrogen, from the
reaction of sodium with water.
2. Once the formulas are correctly written, DO NOT
change them.
2. Use coefficients (numbers in front of the
formulas), to balance the equation.
2. DO NOT CHANGE THE SUBSCRIPTS!
Coefficients are always whole numbers.
_____Na + _____H2O  ____NaOH + _____H2
Subscripts vs. Coefficients
• 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 or
formula units of
the compound.
3. Begin balancing with an element that occurs only
once on each side of the arrow.
Ex: Na
2
2
2
_____Na
+ _____H
+ _____H2
2O  ____NaOH
When you are finished, you should have equal
numbers of each element on either side of the
equation
Na
2
Na 2
H
4
H
4
O
2
O
2
4. To determine the number of atoms of a given
element in one term of the equation, multiply the
coefficient by the subscript of the element.
Ex: In the previous equation (below), how many
hydrogen atoms are there?
4
2
2 2O  ____NaOH
2
____Na
+ _____H
+ _____H2
• Take one element at a time, working left to
right except for H and O. Save H for next-tolast, and O until last.
• IF everything balances except for O, and there
is no way to balance O with a whole number,
double all the coefficients and try again.
(Because O is diatomic as an element)
• (Shortcut) Polyatomic ions that appear on both
sides of the equation should be balanced as
independent units.
(NH4)2SO4 (aq) + BaCl2 (aq)  BaSO4 (s) + NH4Cl (aq)
Balancing
Equations
2 Al(s) + ___
3 Br2(l) ---> ___ Al2Br6(s)
___
Practice:
• Balance the equation for the formation of
magnesium nitride from its elements.
Mg2+
N3Mg3N2
3
____Mg
+ ____N2 
____Mg3N2
Balance the reaction of sodium metal with
chlorine gas to form sodium chloride.
Na+
Cl-
NaCl
2
2
____Na
+ ____Cl2  ____NaCl

Ex: NH3 + O2
NO2 + H2O
• H can be balanced by placing a 2 in front
of NH3 and a 3 in front of H2O. Then put a
2 in front of NO2 for nitrogen to balance.
2
_____NH
3 + _____O2

2
____NO
2 +
3
____H
2O
2
_____NH
3 + _____O2

2
____NO
2 +
3
____H
2O
• Now all that is left to balance is the
oxygen. There are 2 O on the reactant
side and 7 on the product side. Our only
source of oxygen is the O2. Any whole
number we place in front of the O2 will
result in an even number of atoms. The
only way to balance the equation is double
all the coefficients.
2
_____NH
3 + _____O2

2
____NO
2 +
3
____H
2O
• Double all the coefficients, then add the 7
for the O2.
2
2
( ____NH
3

+ _____O2
____NO
2
2 +
)
____H
3
2O
=
4
7
_____NH
3 + _____O
2

4
____NO
2 +
6
____H
2O
____H2 + ____O2
 ____H2O
___NH3 + ____O2  ____NO2 +
____H2O
___Ca + ___H2O  ___Ca(OH)2 + ___H2
__NH4Cl +__Ca(OH)2  __NH3 + __H2O+__CaCl2
___ZnO + ___HCl  ___ZnCl2 + ___H2O
____K + _____F2

_____KF
____C2H4 + ____O2  ____CO2 + ____H2O
Types of Reactions
•
There are five types of chemical
reactions we will talk about:
1.
2.
3.
4.
5.
•
Synthesis reactions
Decomposition reactions
Single displacement reactions
Double displacement reactions
Combustion reactions
You need to be able to identify the type
of reaction and predict the product(s)
Steps to Writing Reactions
•
Some steps for doing reactions
1. Identify the type of reaction
2. Predict the product(s) using the type of reaction
as a model
3. Balance it
Don’t forget about the diatomic elements!
(BrINClHOF) For example, Oxygen is O2 as an
element.
In a compound, it can’t be a diatomic element
because it’s not an element anymore, it’s a
compound!
Synthesis reaction (combination
reaction)•
the combination of two or more substances to
form a compound
Elem. or cmpd. + elem. or cmpd
•

cmpd.
General form A + B  AB
The product in a reaction will have different
properties from either of the reactants that
formed it.
Practice
• Predict the products. Write and balance
the following synthesis reaction equations.
• Sodium metal reacts with chlorine gas
2 Na(s) + Cl2(g)  2NaCl(s)
• Solid Magnesium reacts with fluorine gas
Mg(s) + F2(g)  MgF2(s)
• Aluminum metal reacts with fluorine gas
2Al(s) + 3F2(g)  2 AlF3(s)
Decomposition Reaction:
•
•
•
•
•
is the breakdown of one
substance into two or
more other substances
compound  two or
more elements
AB  A + B
2 H2O  2H2 + O2
2 HgO  2Hg + O2
Decomposition Exceptions
• Carbonates and chlorates are special case
decomposition reactions that do not go to
the elements.
• Carbonates (CO32-) decompose to carbon
dioxide and a metal oxide
• Example: CaCO3  CO2 + CaO
• Chlorates (ClO3-) decompose to oxygen gas
and a metal chloride
• Example: 2 Al(ClO3)3  2 AlCl3 + 9 O2
• There are other special cases, but we will not
explore those in Chemistry I
Practice
• Predict the products. Then, write and
balance the following decomposition
reaction equations:
• Solid Lead (IV) oxide decomposes
PbO2(s)  Pb(s) + O2(g)
• Aluminum nitride decomposes
2 AlN(s)  2Al(s) + N2(g)
Practice
Identify the type of reaction for each of the
following synthesis or decomposition
reactions, and write the balanced equation:
N2(g) + O2(g)  Nitrogen
2 NO (g) monoxide Synthesis
BaCO3(s)  BaO(s) + CO2 (g) Decomposition
Co2S3Co
2 Co(s)+3 S(s)  (make
Synthesis
(s) be +3)
2 NI3(s)  N2 (g) + 3 I2 (s)
Decomposition
Single Replacement Reaction:
•
•
One element replaces another element in a
compound.
A metal can replace a metal (+) OR
a nonmetal can replace a nonmetal (-).
element + compound  element + compound
A + BC  AC + B
When H2O splits into ions, it splits into
H+ and OH- (not H+ and O-2 !!)
Single Replacement Reactions
• Write and balance the following single
replacement reaction equation:
• Zinc metal reacts with aqueous
hydrochloric acid
Zn(s) + 2 HCl(aq)  ZnCl2 + H2(g)
Note: Zinc replaces the hydrogen ion in the
reaction
Single Replacement Reactions
• Sodium chloride solid reacts with fluorine gas
2 NaCl(s) + F2(g) 
2 NaF(s) + Cl2(g)
Note that fluorine replaces chlorine in the compound
• Aluminum metal reacts with aqueous copper
(II) nitrate
2 Al(s)+3 Cu(NO3)2(aq)
3 Cu(s)2+ Al(NO3)3(aq)
To determine if a single replacement reaction
will take place you must compare the
activities of the elements involved.
• For metals, use the Activity Series. A
metal will replace any metal below it on
the activity series.
Activity Series of Metals and Halogens
Metals
Halogens
Deceasing activity
Lithium
Potassium
Calcium
Sodium
Magnesium
Aluminum
Zinc
Chromium
Iron
Nickel
Tin
Lead
HYDROGEN
Copper
Mercury
Silver
Platinum
Gold
Fluorine
Chlorine
Bromine
Iodine
Will Na replace Cr
in a single
replacement
reaction?
Yes!
Practice:
___I2 + ___NaCl 
___AgNO
2
3 + ___Mg 
N.R.
2
___Mg(NO3)2 + ___Ag
2
2
+ ___Br2
___KBr
+ ___F2  ___KF
N.R.
Decreasing Activity
___Mg(NO3)2 + ____Cu 
Activity Series of Metals
Lithium
Potassium
Barium
Calcium
Sodium
Magnesium
Aluminum
Zinc
Iron
Cadmium
Nickel
Tin
Lead
Hydrogen (a nonmetal)
Copper
Mercury
Silver
Gold
Platinum
Metals from Li to Na will replace H from water
and acids; metals from Mg to Pb will replace H
from acids only.
Double Replacement Reaction:
•
•
Two elements replace each other in
compounds.
occur when a metal replaces a metal in a
compound and a nonmetal replaces a
nonmetal in a compound
AB + CD  AD + CB
MgCO3 + 2HCl  MgCl2 + H2CO3
AgNO3 + NaCl  AgCl + NaNO3
Double Replacement Reactions
• Think about it like “foil”ing in algebra, first and
last ions go together + inside ions go together
• Example:
AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq)
• Another example:
K2SO4(aq) + Ba(NO3)2(aq) 2 KNO3(aq) + BaSO4(s)
In order for double replacement reaction to
take place, one of the products must be an
insoluble solid (ppt), a gas, or water.
Negative Ion
Plus
Positive Ion
Form a Compound
Which is:
Any negative ion
+
Alkali metal ions
(Li+, Na+, K+, Rb+, Cs+)
Soluble
Any negative ion
+
Ammonium ion
Soluble
Nitrate
+
Any positive ion
Soluble
Acetate
+
Any positive ion
Ag+
Soluble
Not soluble
Chloride, Bromide,
or Iodide
+
Ag+, Pb2+, Hg22+, Cu+
Any other positive ion
Not soluble
Soluble
Sulfate
+
Ca2+, Sr2+, Ba2+, Ra2+, Ag+, Pb2+
Any other positive ion
Not soluble
Soluble
Sulfide
+
Alkali ions or Ammonium, Be, Mg, Ca, Sr,
Ba, Ra,
Any other positive ion
Soluble
Soluble
Not soluble
Hydroxide
+
Alkali ions or Ammonium
Any other positive ion
Soluble
Not soluble
Phosphate,
Carbonate, or
Sulfite
+
Alkali ions or Ammonium
Any other positive ion
Soluble
Not soluble
Compound Precipitate Formed?
•
•
•
•
•
•
BaSO4
Pb(NO3)2
Ag2S
PbCl2
NH4Cl
Cr PO4
_______
Yes
_______
No
_______
Yes
Yes
_______
No
_______
_______
Yes
__Na2SO4 + __Ba(NO3)2  __NaNO
2
3 + __BaSO4
Na+
NO3NaNO3
Ba2+
SO42BaSO4
__NaOH
+ __Fe(NO3)3  __NaNO
3
3
3 + __Fe(OH)3
Na+
NO3-
NaNO3
Fe3+
OH-
Fe(OH)3
Practice
•
Predict the products. Balance the equation
HNO3(aq) + AgCl(s)
1. HCl(aq) + AgNO3(aq) 
2. 3 CaCl2(aq) +2 Na3PO4(aq)  Ca3(PO4)2(s) + 6 NaCl(aq)
3. Pb(NO3)2(aq) + BaCl2(aq)  PbCl2(s) + Ba(NO3)2(aq)
4. FeCl3(aq) + 3 NaOH(aq)  Fe(OH)3(s) +3 NaCl(aq)
5. H2SO4(aq) +2 NaOH(aq) 2 H2O(l) + Na2SO4(aq)
6. 2 KOH(aq) + CuSO4(aq) 
K2SO4(aq) + Cu(OH)2(s)
Combustion Reactions
• Combustion reactions
occur when a hydrocarbon
reacts with oxygen gas.
• This is also called
burning!!! In order to burn
something you need the 3
things in the “fire triangle”:
– 1) A Fuel (hydrocarbon)
– 2) Oxygen to burn it with
– 3) Something to ignite the
reaction (spark)
General form for combustion of a
hydrocarbon:
CxHy + O2  CO2 + H2O
• Products in combustion are ALWAYS carbon
dioxide and water. (although incomplete
burning does cause some by-products like
carbon monoxide)
• Combustion is used to heat homes and run
automobiles (octane, as in gasoline, is
C8H18)
Combustion
• Example
•
C5H12 + 8 O2  5 CO2 + 6 H2O
• Write the products and balance the
following combustion reaction:
10 CO2 +11
22 H2O
• 2 C10H22 +31O2 20
Examples
____C3H8 + ____O
5
3
4
2  ____CO
2 + ____H
2O
____C6H12O6 + ____O
6 2  ____CO
6
6
2 + ____H
2O
Mixed Practice
•
State the type, predict the products,
and balance the following reactions:
1. BaCl2 + H2SO4  BaSO4 + 2HCl
2. C6H12 +9 O2 6CO2 +6 H2O
3. Zn + CuSO4  ZnSO4 + Cu
4. 2Cs + Br2  2 CsBr
5. FeCO3 FeO + CO2