Download + H 2 (g)

 Chemical
Reactions
Chapter 9
 Section 1

Indications of a Chemical Reaction


Chemical changes alter the molecular
structure of the substances involved.
These observations suggest that a chemical
change has occurred:
1. Evolution of heat(temp change) and light.
2. Production of a gas.
3. Formation of a precipitate (solid).
4. Color change.
Chemical Equations


Used to represent chemical reactions (rx).
Chemical equations have the following
characteristics:
a. equation must represent known facts.
b. equation must contain the correct
formulas for the reactants and products.
c. law of conservation of mass must be
satisfied.
Chemical Equations

Let’s diagram the following equation:
2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g)
Reactants
Products
* is read as yield (also produce or form)
*number that appears in front of a formula is
called a coefficient. It represents relative
number of moles of a substance.
*(g) refers to the state of matter of the
substance.
The following is a list of symbols used
in chemical equations:
= reversible rx
heat
or Δ
= reactants
are heated
(aq) = aqueous
2 atm = pressure at which
(s) = solid phase
rx took place
(cr) crystalline
0˚ = temp at which rx
(l) = liquid phase
took place
(g) = gas phase
= formula of catalyst
MnO2
(manganese dioxide)
*add to the right of rx conditions
(s) if: single metal, solid, ash, ribbon, salt,
crystalline.
(g) if: any “big 7” , CO2, CO.
(aq) if: all acids, dissolved in water, solution.
electric if electricity is added.
*If substance does not fit above criteria, do not
put any state of matter.
Balancing Chemical Equations
Balancing Steps:
Step 1: Identify reactants and products.
Write a formula equation by
substituting correct formulas for the
names of reactants and products.
EX: Water breaks down into hydrogen
and oxygen gases when heated.
H2O(l)  H2(g) + O2(g)

Diatomic Molecules




There are seven elements that are not
found as single atoms in nature.
They are found bound to other elements
or to themselves in molecular compounds.
They are referred to as the “Big 7”
because they form the shape of a 7 on the
periodic table.
These elements are: Hydrogen, Nitrogen,
Oxygen, Fluorine, Chlorine, Bromine, and
Iodine.
Balancing Chemical Equations
Step 2: Balance the formula equation
according to the law of conservation of
mass.
a. Balance the different types of atoms one
at a time changing only the coefficients.
b. Balance unique atoms first.
c. Balance polyatomic ions if they appear
on both sides as single units.
d. Balance H atoms and O atoms last.
Write after d.
**If an odd # on one side and even on
another, make odd even with a 2**
EX:
H2O(l)  H2(g) + O2(g)
*Is this balanced? Why or Why not?


Not balanced.
Because there are more oxygen atoms on
the product side. This violates the law of
conservation of mass.
Balancing Chemical Equations
H2O(l)  H2(g) + O2(g)
How to balance:
1. There are no unique atoms to balance
first.
2. H atoms are already balanced.
3. Balance the O atoms using only
coefficients.
2H2O(l)  H2(g) + O2(g)
4.
By adding a coefficient of 2 to H20 to
balance the O atoms, the H atoms
became unbalanced. Balance the H
atoms.
2H2O(l)  2H2(g) + O2(g)

Step 3: Count atoms to be sure that the
equation is balanced.
2H2O(l)  2H2(g) + O2(g)
(4H + 2O) = (4H) + (2O)
2:2:1 ratio

Avoid the following when balancing:
1.
Writing incorrect chemical formulas.
Balancing equations by changing the
subscripts.
Coefficients do not represent the smallest
whole number ratio.
2.
3.
EX: 4H2O(l)  4H2(g) + 2O2(g)
4:4:2  2:2:1
* Factor out the LCM.

Hint to balancing hydrocarbons:
-hydrocarbons are CxHx or CxHxOH + O2
-place a coefficient of 2 in front of
hydrocarbon and then balance.
-may have to factor 2 out when finished.
Practice Balancing
1.
Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g)
Zn(s) + 2HCL(aq)  ZnCl2(aq) + H2(g)
2. HNO3(aq) + Mg(OH)2(s) 
Mg(NO3)2(aq) + H2O(l)
2HNO3(aq) + Mg(OH)2(s) 
Mg(NO3)2(aq) + 2H2O(l)
Types of Chemical Reactions

There are 5 basic types of chemical rxs.
1. Synthesis rx
2. Decomposition rx
3. Single replacement (displacement) rx
4. Double replacement (displacement) rx
5. Combustion rx
Synthesis Rxs


In a synthesis rx, two or more reactants
combine to form a single new product.
Represented by:
A + X  AX
EX: 2Mg(s) + O2(g)  2MgO(s)
4Fe(s) + 3O2(g)  2Fe2O3(s)
2Na(s) + F2(g)  2NaF(s)
Decomposition Rxs


In a decomposition rx, a single reactant
undergoes a rx that produces two or more
simpler products.
Represented by:
AX  A + X
EX: 2H2O(l)  2H2(g) + O2(g)
2KClO3(s)  2KCl(s) + 3O2(g)
H2CO3(aq)  CO2(g) + H2O(l)
Decomposition Rxs

A metal carbonate breaks down to form
a metal oxide and carbon dioxide gas.
CaCO3(s)  CaO (s) + CO2(g)

A metal hydroxide (except those metals
in Group 1) break down to form a metal
oxide and water.
Ca(OH)2(s)  CaO(s) + H2O

A metal chlorate breaks down to form a
metal chloride and oxygen gas.
2KClO3(s)  2KCl(s) + 3O2(g)
Single Replacement Rxs


In a single replacement rx, one elemental
reactant replaces a similar type element in a
reactant compound to form a new product
compound and a new elemental product.
Represented by:
A + BX  AX + B
EX: 3Fe(s) +4H2O(l)  Fe3O4(s) + 4H2(g)
2Al(s) + 3Pb(NO3)2(aq) 
3Pb(s) + 2Al(NO3)3(aq)
Wow!
He’s the
bomb.
Mg(s) + 2HCl(aq)

Stupid
Jerk!
MgCl2(aq) + H2(g)
Single Replacement Rxs
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

The ability of an element to react is referred
to as the element’s activity.
The more readily an element reacts with
other substances, the greater its activity is.
An activity series is a list of elements
organized according to the ease with which
the elements undergo single replacement
reactions.
Activity Series of Elements


In an activity series, the most active
metals are placed at the top. An active
metal can replace each of the elements
below it but not above it.
Activity series are used to help predict
whether certain rxs will occur.
Using the Activity Series of
Elements



Aluminum is more reactive than Zinc so
the following rx will occur:
2Al(s) + 3ZnCl2(aq)  3Zn + 2AlCl3(aq)
Cobalt is less reactive than Sodium so the
following rx will not occur:
Co(s) + 2NaCl(s)  CoCl2(s) + Na2(s)
This rx should be written as:
Co(s) + NaCl(s)  no reaction
Using the Activity Series of
Elements

Use the activity series to predict whether
each of the following rxs will occur:
1. Zn(s) + H2O(l) 
Will Occur
2. Cu(s) + HCl(aq) 
No Reaction
3. Cd(s) + Pb(NO3)2(aq) 
Will Occur
Single Replacement Rxs

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Indicate whether the metal or nonmetal
is being replaced.
EX: Mg + FeCl2  Fe + MgCl2
SR-metal
Cl2 + KI  KCl + I2
SR-nonmetal
Double Replacement Rxs
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In a double replacement rx, the ions of two
reactant compounds exchange places in an
aqueous solution to form two new product
compounds.
Represented by:
AX + BY  AY + BX
EX: 2KI(aq) + Pb(NO3)2(aq) 
PbI2(s) + 2KNO3(aq)
Combustion Rxs
In a combustion rx, a hydrocarbon/alcohol
(consisting of carbon and hydrogen)
combines with oxygen, releasing a large
amount of energy in the form of heat and
light.
 Represented by:
(CxHx OH) or CxHx + O2  CO2 + H2O
EX: C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)
*combustion of hydrocarbons always result in
the formation of CO2 and water.

Identification of Rx Types
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Synthesis
Combustion (combust)
Double Replacement (DR)
Single Replacement (SR)
-Indicate whether metal or nonmetal
Decomposition (decomp)
-Indicate metal carbonate, metal hydroxide,
or metal chlorate.
-If none of the above, general.
Identifying Rxs

1.
2.
3.
4.
5.
6.
Use your knowledge of rx types to
classify the following rxs:
NH3(g) + HCl(g)  NH4Cl(s)
C2H5OH(l) + O2(g)  CO2(g) + H2O(g)
2KClO3(s)  2KCl(s) + 3O2(g)
Zn + H2SO4  ZnSO4 + H2
S(s) + O2(g)  SO2(g)
AgNO3(aq) + NaCl(aq) 
AgCl(s) + NaNO3(aq)
Reaction Prediction Steps
Step 1: Find the reactants and write them in
formula form.
Step 2: Identify the type of rx based on the
reactants.
Step 3: Write products
-positive oxidations bond with negative
oxidations.
Step 4: Balance equation.
Hints:
1.
2.
3.
4.
5.
6.
Know the 3 types of decomp rxs and
what products they produce.
Combustion products, CO2 + H2O
H2O as a reactant, HOH
2 single elements always synthesis
SR rxs, use Activity Series
If you need oxidation for metals, darker
number on periodic table is most
common ion so use that.
Predicting Products

1.
2.
3.
Use your knowledge of rx types to predict
the products of the following rxs:
Na + H2O [HOH]
NaOH + H2
HNO3 + Ca(OH)2 
Ca(NO3)2 + H2O
Mg + O2 
MgO
Predicting Products
4.
5.
6.
7.
Ca + Cl2 
CaCl2
C6H14 + O2 
CO2 + H2O
Br2 + KI 
KBr + I2
MgO + Pb 
No Reaction
8.
Δ
HgO 
Hg + O2
9.
Na + Cl2 
NaCl
10.
NaI + Cl2 
NaCl + I2
*Now, balance these rxs to make them
correct.
In Summary


Five observations that suggest a
chemical reaction is taking place are the
evolution of light and heat, the
production of gas, a change in color, and
the formation of a precipitate.
Reactants are the starting substances in
a reaction. Products are the substances
resulting from a reaction.
In Summary


Physical states of substances are shown
by; (g) = gas, (l) = liquid, (s) = solid, and
(aq) = aqueous, which indicates
substance is dissolved in water.
Balancing an equation means adjusting
coefficients so that there is the same
number of atoms of each element on the
left and right sides of the equation.
In Summary

There are 5 basic types of chemical reactions:
1. Synthesis Rx: A + X  AX
2. Decomposition Rx: AX  A + X
3. Single Replacement Rx: A + BX  AX + B
4. Double Replacement Rx:
AX + BY  AY + BX
5. Combustion Rx:
CxHx + O2  CO2 + H2O
In Summary


Activity series list the elements in order
of their chemical reactivity and are
useful in predicting whether a chemical
reaction will occur.
Products of reactions can be predicted
by a general knowledge of the reaction
types.
In Summary


For the exam you must be able to:
1. Make a formula equation out of a
word equation. (or the opposite)
2. Identify the reaction type.
3. Predict the products for the reaction.
4. Balance the formula equation.
Be familiar with the entire contents of
the notepacket and chapter in book.

A C6H12O6 production