Transcript Reaction Type Notes

Reaction Type Notes
Reaction Type Notes
• Most chemical reactions can be
categorized into one of five types.
• You can usually identify the reaction type
by looking at the reactants. Once the type
of reaction is identified, we can predict the
products
Types of Chemical Reactions
• Chemists classify reactions in order to
organize the many types.
• A synthesis reaction is a reaction in which
two or more substances react to produce a
single product.
• General form:
A + B  AB
or
A + BC  ABC
or
AB + CD  ABCD
Types of Chemical Reactions (cont.)
• When two elements react, the reaction is
always a synthesis reaction.
Reaction Type Notes
Example: 2 H2 + O2  2 H2O
Reaction Type Notes
• Synthesis
To predict the products: for binary
compounds, put elements together and
balance the charges. Otherwise, just
combine.
These reactions generally happen
spontaneously, and are generally
exothermic (release energy).
Types of Chemical Reactions (cont.)
• In a combustion reaction, oxygen
combines with a substance and releases
energy in the form of heat and light.
• Heated hydrogen reacts with oxygen to
produce heat and water in a combustion
reaction. This is also a synthesis reaction.
Reaction Type Notes
• Hydrocarbon Combustion—Involves a
specific case of combustion in which a
hydrocarbon (a substance containing
carbon and hydrogen) reacts with oxygen
to form carbon dioxide and water
• General form:
CxHy + O2  CO2 + H2O
Reaction Type Notes
Example:
2C2H6 + 7O2  4CO2 + 6H2O
Reaction Type Notes
• Hydrocarbon Combustion
• To predict products:
• At least Carbon Dioxide and water.
Always exothermic, but often requires a
large activation energy, leading it to occur
spontaneously
Reaction Type Notes
Practice type of reaction and balance
1. Al(s) + S(s)  Al2S3;
2. H2O(l) + N2O5(g)  HNO3(aq)
3. NO2(g) + O2(g)  N2O5 (g)
Decomposition Reactions
• A decomposition reaction is one in which
a single compound breaks down into two or
more elements or new compounds.
• Decomposition reactions often require an
energy source, such as heat, light, or
electricity, to occur.
• General form: AB  A + B
Reaction Type Notes
• Example: 2H2O2  2 H2O + O2
(it needs a catalyst—Potassium Iodide)
http://www.youtube.com/watch?v=OTEX38bQ-2w&feature=related
Reaction Type Notes
• Decomposition
To predict the products:
• Binary compounds separate into their two
elements
• You will be given a handout to predict
others
• Generally not spontaneous, and generally
endothermic
Reaction Type Notes
Practice type of reaction and balance
4. Al2O3(s)  Al(s) + O2(g)
5. Ni(OH)2(s)  NiO(s) + H2O(l)
6. NaHCO3(s)  Na2CO3(aq) + CO2(g) +
H2O(l)
Replacement Reactions
• A reaction in which the atoms of one
element replace the atoms of another
element in a compound is called a single
replacement reaction.
A + BX → AX + B
Replacement Reactions (cont.)
• A metal will not always
replace a metal in a
compound dissolved in
water because of differing
reactivities.
• An activity series can be
used to predict if reactions
will occur.
Replacement Reactions (cont.)
• Halogens frequently replace other
halogens in replacement reactions.
• Halogens also have different reactivities and
do not always replace each other.
Reaction Type Notes
Example: 2 Na + 2 H(OH)  2 Na(OH)+ H2
Reaction Type Notes
• Single displacement
To predict the products: The element switches
places with the element of similar charge within
the compound.
If the element is more reactive then the one it
attempts to replace, then the reaction will be
spontaneous and exothermic. Otherwise, it will
not be spontaneous and will be endothermic
(require the input of energy).
Reaction Types
Activity Series:
Most Active Cations  Least
Active
• Lithium
• Rubidium
• Potassium
• Barium
• Calcium
• Sodium
• Hydrogen (in water)
• Magnesium
• Aluminum
• Manganese
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Zinc
Chromium
Iron
Nickel
Tin
Lead
Hydrogen (in acids)
Copper
Mercury
Silver
Platinum
Gold
*Red not included in book values
Reaction Type Notes
Activity Series:
Most Active Anions 
Least Active
• Fluorine
• Oxygen
• Chlorine
• Nitrogen
• Bromine
• Iodine
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Sulfur
Selenium
Astatine
Phosphorus
Tellurium
Arsenic
Polonium
*Red not included in book
values
Reaction Type Notes
Practice
Type of reaction/ will it react and balance
7. K(s) + ZnCl2(aq)  Zn(s) + KCl(aq)
8. Al(s) + Pb(NO3)2(s)  Pb(s) +
Al(NO3)3(aq)
Replacement Reactions (cont.)
• Double replacement reactions occur
when ions exchange between two
compounds.
• This figure shows a generic double
replacement equation.
Reaction Type Notes
• Double displacement
To predict the products:
Like charged particles switch places
• Both compounds are initially stable and so
reactions will usually not be spontaneous as
solids. If compounds can be dissolved and
dissociated (broken apart) then reaction will
usually occur spontaneously to some degree,
but not be highly exothermic
Replacement Reactions (cont.)
• This table shows the steps to write double
replacement reactions.
Replacement Reactions (cont.)
• A solid product produced during a chemical
reaction in a solution is called a
precipitate.
• All double replacement reactions produce
either water, a precipitate, or a gas.
• Example: 2 NaI(aq) + Pb(NO3)2(aq)
PbI2(s) + 2NaNO3(aq)
Reaction Type Notes
Practice type of reaction and balance
9. LiI(aq) + AgNO3(aq)  AgI(s) +
LiNO3(aq)
10. BaCl2(aq) + K2CO3(aq)  BaCO3(s) +
KCl(aq)
11. Na2C2O4(aq) + Pb(NO3)2(aq) 
PbC2O4(s) + NaNO3(aq)
Reaction Type Notes
• Most reactions which do not appear to fit
any of these five patterns are usually a
combination of two or more of them
happening simultaneously
Replacement Reactions (cont.)
• This table summarizes different ways to
predict the products of a chemical reaction.