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Types of Reactions
It is most important for a chemist to be able to write correctly balanced equations and to interpret
equations written by others. It is also very helpful if he/she knows how to predict the products of
certain specific types of reactions.
I.
Formulas show chemistry at a standstill. Equations show
chemistry in action!
A. Equations show:
1.
the reactants which enter into a reaction.
2. the products which are formed by the reaction.
3. the moles (coefficients) of each substance used and each substance produced.
B. Two important principles to remember:
1.
Every chemical compound has a formula that cannot be altered.
2. A chemical reaction must account for every atom that is used. This is an application of the
Law of Conservation of Matter, which states that in a chemical reaction atoms are neither
created nor destroyed.
C. Some things to remember about writing equations:
1.
The diatomic elements when they stand alone are always written H2, N2, O2, F2, Cl2, Br2, I2 .
2. The sign, , means "yields" and shows the direction of the action.
3. A small delta, (∆), above the arrow shows that heat has been added.
4. Before beginning to balance an equation, check each formula to see that it is correct.
NEVER change a formula during the balancing of an equation.
5. Balancing is done by placing coefficients in front of the formulas to insure the same number
of atoms of each element on both sides of the arrow.
6. If a reactant or product is a solid, (s) is placed after the formula.
7. If a reactant or product is a gas, (g) is placed after it.
8. If a reactant or product is in water solution, (aq) is placed after it.
II.
Five basic types of chemical reactions:
A. Synthesis (combination):

two or more elements or compounds may combine to form a more complex compound.

Basic form: A + X  AX
Examples of synthesis reactions:
1. Metal + oxygen  metal oxide
EX. 2Mg(s) + O2(g)  2MgO(s)
2. Nonmetal + oxygen  nonmetallic oxide
EX. C(s) + O2(g)  CO2(g)
3. Metal oxide + water  metallic hydroxide (a basic solution)
EX. MgO(s) + H2O(l)  Mg(OH)2(aq)
4. Nonmetallic oxide + water  an acid
EX. CO2(g) + H2O(l)  H2CO3(aq)
5. Metal + nonmetal  a salt (any ionic compound composed of cations and anions)
EX. 2 Na(s) + Cl2(g)  2NaCl(s)
6. A few nonmetals combine with each other. These two reactions must be remembered:
2P(s) + 3Cl2(g)  2PCl3(g)
N2(g) + 3H2(g)  2NH3(g)
NH3(g) + H2O(l)  NH4OH(aq)
Practice Predicting Products of Synthesis Reactions
1.
sulfur dioxide gas and liquid water to produce a solution.
2. hydrogen gas reacts with nitrogen gas to produce a gas.
3. magnesium metal and chlorine gas react to produce a solid.
4. calcium oxide solid is added to liquid water to produce a base.
B. Decomposition:

A single compound breaks down into its component parts or simpler compounds.

Basic form: AX  A + X
Examples of decomposition reactions:
1. Metallic carbonates, when heated, form metallic oxides and CO2(g).
EX. CaCO3(s)  CaO(s) + CO2(g)
2. Most metallic hydroxides (basic solutions), when heated, decompose into metallic oxides
and water.
EX. Ca(OH)2(aq)  CaO(s) + H2O(g)
3. Metallic chlorates, when heated, decompose into metallic chlorides and oxygen.
EX. 2KClO3(s)  2KCl(s) + 3O2(g)
4. Some acids, when heated, decompose into nonmetallic oxides and water.
EX. H2SO4  H2O(l) + SO3(g)
5. Some oxides, when heated, decompose.
EX. 2HgO(s)  2Hg(l) + O2(g)
6. Some decomposition reactions are produced by electricity.
EX. 2H2O(l)  2H2(g) + O2(g)
EX. 2NaCl(l)  2Na(s) + Cl2(g)
Practice Predicting Products of Decomposition Reactions
1.
Solid barium hydroxide breaks down when heated to form a solid and a liquid
2. Sodium carbonate solid when heated breaks down into a solid and a gas.
3. Solid lithium chlorate breaks down when heated into a solid product and a gaseous product.
4.
electrolysis of solid aluminum oxide produces a solid and a gas.
C. Single Replacement:

a more active element takes the place of another element in a compound and sets the less
active one free.

Basic form: A + BX  AX + B
Examples of single replacement reactions:
1. Replacement of a metal in a compound by a more active metal.
EX. Fe(s) + CuSO4(aq)  FeSO4(aq) + Cu(s)
2. Replacement of hydrogen in water by an active metal.
EX. 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g)
EX. Mg(s) + H2O(g)  MgO(s) + H2(g)
3. Replacement of hydrogen in acids by active metals.
EX. Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)
4. Replacement of nonmetals by more active nonmetals.
EX. Cl2(g) + 2NaBr(aq)  2NaCl(aq) + Br2(l)
ACTIVITY SERIES
Metal Reactivity
Li
Rb
reacts with cold
K
water and
Ba
acids, replacing
Ca
hydrogen
Na
Mg
Al
reacts with acids or
Mn
steam, but usually not
Zn
liquid water, to
Cr
replace hydrogen
Fe
Co
reacts with
Ni
acids, but not
Sn
water, to replace
Pb
hydrogen
H2
Cu
react with O2
Ag
to form oxides
Hg
Pt
mostly
Au
unreactive
Halogen Reactivity
F2 ………most reactive
Cl2
Br2
I2 …….…least reactive
Practice Predicting Products of Single Replacement Reactions
1. Aluminum metal reacts with hydrochloric acid
2. potassium metal added to cold water
3. zinc metal added to mercury(II) nitrate solution
4. silver metal added to copper(II) sulfate solution
5. chlorine gas bubbled through a solution of calcium bromide
D. Double Replacement:

occurs between ions in aqueous solution. A reaction will occur when a pair of ions come
together to produce at least one of the following:
1. a precipitate
2. a gas
3. water or some other non-ionized substance.

Basic form: AX + BY  AY + BX
Some products are unstable and break down (decompose) as they are produced during
the reaction. You need to be able to recognize these products when they occur and
write the decomposition products in their places.
Examples: MEMORIZE THESE THREE EXAMPLES * H2CO3(aq)  H2O(l) + CO2(g)
Carbonic acid, as in soft drinks, decomposes when it is formed.
* H2SO3(aq)  H2O(l) + SO2(g)
Sulfurous acid also decomposes as it is formed.
* NH4OH(aq)  NH3(g) + H2O(l)
You can definitely smell the odor of ammonia gas because whenever ammonium hydroxide is
formed it decomposes into ammonia and water.
Examples of double replacement reactions:
1. Formation of precipitate.
EX. NaCl (aq) + AgNO3(aq)  NaNO3(aq) + AgCl(s)
EX. BaCl2(aq) + Na2 SO4(aq)  2NaCl(aq) + BaSO4(s)
2. Formation of a gas.
EX. HCl(aq) + FeS(s)  FeCl2(aq) + H2S(g)
3. Formation of water. (If the reaction is between an acid and a base it is called a
neutralization reaction.)
EX. HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
4. Formation of a product which decomposes.
EX. CaCO3(s) + HCl(aq)  CaCl2(aq) + ( H2CO3  CO2(g) + H2O(l) )
NOTE: Use the solubility rules to decide whether a product of a double replacement
reaction is insoluble in water and will thus form a precipitate. If a compound is
soluble in water then it should be shown as being in aqueous solution.
Solubility Rules
1. All common compounds of Group I and ammonium ions are soluble.
2. All nitrates, acetates, and chlorates are soluble.
3. All binary compounds of the halogens (other than F) with metals are
soluble, except those of Ag, Hg (I), and Pb. (Pb halides are soluble in hot
water.)
4. All sulfates are soluble, except those of barium, strontium, calcium, lead,
silver, and mercury (I). The latter three are slightly soluble.
5. Except for rule 1, carbonates, hydroxides, oxides, silicates, and phosphates
are insoluble.
6. Sulfides are insoluble except for calcium, barium, strontium, magnesium,
sodium, potassium, and ammonium.
Practice Predicting Products of Double Replacement Reactions
Remember all reactants begin as water solutions!
1. potassium iodide added to lead(II) nitrate
2. sodium sulfite combined with acetic acid
3. sodium chloride added to sulfuric acid
4. barium nitrate added to sodium oxalate
5. sodium bicarbonate added to hydrochloric acid
E. Combustion of Hydrocarbons:
Another important type of reaction is that of the combustion of a hydrocarbon. When a
hydrocarbon is burned with sufficient oxygen supply, the products are always carbon dioxide and
water vapor. If the supply of oxygen is low or restricted, then carbon monoxide will be produced.
This is why it is so dangerous to have an automobile engine running inside a closed garage or to use a
charcoal grill indoors.
* Hydrocarbon (CxHy) + O2(g)  CO2(g) + H2O(g)
* EX. (methane) CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
* EX. (butane) 2C4H10(g) + 13O2(g)  8CO2(g) + 10H2O(g)
Practice Predicting Products of a Combustion reaction
1. (napthalene)
C10H8
2.
(heptane)
C7H16
2.
(benzene)
C6 H 6