Download Chemical Reactions Chemistry - is the study of matter, its properties

Science 1206
Unit I - Chemical Reactions
Chemistry - is the study of matter, its properties, and its changes or transformations.
Matter - is anything that has mass and occupies space. All types of matter have physical and
chemical properties.
Physical Property - is a characteristic of a substance. Physical properties of matter include:
state of matter at room temperature (solid, liquid, gas), color, odor, luster, solubility,
melting and boiling points. A change (such as dissolving or melting) in the size or form
of a substance does not change the chemical properties of a substance, is called a
physical change.
Chemical Property - is a characteristic behavior that occurs when a substance
changes to a new substance. It may determine the transformation which is about to
take place. The change, itself, which occurs is called the chemical change. The starting
materials in such a change are called reactants and the new materials produced are
called the products.
Pure Substance - A substance in which all the particles that make up a substance are the same.
As a result, the substance has constant properties. Ex. Pure water freezes at 0 0C and boils at
100 0C. There are two main types of pure substances.
1. Elements - are pure substances which can not be broken down into
simpler substances. Any substance on the Periodic Table is
considered an element because it contains only one kind of atom. Some atoms form
molecules when two atoms combine which occurs naturally. ie. O2, N2
2. Compounds - are pure substances that contain two or more different elements in a
fixed proportion. Compounds can be identified with chemical formulas. Ex.
H2O, CO2
Mixtures - are substances which contain two or more pure substances. They are not usually
found in fixed proportions. Two examples of mixtures are homogeneous mixtures (solutions)
and heterogeneous mixtures.
1. Solutions - These are substances which contain at least two pure substances but only one is
visible.
2. Heterogenous Mixtures - These contain two or more visible substances.
Safety and Chemicals
How can we check the properties of unknown chemicals to understand or predict the reaction
with another chemical?
Many chemicals can be hazardous to human health or the environment if they are not handled
safely. There are a variety of symbols used to identify hazardous chemicals.
Many household products are labeled with Hazardous Household Product Symbols (HHPS).
Dangerous materials in the workplace are labeled using Workplace Hazardous Materials
Information System (WHMIS). Make sure you know the symbols for each.
Every chemical that is ordered for the school arrives with a Materials Safety Data Sheet
(MSDS). This sheet describes the hazards associated with the chemical protective coating
which should be worn, and necessary steps to be taken if the chemical is spilled.
Elements and the Periodic Table
Periodic Table is a structured arrangement of elements that helps us and predict chemical and
physical properties. This was first devised by a Russian chemist named Mendeleev. He had
arranged the twenty something known elements in a pattern based on their behavior and
properties. He even had spaces left so that unknown elements which were to be discovered at
a later date could occupy a specific place in the pattern.
The Periodic Table has the elements arranged based on their physical properties. The metals
are located on the left-hand side of the Periodic Table and the non-metals are located on the
right-hand side of the Periodic Table. The only exception is hydrogen which behaves like a nonmetal but is located on the top left-hand side of the Table.
Each of the elements are also categorized based on their molar mass. If you noticed the mass
of the elements increases as you move from left to right, horizontally across the Table. It also
increases as you move vertically down the Table.
Each vertical column of the Periodic Table is called a Family or Group. The horizontal rows of
the Periodic Table are known as Periods.
A detailed look at each Family of the Periodic Table.
Group IA
This Family located on the far left of the Periodic Table are known as the Alkaline
Metals. Each of these elements has exactly one electron in its valence shell. All these
metals readily donate their electron to become more stable ions. Therefore, they are
reactive in that they form bonds via ionic bonding.
Group IIA
This family which consists of all the elements in the second column on the Periodic
Table are known as the Alkaline Earth Metals. Each of these elements has two
electrons in its outer shell. Therefore, they readily give up these electrons to become
more stable and are somewhat reactive.
The B Elements
All the B elements are true metals and have either two or three electrons in their
valence shell which they are ready to donate so that they may form a more stable
compound. Because all the mentioned elements are so far are metals they conduct
electricity readily. Some of the B elements are well known isotopes and so they may
have more or less protons than stated on the chart. Therefore, they result in a product
which may have one of two forms of the element. Iron for example, Fe 2+ (ferric) Fe
3+ (ferrous)
Group III A
******check metals and transition****
This group of elements contains a mixture of transition elements which mean they
exhibit behaviors similar to both metals and non-metals. However, all members of this
Family are ready to donate three electrons found in their valence shell. The non-metals
in the Groups usually form compounds by sharing electrons.
Group IV A *******check metals and covalent******
This group which also consists of metal, transitional elements, and non-metals all have
four electrons in their valence shell. It would be to energetically expensive to donate all
four electrons, so all members of this group combine with other elements through
covalent bonding (sharing of electrons).
Group VA
These elements are mainly all non-metals which means they do not conduct electricity
in solution, however, they readily accept electrons to form stable compounds. These
elements can form compounds either through ionic bonding or through covalent
bonding. Each of these metals has 5 electrons in its valence shell.
Group VI A
These metals are all non-metals and all contain six electrons in their valence shell.
These elements will also readily accept two electrons to become more stable. In doing
so, they become negatively charged ions called anions.
Group VII A
This Family of non-metals are known as the Halogen Family. They each have seven
electrons in their valence shell and will readily accept one electron to become a more
stable compound.
Group VIII A
This Family of elements are known as the Noble Gases and are electrically stable
because their valence shell are already filled with electrons. (Draw several BohrRutherford Diagrams) Therefore, these elements will not react with the other elements
and all other elements try to be like this Family.
Naming Compounds
The International Union of Pure and Applied Chemistry (IUPAC) have devised systematic
ways in which we name all chemical compounds. Chemical compounds are usually in
one of three forms: 1. Ionic 2. Molecular 3. Acids/Bases
Ionic Compounds
An ionic compound forms when atoms of elements transfer (donate or accept)
electrons to become more electrically stable. This compound forms as a result of the
attraction between the positive and negative charges (cations and anions) as the metal
gives its electrons to a non-metal to achieve stability. (Remember: An ionic bond only
occurs between a metal and a non-metal.)
Naming of Ionic Compounds (IUPAC)
Rule 1: Name the metal found in the compound first.
Rule 2: Name the non-metal in the compound next.
Rule 3: Drop the ending of the non-metal and add the suffix -ide.
Example:
Table salt - NaCl (a metal and non-metal) Sodium chloride
CaF2 Calcium flouride
MgO Magnesium oxide
Writing Formulas for Ionic Compounds
What is the chemical formula for Calcium and Bromine?
Step 1: Make sure you are dealing with an ionic compound (metal and nonmetal). Write the chemical symbols placing the metal before the Non-metal.
Ex.
Ca Br
Step 2: Write the ionic charge above each symbol to indicate the stable ion
each element forms. Ex.
2+ 1Ca Br
that
Step 3: Determine how many ions of each type you need so that the total
ionic charge is zero.
Ex.
1 (2+) 2(1-)
Ca
Br
Step 4: Write the formula using the subscripts to indicate the number of ions of each
type. The formula is Ca1Br2 , however, we never use 1 as a
subscript; so the
formula is: CaBr2 .
The total ionic charge is zero. (2+) + 2(1-) = 0
If you have two elements with charges of 3+ and 2- , then you must find the lowest
common multiple or simply criss cross the numbers for the charge, to use them as
subscripts.
Ex.
Aluminum and Sulfur
3+
Al
2S
LCM is 6. Therefore, how many (3+) = 6?
How many (2-) = 6?
Therefore, the chemical formula is: Al2S3
Some elements have more than one ionic charge. The charge for such elements is
usually written with a Roman Numeral in its name. The Roman Numeral appears in a
bracket after the metal with the specific charge. For example, copper can be Cu+ or
Cu2+. If Cu+ combined with iodine, the proper name for this compound would be:
Copper (I) iodide, whereas if Cu2+ combined with iodine, the name would be Copper (II)
iodide.
If you are give a chemical formula and asked to write the name, you can infer the charge on the
metal based on the static (never-changing) charge of the non-metal in the ionic compound.
Ex. Does the compound Fe2O3 have Fe2+ or Fe3+ as its metal? simply, check the math from the
subscripts, so that you work backwards. O has a 2- charge. If there are 3 O atoms, then there
is a negative charge of 6-. Remember we must have a net charge of 0, and because there are
two Fe atoms present,
the charge must be 3+.
Polyatomic Ions
There are some ionic compounds which we may have encountered that do not seem to
fit the naming pattern. Some compounds are pure substances that tend to involve
combinations of metals with polyatomic ions. These are groups of atoms that tend to
stay together and carry a net ____ charge.
These groups of atoms now behave just as a single non-metal element, they have one
charge! We write the chemical formula in the same way!
Potassium carbonate
+
CO32K
2(1+) + 1(2-)
=0
2+
+
2=0
K2CO3
It is easy to name such compounds. You simply state the metal and then the
polyatomic ion.
Ex. Na2SO4 = Sodium Sulfate
Please do Assignment # 1
Acids
There are many types of polyatomic ions, but one special group is called the
oxyacids . These are compunds formed when hydrogen combines with polyatomic ions
that contain oxygen.
Some Common
Polyatomic Ions
Ion Name
Ion
Most common acids are known because of the combination of hydrogen with one of the
elements from the halogen family. They are considered acids because they dissociate or
separate into ions easily in water.
Molecular Compounds
Molecular compounds are formed when two non-metals combine. Molecular compounds are
non-electrolytes (do not conduct electricity readily) while ionic compounds are electrolytes.
Most compounds consist of neutral groups of atoms called molecules.
Molecular compounds exist in all three states: solid, liquid, and gas. All molecular compounds
exist because they share electrons.
Each compound which is molecular in nature, shares its electrons to become more stable. Each
compound would like to be more like the noble gas family; meaning they would have a full
valence shell. When atoms have full valence shells, they are relatively unreactive or stable!
When two non-metal atoms share a pair of electrons; then they form a covalent bond. This
bond holds the atom together in a molecule.
Example:
CH4
Draw the Lewis Dot Diagram.
How many electrons are needed to fill the valence shell of carbon?
Writing Chemical Formulae for Molecular Compounds
You can write the chemical formula between two unknown non-metals by using one of
two methods:
1.
You can draw the Lewis Dot Diagram, which will ultimately give you the
structural formula.
or
2.
You can use the Combining Capacities of Non-metals.
Write a chemical formula for Carbon and oxygen combined.
Example #1:
There are two electrons left, so you need another oxygen atom.
Example #2: Use the following Combining Capacity Table
4
3
2
1
H
C
N
O
F
Si
P
S
Cl
As
Se
Br
I
Step 1: Write the symbols with the left-hand element from the above Table first,
with the combining capacity written overhead.
4
2
C
O
Step 2: Criss-cross the combining capacities to produce subscripts.
4
2
C
O -------> C2O4
Step 3: Reduce the subscripts if possible; and do not write 1 as a subscript.
C1O2 ---------> CO2
Naming Molecular Compounds
Common names for some molecular compounds have been used for centuries. You should
memorize these names.
Water
H2O
Hydrogen peroxide H2O2
Methane
CH4
Ammonia
NH3
Ammonium
NH4
Step 1: Identify that the molecule is indeed molecular by ensuring it consists of all non-metals.
Step 2: Mane the atom with the greatest combining ability first. (Most bonding electrons)
Step 3: Use prefixes from the Greek Number System to describe the number of atoms for each
element in the compound or molecule.
1
2
3
4
5
mono
di
tri
tetra
penta
6
7
8
9
10
Step 4: Name the second element using the suffix -ide.
Example:
Name
CBr4
Carbon tetrabromide
hexa
hepta
octa
nona
deca
Organic or Inorganic??
Organic molecules are special molecular substances that contain certain carbon atoms as the
basic building blocks. The organic component occurs when the carbon atom is attached to
hydrogen atoms.
Organic compounds are the most abundant compounds on Earth. They are the most abundant
because carbon has the highest combining capacity (4) than all other non-metals. It also has
the ability to combine with all non-metals, but especially to hydrogen, nitrogen, and oxygen to
form very stable compounds. All organic compounds must at least contain carbon and
hydrogen atoms, and secondly it could contain other elements bonded to either of the above
mentioned elements.
Inorganic compounds are any compound which does not involve any form of hydrocarbons.
Inorganic compounds are molecular compounds which may contain carbon, but it will be
bonded to an element other than hydrogen.
Example:
CO2
Carbon dioxide
Hydrocarbons is the largest category of organic chemistry, where long chains of carbon and
hydrogen are linked together in various combinations. These hydrocarbons were produced
millions of years ago as once-living plants and animals decayed and were changed by heat and
pressure under the Earth’s surface. They are also known as fossil fuels. The general formula
for most hydrocarbons is: CnH2n+2. These hydrocarbon are called alkanes.
CH4
C2H6
C3H8
C4H10
Methane
Ethane
Propane
Butane
C5H12
C6H14
C8H18
Pentane
Hexane
Octane
Natural or Synthetic
Today, everyone in this class will or has used some form of a synthetic material which has been
created as a result of the wizardry of chemistry.
Natural products are obtained from sources like: animals, plants, or minerals. Examples
include: leather, wool, cotton, wood, rubber, hydrocarbon fuels, metals, fertilizers, and
cement.
Synthetic products are products which are strictly made by humans as a result of complex
chemical reactions. These chemical reactions would not occur under normal circumstances
and therefore, the product is only a result of man’s creation or intervention. Some common
products of synthetic materials are: teflon, aspirin, vinyl, styrofoam, neoprene, nylon, and
vulcanized rubber.
Most synthetic substances are normally manufactured from naturally occurring petrochemicals. For example, polyethylene, which is used to make plastic bottles, is formed from
ethene (C2H4). This is usually separated from crude oil by fractional distillation. (Using various
boiling points to separate and produce different products from oil).
Polyethylene and chloroflurocarbons (CFCs) are extremely complex compounds which result
from a process called polymerization. Polymers are formed when hundreds of smaller
molecules are linked together to form one long, thin molecule.
Polymers have very different properties from their reactants. For example, styrene molecules
are colorless, strong-smelling, and liquid at room temperature, and the product polystyrene is
very different.
Almost all plastics we use in our daily lives are created from this process in which the flow of
the polymers is controlled. The melted polymers flow into a mould until cooled, and a plastic
object (spoon, bottle, pen) results.
Synthetic fibers are made in the same way only they are made by drawing the polymer into a
thread as it forms. (Nylon ----> tights)
The Fashion World
Fibers and Fabrics
Fibers are thin, hair-like strands of material that can be spun into a thread or yarn. There are
synthetic fibers which are produces from chemicals or natural fibers which are spun from
naturally occurring materials from plants or animals. These fibers are then woven together to
make fabrics.
The structure of natural fibers give fabric special properties. For example, wool fibers readily
trap air when it is woven which makes it an excellent insulator. Cotton allows good air
circulation and absorbs moisture, which makes it good for warm weather use!
Synthetic fibers do not breathe as easily, probably because of its petroleum base. However,
these fibers are usually less expensive than natural fibers.
Debate: Which is better natural or synthetic?
Chapter 6
Chemical Reactions
Chemical reactions are experienced in our everyday lives thousands of times over. Chemical
reactions occur within our bodies, or have already been performed so that we can make use of
the products that we take for granted.
Word Equations
A word equation is one way of representing a chemical reaction: it tells you what reacts and
what is produced.
Writing Word Equations
We use the chemical which are initially present and we show their mixing or combining with a
plus sign (+). The arrow illustrates the change which occurs to show the products. The
products are found on the right hand side of the arrow and it may be only one compound, or
more than one if they are separated by a plus sign.
Example:
All the reactants -------->
All the products
Reactant 1 + Reactant 2 ---------> Product 1 + Product 2
We will now practice writing some word equations.
1. Solid copper reacts with bromine gas
2. Zinc metal is placed in a silver nitrate solution
3. Iron filings (Fe2+) is mixed with oxygen
Do questions 1 - 6 on pg. 219.
Do Assignment # 2
Measuring Mass in Chemical Changes
You now know how to represent the changes that occur when elements undergo a chemical
change but what happens to its mass. As we remember from last year, the mass of the
elements stay constant even though the elements change form.
The fact that the mass does not change, is common for all reactions; means this statement is
considered a scientific law. A scientific law is a general statement that sums up the
conclusions of many experiments, or a statement that summarizes an observed pattern in
nature.
The Law of Conservation of Mass
The Law of Conservation of Mass states that, in a chemical reaction, the total mass of the
reactants is always equal to the total mass of the products.
Do Lab on pg. 220 - 221.
Let’s examine a combustion reaction in depth:
CH4 + 2O2
--------->
1 atom of carbon
4 atoms of hydrogen
4 atoms of oxygen
CO2 + 2H2O
1 atom of carbon
4 atoms of hydrogen (in the water molecule)
4 atoms of oxygen (2 in CO2 and 2 in water)
An Environmental Perspective
This Law has implications far beyond the laboratory, to becoming one of the world’s
largest environmental problems. If all the gasoline which is combusted daily turns into carbon
dioxide; how much CO2 is currently present in our atmosphere?
In fact, approximately 1 kg of gasoline produces 2 to 3 kilograms of carbon dioxide!
2(C8H18 + 25/2O2 ------> 8 CO2 + 9 H2O)
2 C8H18 + 25O2 ------> 16CO2 + 18H2O
An Introduction to the Mol
Each element listed on the Periodic Table is given a “molar mass”. This means that the density
of this particular element is listed in a unit of grams per 1 mol.
The term mol comes from an arbitrary definition whereby a scientist by the name of Avagadro
theorized the amount of atoms per element. However, he realized that the number of atoms
would be different, unless there was a common unit of measurement for each element
because of the varying densities. If each element had a common measurement, he proposed
that for every mol, each element would contain 6.02 x 1023 . This later, was proven as true and
became known as Avagadro’s Number.
We now use the mol to represent the number of molecules, compounds, or atoms in a reaction
for comparison purposes. Let us compare the varying masses of the elements there are for
every one mol.
Iron
Oxygen
55.85 g/mol
16.00 g/mol
Hydrogen
Carbon
1.01 g/mol
12.01 g/mol
Find the “molar mass” for each of the following elements or Compounds.
Copper
Potassium
Tin
Nitrogen
Bromine
Lead
Sodium
Neon
Water
There is a formula we can use to find the moles of a substance when given the actual
mass. The formula used is: Mol = mass (actual mass)
Molar Mass
Or
n = m/M
Example: Calculate the number of moles in a sample of pure oxygen with a mass
grams.
of 30.0
Step 1: Write the written information and the equation.
mass = 30.0 g
Molar Mass = 16.00 g/mol
n =m/M
n=?
Step 2: Plug the values in for each of the respective symbols of the equation.
n = 30.0g
16.00g/mol
Step 3: Solve the equation.
n = 1.88 mols
Step 4: State the answer to your problem.
There are 1.88 moles in a sample of 30g of pure O2.
Finding the Missing Mass
Prepare Lab pg. 224 - 225 for next class.
Balancing Chemical Equations
Whenever you have an equation, you must ensure the Law of Conservation of Mass holds true
by illustrating the number of atoms on the reactants side equals the number of atoms on the
products side.
How to write a balanced equation?
Firstly, we must be given a reaction. Then, we can begin with writing the word equation for
that reaction.
Iron reacts with oxygen to form magnetic Iron Oxide (Fe3O4).
Step 1: Write the word equation for the reaction.
Iron + Oxygen --------> Magnetic Iron oxide
Step 2: Write the skeleton equation by replacing each name with a correct formula. A skeleton
equation is a representation of a chemical reaction in which the formulae of the
reactants are connected by an arrow to the formula(e) of the product(s).
Fe + O2 --------> Fe3O4
Step 3: Count the numbers of atoms of each type in the reactants and products. The number
of atoms can be recorded in a table.
Type Of Atom
Reactants
Products
Fe
1
3
O
2
4
Step 4: Multiply each of the formulas by the appropriate coefficients to balance the number of
atoms.
3 Fe + 2 O2 -----------> Fe3O4
Again, check to see if the number of atoms for each element on the reactants
side equals the number of atoms for the appropriate element on the product
side. You may use a table if you wish.
Step 5: We use the following subscripts in brackets at the end of each element or compound to
indicate the state.
(s) indicates solid
(g) indicates gas
(l) indicates liquid
(aq) indicates aqueous
3 Fe(s) + 2 O2 (g) -----------> Fe3O4 (s)
A balanced equation has been written when the formulae are unchanged and the atoms on
each side are balanced.
Please do Assignment #2.
Reaction Types
There are 5 main reaction types which we will discuss in detail. At the end of this topic, you
should be able to predict the end products and balance the equation for any reaction. The 5
types of reactions are: 1.) Combustion, 2.) Neutralization, 3.) Synthesis/Decomposition
Reactions, 4.) Single Displacement and 5.) Double Displacement Reactions.
Combustion Reactions
Combustion is the very rapid reaction of a substance with oxygen to produce compounds called
oxides. We also call this process burning. We can represent combustion reactions using a
simple word equation :
Fossil fuel + oxygen ---------> oxides + energy
This fuel may be in the form of a number of elements or compounds; while the energy
produced is in the form of heat and light. The fuels we most commonly burn are called
hydrocarbons. When hydrocarbons burn there are three main products: carbon dioxide, water
vapor, and energy.
Hydrocarbon + oxygen ---------> carbon dioxide + water vapor + energy
The complete combustion of hydrocarbons release millions of tonnes of water vapor and
carbon dioxide into our atmosphere which is the major contributor to the Green house Effect.
Incomplete Combustion
Hydrocarbons can also undergo a chemical reaction called incomplete combustion. This occurs
when there is not enough O2 present and as a result 5 products are produced. The reaction is
as follows:
Hydrocarbon + low amnt. of O2 --------> CO + C + CO2 + H2O + energy
CO is a very poisonous gas because it clear, colorless and odorless. It binds with the protein
hemoglobin on our red blood cells, not permitting O2 to attach. The body basically suffocates
from a lack of O2 to the organs as both the CO and O2 compete for the hemoglobin bonding
site.
Read pp.231 of text.
2. Neutralization Reactions
This type of reaction occurs when a strong acid reacts with a strong base to produce a neutral
substance. The end products usually include water and salt.
The word equation can be generally wrote as follows:
Acid + Base ------------> salt + water
A strong acid is usually recognized because of the combination of hydrogen with another
element or ion which will readily separate from the hydrogen. A strong base is usually
recognized because a metal or cation is usually attached to a strong negative ion (anion) which
will readily separate in water. A common ion which denotes a strong base is the polyatomic
ion hydroxide (OH-)
HCl + NaOH --------------> NaCl + H2O
3. Synthesis Reactions
The term “synthesis” means to build something or to put something together. Well, a
synthesis reaction is when two smaller elements or molecules combine to produce a larger
molecule. They are also known as combination reactions. The general formula is:
A + B --------> AB
If you see two elements as reactants, then the reaction has to be a synthesis reaction. Some
elements exist as diatomic molecules in nature; which means they naturally exist as two atoms
of the same element bonded together. The following are a list of elements that exist as
diatomic elements in nature:
Element
Diatomic Molecule
hydrogen
H2
oxygen
O2
nitrogen
N2
fluorine
F2
chlorine
Cl2
bromine
Br2
iodine
I2
An example of a synthetic reaction is between hydrogen and oxygen when they combine.
EX.
Hydrogen + Oxygen ---------> Water
Equation:
H2 (g)
+
O2 (g)
----------->
H2O(g)
Balanced:
2H2 (g)
+
O2 (g)
----------->
2H2O(g)
Synthesis reactions can also involve combinations of smaller molecules. An example is when
ammonia and hydrogen chloride vapors combine; they form solid particles of ammonium
chloride.
HCl + NH3 ----------> NH4Cl
4. Decomposition Reactions
Decomposition reactions involve the splitting of a large molecule into elements or smaller
molecules. Decomposition reactions have the following general formula:
AB ----------> A +
B
If you see a binary compound (a compound made up of only two elements) as the reactant,
you will know the reaction will produce two elements as the products.
Ex. The electrolysis of water uses electricity to split water molecules into
elements.
Word Eqn:
Skeleton Eqn:
Balanced Eqn:
Water
H2O(g)
------------>
------------>
2H2O(g)
its two
Hydrogen + Oxygen
H2 (g) +
O2 (g)
------------> 2H2 (g) +
O2 (g)
Decomposition reactions can also involve the production of two small molecules from a large
molecule.
Ex. Ammonium nitrate is heated to the point where it decomposes to form nitrous oxide and
water molecules. Write the written, skeleton and balanced equation for the above example.
Written –> Ammonium nitrate --------> Nitrous oxide + Water
skeleton –>
NH4NO3 (aq) ------------>
N2O (g)
Balanced ---->
NH4NO3 (aq) ----------->
N2O (g)
5.
+
+
H2O (l)
2H2O (l)
Single Displacement Reactions
Single Displacement reactions are chemical changes that involve an element and compound as
reactants. One element displaces another element from a compound. Single displacement
reactions have the following general formula:
Z + AB -------> ZB + A
OR
Y + AB -------> AY + B
In the first case, the metal z has taken the place of the metal A which is in the compound AB.
In the second case, the non-metal, has taken the place of the non-metal in the compound AB.
Ex. 1 Calcium metal is placed in a solution of lead (III) nitrate.
3 Ca(s) + 2 Pb(NO3)3(aq) ----------> 2 Pb(s) + 3 Ca(NO3)2 (aq)
Ex. 2 Iodine reacts with Barium fluoride
I2 (g) + BaF2 (aq) ----------> F2 (g) + BaI2 (aq)
6.
Double Displacement Reactions
Double displacement reactions occur when elements in different compounds displace each
other or exchange places. Double displacement reactions have the general formula:
1.
AB + XY --------> AY + XB
(Metal replaces metal) (non-metal replaces non-metal)
This is where A and X are metallic elements and B and Y are non-metallic elements.
During the reaction, B and Y or (A and X) exchange places.
OR
2.
(A precipitate forms)
Where two compounds form which result in aqueous soluble solution while the
remaining two elements form an insoluble element called a precipitate.
Ex.
Write the written, skeleton and balanced equation for the following reaction.
Silver Nitrate reacts with Calcium Iodide
silver nitrate + calcium iodide -------> silver iodide + calcium nitrate
Ag NO3 +
2Ag NO3 +
CaI2
CaI2
--------->
--------->
AgI
2AgI
+
Ca(NO3)2
+
Ca(NO3)2