What is a chemical reaction?

What is a chemical reaction?
 When reactants are converted to products, bonds
holding the atoms together are broken and new
bonds are formed.
 Reactants
 Recall that atoms themselves are neither created nor
destroyed; they are merely rearranged.
What is a word equation?
 Chemical reactions can be described using words.
 Either “Iron reacts with oxygen to produce iron (III)
oxide (rust)”
 Or Iron + Oxygen
iron (III) oxide
How do we represent chemical equations?
 Easier to use chemical shorthand to represent chemical
Reactants on the left of the arrow and products to the
right of the arrow
Fe (s) + O2(g)
Where (s)= solid
(l) = liquid
(g) = gas
(aq)= aqueous solution (dissolved in water)
Heat or catalyst added to a reaction would appear above
the arrow. See Table 8.1
Balancing Chemical Equations
 H2(g) +
O2 (g)
Recall that matter is neither created or destroyed, so
what is wrong with this picture?
It’s not balanced, we lost an oxygen, this is not
possible so we balance the equation with coefficients,
whole numbers that are placed in front representing
the relative quantities of each compound.
2 H2(g) + O2 (g)
2 H2O(l)
Now both sides are equal.
Rules for Balancing Equations
Determine the correct formulas for all reactants and
products in the reaction. Use parentheses when necessary.
Count the number of atoms of each element in the reactants
and products.
Balance the elements one at a time using coefficients.
For simplicity, a polyatomic ion appearing unchanged on both sides
can be counted as a single unit.
if no coefficient is written, it is assumed to be one.
You cannot change the subscripts to balance the equation.
Check each atom or polyatomic ion to make sure it is
Finally make sure all the coefficients are in lowest possible
Flow Chart for Balancing Chemical Equations
Types of chemical equations
Plan of the Day
 POD—for extra credit
 Questions on lab? Homework?
 Types of Reactions Powerpoint
Plan of the day
 Major Reaction Types
 Get into a 5 groups
 Make a quick poster (big, bold, letters)
 These will be your notes for Reaction Types
 On your poster:
 Define your reaction
 Show an example
 How can you tell a reaction is your type of
 Show the skeleton reaction!
Plan of the day
 Finish your notes in the lab while I get set
 Finish demos
 Work on our learning goal:
 Be able to identify types of reactions!
 Finish Worksheet from yesterday
 Please Bring in your Textbooks--Tomorrow!
Plan of the day
 Business
 Test corrections, retakes.
 Lab tomorrow—wear appropriate clothing!
 Thus far in the Reaction Unit?
Balancing Equations√
Identifying the 5 types of reactions √
 What is left?
 Predicting Products
 Using solubility rules to predict double replacement reactions
 Net-Ionic Equations
Combination Reactions
 Two or more substances combine to form a single
substance, or…
 Two or more products combine to form a single
 Example:
 Mg(s) + O2 (g)
MgO (s)
Predicting Combination Reactions
4 Possibilities:
Metal + Non-Metal -- Ionic Compound
K + Cl2  KCl
Non-metal + Non-Metal  (more than one product
S + O2  SO2 or SO3
Non-metal oxide + H2O  acid
SO2 + H2O  H2SO4
Metallic oxide + H2O  metal hydroxide
CaO + H2O  Ca (OH)2
Decomposition Reactions
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.
 Hard to predict! usually a gas or
CaO(s) +
Combustion Reactions
In a
, 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
combination reaction.
Predicting Combustion
 Element + Oxygen  oxides
Mg + O2  MgO
 Hydrocarbons (or alcohols) + Oxygen  CO2 + H2O
CH4 + O2  CO2 + H2O
Single Replacement Reactions
A reaction in which the atoms of one
element replace the atoms of another
element in a compound is called a
A + BX → AX + B
Cu + AgNO3  Ag + CuNO3
Single Replacement Reactions
Predicting Products —
if the activity of the metal is higher
than the metal cation in solution there
will be a reaction, otherwise there is
not a reaction.
What is happening?
The more reactive metal will form a
compound with the anion, and the other metal
will be pulled out of solution and become a solid
metal again.
Mg (s) + Zn(NO3)2 (aq)
Mg(NO3)2 (aq)+ Zn(s)
A metal will not always
replace a metal in a
compound dissolved in water
because of differing
An activity series can be used
to predict if reactions will
Double Replacement
Double replacement reactions occur when ions
exchange between two compounds. A
precipitate, gas, or molecule will form.
This figure shows a generic double
replacement equation.
Predicting Double Replacement
The solid product produced during a
chemical reaction in a solution is called a
All double replacement reactions produce either
water, a precipitate, or a gas.
Double Replacements Continued
This table shows
the steps to
write double
Summary of Reactions
This table summarizes different ways to predict the
products of a chemical reaction.
Pop Quiz
Ca(OH)2 + Al2(SO4)3  CaSO4 + Al(OH)3
Mg + Fe2O3  Fe + MgO
C2H4 + O2  CO2 + H2O
PbSO4  PbSO3 + O2
Plan of the day
 Finals
 Revisit course expectations
 Check your grades to make sure they are accurate.
 Homework for Chapter 8: 33-53 (odd) due Friday!
What is a solution?
An aqueous solution contains one or more dissolved
substances (called solutes) in water.
The solvent is the most plentiful substance in a solution.
Aqueous Solutions
Water is always the solvent in an aqueous solution.
There are many possible solutes—sugar and alcohol are
molecular compounds that exist as molecules in
aqueous solutions.
Compounds that produce hydrogen ions in aqueous
solutions are acids.
Ionic Compounds in Solution
Ionic compounds can also be solutes in
aqueous solutions.
When ionic compounds dissolve in water, their
ions separate in a process called dissociation.
Aqueous Reactions Continued
When two solutions that contain ions as solutes are
combined, the ions might react.
If they react, it is always a double replacement reaction.
Three products can form: precipitates, water, or gases.
Complete Ionic Equations
Aqueous solutions of sodium hydroxide and copper(II)
chloride react to form the precipitate copper(II)
2NaOH(aq) + CuCl2(aq) → 2NaCl(aq) + Cu(OH)2(s)
Ionic equations that show all of the particles in a solution as
they actually exist are called complete ionic equations.
2Na+(aq) + 2OH–(aq) + Cu2+ (aq)+ 2Cl–(aq) → 2Na+(aq) +
2Cl–(aq) + Cu(OH)2(s)
Ions that do not participate in a reaction are called
spectator ions and are not usually written in ionic
Formulas that include only the particles that participate
in reactions are called net ionic equations.
2OH–(aq) + Cu2+(aq) → Cu(OH)2(s)
Predicting Precipitates
 Using solubility rules for ionic equations we can
predict whether a precipitate is formed and thus
predicting what the products are.
If the solubility rules predict insolubility we have a
reaction, a precipitate!
Na2SO4 (aq) + BaNO3 (s)
Assume double replacement
Look at the products
Any insoluble?
 NaSO4 + BaNO3
Assume double replacement
Look at the products
Any insoluble?
Na2SO4 + Ba(NO3)2
2NaNO3 + Ba(SO4)
Write the complete ionic equation:
2Na+ (aq) + SO42- (aq) + Ba2+ (aq) + 2NO3-(aq)
2Na+ (aq) + 2NO3- (aq) + Ba(SO4)(s)
Eliminate all of the ions that did not change from the
reactant side to the product side.
Ba2+ (aq) + SO42- (aq)
Ba(SO4)(s) (net ionic eqn)
Plan of the day
 Problems of the day
 Questions on homework.
 Lab Write Up.
Plan of the day
 Lab write up!
 Examples?

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