Download Single-Replacement Reactions

Chemical Equations
and Reactions
Chapter 8
General Chemistry
Chemical Reactions
Basics
Chemical Reactions


A chemical reactions are
______________________.
Recall: chemical changes are when
one or more substances are changed
into different substances
• Examples: wood burning, metal rusting
Indications of a Chemical Reaction

Certain easily observed changes
indicate that a chemical reaction has
occurred:
 _______________by heat and/or light
color change
production of _________
production of __________

A solid that is produced as a result of a
chemical reaction in solution and that
separates from the solution is known as a
precipitate
Law of Conservation of Matter

Chemical reactions obey the Law of
Conservation of Matter


in all chemical and physical changes,
matter is neither created or destroyed
__________________________________
__________________________________
Chemical Equations



A chemical equation represents, with symbols
and formulas, the identities and the amounts of
the reactants and products in a chemical
reaction.
Has two parts:
• Reactants: __________________________
• Products: ____________________________
The reactants turn into the products
4 Fe + 3 O2  2 Fe2O3
Reactants  products
Ways to Express a Chemical
Reaction
The way atoms are joined is changed in a
chemical reaction.
Can be described several ways:
1. In a sentence

Copper reacts with chlorine to form copper (II)
chloride.
2. In a word equation
Copper + chlorine  copper (II) chloride
3. In formula equation:
Cu + Cl2  CuCl2
Symbols Used in Chemical
Equations
Additional Symbols Used in
Equations

heat
  ,   


shows that heat is supplied to
the reaction
Pt
is used to indicate a
 
catalyst is supplied, in this case,
platinum.
What is a catalyst?


A catalyst is _______________
___________________, without
being changed or used up by the
reaction.
Enzymes are biological or protein
catalysts.
Study Buddy Review




What are four things that indicate a
chemical reaction has taken place?
What is the Law of Conservation of
mass?
What does the symbol (l) mean?
What does (aq) mean?
Balancing Chemical
Equations
Skeleton and Balanced
Equations


_____________________do not
indicate how many of each
element/compound
_______________________the
number of atoms of each
element is the same on both
sides of the reaction.
Numbers in Balanced Equations



Use coefficients to balance equation
Coefficients: _______________________
______________which represents
number of units of that compound
Subscript: small whole number placed in
chemical formula to represent number of
atoms of an element in a compound
4 Fe + 3 O2
Coefficient
 2 Fe2O3
subscript
Balanced Equation



A balanced equation has the
_____________________ of
each element on both sides of
the equation
Atoms can’t be created or
destroyed
All the atoms at the beginning
must appear in the end
C



+
O
O

C
O
C + O2  CO
We need one more oxygen in the
products.
Can’t change the formula, because it
describes what it is (carbon
monoxide in this example)
C


+
O
O

C
O
C
O
Must be used to make another
CO
But where did the other C come
from?
C
+
C


O
O

C
O
C
O
Must have started with two C
2 C + O2  2 CO
Rules for balancing:
 Assemble, write the correct formulas for



all the reactants and products
Count the number of atoms of each type
of element appearing on both sides
Balance the atoms of an element one at a
time by adding coefficients (the numbers
in front) - save H and O until LAST!
Check to make sure it is balanced.

Never change a subscript to balance an
equation.
• If you change the formula you are
describing a different reaction.
• H2O is a different compound than H2O2

Never put a coefficient in the middle of
a formula
• 2 NaCl is okay, Na2Cl is not.
Balancing Equations Examples

H2 (g) + O2 (g) 

Zn +

Pb (NO3)2 +
HCl

H2O (l)
H2 +
K2S 
ZnCl2
PbS + KNO3
Word Equation Examples

Write a balanced chemical equation
for the following:
Aqueous solutions of sulfuric acid
and sodium hydroxide react to form
aqueous sodium sulfate and water.
Five General Types of
Chemical Reactions
Five General Types of
Chemical Reactions
1.
2.
3.
4.
5.
Synthesis (Composition)
________________________
Single-Replacement
________________________
Combustion
By knowing the type of reaction that is
occurring, you can predict the products
that will be formed.
General Types of Chemical
Reactions





Combination:
A + B  AB
Decomposition:
AB  A + B
Single Replacement :
AX +B  A + BX
Double Replacement:
AX + BY  AY + BX
Combustion:
CxHy+ O2  CO2 + H2O
Synthesis (Combination)
General form: A + B  AB
____________________________
A, B = elements or compounds
AB = compound consisting of A and B
This is the only type of chemical reaction in which
there is a single product formed. This single product is
always more complex than the reactants.
Examples of Synthesis Reactions
a. calcium + oxygen yields calcium oxide
2Ca + O2  2CaO
b. carbon dioxide + water yields carbonic acid
CO2
+
H2O 
H2CO3
Notice: All equations show two (or more) reactants,
but only one product.
http://www.ric.edu/ptiskus/reactions/Index.htm
Decomposition Reactions
(Decomposing = breaking down into
smaller parts; microorganisms)
 _______________________________
______________________________The
opposite of direct combination/synthesis.
 You can identify this reaction because
there is only one reactant.
General form: AB  A + B
AB = compound
A, B = elements or simpler compounds

Examples of Decomposition
Reactions




Water yields hydrogen and oxygen
2H2O 
2H2
+
O2
marble (rock) yields (with heating)
calcium oxide and carbon dioxide
CaCO3

CaO
+
CO2
Notice: single compound
decomposes into two (or more)
products.
http://www.ric.edu/ptiskus/reactions/Index.htm
Single-Replacement Reactions

_____________________________
_____________________________
General Form: A + BX  AX + B
AX, BX = ionic compounds
A, B = elements
X = ion that switches partners
Examples of Single-Replacement
Reactions


Magnesium metal and copper (II)
sulfate
Mg + CuSO4  MgSO4 + Cu
Iron metal and copper (II) sulfate)
Fe + CuSO4  FeSO4 + Cu
www.ric.edu/ptiskus/reactions/Index.
htm
Double-Replacement Reactions
_______________________________
_______________________________
 Look for: 2 compounds as reactants
and 2 compounds as products.
 Reactants are usually ionic compounds.
 Specific example: neutralization
reactions between acid and base
General form: AX + BY  AY + BX
(Notice: X and Y “change partners”)

Examples of Double Replacement
Reactions

Calcium carbonate and hydrochloric
acid yield calcium chloride and
carbonic acid.
CaCO3 + 2HCl  CaCl2 + H2CO3
www.ric.edu/ptiskus/reactions/Index.
htm
Rules of Double-Displacement
Reactions


Reactants must be dissolved in
water (releasing the ions).
Will occur if:
1. ______________________________
2. ______________________________
3. _____________________
Combustion Reactions

Reactants: a fuel (usually a
hydrocarbon) and oxygen.

Products: water, carbon dioxide, and lots
of energy! (heat, light)

Examples:
CH4 (methane) + 2O2  2H2O + CO2
C2H5OH (gasohol) + 3O2  3H2O + 2CO2
www.ric.edu/ptiskus/reactions/Index.htm
Study Buddy Review
Describe each of the following to your
study buddy:
•
Synthesis (combination)
•
Decomposition
•
Single-Replacement
•
Double-Replacement
•
Combustion
Activity Series
Activity Series and Single
Replacement Reactions

Al +

Cu + AlCl3  ???


CuCl2  ???
Only one of the following reactions
will occur
How do you know which one?
Activity Series of Metals
http://wps.prenhall.com/wps/media/objects/165/169060/tool0403.gif
Activity Series Rules
Elements at top of series are most
active
 Elements at bottom of series are
least active (coinage metals)
 _____________________________
_____________________________
Example: Al + CuCl2  will occur
Cu + AlCl3  will NOT occur

Activity Series Examples

Using the activity series, predict
whether each of the possible
reactions will occur:
• Cr + H2O 
• Pt + O2 
• Cd + 2HBr 
References
Dr. Stephen L. Cotton Charles
Page High School
Mrs. Lijek