Transcript Calculating Chemical Equations

Calculating Chemical Equations
Why and How Many Atoms Bond
Counting Atoms
• A Chemical Formula
shows how many of
which atoms are in a
molecule
• A Subscript is a
number placed
below and behind a
symbol to show how
many of which
atoms are present
H2O
Counting Atoms
• A Coefficient is
placed in front of a
molecule to show
more than one
molecule
3H2O
Counting Atoms
• A Diatomic Molecule
shows two atoms of the
same nonmetal (usually
in gas form) that have
bonded together
• Reactive nonmetals will
bond with one another if
no other substance is
available for bonding
H2 N2
O2 F2
I2 Cl2
Br2
Polyatomic Ions
• A group of atoms that
behave as one atom
• Keep together as a unit
• Listed on p. 619
• If more than one
polyatomic ion is present
in a molecule,
parentheses set it apart
• Still use a subscript to
show how many
Ca(OH)2
NH4Cl
Counting Atoms
• Write the molecule to be counted
• List the participating atoms (or
polyatomic ions) under the formula
• Write all subscripts, including
parentheses
• Multiply by the coefficient
• Some problems call for a total of atoms,
some call for individual atoms
How many total atoms are in
Methane, CH4?
1.
2.
3.
4.
5.
2
3
4
5
6
How many atoms of Chlorine are in
Carbon Tetrachloride, CCl4?
1.
2.
3.
4.
5.
2
3
4
5
6
How many total atoms are in
Magnesium Hydroxide, Mg(OH)2?
1.
2.
3.
4.
5.
2
3
4
5
6
How many atoms of Oxygen are in
Acetic Acid, CH3COOH?
1.
2.
3.
4.
5.
2
3
4
5
6
How many total atoms are in Acetic
Acid, CH3COOH?
1.
2.
3.
4.
5.
6.
4
5
6
7
8
9
Oxidation Numbers
• A positive or negative sign used to show
what type of ion is formed after an atom
has gained or lost enough electrons to
be chemically stable
• Written like a charge sign (upper right)
• Always included with a list of polyatomic
ions
BASE OXIDATION NUMBERS BY GROUP
+1
0
+3 ±4 -3 -2 -1
+2
USE ROMAN NUMERALS
What is the Oxidation Number for
Sulphur (Group 16)?
1.
2.
3.
4.
5.
6.
7.
+1
+2
+3
4
-3
-2
-1
What is the Oxidation Number for
Aluminium (Group 13)?
1.
2.
3.
4.
5.
6.
7.
+1
+2
+3
4
-3
-2
-1
What is the Oxidation Number for
Potassium (Group 1)?
1.
2.
3.
4.
5.
6.
7.
+1
+2
+3
4
-3
-2
-1
What is the Oxidation Number for
Chlorine (Group 17)?
1.
2.
3.
4.
5.
6.
7.
+1
+2
+3
4
-3
-2
-1
What is used to show the Oxidation
Number for Transition Metals
(Groups 3 – 12)?
1.
2.
3.
4.
5.
6.
Alchemical Symbols
Transition Icons
Arabic Numerals
Roman Numerals
Hieroglyphics
Kanji
Making formulæ
“The Criss-Cross Method”
• Write the element with the positive oxidation
number
• Write the element with the negative oxidation
number
• Rewrite the two symbols together below the
symbols with their oxidation number
• Drop the positive or negative sign
• Write the oxidation number from one symbol
on the other symbol as a subscript
• Remember to add parentheses for polyatomic ions
• Don’t write “1”s
• Reduce any evenly-divisible subscripts
What is the correct formula for a
bond between Carbon and
Hydrogen?
1.
2.
3.
4.
5.
CH
C 2H 2
CH3
C 2H 3
CH4
What is the correct formula for a
bond between Sodium and Nitrogen?
1.
2.
3.
4.
5.
NaN
Na2N2
Na3N
Na2N3
Na3N4
What is the correct formula for a
bond between Calcium and
Chlorine?
1.
2.
3.
4.
5.
CaCl
Ca2Cl2
Ca2Cl
CaCl2
Ca3Cl4
What is the correct formula for a
bond between Sodium and
Hydroxide?
1.
2.
3.
4.
5.
NaOH
Na(OH)2
Na(OH)3
Na2(OH)3
Na(OH)4
What is the correct formula for a
bond between Aluminum and
Sulfate?
1.
2.
3.
4.
5.
AlSO4
Al2(SO4)2
Al2(SO4)3
Al3(SO4)3
Al(SO4)4
Binomial Nomenclature
• Naming a two-part name
• Used to differentiate between Fluorine
(an element) and Fluoride (part of a
compound)
• Never change the name of a Polyatomic
Ion
• Big difference between Sulfide and Sulfite
Ionic Compounds
• List the positive ion (or metal) first
• Use Roman Numerals to show the
Oxidation number of a transition metal
• Begin the negative ion (or nonmetal),
changing the ending to –ide
• Oxide
• Sulfide
• Phosphide
Covalent Compounds
• Prefixes are used to show how many of which
atoms
• Prefixes are number-words from Greek &
Latin
• Write the name of the first atom
• Add a prefix only if there is more than one of the
first
• Write the name of the second atom
• Add a prefix showing how many of the second are
present
• Change the ending to -ide
Numbering Prefixes
1 – Mono2 – Di3 – Tri4 – Tetra-,
5 – Penta-
6 – Hexa7 – Hepta8 – Octa9 – Nona10 – Deka-
What is the name for N2O4?
1.
2.
3.
4.
5.
Nitrogen Oxide
Dinitrogen Oxide
Dinitrogen Dioxide
Dinitrogen Tetraoxide
Nioxx (Nioxalate)
What is the name for Na2S?
1.
2.
3.
4.
5.
Sodium Sulfide
Sodium Sulfite
Sodium Sulfate
Disodium Sulfide
Disodium Sulfate
What is the name for CO2?
1.
2.
3.
4.
5.
Carbon Oxide
Carbon Dioxide
Monocarbon Oxide
Monocarbon Dioxide
Mi-Bref (B-hot)
What is the name for (NH4)2O?
1.
2.
3.
4.
5.
Nitrogen Hydrogen Oxide
Mononitrogen
Tetrahydrogen Oxide
Ammonium Oxide
Diammonium Oxide
Ammonium Oxalate
Chemical Equations
• A shorthand way to describe a chemical
reaction using chemical symbols and
formulæ
Chemical Equations
• Has three parts
• Reactants
• Substances present before the reaction
• Products
• Substances present after the reaction
• Yield Arrow
• Indicates the direction of a reaction
• Some reactions are reversible
Writing a Chemical Equation
Chemical symbols give a “before-and-after”
picture of a chemical reaction
Reactants
MgO
+
Products
C
magnesium oxide
reacts with carbon
CO
to form
+
Mg
carbon monoxide
and magnesium
Balancing Chemical Equations
• Equations must be balanced to observe
the Law of Conservation of Matter
• Matter can not be created or destroyed
under normal reactions
• If you begin a reaction with 5 g of
Hydrogen, you must end up with 5 g of
Hydrogen
A Balanced Chemical Equation
Same numbers of each type of atom on each
side of the equation
Al
+
S
Al2S3
Not Balanced
2Al
+
3S
Al2S3
Balanced
Balancing Chemical Equations
• Count atoms on both sides of the yield
arrow
• Determine which elements are unequal
• Use coefficients to balance the number
of atoms on both sides
• If you multiply one element in a compound,
you multiply both elements in a compound
• You can treat Polyatomic Ions as one if
they appear on both sides of the equation
• Go for the highest unequal elements first
• Leave solitary elements for last
Steps in Balancing An Equation
Fe3O4 + H2
Fe + H2O
Fe: Fe3O4 + H2
3 Fe + H2O
O:
Fe3O4 + H2
3 Fe + 4 H2O
H:
Fe3O4 + 4 H2
3 Fe + 4 H2O
Balancing Chemical Equations
Mg
Al
+
+
N2
Mg3N2
Cl2
AlCl3
Balancing Chemical Equations
Fe2O3
+
C
Fe
+
CO2
Al
+
FeO
Fe +
Al
+
H2SO4
Al2(SO4)3
Al2O3
+ H2
Types of Chemical Reactions
• Synthesis
• Two or more substances form one new
substance
H2
+
O2

H 2O
N2
+
H2

NH3
Types of Chemical Reactions
• Decomposition
• One substance breaks down to form two or
more new substances
PbCO3

PbO
+
CO2
H2CO3

H 2O
+
CO2
Types of Chemical Reactions
• Single Displacement
• One substance replaces another in a
compound
Li
+
AlCl3 
LiCl +
Al
Types of Chemical Reactions
• Double Displacement
• Two substances “swap partners” in two
compounds
KOH
+
HBr 
KBr +
H 2O
NaOH + H2CO3  Na2CO3 + H2O
Types of Chemical Reactions
• Neutralization
• Double-displacement reaction where an
acid and a base form a salt and water
KOH
+
HBr 
KBr +
H 2O
NaOH + H2CO3  Na2CO3 + H2O
• Acids
•
•
•
•
Acids and Bases
Taste Sour
Have a pH of less than 7
Produce Hydronium H3O+1 in solution
Have an “extra” H- on the beginning of the
formula
H2SO4 – (Hydro)Sulfuric Acid
H3PO4 – (Hydro)Phosphoric Acid
HNO3 – (Hydro)Nitric Acid
HCl – Hydrochloric Acid
Acids and Bases
• Bases
•
•
•
•
Taste bitter
Have a pH of more than 7
Produce Hydroxide OH–1 in solution
Have an –OH on the end of the formula
NaOH – Sodium Hydroxide
KOH – Potassium Hydroxide
Ca(OH)2 – Calcium Hydroxide
NH4OH – Ammonium Hydroxide
Types of Chemical Reactions
• Combustion
• Where a carbon compound combusts with
oxygen gas to form carbon dioxide and
water
CH4 + O2  CO2 + H2O
C2H6 + O2  CO2 + H2O
Change in ENERGY
• Every reaction has some change in
energy
• Two possibilities:
• Endothermic – absorbs energy from the
environment to complete reaction
• Feels “COLD” to its surroundings
• Products have MORE energy than the
reactants
• Exothermic – releases energy to the
environment as the reaction proceeds
• Feels “HOT” to its surroundings
• Products have LESS energy than reactants
Let’s get it started
• Some reactions require a little “jump
start” to proceed
• Activation Energy
• Energy required to be applied to start a
reaction
• Examples
• Applying friction to start a match
• The match causing a log to burn
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Counting Atoms
Subscripts
Coefficients
Diatomic Molecules
Polyatomic Ions
Parenthesis
Oxidation Numbers
Binary Formulæ
• Criss-cross method
• Naming Rules
• Ionic
• Roman Numerals
• Covalent
• Prefixes
• Balancing Equations
• NEVER change
subscripts
• Law of Conservation
of Matter
• Types of Reactions
• Changes in Energy
during reactions