Transcript Chemical Equations - Rose Tree Media School District

CHEMICAL
REACTIONS
Reactants: Zn + I2
Product: Zn I2
Introduction
– Chemical reactions occur when
– Chemical reactions involve
 changes in the___________________________
(the making of new materials with new properties)
 ___________________changes
– Symbols represent elements
– Formulas describe compounds
– Chemical equations describe a chemical reaction
Types of Chemical Reactions (rxns.)
Types of Reactions
•
•
Reactions are classified by their products.
There are five types of chemical reactions we will
talk about:
1.
2.
3.
4.
5.
•
You need to be able to identify the type of reaction
and predict the product(s)
Steps to Writing Reactions
Some steps for doing reactions:
1. Identify the
2. Predict the product(s) using the
3. Balance it
Don’t forget about the diatomic elements!
(_________________) For example, Oxygen is O2
as an element.
In a compound, it can’t be a diatomic element because
it’s not an element anymore, it’s a compound!
Synthesis Reactions
 Synthesis (meaning to make) are
– Also called
 Direct combination or combination reactions
 Addition reactions
– typified by their
______________________________________
___.

If you have a reaction in which at least 2
elements or compounds are reacted and
produce a single product, the reaction is a
synthesis reaction.
Synthesis reactions
•
Synthesis reactions are sometimes called
________________________________________.
reactant + reactant  1 product
• Basically: A + B  AB
• Example: 2H2 + O2  2H2O
• Example: C + O2  CO2
• Note: Single Product! This is your clue that this is a synthesis or combination
reaction.
Synthesis Reactions
•
Here is another example of a synthesis
reaction
Examples of Synthesis Reactions

2Na + S
Na2S
– This one is an example of two elements in
atomic form (Na and S) combining to form a
compound (sodium sulfide).

2H2 + O2
2H2O
– In this example, A and B are two elements in
molecular form (hydrogen and oxygen
molecules), and the product is water, which is
simply the chemical combination of hydrogen
and oxygen.
Examples of Synthesis Reactions

2Fe + O2
– In this example, substance “A” is an element in atomic
form (Fe), and substance “B” is an element in
molecular form (O2). The result is a direct chemical
combination of the two elements (FeO, iron oxide,
which is “rust”).

CuO + H2O
– This is an example where both substances going into
the reaction are molecules. The result is what you get
when you “add” all of the atoms in the reaction
together.
Practice
•
•
•
•
Predict the products. Write and balance the
following synthesis reaction equations.
Sodium metal reacts with chlorine gas
Na(s) + Cl2(g) 
Solid Magnesium reacts with fluorine gas
Mg(s) + F2(g) 
Aluminum metal reacts with fluorine gas
Al(s) + F2(g) 
Decomposition Reactions
Decomposition reactions are really ______________
________________ ____________. Remember,
if you can make a substance, you should be able to
break it back apart into its components.
A good way to remember decomposition reactions to
to remember what happens when something
decomposes. It falls apart!
Decomposition Reactions
•
•
•
•
•
Decomposition reactions occur when a
compound __________________________
_____________________________________
1 Reactant  Product + Product
Basically: AB  A + B
Example: 2 H2O 
Example: 2 HgO 
Note: Single Reactant! The single reactant is your clue that this is a
decomposition reaction.
Decomposition Reactions
•
Another view of a decomposition reaction:
Decomposition Exceptions
•
Carbonates and chlorates are special case
decomposition reactions that do not go to the
elements.
• Carbonates (CO32-) decompose to
•
Example: CaCO3 
• Chlorates (ClO3-) decompose to
•
•
Example: 2 Al(ClO3)3 
There are other special cases, but we will not explore
those in this class
Practice
•
•
•
Predict the products. Then, write and
balance the following decomposition
reaction equations:
Solid Lead (IV) oxide decomposes
PbO2(s) 
Aluminum nitride decomposes
AlN(s) 
Practice
Identify the type of reaction for each of the
following synthesis or decomposition reactions,
and write the balanced equation:
 N2(g) + O2(g) 
 BaCO3(s) 
 Co(s)+ S(s) 
 NH3(g) + H2CO3(aq) 
 NI3(s) 
Single Replacement Reactions
Single replacement reactions occur when one
chemical
In the typical single replacement reaction,
Single Replacement Reactions
•
Single Replacement Reactions occur when one element
replaces another in a compound.
• A metal can
•
OR
•
element + compound product + product
A + BC  AC + B (if A is a metal) OR
A + BC  BA + C (if A is a nonmetal)
(remember the cation always goes first!)
When H2O splits into ions, it splits into
H+ and OH- (not H+ and O-2 !!)
Single Replacement Reactions
•
Another view:
The Activity Series

Not all single replacement reactions


This depends upon

Elements above _______ replace elements
below; elements below _____________
replace elements above them on the series
Single Replacement Reactions
•
•
Write and balance the following single
replacement reaction equation:
Zinc metal reacts with aqueous hydrochloric
acid
Note: Zinc replaces the hydrogen ion in the
reaction
Single Replacement Reactions
•
Sodium chloride solid reacts with fluorine gas
Note that fluorine replaces chlorine in the compound
•
Aluminum metal reacts with aqueous copper (II)
nitrate
4. Double Replacement Reactions
Double replacement reactions are identified
by
Double Replacement Reactions
•
Double Replacement Reactions occur when a
•
Compound + compound  product + product
•
Notice that one ion from
compound AB replaces one
ion from compound CD.
Double Replacement Reactions
•
•
•
Think about it like “foil”ing in algebra, first and last
ions go together + inside ions go together
Example:
AgNO3(aq) + NaCl(s) 
Another example:
K2SO4(aq) + Ba(NO3)2(aq) 2
Solubility


For a double replacement reaction to have
occurred,
There are rules to determine which of the
materials formed is the solid
 If no solid is formed, there is said to be
Solubility Tables


Solubility tables help determine which materials are soluble in
water and which are not
In general, Solubility Rules can be summarized as follows
1. All compounds containing alkali metal cations and the ammonium ion
2.
3.
4.
5.
6.
are soluble.
All compounds containing NO3-, ClO4-, ClO3-, and C2H3O2- anions are
soluble.
All chlorides, bromides, and iodides are soluble except those containing
Ag+, Pb2+, or Hg22+.
All sulfates are soluble except those containing Hg22+, Pb2+, Sr2+, Ca2+, or
Ba2+.
All hydroxides are insoluble except compounds of the alkali metals,
Ca2+, Sr2+, and Ba2+.
All compounds containing PO43-, S2-, CO32-, and SO32- ions are insoluble
except those that also contain alkali metals or NH4+.
Practice
•
Predict the products. Balance the equation
1.
HCl(aq) + AgNO3(aq) 
2.
Pb(NO3)2(aq) + BaCl2(aq) 
3.
FeCl3(aq) + NaOH(aq) 
4.
H2SO4(aq) + NaOH(aq) 
Combustion Reactions
Combustion reactions are the ones that burn (or
explode!). There are two types of combustion
reactions—
These reactions are identified by their products.
They either produce
Complete Combustion Reactions
These reactions burn “efficiently” which
means they produce _____________and
____________. These reactions typically
burn cleanly and leave very little residue
behind.
5. Combustion Reactions
•
•
•
•
Combustion reactions occur
when a hydrocarbon reacts with
_____________.
This is also called burning!!! In
order to burn something you need
the 3 things in the “fire triangle”:
1)
2)
3)
Combustion Reactions
•
In general:
CxHy + O2  CO2 + H2O
• Products in combustion are ALWAYS
•
(although incomplete burning does cause
some by-products like carbon monoxide)
• Combustion is used to heat homes and
run automobiles (octane, as in gasoline,
is C8H18)
Complete Combustion Reactions

CH4 + O2  CO2 + H2O

They may also be written:

Clues: CO2 (carbon dioxide) in the product
along with water
Combustion
•
Example
•
Write the products and balance the
following combustion reaction:
Incomplete Combustion Reactions
Incomplete combustion reactions occur
This can cause a lot of harm if the gases
produced cannot escape. Carbon monoxide,
an odorless and colorless gas,
. People poisoned by this gas usually become
.
Incomplete Combustion Reactions

CH4 + O2  CO + H2O

These reactions may also be written by:

Clue: CO (Carbon monoxide as a product.)
Mixed Practice
•
1.
2.
3.
4.
5.
State the type, predict the products, and
balance the following reactions:
BaCl2 + H2SO4 
C6H12 + O2 
Zn + CuSO4 
Cs + Br2 
FeCO3 
Predicting Products of Reactions

Completing reactions requires knowledge
of the

You must first identify the reaction type by

The only type of reaction that cannot be
predicted this way
First Step:

Identify reaction type
Example:
Al + O2 
Second Step:

Write the net ionic equation for the reactants
Step 3

Using clues, complete reaction taking care
to write each formula correctly by checking
charges and “criss-crossing” if necessary.
Predicting Products of Reactions (cont.)

For Single Replacement reactions, check

Once you write the molecular equation, you
should check for reactants and products that
are
Reactions in Aqueous Solutions

a.k.a. Net Ionic Equations
 Molecular Equations:

Does not show what happens on the molecular level
 Total (or Complete) Ionic Equations:

Some ions participate in the reaction
– Some ions do NOT participate in the reaction-called spectator
ions.

Net Ionic Equations: show only the ions that participate
in the reaction
Writing Total Ionic Equations





Once you write the molecular equation (synthesis,
decomposition, etc.), you should check for reactants and
products that are soluble or insoluble.
We usually assume the reaction is in__________
We can use a solubility table to tell us what compounds
dissolve in water.
If the compound is soluble (does dissolve in water), then
splits the compound into its ___________________
If the compound is insoluble _____________________
then it remains as a compound
Writing Total Ionic Equations
Molecular Equation:
K2CrO4 + Pb(NO3)2  PbCrO4 + 2 KNO3
Total Ionic Equation:
Net Ionic Equations

These are the same as total ionic equations, but
you should cancel out ions that appear on
BOTH sides of the equation
Total Ionic Equation:
Net Ionic Equation:
Net Ionic Equations

Try this one! Write the molecular, total ionic, and net ionic
equations for this reaction: Silver nitrate reacts with Lead
(II) Chloride in hot water.
AgNO3 + PbCl2 
Molecular:
2 AgNO3 + PbCl2  2 AgCl + Pb(NO3)2
Total Ionic:
2 Ag+ + 2 NO3- + Pb+2 + 2 Cl-  2 AgCl (s) + Pb+2 + 2 NO3Net Ionic:
Acid-Base Reactions

Acid:

Base:

The reaction ALWAYS forms water and an
ionic compound (mostly aqueous, known as a salt).
– The actual definition of a _______is the ionic product of an acid-base
neutralization reaction)
Acid-Base Neutralization

Chemically the reaction looks like this:
Acid + Base
Salt + Water
 A classic example:
HCl + NaOH
NaCl + H2O
Acid-Base Reactions

Example
HNO3 (aq) + KOH (aq) 
Molecular:
Total Ionic:
Net Ionic:
Acid-Base Neutralization

Here’s the equation again:
– HCl + NaOH
NaCl + H2O
– Chemically, this is a double replacement
reaction:


The H traded its
The Na traded its
Oxidation-Reduction Reactions

a.k.a. _______________________
 Between ___________ and a ________
forming an ________ compound
– _________ ___________ occurs
– Oxidation numbers: assigning an __________
______________________ in electrons for
each element (the charge based on the
compound).
Rules for Oxidation Number (ox. #)
Determination
1.
The sum of the oxidation numbers add up to
the _________
a. all elements have an ox. # of ____
b. for ions of elements, ox. # is the charge ______
c. the sum of the ox. # of a complex ion equals the
charge _________
2.
H is _____ when combined with a nonmetal
and ______ with a metal
H3PO4
CaH2
Rules for Oxidation Numbers (cont.)
1.
2.
3.
F is always 1-; Cl, Br, I are 1- except when
combined with ____________________
O is 2- except when combined with F (F2O)
Group I is ____ and Group II is _____ in their
compounds
Recognizing Redox Rxns.
oxidation
1+

0
2+
2 HCl (aq) + 0Mg (s)  MgCl
2 (aq) + H2 (q)
reduction

Net:
2 H+ (aq) + Mg2+ (aq)  Mg 2+ (aq) + H2 0 (q)


Loss of electron = oxidation
Gain of electron = reduction
– “LEO the lion goes GER"
Half Reactions

Separate the individual oxidation and reduction
reactions.
 Look at electron movement
 Half rxn.:
Mg0 (aq)  Mg 2+ + 2 e2e- + 2 H+  H20

Net:
2 H+ (aq) + Mg0 (aq)  Mg 2+ (aq) + H2 0 (q)

Oxidizing agent: the one reduced (H+)
 Reducing agent: the one oxidized (Mg0)
Recognition of Redox rxns.



Oxidation # changes
Reactions with oxygen
Reaction of any element (forms a new
compound)
Balancing



Balance by mass
Balance by charge
Balance net ionic equation
Example Problem:
Fe (s) + Cl2 (aq)  Fe3+ (aq) + Cl- (aq)

Balance by mass
2

Write half reaction

Net Ionic Equation:
3. Balance by charge (want # of e- to cancel)
(Fe0 (s)  Fe 3+ + 3e-)
(2e- + Cl2  2 Cl- )
+
Final eqn.:
The Myth!

MYTH: Little Mikey
(“Mikey Likes It”)
from the LIFE cereal
commercials in the
late 70s died when he
ate pop rocks then
drank a coke, causing
the pop rocks to
explode inside his
stomach.
The Myth!


Not surprisingly, this one
is completely false.
The Evidence:
– Mikey is alive and well.
His real name is John
Gilchrist and he’s an
advertising manager for a
New York Radio Station.
– There isn’t enough
carbonation in pop rocks to
release more than a tiny
amount of CO2 – much less
than in a coke. If the myth
were true, coke alone
should be able to explode
your stomach.