Transcript Types of Chemical Reactions

CHEMICAL
REACTIONS
Objectives- Describing Chemical
Reactions
• Describe how to write a word equation.
• Describe how to write a skeleton equation.
• Describe the steps for writing a balanced chemical
equation.
Word Equations
• These word equations are exactly as they sound.
• To write a word equation, we write the names of the
reactants to the left of the arrow separated by plus signs.
• On the right we write the products, also separated by plus
signs.
Examples
• H2 + O2  H2O
• Hydrogen + Oxygen  Water
• Fe + O2  Fe2O3
• Iron + Oxygen  Iron(III) Oxide
• H2O2  H2O + O2
• Hydrogen Peroxide  Water + Oxygen
Chemical Equations
• A chemical equation is a representation of a chemical
reaction, with reactants on the left of the arrow, and
products on the right.
• We should already be aware of what a chemical equation
is, but a subsect of these equations is known as a
skeleton equation.
• A skeleton equation is one where the formulas of the
reactants and products are listed but no amounts are
shown. (sometimes called unbalanced equations)
Common Symbols
• “+” used to separate two reactants/products
• “” a way to show reactants that “yield” a product
• “⇌” used in the case of a reversible reaction
• (s) used for a solid substance
• (l) designates a substance in the liquid state
• (g) designates a substance in the gaseous state
• (aq) designates an aqueous solution, or one dissolved in
water
Balancing Chemical Equations
(Refresher)
• H2 + O2  H2O
• Al2O3  Al + O2
• S8 + O2  SO2
• P4 + O2  P2O5
• Cr + O2  Cr2O3
Objectives- Types of Chemical Reactions
• Describe the five general types of reactions.
• Predict the products of the five general types of reactions.
Classifying Chemical Reactions
• Five types of reactions
• Synthesis (Combination)
• Decomposition
• Single Replacement
• Double Replacement
• Combustion
Synthesis Reactions
(Combination)
• Two or more compounds react to form a single
product
• Identifying characteristic: SINGLE PRODUCT
• General form
A + B  AB
2 Na + Cl2  2 NaCl
4 Fe + 3 O2  2 Fe2O3
CO2 + H2O  H2CO3
An analogy:
•Two single people go to a
dance and leave as couple
Decomposition
• Single compound breaks down into two or more
simpler substances
• Identifying characteristic: ONE REACTANT
• General format
AB  A + B
2 H2O  2 H2 + O2
CaCO3  CaO + CO2
An analogy:
•A couple breaks up…
Single-Replacement Reactions
• One substance replaces another similar substance
(like replaces like)
• Identifying characteristic: REACTANTS are always 1
ELEMENT & 1 COMPOUND.
• General form: A + BX  AX + B
2Al + 3CuCl2  2AlCl3 + 3Cu
Fe + Ni(NO3)2  Fe(NO3)2 + Ni
Cl2 + 2 KI  2 KCl + I2
An analogy:
•During a dance, someone
cuts in
Remember metal replaces metal
The Activity Series of Metals & Single
Replacement Reactions
• Not all metals have the ability to replace another metal
in a compound
• Must use the “Activity Series of Metals” to determine if
a single replacement reaction will occur
Decreasing Activity
Activity Series of Metals
Metals
Metals cont’d.
Li
Cd
K
Co
Ba
Ni
Sr
Sn
Ca
Pb
Na
H
Mg
Cu
Al
Ag
Mn
Hg
Zn
Au
Fe
Metals from Li to Na
will replace H from
acids and water.
Metals from Mg to Pb
will replace H from
acids only.
• If an element is higher on the activity series it will
replace the other. This means the reaction will occur.
• Li + NaCl 
Na
+
LiCl
• Ca + BaSO4 
No reaction
• Cu + AgNO3 
CuNO3 + Ag
Double-Replacement Reactions
• Identifying characteristic: presence of 2 COMPOUNDS
AS REACTANTS, and the switching of two cations
between compounds.
• General form:
AX(aq) + BY(aq)  AY + BX
K2CO3(aq) + BaCl2(aq)  KCl(aq) + BaCO3(s)
NaCl(aq) + AgNO3(aq)  NaNO3(aq) + AgCl(s)
An analogy:
•Two couples swap partners
Double-Replacement Reactions (cont)
• Not all double replacement reactions will occur. This
depends on the solubility rules which we will discuss later.
• For now assume they occur when writing or balancing
equations
Combustion Reactions
• Oxygen and a carbon/hydrogen compound are
reactants
• Identifying characteristic: have 2 PRODUCTS;
CO2 & H2O.
• General form:
CxHy + O2  CO2 + H2O
C2H5OH + O2  2 CO2 + 3 H2O
C3H8 + 5 O2  3 CO2 + 4 H2O
Review of General Forms for Reactions
The five types of reactions have the following
general forms:
• A + B  AB (synthesis)
• AB  A + B (decomposition)
• A + BX  AX + B (single)
• AX + BY  AY + BX (double)
• CnHm + O2  CO2 + H2O (combustion)
Answer the following questions:
1. Name the five main types of reactions.
2. What is the identifying characteristic of a synthesis reaction?
3. What is the identifying characteristic of a decomposition
reaction?
4.
What are the substances on the left side of a
chemical reaction called?
5. What is the activity series used for?
6. What are the products of a combustion reaction?
Name That Rxn Type!
2H2O2  2H2O + O2
2Cu + O2  2CuO
Zn + 2AgNO3  Zn(NO3)2 + 2Ag
4NaCl + 2H2SO4  2Na2SO4 + 4HCl
2C2H2 + 3O2  2CO2 + 2H2O
Balancing Equations Reminders
• All chemical equations must be balanced
• All reactants and products must be correctly written (i.e.,
correct formulas!)
• ID reaction type & predict products
• Coefficients may be added to satisfy Law of Conservation
of Matter
• NEVER CHANGE A CORRECT SUBSCRIPT !!!!!!!!!!!!!!!!
Balancing Equations Reminders(cont)
• Never automatically bring subscripts from reactant
side to product side
• Remember diatomic elements!!!
• H2, N2, O2 and the halogens (Group 7A)
• Use pencil and check your work!
Predicting Products
• Use Activity Series for SR rxns.
• If the rxn will not proceed:
• Put a diagonal line through the arrow
• Or write NR after the arrow
• For double replacement reactions you will need to use
the solubility rules to determine if the reaction will occur.
Phase Indicators
• Tells the phase of the reactants and products
in a chemical equation
• Solid (s) [formation of a solid]
• Ca3(PO4)2(s)
• Liquid (l) [formation of a liquid]
• HOH(l) - same as –H2O(l)
• Gas (g) [formation of a gas]
• H2(g), CO2(g), O2(g)
• Aqueous (aq) [dissolved ions]
• NaCl(aq)
Solubility Definitions
• Soluble
• Can Dissolve in Water
• Aqueous is the phase indicator (aq)
• Slightly Soluble
• Only a insignificant amount dissolves
• Solid the phase indicator (s)
• Insoluble
• Does not Dissolve
• Solid the phase indicator (s)
• On the next slide is a table of solubilities. What
trends do you notice?
Solubility Rules
The previous table is time consuming to remember and
use. Although you do not need to memorize we will
instead use “Solubility Rules” located with your periodic
table.
• Question: The solubility rules are mostly based on the
anion or cation? (Which one do you look at in order to
determine which rule to use?)
Identify the following as SOLUBLE or
INSOLUBLE. Write the correct phase
indicator.
NaNO3
NaCl
CaCrO4
BaSO4
BaS
(NH4)2CO3
AgNO3
K2CrO4
Ca(OH)2
See wksht:
Implications for DR Reactions
• A reaction takes place when:
• A new substance forms
• Solids, liquids, or gases
• No reaction takes place when:
• Only soluble ions exist
• Aqueous
Double Replacement Rxns
• Reactants must always be dissolved in water; i.e.,
phase subscript = (aq)
• Always write formulas for products (predict
products)
• Use solubility rules to determine if at least one of
the products will be a solid, liquid or gas--NOT
AQUEOUS
• If both products are (aq), no reaction takes place
• Put a diagonal line through the arrow
or
• Write NR over the arrow
Practice
• AgNO3(aq) + Na2S(aq) 
•
Ag2S(s) + NaNO3(aq)
• 2KNO3(aq) + Na2S(aq) 
•
K2S(aq) +2NaNO3(aq)
• SO NO REACTION
• NaOH(aq) + Pb(NO3)(aq) 
•
NaNO3(aq) + Pb(OH)2(aq)
• NaOH(aq) + KNO3(aq) 
•
NR
Law of Conservation of Mass
Matter cannot be created or destroyed, it may be
recombined to form new substances
• Starting mass must equal ending mass
• Starting # of atoms must equal ending # of atoms
Evidence of a Reaction
• New substance forms
• Precipitate (solids falls from a solution)
• Gas (bubbles…)
• Water (neutralization [acid/base] reaction)
• Change in Temperature
• Exothermic or Endothermic
• Transfer of Electrons
• “Oxidation-Reduction” Reaction
Objectives- Reaction in Aqueous
Solutions
• Describe the information found in a net ionic equation.
• Predict the formation of a precipitate in a double
replacement reaction.
Net Ionic Equations
• First lets look at the following reaction:
• AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)
• If we separate all the pieces involved in this reaction we
would arrive at the following:
• Ag+ (aq) + NO3-1 (aq) + Na+(aq) + Cl-1 (aq) 
AgCl (s) + Na+1 (aq) + NO3-1 (aq)
• What looks out of place with this equation?
Net Ionic Equations
• Our next step is to cancel out anything that appears on
each side PERFECTLY.
• Ag+ (aq) + NO3-1 (aq) + Na+(aq) + Cl-1 (aq) 
AgCl (s) + Na+1 (aq) + NO3-1 (aq)
• That what we have canceled out is known as a spectator
ion, something that does not directly involved in the
reaction.
• What are we left with?
• This is called the net ionic equation, this shows only
those particles that are directly involved in a chemical
change.
Balancing the Net Ionic EQ
• Pb(s) + AgNO3 (aq)  Ag(s) + Pb(NO3)2 (aq)
• Let’s work through this one together.
Predicting the Formation of a Precipitate
• We can predict the formation of a precipitate by using the
general rules of solubility.
Predicting the Formation of a Precipitate
• Looking at the list of soluble and insoluble compounds we
should be able to predict the possible products from the
following reaction.
• 2Na+ (aq) + CO32- (aq) + Ba+2 (aq) + 2NO3-1 (aq)  ?