Download File

Pick up Homework sheet!
Chemical Reactions
Chapter 11
Today’s Objectives
1. Be able to indicate
when a chemical
change has
occurred.
2. Understand the Law
of Conservation of
Mass
What is a chemical reaction?
 A change in which one or more reactants change into
one or more products
 Characterized by the breaking of bonds in reactants
and the formation of bonds in products
 A change that produces matter with a different
composition than the original matter
 Taking one thing and making it something completely
different!
Indicators of a Chemical Change
 Change in color
 Heat absorbed or released
 Formation of a gas
 Formation of a precipitate
 Odor given off
Balancing Equations
 Chemical Equation:
 an expression that represents a chemical reaction.
 Law of Conservation of Mass: No atoms are created or destroyed in
chemical reactions.
Atoms are just rearranged.
Reactants  Products
 #atoms of each element in the reactants =
# atoms of each element in the products
CHEMICAL REACTIONS
4 Types of Chemical Reactions
1.
2.
3.
4.
Synthesis
Decomposition
Single Replacement
Double Replacement
Synthesis
 Two or more reactants combine to form a single
product.
4Fe (s) + 3O2 (g)  2Fe2O3 (s)
A + B
 AB
Decomposition
 A single reactant forms two or more products.
NH4NO3 (s)  N2O (g) + 2H2O (g)
AB
 A
+ B
Single-Replacement
(Single Displacement)
 One element takes the place of another element in
a compound. (“cutting in”)
Cationic:
Fe (s) + CuSO4 (aq)  FeSO4 (aq) + Cu (s)
A + BC
 AC
+B
Anionic:
Cl2 (g) + 2NaBr (aq)  2NaCl (aq) + Br2 (l)
A
+ BC
 BA
+C
Double-Replacement
(Double Displacement)
 The positive ions of two ionic compounds switch places.
(“switching partners”)
 At least one of the products is a precipitate, water, or a
gas.
Pb(NO3)2 (aq) + 2 KI (aq)  PbI2 (s) + 2 KNO3 (aq)
AB
+ CD  AD + CB
Acid-Base
(Double Replacement)
 An acid and base react to form water and a salt.
HCl(aq) + NaOH(aq)  H2O(l) + NaCl (s)
AB + CD  AD + CB
acid + base
 water + salt
Combustion Reaction
2 C2H2 (g) + 5 O2 (g)  4 CO2 (g) + 2 H2O (g) + energy
 What makes our engines run.
 Any time you burn an organic substance, you are
creating a combustion reaction.
 Often a hydrocarbon fuel burning in oxygen to
produce CO2 & H2O.
Predicting Products
 Use Reference Table to predict type of reaction.
 Guidelines for Predicting the Products of Selected Types
of Chemical Reaction
Key: M = Metal
NM = Nonmetal
Practice
 Match each reaction to the best fitting reaction type.
1. ____ C3H8 + O2 -> H2O + CO2
2. ____ Mg + O2 -> MgO
3. ____ Ca + HCl -> CaCl2 + H2
4. ___ KClO3 -> KCl + O2
5. ___ HCl + NaOH -> NaCl + H2O
6. ___ NaNO3 + Ag -> AgNO3 + Na
7. ___ CH4 + O2 -> CO2 + H2O
Reactions
A. Synthesis
B. Decomposition
C. Combustion
D.Single Displacement
E. Double Displacement
Chemical Reactions
Chapter 11
WARM UP FOR TUESDAY, OCTOBER 28
Match each reaction to the best fitting reaction type.
1. ____ C3H8 + O2 -> H2O + CO2

2. ____ Mg + O2 -> MgO
3. ____ Ca + HCl -> CaCl2 + H2
4. ___ CH4 + O2 -> CO2 + H2O
5. ___ Na + O2 -> Na2O
6. ___ H2SO4 + MgO -> H2O + MgSO4
7.___ H2O2 -> H2O + O2
Reactions
A. Synthesis
B. Decomposition
C. Combustion
D.Single Displacement
E. Double Displacement
Writing Chemical Reactions
 Chemical Equation:
 an expression that represents a chemical reaction.
 A balanced chemical equation tells:
 What elements and/or compounds are involved
 The relative amounts of each substance involved
 Chemical equations MUST:
 Include the correct formula for the species involved
 Satisfy the Law of Conservation of atoms
 Tell the relative number of moles (quantity) of each species
Symbols you might see:
 Physical States:
 (g) – gas
  - reversible arrow
 reaction can go forward
or backwards
 (l) – liquid
 Δ – heat involved in the
reaction
 (s) – solid or precipitate
 (aq) – substances
dissolved in water
 MnO2 – catalyst
 Substance that speeds
up the reaction but is
not used up in the
reaction
How to write a balanced chemical equation:
 1. Decide which species are reactants & which are products
 2. Write each species as a correct chemical formula.
 3. Write the formulas for the reactants on the left side of the paper.
 4. Place an arrow () after the reactants to indicate what is produced.
 5. Write formulas for the products on the right side of the arrow.
 6. Balance the chemical equation by adjusting the coefficients in front of
the species to satisfy the Law of Conservation of Atoms.
 Same number of atoms of each element on both sides of the arrow
Products
Reactants
Yields
Law of Conservation of Atoms
 During any chemical reaction, the mass of the products is
always equal to the mass of the reactants.
 Matter cannot be created or destroyed.
 In any chemical reaction, mass is conserved.
We use coefficients to balance chemical
equations so that it obeys the
Law of Conservation of Atoms!
Rules for Balancing an Equation:
 1. Write out the numbers of each element for each side.
 2. Add coefficients to balance elements ONE AT A TIME.
 Keep a running tally of the numbers of each element.
 Check each number after each coefficient added.
 Balance complicated compounds FIRST.
 Balance elements that appear alone or as diatomic molecules LAST.
 Save Oxygen & Hydrogen for LAST.
 3. Reduce coefficients to simplest ratio, if necessary.
Example:
 Ammonium chloride reacts with calcium hydroxide to produce
calcium chloride, ammonia, and water.
2 NH4Cl
+
Ca(OH)2
CaCl2 + 2 NH3
+ 2 H2O
N
: 1
2
N
: 1
2
H
:
10
H
:
8 10
2
Cl : 2
6
Cl : 1
5
Ca :
1
Ca :
1
O :
2
O :
1 2
Practice:
 Write the chemical equation & balance:
 Sodium hydrogen carbonate decomposes into sodium
carbonate, carbon dioxide, and water.
2 NaHCO3  Na2CO3 + CO2 + H2O
Na
H
C
O
---1
---1
---1
---3
2
2
2
6
Na
H
C
O
2
2
2
6
Practice
1)
____ NaCl + ____ F2  ____ NaF + ____ Cl2
2)
____ H2 + ____ O2  ____ H2O
3)
____ Pb(OH)2 + ____ HCl  ____ H2O + ____ PbCl2
Today’s Objective
- Predict Products for Reactions
using Reference Table
- Understand the rules governing
Single-Replacement Reactions
- Complete the Reactivity of
Metals Lab
Predicting Products using
Reference Table
 If you are two different elements as reactants
 SYNTHESIS
 If you have only one reactant
 DECOMPOSITION
 If you have an element (exculding O2) & a compound
 SINGLE-REPLACEMENT
 If you have two aqueous compounds
 DOUBLE-REPLACMENT
 If you have a hydrocarbon & O2
 COMBUSTION
Use Reference Table to
Decide which rule to use!
Example:
Mg + O2 ->Mg+ O2
Mg + N2 -> Mg3N2
Practice Predicting Products:
1.Ca + Cl2 ->
2.ZnCl2 ->
3.Li2O ->
4.K + S ->
Single Replacement
Reactions
 Use Activity Series to
Determine if a Reaction Will
Occur.
 A lone element will replace an
element in a compound if it is
MORE REACTIVE (higher on
chart).
 The element that is by itself
MUST be higher on the chart
than the one in the compound!
Decide if the
reaction will occur:
1) Fe (s) + Pb(NO3)2 (aq)  1) YES
2) Ni (s) + MgCl2 (aq) 
2) NO
3) Cl2 (aq) + NaI (aq) 
3) YES
4) Ca (s) + CuBr2 (aq) 
4) YES
5) K (s) + Al(NO3)3 (aq)  5) YES
6) I2 (s) + MnBr2 (aq) 
6) NO
7) Mg (s) + AgNO3 (aq)  7) YES
8) Cl2 (s) + SrF2 (aq) 
8) NO
Predict the Products
1) Ca (s) + CuBr2 (aq) 
2) K (s) + Al(NO3)3 (aq) 
3) I2 (s) + MnBr2 (aq) 
4) Mg (s) + AgNO3 (aq) 
5) Cl2 (s) + SrF2 (aq) 
Double Replacement Reactions
 Reminder:
 At least one product is a precipitate, water, or a gas.
 Use solubility rules to determine which product is the
precipitate.
 Precipitate = solid (insoluble)
 Both reactants are AQUEOUS.
 Only ONE product can be AQUEOUS.
 The other must be SOLID, LIQUID, or GAS.
Solubility Rules
Must know the NAME of the compound before determining its solubility!
Predicting Products
 Single Replacement
 Use ACTIVITY SERIES
 The element that is by itself MUST be higher on the chart
than the element in the compound for the reaction to occur
 Metal replace Metals
 Nonmetals replace Nonmetals
 Double Replacement
 Use SOLUBILITY RULES
 One product MUST be INSOLUBLE
 Do NOT check solubility of reactants!
 RbI (aq) + AgNO3 (aq)  PbNO3(aq) + AgI(s)
 Na3PO4 (aq) + MnCl2 (aq)  NaCl(aq) + Mn3(PO4)2(s)
 Li2CO3 (aq) + MoBr6 (aq)  LiBr(aq) + Mo(CO3)3(s)
 Ca(NO3)2 (aq) + Al(OH)3 (aq)  Ca(OH)2(s) + Al(NO3)3(aq)
 CuCl2 (aq) + Na2CO3 (aq)  NaCl(aq) + CuCO3 (s)
 BaCl2 (aq) + K2SO4 (aq)  KCl(aq) + BaSO4 (s)
Reactions in Aqueous Solution
 Ionic compounds dissociate into ions in water!
 Overall equation:
AgNO3(aq) + NaCl(aq) AgCl(s)+ NaNO3(aq)
 Ionic Equation:
Ag+(aq) +NO3- (aq) +Na+ (aq) +Cl- (aq) AgCl (s) +Na+ (aq) +NO3 (aq)
 Shows dissolved ionic compounds as dissociated free ions
 Only separate AQUEOUS compounds into ions!
Net Ionic Equations
Ag+(aq) +NO3- (aq) +Na+ (aq) +Cl- (aq) AgCl (s) +Na+ (aq) +NO3 (aq)
 Spectator ions:
 Ions that do not participate in the reaction: Na+, NO3-
 Net ionic equation:
 Shows only ions that are active in the reaction:
Ag+ (aq) + Cl- (aq)  AgCl (s)
 Balancing Net Ionic Equations: must be balanced
with respect to both mass (atoms) and charge.
Practice:
Write the balanced net ionic equation.
1) Pb (s) + AgNO3 (aq)  Ag (s) + Pb(NO3)2 (aq)
2) FeCl3 (aq) + KOH (aq)  Fe(OH)3 (s) + KCl (aq)