Download Chapter 7

Do Now!!!
What is the name of NaOH?
Sodium Hydroxide
What is the formula of copper (II) chloride?
CuCl2
Chapter 7
Chemical Reactions
Objectives
• Interpret chemical equations in terms of
reactants, products, and conservation of
mass.
• Balance chemical equations by
manipulating coefficients.
Reactants
A Substance that undergoes change in a
chemical reaction.
Products
New substances formed as a result of a
chemical reaction.
Chemical Equation
A representation of a chemical reaction in
which the reactants and products are
expressed as formulas.
Reactants  Products
Example
Reactants  Products
Carbon + Oxygen  Carbon dioxide
C + O2  CO2
Conservation of Mass
Mass is neither created nor destroyed in a
chemical reaction, it just changes forms.
Coefficients
Number that appear before a formula in a
chemical equation to show the relative
proportions of each reactant and product.
Note: Coefficients are necessary to show
that mass is conserved during a reaction, a
chemical equation must be balanced.
Balancing Equations
Important: You should never change the
subscripts in a formula!!! Changing the
formula changes the identity of that
reactant or product.
Balancing Equations
1. Count the number of atoms of each
element on each side of the equation.
2. Change one or more coefficients until the
equation is balanced.
3. Once the equation is balanced, recount
the number of atoms of each element to
ensure that they are the same on each
side.
Balancing Equations Example
N2H4 + O2 
N=2
O=2
H=4
N2 + H2O
N=2 H=2
O=1
N2H4 + O2 
N=2
O=2
H=4
N2 + 2H2O
N=2 H=4
O=2
Do Now!!!
For each type of atom in copper (II) nitrate,
determine the number of atoms that are
present?
Cu(NO3)2
Cu = 1
N=2
O=6
Objectives
• Interpret chemical equations in terms of
reactants, products, and conservation of
mass.
• Balance chemical equations by
manipulating coefficients.
Balancing Equations Examples
Cl2
Cl2
 HCl
 2HCl
+ HCl
+ 2HCl


H2
H2
+ O2
+ 3O2


CO2
2CO2
H2
H2
Mg
Mg
C2H4
C2H4
+
+
+
+
MgCl2
MgCl2
+ H2O
+ 2H2O
Do Now!!!
Balance the following chemical equation:
Na2O + H2O 
NaOH
Na2O + H2O  2NaOH
Mole
An amount of a substance that contains
approximately 6.02  1023 atoms,
molecules, or ions of the substance.
Because chemical reactions often involve
large numbers of small particles, chemists
use a counting unit called the mole to
measure amounts of a substance.
Molar Mass
The mass of one mole of a substance.
For an element:
the molar mass is the same as its atomic
mass expressed in grams.
For a compound:
Add up the atomic masses of its
component atoms, then expressing the
sum in grams.
Calculating Molar Mass
Carbon dioxide (CO2)
1. Calculate the molar mass of C:
Molar Mass of C = 12.011  1 = 12.011
2. Calculate the molar mass of O:
Molar Mass of O = 15.999  2 = 31.998
3. Calculate the total molar mass of CO2:
Molar Mass of CO2 = 12.011 + 31.998
Molar Mass of CO2 = 44.009
Molar Mass Examples
1. Water (H2O) = 18.0148
2. Magnesium oxide (MgO) = 40.304
3. Sodium Chloride (NaCl) = 58.443
4. Ammonia (NH3) = 17.0307
Do Now!!!
Calculate the molar mass of the following:
NH4Cl
53.50 g
Mg3(PO4)2
262.87 g
Copper (II) fluoride
CuF2
101.54 g
Objective
• Convert between moles and mass of a
substance using molar mass.
Mole - Mass Conversions
Molar Mass Conversion Factors:
Molar mass of sample
1 mole of sample
1 mole of sample
Molar mass of sample
Mole - Mass Conversions
Molar Mass Conversion Factors:
Molar mass of sample 44.009 g of CO2
=
1 mole of sample
1 mole of CO2
1 mole of sample
1 mole of CO2
=
Molar mass of sample 44.009 g of CO2
Mole - Mass Calculations
Molar Mass Conversion Factor:
44.009 g of CO2
1.25 mol CO2 
1 mole of CO2
1 mole of CO2
55.0 g CO2 
44.009 g of CO2
Do Now!!!
Calculate the molar mass of the following:
NaBr
102.90 g
Na2CO3
134.06 g
Aluminum sulfide
Al2S3
150.14 g
Objective
• Convert between moles and mass of a
substance using molar mass.
Mole - Mass Calculations
Molar Mass Conversion Factor:
44.009 g of CO2
1.25 mol CO2 
= 55.0 g CO2
1 mole of CO2
1 mole of CO2
55.0 g CO2 
= 1.25 mol CO2
44.009 g of CO2
Mole - Mass Examples
1. 2 mol H2O = 36.0296 g H2O
2. 3.1 mol MgO = 124.9424 g MgO
3. 16.2 g NaCl = 0.277 mol NaCl
4. 30.8 g NH3 = 1.808 mol NH3
Chemical Calculations
In a chemical reaction, the mass of a
reactant or product can be
calculated by using a balanced
chemical equation and molar masses
of the reactants and products.
Using Molar Ratios
2 H2 + O2  2 H2O
Conversion Factors for O2 and H2O:
1 mole O2
2 mol H2O
or
2 mol H2O
1 mole O2
Do Now!!!
1. 4.6 mol HC2H3O2 =
276.28 g HC2H3O2
2. 143.6 g CH3CH2OH =
3.12 mol CH3CH2OH
Objective
• Classify chemical reactions as synthesis,
decomposition, single-replacement,
double-replacement, or combustion
reactions.
General Types of Reactions
1.
2.
3.
4.
5.
Synthesis Reaction
Decomposition Reactions
Single-replacement Reactions
Double-replacement Reactions
Combustion Reactions
Synthesis Reaction
A chemical reaction in which two or
more substances react to form a
single substance.
Example of Synthesis Reactions
2 Na + Cl2  2 NaCl
2 H2 + O2  2 H2O
Decomposition Reaction
A chemical reaction in which a
compound breaks down into two or
more simpler substances.
Examples of
Decomposition Reactions
2 H2O  2 H2 + O2
CaCO3  CaO + CO2
Single-Replacement Reaction
A chemical reaction in which one
element takes the place of another
element in a compound.
Examples of
Single-Replacement Reactions
Cu + 2 AgNO3  Cu(NO3)2 + 2 Ag
2 K + 2 H2O  H2 + 2 KOH
2 K + 2 HOH  H2 + 2 KOH
Double-Replacement Reaction
A chemical reaction in which two
compounds exchange positive ions
and form two new compounds.
Examples of
Double-Replacement Reactions
Pb(NO3)2 + KI  PbI2 + 2 KNO3
CaCO3 + 2 HCl  CaCl2 + H2CO3
Do Now!!!
Balance the following chemical equation:
Ba3N2 +
H2O 
Ba(OH)2 +
NH3
Ba3N2 + 6 H2O  3 Ba(OH)2 + 2 NH3
(NH4)2Cr2O7 
Cr2O3 +
N2 +
H 2O
(NH4)2Cr2O7  Cr2O3 + N2 + 4 H2O
Objective
• Classify chemical reactions as synthesis,
decomposition, single-replacement,
double-replacement, or combustion
reactions.
Combustion Reaction
A chemical reaction in which a
substance reacts rapidly with
oxygen, often producing heat and
light.
Example of a
Combustion Reaction
CH4 + 2 O2  CO2 + 2 H2O
Material for Chpt. 7 Exam
 Chemical
equations
 Balancing chemical equations
 Molar mass
 Mass – mole conversions
 Type of chemical reactions
Do Now!!!
1. 2.67 mol Pb(NO3)4 =
1215.49 g Pb(NO3)4
2. 285.26 g PCl5 =
1.37 mol PCl5
Objectives
• Describe the energy changes that takes
place during chemical reactions.
• Classify chemical reactions as
exothermic or endothermic.
• Explain how energy is conserved during
chemical reactions.
Oxidation-Reduction Reaction
A chemical reaction in which
electrons are transferred from one
reactant to another.
Chemical Energy
The energy stored in the chemical
bonds within a substance.
Chemical Reactions
Chemical reactions involve the
breaking of chemical bonds in the
reactants and the formation of
chemical bonds in the products.
Chemical Reactions
Breaking bonds: Requires energy
Forming bonds: Releases energy
Exothermic Reaction
A chemical
reaction that
releases energy
to its
surroundings.
Exothermic Reaction
The combustion of propane:
C3H8 + 5 O2  3 CO2 + 4 H2O + 2220 kJ
Endothermic Reaction
A chemical
reaction that
absorbs energy
from its
surroundings.
Endothermic Reaction
The decomposition of mercury(II) oxide:
2 HgO + 181.7 kJ  2 Hg + O2
Conservation of Energy
The total amount of energy before and after
the reaction is the same.
Objectives
• Explain what a reaction rate is.
• Describe the factors affecting
chemical reaction rates.
Reaction Rate
The rate at which reactants change
into products over time.
Catalyst
A substance that affects the rate of a
chemical reaction without being used
up in the reaction.
Objectives
• Identify and describe physical and
chemical equilibria.
• Describe the factors affecting
chemical equilibrium.
Equilibrium
A state in which the forward and
reverse paths of a physical or
chemical change take place at the
same rate.
Reversible Reaction
A chemical reaction in which the
conversion of reactants into products
and the conversion of products into
reactants happens at the same time.
Balancing Equations Examples
Cl2

HCl
HCl

H2
+
O2

CO2
H2
Mg
C2H4
+
+
+
MgCl2
+
H2O