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Chapter 8. Chemical Reactions. Indications of a Chemical Reaction. Evolution of heat and light Production of a gas Formation of a precipitate Color change. All chemical reactions. have two parts Reactants - the substances you start with Products - the substances you end up with

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chapter 8

Chapter 8

Chemical Reactions

indications of a chemical reaction
Indications of a Chemical Reaction
  • Evolution of heat and light
  • Production of a gas
  • Formation of a precipitate
  • Color change
all chemical reactions
All chemical reactions
  • have two parts
  • Reactants - the substances you start with
  • Products- the substances you end up with
  • Reactants yield Products
characteristics of chemical equations
Characteristics of Chemical Equations
  • Represent the known facts
  • Contain correct formulas and symbols
  • Satisfy the law of conservation of mass (they must be balanced using coefficients)
word and formula equations
Word and Formula Equations
  • Copper reacts with oxygen to form copper (II) oxide.
  • word equation
  • Copper + oxygen ® copper (II) oxide
  • formula equation
  • Cu + O2® CuO
  • balanced chemical equation
  • 2Cu + O2® 2CuO
symbols used in chemical equations
Symbols Used In Chemical Equations
  •  yields
  • + and
  • (s) or (cr) solid
  • (g) gas
  • (l) liquid
  • (aq) aqueous

solution

symbols used in chemical equations7
Symbols Used In Chemical Equations
  • ­ gaseous product
  • ¯ precipitate
  • reversible reaction
  • reactants are heated
  • A catalyst used to change the rate of the reaction
what is a catalyst
What is a catalyst?
  • A substance that speeds up a reaction without being changed by the reaction.
  • Enzymes are biological or protein catalysts.
what is a reversible reaction
What is a reversible reaction?
  • A chemical reaction in which the products reform the original reactants.
write the formula equation
Write the formula equation
  • Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form solid iron (II) chloride and hydrogen sulfide gas.
  • Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.
write the word equations
Write the word equations
  • Fe(s) + O2(g) ® Fe2O3(s)
  • Cu(s) + AgNO3(aq) ® Ag(s) + Cu(NO3)2(aq)
  • NO2 (g) N2(g) + O2(g)
balancing chemical equations

Balancing Chemical Equations

A step by step approach

balanced equation
Balanced Equation
  • Atoms can’t be created or destroyed
  • All the atoms we start with we must end up with
  • A balanced equation has the same number of each element on both sides of the equation.
slide14

®

O

+

C

C

O

O

O

  • Carbon + oxygen yields carbon dioxide
  • C + O2® CO2
  • This equation is already balanced
slide15

®

O

+

C

C

O

O

  • Carbon + oxygen yields carbon monoxide
  • C + O2® CO
  • We need one more oxygen in the products.
  • Can’t change the formula
slide16

C

O

®

O

+

C

O

  • Must be another CO
  • But where did the other C come from?

C

O

slide17

C

C

O

®

O

+

O

  • Must have started with two C
  • 2 C + O2® 2 CO

C

O

C

rules for balancing
Rules for balancing
  • Write the correct formulas for all the reactants and products
  • Count the number of atoms of each type appearing on both sides
  • Balance the elements one at a time by adding coefficients (the numbers in front)
  • Balance polyatomic ions that appear on both sides of the equation as single units
always
Always
  • Recount atoms as coefficients are added or changed
  • Reduce the coefficients to represent the smallest whole number ratio of reactants and products
never
Never
  • Add, delete, or change a subscript to balance an equation.
  • Never put a coefficient in the middle of a formula
example
Example

H2 +

O2

®

H2O

Make a table to keep track of atoms

slide22

Example

H2 +

O2

®

H2O

2

H

2

2

O

1

Need twice as much O in the product

slide23

Example

H2 +

O2

®

2

H2O

2

H

2

2

O

1

Changes the O

slide24

Example

H2 +

O2

®

2

H2O

2

H

2

2

O

1

2

Also changes the H

slide25

Example

H2 +

O2

®

2

H2O

2

H

2

4

2

O

1

2

Need twice as much H in the reactant

slide26

Example

2

H2 +

O2

®

2

H2O

2

H

2

4

2

O

1

2

Recount

slide27

Example

2

H2 +

O2

®

2

H2O

4

2

H

2

4

2

O

1

2

The equation is balanced, has the same

number of each kind of atom on both sides

slide28

Example

2

H2 +

O2

®

2

H2O

4

2

H

2

4

2

O

1

2

This is the answer

Not this

examples
Examples
  • P. 252 – example problem 8-3
  • P. 252 – practice problems
  • P. 253 – example 8-4,8-5
  • P. 254 – practice problems
  • H.W. p. 254 Section Review

P. 270 # 18,19, 22

Website for balancing equations

http://funbasedlearning.com/chemistry

Classic Chembalancer

synthesis
Synthesis
  • the combination of 2 or more substances to form a compound
  • Two reactants one product

A + B  AB

synthesis32
Synthesis

H2(g) + Cl2(g)  2 HCl(g)

synthesis33
Synthesis
  • 2 elements, or compounds combine to make one compound.
  • Three types:
  • Reaction of elements + oxygen or sulfur
  • Reaction of metals + halogens
  • Reactions with oxides
synthesis34
Synthesis
  • Examples (see pages 256-258)
decomposition
Decomposition
  • a compound breaks down into 2 or more simpler substances
  • one reactant two products

AB  A + B

decomposition36
Decomposition
  • one reactant breaks apart into two or more elements or compounds.
  • Usually requires heat or electricity
  • A catalyst may be used to speed up the reaction
  • The decomposition of a substance by electricity is called electrolysis
decomposition37
Decomposition
  • Can predict the products easily if it is a binary compound
  • 2H2O 2H2 + O2
  • 2NaCl 2Na + Cl2
decomposition38
Decomposition

2 H2O(l)  2 H2(g) + O2(g)

decomposition39
Decomposition
  • decomposition of metal carbonates
  • decomposition of metal hydroxides
  • decomposition of metal chlorates
  • decomposition of acids.
decomposition40
Decomposition
  • Examples (see pp. 259-260)

h.w. handout

single replacement
Single Replacement
  • one element replaces another in a compound
    • metal replaces metal (+) and hydrogen
    • nonmetal replaces nonmetal (-)

A + BC  B + AC

single replacement42
Single Replacement

Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)

single replacement43
Single Replacement
  • Examples: (see p. 261-262)
double replacement
Double Replacement
  • ions in two compounds “change partners”
  • cation of one compound combines with anion of the other

AB + CD  AD + CB

double replacement45
Double Replacement

Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq)

double replacement46
Double Replacement
  • Formation of a precipitate, gas, or water
  • Examples ( see pages 262-263)
  • H.w. handout
combustion
Combustion
  • the burning of any substance in O2 to produce a large amount of energy in the form of heat and light

CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

combustion48
Combustion
  • Combustion of a hydrocarbon with oxygen
  • the products will be CO2 and H2O.

(may get C and CO under less than perfect conditions)

Balance C, H, then O

examples49
Examples
  • C2H6 + O2®
  • C3H8 + O2®
  • C4H10 + O2®
  • C7H16 + O2®
homework
Homework
  • P. 269 # 1-11
  • P. 264 # 1-4
  • P. 270 # 20, 21
  • P. 271 # 25-29, 33
  • P. 272 # 44, 48
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