Transcript Ch. 3 - Chemical Reactions

Ch. 8 – Chemical Equations &
Reactions
I
II III IV V
Describing Chemical Reactions
Process by which one or more
substances are changed into one or
more different substances
 Chemical equation- represents with
symbols & formulas identities and
amounts of reactants and products

All Chemical Reactions
have two parts
 Reactants - the substances you start
with
 Products- the substances you end up
with
 The reactants turn into the products.
 Reactants  Products

Chemical Equations
A+B  C+D
REACTANTS
PRODUCTS
Chemical Equation
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Law of Conservation of Mass

mass is neither created nor destroyed
in a chemical reaction
total mass stays the same
 atoms can only rearrange

4H
36 g
2O
4H
2O
4g
32 g
C. Johannesson
Signs of a Chemical Reaction

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

Creation of heat and
light
Formation of a gas
Formation of a
precipitate – solid
produced and
separated from a
solution
Color change
Signs of a Chemical Reaction
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Chapter 8
Section 1 Describing Chemical
Reactions
Characteristics of Chemical Equations, continued
Additional Symbols Used in Chemical Equations
Chapter 8
Section 1 Describing Chemical
Reactions
Characteristics of Chemical Equations, continued
Additional Symbols Used in Chemical Equations
Symbols Used in Chemical Equations
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Visual Concept
Writing Equations
2H2(g) + O2(g)  2H2O(g)

Identify the substances involved.

Use symbols to show:
 How many? - coefficient
 Of what? - chemical formula
 In what state? - physical state
Describing Equations

Describing Coefficients:
 individual atom = “atom”
 covalent substance = “molecule”
 ionic substance = “unit”
3CO2  3 molecules/MOLES of carbon dioxide
2Mg
 2 atoms/MOLES of magnesium
4MgO 
4 units/MOLES of magnesium oxide
Interpreting Chemical Equations
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DAY 3

Ch. 8 – Chemical Equations &
Reactions
Synthesis

the combination of 2 or more
substances to form a compound

only one product
A + B  AB
Synthesis Reactions
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Decomposition

a compound breaks down into 2 or
more simpler substances

only one reactant
AB  A + B
Electrolysis
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Single Replacement


one element replaces another in a compound
Reactants must be an element and a
compound.
 metal replaces metal (+)
 nonmetal replaces nonmetal (-)
A + BC  B + AC
C. Johannesson
Double Replacement

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
Two things replace each other.
Reactants must be two ionic compounds or
acids.
ions in two compounds “change partners”
 cation of one compound combines with
anion of the other
AB + CD  AD + CB
C. Johannesson
E. Double Replacement

Products:
 switch negative ions
 one product must be insoluble
Pb(NO3)2(aq)+ 2KI(aq)  PbI2(s)+2KNO3(aq)
NaNO3(aq)+ KI(aq)  N.R.
Types of Reactions: Combustion

the burning of any substance in O2 to
produce heat
A + O2  B
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Combustion

Products:
 contain oxygen
 hydrocarbons form CO2 + H2O
4 Na(s)+ O2(g)  2 Na2O(s)
C3H8(g)+ 5 O2(g)  3 CO2(g)+ 4 H2O(g)
Combustion Reaction
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DAY 4

Ch. 8 – Chemical Equations &
Reactions
B. Exothermic Reaction
reaction that
releases
energy
 products have
lower PE
than reactants

energy
released
2H2(l) + O2(l)  2H2O(g) + energy
C. Endothermic Reaction
reaction that
absorbs
energy
 reactants have
lower PE
than products

energy
absorbed
2Al2O3 + energy  4Al + 3O2
Activity Series
Activity- ability of an element to react
 Activity Series- list of elements
organized according to the ease with
which they undergo certain reactions
 Metals greater activity greater ease
of loss of electrons (cations)
 Nonmetals greater activity greater
ease of gain of electrons (anions)

Activity Series of the Elements
Activity Series
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