Chemical Reactions

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Chemical Reactions
Which of the following are
examples of chemical change?
•
•
•
•
•
•
•
•
•
Digestion
Melting an ice cube
Running a car
Decomposition
Dissolving sugar in water
Boiling water
Photosynthesis
Cellular Respiration
A nail rusting
Chemical Reaction (or Chemical
Change)
• The process by which the atoms of one
or more substances are REARRANGED
to form different substances
Evidence of a Chemical Reaction
1. Temperature change
Exothermic Reaction-heat is given off
Endothermic Reaction-heat is absorbed
Exothermic Reaction
Endothermic Reaction
Classify each of the following as
endothermic or exothermic.
• A log burning in the fireplace.
• A chemical ice pack
• Baking soda is added to vinegar causing the test
tube to become cold to the touch.
• A hand warmer
• Drain cleaner is added to a clogged pipe
causing the pipes to become warm.
• Photosynthesis
• Cellular respiration
• Baking a cake
Evidence of a Chemical Reaction
2. Color Change
Evidence of a Chemical Reaction
3. Production of an Odor
Evidence of a Chemical Reaction
4. Production of a gas (bubbles)
Evidence of a Chemical Reaction
5. Formation of a solid called a precipitate
Evidence of a Chemical
Reaction
6. Production of other forms of energy such
as light.
Chemical equation
A written expression of a
chemical reaction
Reactant  Product
(Starting Substance) (New substance
that forms)
Symbols used in
chemical equations
+
Separates 2 or
more reactants
or products

Separates
reactants from
products
(s)
Solid state
(l)
Liquid state
(g)
Gaseous State
(aq)
Dissolved in
water
∆
Heat is added
Chemical Equations
Reaction: Solid aluminum reacts with liquid
bromine to produce solid aluminum
bromide.
Word Equation-the description of a reaction
is written according to the following format:
Reactant 1 + Reactant 2  Product 1
Aluminum (s) + Bromine (l)  Aluminum
Bromide (s)
Chemical Equations
Word Equation
Aluminum (s) + Bromine (l)  Aluminum
Bromide (s)
Skeleton Equation-formulas/symbols are
used to represent names of compounds
and elements.
Al (s) + Br2(l)  AlBr3 (s)
Practice writing word and
skeleton equations:
• Write the equation for the reaction
observed in lab.
• Write the equation for the endothermic
reaction that was observed.
Chemical Equations
• A complete chemical equation is a
statement that uses chemical formulas,
states of matter and coefficients to
represent the substances involved and
how much is needed to fully react.
Balancing Chemical Equations
A chemical equation is not complete until the
atoms on the reactant side equal the
atoms on the product side.
COEFFICIENTS (NUMBERS IN FRONT
OF THE FORMULA) are used to balance
equations.
___Al (s)
+
___Br2(l) 
___AlBr3 (s)
Why must we balance
equations?
• Law of conservation of mass-during
chemical equations, matter cannot be
created or destroyed. Atoms are only
rearranged.
• Therefore, the number and kinds of atoms
making up the reactants must be the same
as those making up the products.
• Mass of reactants = Mass of products
Types of Chemical Reactions
Synthesis ReactionsTwo or more substances combine to form a
single product
• General Form: A + B  AB
• Example
N2 (g) + 3H2(g)  2NH3 (g)
Na2O + H2O  2NaOH
Types of Chemical Reactions
Decomposition ReactionsA single reactant breaks down into two or
more elements or new compounds
• General Form: AB  A + B
• Example:
NH4NO3 (s)  N2O (g) + 2H2O (g)
2HgO  2Hg + O2
Types of Chemical Reactions
Single Replacement reactionsAtoms of one element replace atoms of another element in a
compound
• General Form: A + BC  B + AC
• Metals replace metals and nonmetals replace nonmetals
• Example:
Cu(s) + AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq)
Cu (metal) replaces Ag (metal) in the compound because it is
more reactive.
Cl2 + NaBr  Br2 + NaCl
Cl2 (nonmetal) replaces Br2 (nonmetal) because it is more
reactive.
Types of Chemical Reactions
How do I know if an one atom can replace
another?
There is a table of reactivity. It ranks metals
from most reactive (at the top) to least
reactive (at the bottom)
Reactivity Table
Most Active Metals
Least Active Metals
Li
Rb
K
Ca
Na
Mg
Al
Mn
Zn
Fe
Ni
Sn
Pb
Cu
Ag
Pt
Au
Most Active Nonmetals
F
Cl
Br
I
Least Active Nonmetals
Which of the following reactions
can take place?
• I2 + NaF  F2 + NaI
• Mg + HCl  MgCl2 + H2
• Cu + MgSO4  CuSO4 + Mg
• K + NaOH  KOH + Na
Types of Chemical Reactions
Double Replacement ReactionsAtoms in one compound replace atoms in
another compound
General Form: AB + CD  AD + CB
NaOH (aq) + CuCl2(aq)  2NaCl(aq) + Cu(OH)2 (s)
Types of Chemical Reactions
Combustion ReactionCombustion reactions occur when oxygen
combines with a substance and energy is
released (exothermic)
• General Form: CxHy + O2  CO2 + H2O
• Examples:
C (s) + O2 (g)  CO2(g)
CH4 + O2  CO2 + H2O
For each of the following,
identify the type of reaction
•
Fe + H2SO4  Fe2(SO4)3 +
•
C 2H 6 +
•
Al +
•
KClO3 
•
KNO3 +
O2 
O2 
H 2O +
H2
CO2
Al2O3
KCl +
H2CO3 
O2
K2CO3 +
HNO3
Specific Rules for Reactions
• Decomposition
– Metallic Carbonates, when heated,
breakdown to form metallic oxides and carbon
dioxide
ZnCO3 (s)  ZnO (s) + CO2 (g)
Specific Rules for Reactions
• Decomposition
– Many Metallic Hydroxides when heated,
decompose into metallic oxides and water
Mg(OH)2 (s)  MgO(s) + H2O (g)
Specific Rules for Reactions
• Decomposition
– Metallic chlorates, when heated, decompose
into metallic chlorides and oxygen gas.
KClO3 (s)  KCl (s) + O2 (g)
Specific Rules for Reactions
• Single Replacement Reaction
– Replacement of hydrogen in acids by metals
2Al (s) + 6HCl (aq)  2AlCl3 (aq) + 3H2 (g)
Specific Rules for Reactions
• Single Replacement
– Replacement of hydrogen in water by metals
Fe (s) + 2H2O (l)  Fe(OH)2 (s) + H2 (g)
Specific Rules for Reactions
• Double Replacement Reaction
– Neutralization Reaction is a type of chemical
reaction that occurs between an acid and
base to produce a salt and water.
Ca(OH)2 (aq) + 2HCl (aq)  CaCl2(aq) + 2H2O (l)
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