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The highlights are:
1. Chemical reactions
2. Signs of chemical reactions
3. Writing a chemical equation
4. Characteristics of chemical equations
1.
Chemical Equations &
Reactions
Chemistry A
2.
Chemical Reactions
You should be able to
Classify reactions by type.
Write a balanced molecular equation, complete ionic equation,
and a net ionic equation.
Predict products of reactions given the chemical names of the
reactants.
3.
Organize Your Thoughts
Chemical
reactions
Chemical Chemical
equations equations
• Synthesis
• Balancing equations • Decomposition
• Single replacement
• Predicting products • Double replacement
from reactants • Combustion
Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175
4.
Chemical Reaction
A process in which at least one new
substance is produced as a result of
chemical change.
5.
A Chemical Reaction
Reactants Products
6.
Describing a Chemical Reaction
Indications of a Chemical Reaction
– Evolution of heat, light, and/or sound
– Production of a gas
– Formation of a precipitate
– Color change
7.
Signs of Chemical Reactions
There are five main signs that indicate a chemical reaction has taken place:
release
input
change in color change in odor production of new input or release difficult to reverse
gases or vapor of energy
8.
Writing a Chemical Equation
Chemical symbols give a “before-and-after”
picture of a chemical reaction
Reactants Products
MgO + C CO + Mg
magnesium oxide to form carbon monoxide
reacts with carbon and magnesium
9.
Learning Check E3
12 oz of dough, 4 oz mushrooms, 12 slices
pepperoni, 8 oz cheese and 5 oz tomato sauce
are used to make a pizza. Write a recipe in
words for putting together a pizza.
How would you write the recipe as an
10.
Solution E3
Example: Combine 12 oz dough + 4 oz
mushrooms + 12 slices pepperoni + 8
oz cheese + 5 oz tomato sauce and heat
30 minutes at 350°C to produce 1 pizza
12 oz dough + 4 oz mshrm
+ 12 pep + 8 oz chse 1 pizza
+ 5 oz tom sauce
11.
Chemical Equations
aluminum oxide
Depict the kind of reactants and product
products
and their relative amounts in a reaction.
4 Al(s) + 3 O2(g) 2 Al2O3(s)
The letters (s), (g), and (l) are the
physical states of compounds.
The numbers in the front are called
stoichiometric coefficients.
coefficients
12.
Chemical Equations
aluminum oxide
sandpaper
4 Al(s) + 3 O2(g) 2 Al2O3(s)
4 g Al + 3 g O2 yield 2 g Al2O3
This equation means:
4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3
or
4 Al moles + 3 O2 moles yield 2 moles of Al2O3
4 mol Al@27g/mol 3 mol O2@32g/mol 2 mol Al2O3@102g/mol
108 g + 96 g = 204 g
13.
Chemical Equations
Because the same atoms are present
in a reaction at the beginning (reactants)
and at the end (products), the amount
of matter in a system does not change.
The Law of Conservation of Matter
20%
100% 100%
Chemical
80%
Factory
Kotz web
14.
Chemical Equations
Because of the principle of the conservation of matter,
matter
An equation must be balanced.
balanced
It must have the same number of atoms
of the same kind on both sides.
Lavoisier, 1788
15.
Characteristics of Chemical Equations
• The equation must represent known
facts.
• The equation must contain the correct
formulas for the reactants and products.
• The law of conservation of mass must
be satisfied.
16.
Chemical Equations
• Reactants – the substances that exist before a
chemical change (or reaction) takes place.
• Products – the new substance(s) that are formed
during the chemical changes.
• CHEMICAL EQUATION indicates the reactants and
products of a reaction.
REACTANTS PRODUCTS
17.
Word Equations
• A WORD EQUATION describes chemical change using
the names of the reactants and products.
Write the word equation for the reaction of methane gas
with oxygen gas to form carbon dioxide and water.
methane + oxygen carbon dioxide + water
Reactant Product
CH4 + 2 O2 CO2 + 2 H2O
18.
Unbalanced and Balanced Equations
H
Cl Cl H H
Cl H
H
Cl Cl Cl
Cl
H2 + Cl2 HCl (unbalanced) H2 + Cl2 2 HCl (balanced)
reactants products reactants products
H 2 1 H 2 2
Cl 2 1 Cl 2 2
19.
Visualizing a Chemical Reaction
2 Na + Cl 2 2 NaCl
10 mole Na
___ 5 mole Cl2
___ 10
? mole NaCl
___
20.
Visualizing a Chemical Reaction
2 Na + Cl 2 2 NaCl
21.
Meaning of Chemical Formula
Symbol Meaning Composition
H2O One molecule Two H atoms and one O atom
of water:
2 H 2O Two molecules Four H atoms and two O atoms
of water:
H 2O 2 One molecule Two H atoms and two O atoms
of hydrogen
peroxide:
22.
Balancing Chemical Equations
Balanced Equation – one in which the number of
atoms of each element as a reactant is equal to the
number of atoms of that element as a product
What is the relationship between conservation of mass and
the fact that a balanced equation will always have the same
number of atoms of each element on both sides of an equation?
Determine whether the following equation is balanced.
2 Na + H2O 2 NaOH + H2
2 Na + 2 H2O 2 NaOH + H2
23.
Balancing Chemical Equations
• Write a word equation for the reaction.
• Write the correct formulas for all reactants
and products.
• Determine the coefficients that make the
equation balance.
24.
Balancing Chemical Equations
Other examples
NO(g) + O2(g) NO2(g) is it balanced?
Is this balanced? NO(g) + O(g) NO2(g)
Is this OK?
Is this balanced? NO(g) + ½ O2(g) NO2(g)
Is this OK?
25.
Balancing Chemical Equations
An important point to remember
2 NO(g) + O2(g) 2NO2(g)
The 2 to the left of NO(g) and NO2(g) refers to the number
of molecules present in the balanced equation.
It is a “multiplier” for every atom in the molecule.
The subscript 2 in O2 (g) and NO2(g) refers to the number
of atoms of this type that are present in each molecules
(or ionic compound).
26.
Write a balanced equation for the reaction between chlorine
and sodium bromide to produce bromine and sodium chloride.
1) Write a word equation for the reaction.
chlorine + sodium bromide bromine + sodium chloride
2) Write the correct formulas for all reactants and products.
Cl2 + NaBr Br2 + NaCl
3) Determine the coefficients that make the equation balance.
Cl2 + 2 NaBr Br2 + 2 NaCl
27.
Write the balanced equation for the reaction between
aluminum sulfate and calcium chloride to form a white
precipitate of calcium sulfate.
1) Write a word equation for the reaction.
? ?
aluminum sulfate + calcium chloride calcium sulfate + aluminum chloride
2) Write the correct formulas for all reactants and products.
Al2(SO4)3 + CaCl2 CaSO4 + AlCl3
3) Determine the coefficients that make the equation balance.
Al2(SO4)3 + 3 CaCl2 3 CaSO4 + 2 AlCl3
28.
CH4 + 2 O2 CO2 + 2 H2O
Reactants Products
1 C atom 1 C atom
4 H atoms 4 H atoms
4 O atoms 4 O atoms
29.
Reactants Products
+
C(s) + O2(g) CO2(g)
carbon oxygen carbon dioxide
Reactants Product
1 carbon atom 1 carbon atom
2 oxygen atoms 2 oxygen atoms
catalyst – speeds up reaction
+ Pt
2 H2(g) + O2(g) Pt
2 H2O (l)
hydrogen oxygen water
Reactants Product
2 hydrogen atoms
4 2 hydrogen atoms
4
2 oxygen atoms 1 oxygen atoms
2
Unbalanced
30.
Showing Phases in
Chemical Equations
H2O(s) H2O(l) H2O(g)
Solid Phase – the substance is relatively rigid and has a
definite volume and shape. NaCl(s)
Liquid Phase – the substance has a definite volume, but is
able to change shape by flowing. H2O(l)
Gaseous Phase – the substance has no definite volume or
shape, and it shows little response to gravity. Cl2(g)
31.
Additional Symbols Used in Chemical Equations
“Yields”; indicates result of reaction
Used to indicate a reversible reaction
A reactant or product in the solid state;
also used to indicate a precipitate
Alternative to (s), but used only to indicate a precipitate
A reactant or product in the liquid state
A reactant or product in an aqueous solution
(l) (dissolved in water)
A reactant or product in the gaseous state
32.
Additional Symbols Used in Chemical Equations
Alternative to (g), but used only to indicate a gaseous
product
Reactants are heated
2 atm
Pressure at which reaction is carried out, in this case 2 atm
Pressure at which reaction is carried out exceeds normal
atmospheric pressure
0 oC
Temperature at which reaction is carried out, in this case 0
o
C
MnO2
Formula of catalyst, in this case manganese (IV) oxide,
used to alter the rate of the reaction
33.
Types of Chemical Reactions
Synthesis (Combination) reaction A + B AB
Decomposition reaction AB A + B
Single-replacement reaction A + BC AC + B
element compound compound element
Double-replacement reaction AB + CD AD + CB
compound compound compound compound
Neutralization reaction HX + BOH BX + HOH
acid base salt water
Combustion reaction (of a hydrocarbon) CH + O2 CO2 + H2O
Polymerization Polymer = monomer + monomer + …
A
use activity series to predict
B
driving force…water, gas, or precipitate
34.
Types of Chemical Reactions
Synthesis (Combination) reaction A + B AB
Decomposition reaction AB A + B
Single-replacement reaction A + BC AC + B
Double-replacement reaction AB + CD AD + CB
Neutralization reaction HX + BOH BX + HOH
Combustion reaction (of a hydrocarbon) CH + O2 CO2 + H2O
Polymerization Polymer = monomer + monomer + …
use activity series to predict
A
B
driving force…water, gas, or precipitate
35.
Synthesis Reaction
Direct combination reaction (Synthesis)
2 Na + Cl2 2 NaCl
Na Cl
Cl
Na
General form: A + B AB
element or element or compound
compound compound
36.
Synthesis Reaction
Direct combination reaction (Synthesis)
2 Na + Cl2 2 NaCl
Na Cl Na+ Cl -
Cl Cl - Na+
Na
General form: A + B AB
element or element or compound
compound compound
37.
Decomposition Reaction
Decomposition reaction
2 H 2O 2 H2 + O2
H
O
H
+
H
O
H
General form: AB A + B
compound two or more elements
or compounds
38.
Single and Double Replacement
Reactions
Single-replacement reaction
Mg + CuSO4 MgSO4 + Cu
General form:
A + BC AC + B
Double-replacement reaction
CaCO3 + 2 HCl CaCl2 + H2CO3
General form:
AB + CD AD + CB
39.
Double Replacement Reaction
K2CO3 (aq) + BaCl2 (aq) 2 KCl (aq) + BaCO3 (s)
Potassium carbonate Barium chloride Potassium chloride Barium carbonate
40.
Synthesis Reactions
6 CO2 + 6 H2O C6H12O6 + 6 O2
Formation of water
2 H2 + O2 2 H 2O
Formation of salt
2 Na + Cl2 2 NaCl
General Form
A + B C
41.
Decomposition Reactions
Hydrogen Peroxide
2 H2O2 2 H 2O + O2
Electrolysis of water
electricity
2 H2O 2 H2 + O2
Nitrogen triiodide
2 NI3 N2 + 3 I2
General Form
AB A + B
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