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CHEMICAL REATIONS AND
EQUATIONS
SUBMITTED BY: SUBMITTED TO:
KSHITIJ SHARMA MENU MAM

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CHEMICAL REACTIONS
You should be able to
Classify reactions by type.
Write a balanced molecular equation, complete ionic equation,
and a net ionic equation.
Balance oxidation-reduction reactions.
Predict if a precipitate will form using the solubility rules.
Predict products of reactions given the chemical names of the
reactants.

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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

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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

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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

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CHEMICAL EQUATIONS aluminum oxide
product
Depict the kind of reactants and 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.

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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

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CHARACTERSTICS OF CHEMICAL EQUATION
• 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.

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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

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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

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UNBALANCED AND BALANCED EQUATIONS
H
Cl Cl
H H
Cl H
Cl Cl Cl
H
Cl
H
H
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

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Visualizing a Chemical Reaction
2 Na + Cl2 2 NaCl
10
___ mole Na 5
___ mole Cl2 1___ mole NaCl
10
?
0

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Types of Chemical Reactions
Synthesis (Combination) reaction A + B  AB
Decomposition reaction AB  A + B
ASingle-replacement reaction A + compound compound +element
element
BC AC B
BDouble-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 + …
Ause activity series to predict
Bdriving force…water, gas, or precipitate

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Summary of Classes of Reactions
Chemical reactions
Precipitation Oxidation-Reduction Acid-Base
reactions Reactions Reactions
Synthesis Decomposition
Combustion reactions reactions
Reactions (Reactants are (Products are
elements.) elements.)

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Summary of Classes of Reactions
Chemical reactions
Precipitation Oxidation-Reduction Acid-Base
reactions Reactions Reactions
Combustion Synthesis Decomposition
Reactions reactions reactions

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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

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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

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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

19. 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:
PREVIOUS AB + CD  AD + CB NEXT

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Double Replacement Reaction
K2CO3 (aq) + BaCl2 (aq) 2 KCl (aq) + BaCO3 (s)
Potassium carbonate Barium chloride Potassium chloride Barium carbonate

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Single-Replacement Reactions
“Magic blue-earth”
Fe + CuCl2 FeCl2 + Cu
Can Fe replace Cu? Yes
Zinc in nitric acid
Zn + 2
HNO3 Zn(NO3)2 + H2
Can Zn replace H? Yes
NO REACTION
MgCl2 + Br2 MgBr2 + Cl2
Can Br replace Cl? No
General Form
A + BC AC + B

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OXIDATION & REDUCTION
Oxidation, in its original sense, refers to the combination of oxygen with another substance to produce a compound called an oxide. Iron, in the presence of water,
combines with atmospheric oxygen to form a hydrated iron oxide, commonly called rust.
Oxidation-reduction reactions combine a chemical wanting to gain electrons with a chemical willing to give up electrons. Such a reaction may be generally represented as
follows: X·+ Y ⇄ XY· (where · represents an electron). The material that loses electrons is said to be oxidized and is called a reducing agent; the material that gains electrons
is reduced and is called an oxidizing agent (see Chemical Reaction). The most common examples of oxidation are those reactions involving the combination of materials with
the element oxygen, such as the rusting of iron or the burning of any combustible material in air. The equation for the burning of magnesium is: 2Mg(s) + O2(g) → 2MgO(s).
When magnesium reacts with oxygen, each magnesium atom gives two electrons to oxygen. The positive magnesium ions (Mg 2+) then combine with negative oxygen ions (O2-)
to form solid magnesium oxide (MgO). In this reaction, magnesium (the reducing agent) is oxidized, and oxygen (the oxidizing agent) is reduced.
The reaction between metallic sodium and chlorine gas is an oxidation-reduction reaction that does not involve oxygen:
This way of writing the oxidation-reduction reaction illustrates that both elements attain a noble-gas configuration (completely filled outer
shells). Sodium loses an electron, achieving the noble gas configuration of neon, and chlorine gains an electron, achieving the noble gas
configuration of argon.

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CORROSION
Corrosion, partial or complete wearing away, dissolving, or softening of any substance by chemical or electrochemical reaction with its environment. The term corrosion specifically
applies to the gradual action of natural agents, such as air or salt water, on metals.
The most familiar example of corrosion is the rusting of iron, a complex chemical reaction in which the iron combines with both oxygen and water to form hydrated iron oxide. The oxide is
a solid that retains the same general form as the metal from which it is formed but, porous and somewhat bulkier, is relatively weak and brittle.
Three methods may be used to prevent the rusting of iron: (1) alloying the iron so that it will be chemically resistant to corrosion; (2) coating it with a material that will react with the
corroding substances more readily than the iron does and thus, while being consumed, protect the iron; and (3) covering it with an impermeable surface coating so that air and water
cannot reach it. The alloying method is the most satisfactory but the most expensive. A good example is stainless steel, in which chromium or chromium and nickel are alloyed with the
iron; this alloy is not only absolutely rustproof but will even resist the action of such corrosive chemicals as hot, concentrated nitric acid. The second method, protection with an active
metal, is also satisfactory, but expensive. The most common example of this method is galvanizing, in which iron is covered with zinc. In the presence of corrosive solutions, an electric
potential is set up between the iron and the zinc, causing the zinc to dissolve but protecting the iron as long as any zinc remains. The third method, protection by coating the surface with
an impermeable layer, is the least expensive and therefore the most common. It is satisfactory as long as no crack appears in the coating. Once the coating cracks, however, rusting
proceeds at least as fast as it would have with no protection. If the protective layer is an inactive metal, such as tin or chromium, an electric potential is set up, protecting the layer but
acting on the iron and causing the rusting to proceed at an accelerated rate. The most satisfactory coatings are baked enamels; the least expensive are such paints as red lead.
Some metals, such as aluminium, although very active chemically, appear not to corrode under normal atmospheric conditions. Actually, aluminium corrodes rapidly, and a thin,
continuous, transparent layer of oxide forms on the surface of the metal, protecting it from further rapid corrosion. Lead and zinc, although less active than aluminium, are protected by
similar oxide films. Copper, a comparatively inactive metal, is slowly corroded by air and water in the presence of such weak acids as carbonic acid, producing a green, porous, basic
carbonate of copper. Green corrosion products, called verdures or patina, appear on such copper alloys as brass and bronze, as well as on pure copper.
Some metals, called noble metals, are so inactive chemically that they do not suffer corrosion from the atmosphere; among them are silver, gold, and platinum. A combination of air,
water, and hydrogen sulphide will act on silver, but the amount of hydrogen sulphide normally present in the atmosphere is so small that the degree of corrosion is negligible except for
the black discoloration, called tarnishing, produced by the formation of silver sulphide.
The corrosion of metals is more of a problem than that of other materials. Glass is corroded by strongly alkaline solutions and concrete by sulphate-bearing waters. The corrosion
resistance of glass and concrete can be greatly increased by changes in their composition.

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RANCIDITY
Rancidity is the chemical decomposition of fats, oils and other lipids. There are three basic types of rancidity. Hydrolytic rancidity occurs when water splits
fatty acid chains away from the glycerol backbone in glycerines. Oxidative rancidity occurs when the double bonds of an unsaturated fatty acid react
chemically with oxygen. Microbial rancidity refers to a process in which microorganisms such as bacteria use their enzymes, including lipases, to break down
chemical structures in the fat. In each case, these chemical reactions result in undesirable doors and flavours.
Rancidity refers to the spoilage of a food in such a way that it becomes undesirable (and usually unsafe) for consumption. When people say that a food has "gone bad," what they
're usually talking about is rancidity. Most of the time, but not always, rancidity can change the doors or flavours of a food in such a way that it becomes very unpleasant to smell
or taste.

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