CHEMICAL REATIONS AND EQUATIONS

SUBMITTED BY:KSHITIJ SHARMA

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CHEMICAL REACTIONSYou 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 thereactants.

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Organize Your ThoughtsChemicalreactions

Chemicalequations

Chemicalequations

• Balancing equations

• Predicting products from reactants

• Synthesis• Decomposition• Single replacement• Double replacement• Combustion

Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175

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DESCRIBING A CHEMICAL REACTIONIndications 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 REACTIONSThere are five main signs that indicate a chemical reaction has taken place:

change in color change in odor production of newgases or vapor

input or releaseof energy

difficult to reverse

release

input

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CHEMICAL EQUATIONSDepict the kind of reactants and products and their relative amounts in a reaction.

4 Al(s) + 3 O2(g) 2 Al2O3(s)

The numbers in the front are called stoichiometric coefficients.

The letters (s), (g), and (l) are the physical states of compounds.

reactants product

aluminum oxide

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Chemical Equations

This equation means:

4 Al(s) + 3 O2(g) 2 Al2O3(s)

4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3

4 Al moles + 3 O2 moles yield 2 moles of Al2O3

or

4 g Al + 3 g O2 yield 2 g Al2O3

4 mol Al@27g/mol 3 mol O2@32g/mol 2 mol Al2O3@102g/mol108 g + 96 g = 204 g

aluminum oxide sandpaper

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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

Reactant ProductCH4 O2 CO2 H2O+ + 22

carbon dioxide + water

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ClCl

ClHH

H

ClClCl

Cl HHHH

H2 + Cl2 HCl H2 + Cl2 2 HCl

reactants productsH Cl

reactants products

H Cl

22

2 22 2

11

(unbalanced) (balanced)

UNBALANCED AND BALANCED EQUATIONSPREVIOUS NEXT

?

Visualizing a Chemical ReactionNa + Cl2 NaCl

___ mole Cl2___ mole Na

2

10 5 10

2

10 5 1___ mole NaCl0

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Types of Chemical ReactionsSynthesis (Combination) reaction

Decomposition reaction

ASingle-replacement reaction

BDouble-replacement reaction

Neutralization reaction

Combustion reaction (of a hydrocarbon)

A + B AB

AB A + B

A + BC AC + B

AB + CD AD + CB

HX + BOH BX + HOH

CH + O2 CO2 + H2O

Ause activity series to predictBdriving force…water, gas, or precipitate

Polymerization Polymer = monomer + monomer + …

element compound elementcompound

compound compound compound compound

acid base salt water

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Summary of Classes of Reactions

Chemical reactions

Precipitation reactions

Acid-BaseReactions

Oxidation-ReductionReactions

Combustion Reactions

Decomposition reactions

(Products are elements.)

Synthesis reactions

(Reactants are elements.)

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Summary of Classes of Reactions

Chemical reactions

Precipitation reactions

Acid-BaseReactions

Oxidation-ReductionReactions

Combustion Reactions

Decomposition reactions

Synthesis reactions

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Synthesis ReactionDirect combination reaction (Synthesis)

General form: A + B ABelement or element or compoundcompound

Na

ClNaCl

2 Na + Cl2 2 NaCl

ClNa

NaCl

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Synthesis ReactionDirect combination reaction (Synthesis)

General form: A + B ABelement or element or compoundcompound

Na+Cl -

Na

ClNaCl

Na+ Cl -

2 Na + Cl2 2 NaCl

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H

HH

H

Decomposition Reaction

H

HH

HO

Decomposition reaction2 H2O 2 H2 O2

General form: AB A B

+

+

+compound two or more elements

or compounds

OO

O

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Single and Double Replacement Reactions

Double-replacement reaction

CaCO3 + 2 HCl CaCl2 + H2CO3

General form: AB + CD AD + CB

Single-replacement reaction

Mg + CuSO4 MgSO4 + Cu

General form: A + BC AC + B

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Double Replacement Reaction

K2CO3 (aq)Potassium carbonate

BaCl2 (aq)Barium chloride

2 KCl (aq)Potassium chloride

BaCO3 (s)Barium carbonate

+ +

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Single-Replacement Reactions

FeCl2 + Cu

MgBr2 + Cl2

“Magic blue-earth”

Zinc in nitric acid2

A + BC AC + BGeneral Form

Zn(NO3)2 + H2

Can Fe replace Cu? Yes

Can Zn replace H? Yes

Can Br replace Cl? No

NO REACTION

Fe + CuCl2

Zn + HNO3

MgCl2 + Br2

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OXIDATION & REDUCTIONOxidation, 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 (Mg2+) 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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CORROSIONCorrosion, 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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RANCIDITYRancidity 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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