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Chemical reactions

Course 8

General Chemistry Course

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CHEMICAL REACTIONS

Reactants: Zn + I 2 Product: Zn I 2

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Chemical Equations

Their Job: Depict the kind of reactants andproducts and their relative amounts in areaction.

4 Al (s) + 3 O 2 (g) ---> 2 Al2O 3 (s)The numbers in the front are calledstoichiometric ____________ The letters (s), (g), and (l) are the physical

states of compounds.

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Chemical reactions occur when bonds between theoutermost parts of atoms are formed or broken

Chemical reactions involve changes in matter, themaking of new materials with new properties, and

energy changes. Symbols represent elements, formulas describe

compounds, chemical equations describe a chemicalreaction

Introduction

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Chemical equations show the conversion of reactants (the molecules shown on the left of the arrow) into products (the molecules shownon the right of the arrow).

A + sign separates molecules on the sameside

The arrow is read as yields Example

C + O 2 CO 2 This reads carbon plus oxygen react to yield

carbon dioxide

Parts of a Reaction Equation

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The charcoal used in a grill is basically carbon. The carbonreacts with oxygen to yield carbon dioxide. The chemicalequation for this reaction, C + O 2 CO 2, contains the sameinformation as the English sentence but has quantitativemeaning as well.

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Because of the principle of theconservation of matter ,

an equation must bebalanced .

It must have the same

number of atoms of thesame kind on both sides.

Lavoisier, 1788

Chemical Equations

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Solid ___ Liquid (l) Gas ___ Aqueous solution (aq) Catalyst H2SO 4

Escaping gas ( ) Change of temperature ( )

Symbols Used in Equations

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When balancing a chemical reaction you may add coefficients infront of the compounds to balance the reaction, but you may

not change the subscripts.Changing the subscripts changes the compound. Subscripts

are determined by the valence electrons (charges for ionicor sharing for covalent)

Balancing Equations

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Subscripts vs. Coefficients The subscripts tell

you how many atomsof a particular elementare in a compound.

The coefficient tellsyou about thequantity, or number,of molecules of thecompound.

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All chemical reactions can be placed into one of sixcategories. Here they are, in no particular order:

1. Combustion : A combustion reaction is when oxygen combines withanother compound to form water and carbon dioxide. Thesereactions are exothermic, meaning they produce heat. An exampleof this kind of reaction is the burning of napthalene:

2. Synthesis : A synthesis reaction is when two or more simple compoundscombine to form a more complicated one. These reactions come in thegeneral form of:

One example of a synthesis reaction is the combination of iron and sulfurto form iron (II) sulfide:

A+B AB

8 Fe + S 8 8 FeS

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3. Decomposition : A decomposition reaction is the opposite of asynthesis reaction - a complex molecule breaks down to make simplerones. These reactions come in the general form:

AB A + B

One example of a decomposition reaction is the electrolysis of water tomake oxygen and hydrogen gas:

2 H 2O 2 H 2 + O 2

4. Single displacement : This is when one element trades places with anotherelement in a compound. These reactions come in the general form of:

One example of a single displacement reaction is when magnesium replaceshydrogen in water to make magnesium hydroxide and hydrogen gas:

A + BC AC + B

Mg + 2 H 2O Mg(OH) 2 + H 2

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5. Double displacement : This is when the anions and cations of twodifferent molecules switch places, forming two entirely differentcompounds. These reactions are in the general form:

AB + CD AD + CBOne example of a double displacement reaction is the reaction of lead(II) nitrate with potassium iodide to form lead (II) iodide and potassiumnitrate:

Pb(NO3)2 + 2 KI PbI 2 + 2 KNO 3

6. Acid-base : This is a special kind of double displacement reaction thattakes place when an acid and base react with each other. The H+ ion in theacid reacts with the OH- ion in the base, causing the formation of water.

Generally, the product of this reaction is some ionic salt and water:

One example of an acid-base reaction is the reaction of hydrobromic acid(HBr) with sodium hydroxide:

HA + BOH AB + H 2O

HBr + NaOHNaBr + H

2O

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METALS

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Physical Properties

1. Melting Temperature (T m )Tlow

Gr. 1 and 2

Pb (lead), Sn (tin)

Thigh W, Cr, V, Mo.

2. Density - light metals ( < 5 g / cm 3) Gr. 1, 2, Al, Ti

- heavy metals ( > 5 g / cm3) Pt, Au, Ag, Pb, Hg,etc

3. Colors

a) In bulk, metals are opaque; in fresh cut metals are shining.

White (Ag, Al, Pt, Na) Gray Black (W - tungsten, Pt porous)Violet: K (potassium)Red: Cu (copper)

Yellow: Au (gold), Cd (cadmium). b) in thin film(10 -9m = nm) all the metals are - transparentBrown: AuBlue: Ag, Co.

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Obtaining metals

Metallurgical Processes

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Corrosion

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