Chemistry

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Chemical Reactions

A chemical change: any change in which anew substance is formed.

Evidence of a Chemical Change:

Release of energy as heat

Release of energy as light

Change in colour

Formation of a gas

Change in odour…

Types of Chemical Reactions

Most of the reactions we will study fall intoone of the following categories

1 !reci"itation Reactions

# Acid base reactions $later

% &'idation(Reduction Reactions

Oxidation-Reduction

An alternative de)nition of o'idation(reduction

Heat of Reaction

*n almost all chemical reactions+ heatis either given o, or absorbed.

Types of Chemical Reactions

1. -eutraliation: Acid$/ 0 ase$&/ salt 0 /$&/

#. Combustion: A 0 o'ygen C&# 0

/#&

%. 2ynthesis: A 0 A

3. 4ecom"osition: A A 0

5. 2ingle dis"lacement: A 0 C AC 0

6. 4ouble dis"lacement: A 0 C4 A4

0 C

1.Synthesis Reactions

2ynthesis reactions are also 7nown asF&RMA8*&- reactions.

8wo or more reactants $usually elements 9ointo form a com"ound.

– A + B AB

– where A and re"resentelements

– 8he elements may form ioniccom"ounds+ li7e…

– 2odium metal and chlorine gascombine to form sodiumchloride.

–

#-a 0 Cl# →

#-aCl2.ecomposition Reactions

• 4ecom"osition reactions are theo""osite of synthesis reactions.

– A com"ounds brea7s down intotwo or more "roducts $oftenelements.

– AB → A + B

where A and re"resent

elements

!.Sin"le Replacement Reactions

• 2ingle re"lacement reactions re"laceone element from a com"ound withanother element.

– A com"ound and an elementreact+ and the element switches"laces with "art of the originalcom"ound.

• A + BC B + AC whereA is a metal+ or

• A + BC C + BA where

A is a non(metal

#.ou$le Replacement Reactions

• 4ouble re"lacement reactions swa"elements between # com"ounds thatreact together to form two newcom"ounds.

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– 8wo com"ounds react+ withelements switching "lacesbetween the originalcom"ounds.

AB + C A + CB

%.&eut'ali(ation Reactions

•

-eutraliation reactions occur when anacid $most com"ounds starting with /and a base $most com"ounds endingin &/ react to form a salt and water.

• -eutraliation reactions are a ty"e ofdouble re"lacement.

• Acid 0 base → salt 0

water

H) + *OH *) + H2O

here ; and M are elements

.Com$ustion Reactions

• Combustion reactions occur when acom"ound or element react witho'ygen to release energy and "roducean o'ide.

– Also sometimes referred to ashydrocarbon combustion.

C)H , + O2 CO2 + H2O

where ; and < re"resentintegers

S**AR, O R/ACT0O&S

uide to $alance a Chemical

/uation

Balancin" /uations

Chemical reactions occur whenbonds $between the electrons ofatoms are formed or bro7en

Chemical reactions involve

changes in the chemicalcom"osition of matter

the ma7ing of new materials

with new "ro"erties

energy changes:

ond brea7ing absorbs Energy$endothermic "rocess

ond ma7ing releases Energy$e'othermic "rocess

2ymbols re"resent elements

Formulas describe com"ounds

Chemical e=uations describe achemical reaction

Chemical /uations

A chemical e=uation is written as ane'"ression similar to a mathematic e=uationthat can be com"ared to a reci"e that achemist follows in order to "roduce desiredresults.

8heir >ob: 4e"ict the 7ind of reactants

and "roducts and their relative amounts in areaction.

3 Al $s 0 % &# $g (((? # Al#&% $s

8he numbers in the front are called

2toichiometric coe@cients

8he letters $s+ $g+ and $l are the"hysical states of com"ounds.

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ecause of the "rinci"le of the

conservation of matter $matter cannotbe created or destroyed an e=uationmust be balanced.

*t must have the same number of

atoms of the same 7ind on both sides.

aw of Conservation of Energy MB28

A2& E F&&E4

Energy changes are written in $endo(D

e'othermic reactions All chemicale=uations have reactants and"roducts.

e e'"ress a chemical e=uation as

follows:

Reactants → !roducts

8he arrow is e=uivalent to an math. hen we describe the e=uationwe use the word yieldsG or"roducesG instead of e=uals

E'am"le

C 0 &# C&#

8his reads carbon "lus o'ygen react

to yield carbon dio'ideG

Balancin" a Chemical /uation

A chemical e=uation is balanced when

the ions or atoms found on thereactant side of the e=uation e=ualsthat found on the "roduct side.

8he arrow can be considered the

balance "oint.

Sym$ols sed in /uations

2olid $s

i=uid $l

Has $g

A=ueous solution $a=

Catalyst /#2& 3 or !t

Esca"ing gas $↑

Change of tem"eratureD heat energy

$∆ or 0 %7> or I %7>

Chemical Reactions an d Chemical

/uations

Reactants !roducts

4riving forces:

a Color change

b Formation of a solidD"reci"itate

c Evolution of a gas

d Evolution or absor"tion of heat

Balancin" /uations

hen balancing a chemical reaction

you may add coe@cients in front of

the com"ounds to balance thereaction+ but you may not change thesubscri"ts.

Changing the subscri"ts changes the

com"ound. 2ubscri"ts are determinedby the valence electrons $charges forionic or sharing for covalent

8hin7 bac7 to naming com"oundsD

determining formulas. -aCl e'ists+because -a is 0 and Cl is (+ but -aCl#

does -&8 e'ist since you would nothave a neutral com"ound <ou canJt

9ust add a number to a formula tobalance an e=uation.

*olecula' 3ei"ht and o'mula 3ei"ht

8he molecular weight of a substance is

the sum of the atomic weights of allthe atoms in a molecule of thesubstance.

8he formula weight of a substance is

the sum of the atomic weights of allthe atoms in one formula unit of thecom"ound+ whether molecular or not.

*ass and *oles of a Su$stance

• 8he Mole Conce"t

A mole is de)ned as the =uantity of a givensubstance that contains as many moleculesor formula units

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-aCl

2&#

• 8he molar mass of a substance is themass of one mole of a substance.

– For all substances+ molar mass+in grams "er mole+ isnumerically e=ual to theformula weight in atomic massunits.

– 8hat is+ one mole of anyelement weighs its atomic massin grams.

*ole calculations

– Converting the number of molesof a given substance into itsmass+ and vice versa+ isfundamental to understandingthe =uantitative nature ofchemical e=uations.

A""of massmolecular)(oratomic

A""of mass A""of =moles

o'mula 4ei"ht is the sum of the atomicmasses

$in amu in a formula unit of an ioniccom"ound.

1-a ##.KK amu

1Cl 0 %5.35amu

-aCl 5L.33amu

Atomic 3ei"hts

*olecula' mass $or molecular weight isthe sum of

the atomic masses $in amu in a molecule.

12 %#.N amu

#& 0 # ' 16.

amu

2&# 63.N amu

*ola' *ass

Molar mass $formula weight can be used toconvert from grams to moles+ and frommoles to grams

Moles of AGrams of A

Use molar mass (g/mol)as the conversion factor

You are given one of these

and asked to find the other

ete'minin" Chemical o'mulas

• 8he "ercent com"osition of acom"ound is the mass "ercentage ofeach element in the com"ound.

– e de)ne the mass "ercentageof AG as the "arts of AG "erhundred "arts of the total+ bymass. 8hat is+

%100

wholetheof mass

in wholeA""of mass A""%mass ×=

• ete'minin" the fo'mula of a

compound f'om the pe'cent

composition.

– 8he "ercent com"osition of acom"ound leads directly to itsem"irical formula.

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– An em"irical formula $orsim"lest formula for acom"ound is the formula of thesubstance written with thesmallest integer $wholenumber subscri"ts.

• ete'minin" the empi'ical fo'mula

f'om the pe'cent composition.

– For the "ur"oses of thiscalculation+ we will assume wehave 1. grams of benoicacid.

– 8hen the mass of each elemente=uals the numerical value ofthe "ercentage.

– 2ince '+ y+ and in our formulare"resent mole(mole ratios+ we

must )rst convert these massesto moles.

• ete'minin" the molecula'

fo'mula f'om the empi'ical

fo'mula.

– An em"irical formula gives onlythe smallest whole(number ratioof atoms in a formula.

– 8he molecular formula should

be a multi"le of the em"iricalformula $since both have thesame "ercent com"osition.

– 8o determine the molecularformula+ we must 7now themolecular weight of thecom"ound.

Stoichiomet'y5 6uantitati7e Relations in

Chemical Reactions

• 2toichiometry is the calculation of the

=uantities of reactants and "roductsinvolved in a chemical reaction.

– *t is based on the balancedchemical e=uation and on therelationshi" between mass andmoles.

– 2uch calculations arefundamental to most=uantitative wor7 in chemistry.

*ola' 0nte'p'etation of a Chemical

/uation

• 8he balanced chemical e=uation canbe inter"reted in numbers ofmolecules+ but generally chemistsinter"ret e=uations as mole-to-

moleG relationshi"s.

– For e'am"le+ the /aber "rocessfor "roducing ammonia involvesthe reaction of hydrogen andnitrogen.

8imitin" Rea"ent

8he limitin" 'eactant $or limitin"

'ea"ent is the reactant that is entirelyconsumed when the reaction goes tocom"letion

– 8he limiting reagent ultimatelydetermines how much "roductcan be obtained.

– For e'am"le+ bicycles re=uireone frame and two wheels. *fyou have # wheels but only 5frames+ it is clear that thenumber of frames willdetermine how many bicyclescan be made.

Theo'etical and 9e'cent ,ield• 8he theo'etical yield of "roduct is

the ma'imum amount of "roduct thatcan be obtained from given amountsof reactants.

• 8he pe'centa"e yield is the actualyield $e'"erimentally determinede'"ressed as a "ercentage of thetheoretical yield $calculated.

%100yieldltheoretica

yieldactual

Yield% ×=

8a4 of Conse'7ation of *ass

• hen a chemical reaction occurs+ newcom"ounds are created+ B8…

– &o ne4 matte' is c'eated o'

dest'oyedO atoms are 9ust

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'ea''an"ed as the atomschan"e pa'tne's to form newcom"ounds.

– *f there are % atoms of o'ygenin the reactants+ there MB28 be! atoms of o'ygen in the"roducts.

– &um$e' of each atom in'eactants : num$e' of each

atom in p'oducts.

• 8he law of conservation of mass:

– Mass of reactants mass of"roducts

9e'cent Composition

; the "ercentage by mass of eachelement in a com"ound

o'mulas

!ercent com"osition allow you tocalculate the sim"lest ratio among the atomsfound in com"ound.

/mpi'ical o'mula ; formula of acom"ound that e'"resses lowest wholenumber ratio of atoms.

*olecula' o'mula ; actual formulaof a com"ound showing the number of atoms"resent

&O*/&C8ATR/

o'ms of Chemical Bonds

• 8here are % forms bonding atoms:

• *onicPcom"lete transfer of 1 or moreelectrons from one atom to another$one loses+ the other gains

• CovalentPsome valence electrons

shared between atoms

• QQQQQQQQQ I holds atoms of a metaltogether

9'ope'ties of 0onic Compounds

o'min" &aCl f'om &a and Cl2

• A metal atom can transfer an electronto a nonmetal.

• 8he resulting cation and anion areattracted to each other byelectrostatic forces.

o'mulas of 0onic Compounds

o'mulas of ionic compounds a'e

dete'mined f'om the cha'"es on the

ions

atoms ions

;

&a + 5 &a+ 5 5 &a

sodium + <uo'ine sodium <uo'ide

fo'mula

Cha'"e $alance5 1+ 1-

: =

3'itin" a o'mula

rite the formula for the ioniccom"ound that will form between a#0 and

Cl−.

2olution:

1. alance charge with 0 and I ions

#. rite the "ositive ion of metal )rst+

and the

negative ion a#0 Cl−

Cl−

%. rite the number of ions needed as

subscri"ts aCl#

&amin" Compounds

Bina'y 0onic Compounds5

• 1. Cation )rst+ then anion

• #. Monatomic cation name of theelement

• Ca#0 calcium ion

• %. Monatomic anion root 0 (ide

• Cl( chloride

• CaCl# calcium chloride

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T'ansition *etals

Elements that can have more than one"ossible charge MB28 have a Roman-umeral to indicate the charge on theindividual ion.

9olyatomic 0ons <ou can ma7e additional "olyatomic ions byadding a /0 to the ion

C&% (# is carbonate

/C&%I is hydrogen carbonate

/#!&3I is dihydrogen "hos"hate

/2&3I is hydrogen sulfate

Te'na'y 0onic &omenclatu'e

3'itin" o'mulas

• rite each ion+ cation )rst. 4onJtshow charges in the )nal formula.

• &verall charge must e=ual ero.

• *f charges cancel+ 9ust writesymbols.

• *f not+ use subscri"ts to balancecharges.

• Bse "arentheses to show more thanone of a "articular "olyatomic ion.

• Bse Roman numerals indicate the ionJscharge when needed $stoc7 system

&amin" Te'na'y Compounds

Contains at least ! elements

The'e *ST $e at least one

polyatomic ion

>it helps to ci'cle the ions?

/xamples5

&a&O! Sodium nit'ate

@ 2SO# 9otassium sulfate

Al>HCO!?! Aluminum $ica'$onate

o'

Aluminum hyd'o"en

ca'$onate

&amin" *olecula' Compounds

*olecula' >Co7alent? &omenclatu'e

fo' t4o nonmetals

• !re)' 2ystem $binary com"ounds

1. ess electronegative atomcomes )rst.

#. Add "re)'es to indicate of atoms. &mitmono( "re)' on the F*R28 element. Mono( is&!8*&-A on the 2EC&-4 element $in thisclass+ itJs -&8 o"tional.

%. Change the ending of thesecond element to (ide.

O7e'all st'ate"y fo' namin" chemical

compounds.

A <o4 cha't fo' namin" $ina'y

compounds.

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Acid &omenclatu'e

• Acids

• Com"ounds that form /0 inwater.

• Formulas usually begin with S/J.

• *n order to be an acid instead of a gas+ binary acids must bea=ueous $dissolved in water

• 8ernary acids are A a=ueous

• E'am"les:

• /Cl $a= I hydrochloric acid

• /-&% I nitric acid

• /#2&3 I sulfuric acid

Acid &omenclatu'e lo4cha't

ou' Types of &amin"

• Bina'y compounds

• Te'na'y compounds

• Coo'dination compounds

• O'"anic compounds

Bina'y Compounds

Metals $)'ed o'idation 0 -onmetals

inary com"ounds that contain a metal of)'ed o'idation number

$grou" 1+ grou" #+ Al+ Tn+ Ag+ etc.+ and anon(metal.

8o name these com"ounds+ give the name ofmetal followed by the

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name of the non(metal+ with the endingre"laced by the su@' Iide.

*olecula' Compound

A com"ound containing atoms of two ormore elements that are bonded together bysharing electrons.

Rules fo' 9a'entheses!arentheses are used only when the

following

two condition are met:

1. 8here is a radical $"olyatomic ion

"resent and…

#. 8here are two or more of that radical

in the formula.

Co7alent $ondin"

• Fluorine has seven valence electrons• A second F atom also has seven

• y sharing electrons

• oth end with full orbitals $stableoctets

Chemical Bondin"

Ionic Bonds:

atoms give u" or gain

electrons and areattracted

to each other by

coulombic attraction

Chemical Bond

– attractive force between atomsor ions that binds them togetheras a unit

– bonds form in order to…

• decrease "otentialenergy $!E

• increase stability

Types of Bonds

*&-*C C&UAE-8

*/TA880

C

ondFormation

e( aretransferred frommetal tononmetal

e( aresharedbetweentwononmetals

electronsaredelocaliedamongmetal

atoms

8y"e of2tructure

crystallattice

truemolecules

electronseaG

!hysical2tate

2olid i=uid orHas

solid

Melting!oint

/igh ow veryhigh

2olubilityinater

<es Bsually-ot

no

ElectricalConductivity

<es$solutionor li=uid

-o yes$anyform

&ther!ro"erties

odorous malleable+ductile+lustrous

Properties of Metals

conduct heat and electricityOductileO malleable

Other Types of Bonds

di"ole(di"ole forces

hydrogen bonds

ondon dis"ersion forces

ion(di"ole forces $solutions

8e4is St'uctu'e

ewis structure:

a model of a covalent molecule thatshows all of the valence electrons

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1. 8wo shared electrons ma7e a singlecovalent bond+

four ma7e a double bond+ etc.

#. unshared "airs: "airs of un(bondedvalence electrons

%. Each atom needs a full outer shell+ i.e.+ L

electrons.E'ce"tion: / needs # electrons

covalent com"ounds molecularcom"ounds

$have lower melting "oints than do ioniccom"ounds

3'itin" o'mulas of 0onic Compounds

chemical formula:

has neutral chargeO

shows ty"es of atoms and how manyof each

8o write an ionic com"oundJs formula+ weneed:

1. the two ty"es of ions

#. the charge on each ion

C'iss-C'oss Rule

criss(cross rule:

charge on cation D anion

becomesG subscri"t of anion D cation

VV arning: Reduce to lowestterms.

3'itin" o'mulas 49olyatomic 0ons

!arentheses are re=uired only whenyou need more than one bunchG of a

"articular "olyatomic ion.

3'itin" o'mulas of Co7alent *olecules

Covalent Molecules

contain two types of nonmetals

Key: !"#$% &'A"#$(

)hat to do:

*se #ree+ prefi,es to indicate how many atoms of

each element- .ut don/t use mono on first

element2

1 – mono 3 – he,a

4 – di 5 – hepta

6 – tri 7 – octa

8 – tetra 9 – nona

– penta 10 – deca

T'aditional >O8? System of&omenclatu'e

used historically $and still some todayto name com"ounds wDmulti"le(chargecations

To use5

1. Bse atin root of cation.

#. Bse -ic ending for higher charge

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-ous lower

%. 8hen say name of anion+ as usual.

Element atin root -ic

-ous

gold+ Au aur- Au%0 Au10

lead+ !b plumb- !b30

!b#0

tin+ 2n stann- 2n30 2n#0

co""er+ Cu cupr- Cu#0

Cu10

iron+ Fe ferr- Fe%0 Fe#0

Bina'y Compounds

Metals $variable o'idation 0-onmetals

8o name these com"ounds+ give thename of the metal $8y"e ** cations followedby Roman numerals in "arentheses toindicate the o'idation number of the metal+followed by the name of the nonmetal+ withits ending re"laced by the su@' Iide.

Type 00 Cations

*on 2toc7 2ystem 8raditional 2ystem

Fe %0 iron $***ferric

Fe #0 iron $**ferrous

Cu #0 co""er $** cu"ric

Cu 10 co""er $* cu"rous

Co %0 cobalt $*** cobaltic

Co #0 cobalt $** cobaltous

2n 30 tin $*Ustannic

2n #0 tin $** stannous

!b 30 lead $*U "lumbic

!b #0 lead $**"lumbous

/g #0 mercury $** mercuric

/g# #0 mercury $* mercurous

VMercury $* ions are always boundtogether in "airs to form /g# #+

Bina'y *olecula' Compounds

-onmetal 0 -onmetal

8o name these com"ounds+ give the nameof the less electronegative element )rst withthe Hree7 "re)' indicating the number oatoms of that element "resent+ followed bythe name of the more electronegative non(metal with the Hree7 "re)' indicating thenumber of atoms of that element "resenand with its ending re"laced by the su@' Iide.

-#& dinitrogen mono'ide

-#&% dinitrogen trio'ide

-#&5 dinitrogen "ento'ide

Te'na'y Compounds

8ernary com"ounds are those containingthree di,erent elements.

$-a-&%+ -/3Cl+ etc.. 8he naming of ternarycom"ounds involves the memoriation oseveral "ositive and negative "olyatomicions+ $two or more atoms "er ion+ andadding these names to the element withwhich they combine.

i.e.+ 2odium ion+ -a10 added to the nitrateion+ -&%

1(+ to give the com"ound+ -a-&%+sodium nitrate.

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inary rules for indicating the o'idationnumber of metals and for indicating thenumbers of atoms "resent are followed. 8he"olyatomic ions that should be learned arelisted in a se"arate handout.

Chemistry

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