Ch6 Equilibrium

8/10/2019 Ch6 Equilibrium

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JP.=7 7(26 :.=-6) '.4Q4=3Q.4 ./ '()* #+! 8.PN2.=6ARSB (.@);

T3P6 P)F24 7(26 O.4>3R 8L34=3-R #$;

?RAA3P=6

U)3> 27 7(.-.=F(AR 8)6@):23AAR 4.7)6 .4 >):.-=* 34> P)(3N2.-;

U=A)6 ./ '2N2A27R

I3AC24F 24 :A366

V=)6Q.46

J--2N24F A37)"A)3N24F )3-AR

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'()*2:3A ,-24:2@A)6

Z=*>3(A 34> [):.67) 8\7()>2Q.4S34R -):)47 )>2Q.4 ]4);

'=67.* '()* #+# )>2Q.4 3N32A3PA) 24 P..C67.-)

'()* #+# T3P.-37.-R O34=3A 83N32A3PA) .4AR 24 P..C67.-);

D.FFA)6 34> 3 P.=4> A3P.-37.-R 4.7)P..C X27( :3-P.4 @3F)6

W)P '3*@=6 3::)66

?3@A24F T)3-424F 3::.=47 /.- .4A24) (.*)X.-C

?:2)4Q]: :3A:=A37.- 8B 6=FF)67 3 IB^%+_BB? .- 62*2A3- `a!G;

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W(37 >. B 4))> /.- 7(26 :.=-6)d

ec3*6 8>37)6 X2AA 4.7 :(34F);

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ec3* !K O.4>3R 5)P7 #Gb #+!%

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ec3* %K 5-2>3R O3R %b #+!%

1-24F @(.7. B[ 7. )c3*

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D-3>24F

% g.=- )c3*6K hG+ @76 8hGi;

5243A )c3*K #G+ @76 8#Gi;

g.*)X.-CK !++ @76 8!+i;

T3P.-37.-RK #++ @76 8#+i;

j.= *=67 @366 P.7( 7() :=*=A3QN) ]43A )c3* 34> 7() A3P.-37.-R 7. @366

7() :.=-6)f

JM)4>34:) 34> 1)(3N2.-

JM)4>34:) X2AA 4.7 P) 73C)4 83A7(.=F( Y=2EE)6 *3R P) F2N)4 37 34R Q*);

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1) :.462>)-37) ./ P.7( 7() 2467-=:7.- 34> R.=- /)AA.X 67=>)4760

?)) X)P:3*@=6 /.- 3 7)473QN) A):7=-) 6:()>=A) 24:A=>24F >=)

>37)6 /.- (.*)X.-C 34> )c3* :.N)-3F)0


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'(3@7)- l -)N2)XK eY=2A2P-2=*

T):7=-) m=7A24)

[)]4) )Y=2A2P-2=* 34> )Y=2A2P-2=* :.467347

eY=2A2P-2=* X27( @-)66=-)6

g)7)-.F)4).=6 )Y=2A2P-2=*

U)3:Q.4 Y=.Q)47

T) '(n7)A2)-o6 ,-24:2@A)

[)7)-*2424F eY=2A2P-2=* '.4:)47-3Q.46

eY=2A2P-2=* :.4673476 /.- 6)Y=)4:)6 ./ -)3:Q.468*342@=A3Q4F )Y=2A2P-2=* :.4673476;

The Concept of Equilibrium

Chemical equilibriumoccurs when a reactionand its reverse reaction proceed at the same rate.


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A System at Equilibrium

Once equilibrium is achieved, the

amountof each reactant and product

remains constant.

The Concept of Equilibrium

As a system approachesequilibrium, both the

forward and reverse

reactions are occurring.

At equilibrium, the forward

and reverse reactions are

proceeding at thesame rate.


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Equilibrium Can Be Reached from

Either Direction

It does not matter whether we start with N2and H2or whether we start with NH3, we will have the same

proportions of all three substances at equilibrium.


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What Does the Value of KMean?

If K>>1, the reaction isproduct-favored; productpredominates at equilibrium.

Equilibrium lies toward right(products)

p B/ !qq!b 7() -)3:Q.4 26 "#$%&$'&()$*+"#,r-)3:7347 @-)>.*2437)6 37 )Y=2A2P-2=*0

p eY=2A2P-2=* A2)6 7.X3-> A)s 8-)3:73476;

Figure 6-7 p215


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Changes in Temperature'.8g#m;l

#t8$-; t h'A8$-; '.'Ah8$-; t lg#m8.;

The Haber ProcessIf H2is added to the system, N2will be consumedand the two reagents will form more NH3.


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The Haber ProcessThe transformation of nitrogen and hydrogen into ammonia(NH3) is of tremendous significance in agriculture, where

ammonia-based fertilizers are of utmost importance.

Introduction to Acids and Bases Acids: taste sour

Bases: taste bitter and feel soapy.

Arrhenius definition of acids & bases

Acids - increase [H+] in water

Bases - increase [OH-] in water

BrnstedLowry

Acid: Proton donor

Base: Proton acceptor

Amphiprotic: can be either an acid or base

Lewis Acid/Base

Acid: electron pair acceptor

Base: electron pair donor

Chapter 7 Acids and Bases


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Acid-Base Rxns Are Proton-Transfer Rxns

Example: H3O++ OH

-!2 H

2O

Brnsted Defn of Acid & Base

Acid= proton (H+) donor

must have removable (acidic) proton

(Consider: HCl(aq) + H2O(l)!H3O+(aq) + Cl-(aq) )

Base= proton (H+) acceptor

Must have LP (nonbonding) electrons

(Consider: NH3(aq) + H2O(aq) NH4+(aq) + HO-(aq))

Amphiprotic ions or molecules (either donor or acceptor)

(Examples: H2O; HSO4-; HCO3

-)

The H+ion in water

H+called a proton (is a hydrogen atom with no

electrons.

H+interacts strongly with H2O to form clusters.

The simplest cluster is H3O+(aq). Larger clusters

are H5O2+(aq)and H9O4

+(aq).

H3O+is called the hydronium ion

H+(aq)& H3O+(aq)are used interchangeably to

represent the species giving rise to acidic

properties.


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Conjugate Acid-Base Pairs

Whatever is left of the acid after the proton is donated is called its conjugate base.

Whatever remains of the base after it accepts a proton is called a conjugate acid.

HA(aq)+ H2O(l) H3O+(aq)+ A

-(aq)

Rule:The stronger an acid the weaker its conjugate base.

Relative Strengths of Acids

Acids differ in H

+

donor ability

differ in strength

Three categories of H-containing substances:

Strong acids

react 100% with H2O to form H3O+

Weak acids

react 1-99% with H2O to form H3O+

in practice, most react about 1-5%

Compounds with negligible (or no) acidity

react 0% with H2O to form H3O+


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acid base conj. base conj. acid

Rule: Equilibrium position always favors transferof proton from strongest acid to strongest base

Proton-transfer rxns are extremely fast

If we know something about the strength of an

acid we also know something about the strengthof its conjugate base.

Equilibrium for proton-transfer rxns

HX + B- X- + HB

Acid and Base Strength

Strong acids are completelydissociated in water.

Their conjugate bases areextremely weak.

Weak acids only dissociatepartially in water. Their conjugate bases are

weak bases.

Substances with negligibleacidity do not dissociate inwater.

Their conjugate bases areexceedingly strong.


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Acidic, Basic & Neutral Solns

Neutral soln has [H3O+] = [OH

-]

[H3O+] = 1.0 x 10-7M

Acidic soln has [H3O+] > [OH

-]

Basic soln has [H3O+] < [OH

-]

The pH Scale:

pH = -log[H3O+]

or [H3O+] = 10-pH

Neutral soln has pH = 7.00

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Ch6 Equilibrium

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