Bellwork‐EquilibriumThesystemdescribedbytheequa8onH2O(l)H2O(g)ΔH=40.7kJ

isatequilibrium.

a)Howdoestheconcentra8onofH2Ogaschange?

b)Doescondensa8onoccur?

c)Doesvaporiza8onoccur?

d)Whatcondi8onsmustbemetforequilibriumtooccur?

BellworkThesystemdescribedbytheequa8onH2O(l)H2O(g)ΔH=40.7kJ

isatequilibrium.

a)Howdoestheconcentra8onofH2Ogaschange?itdoesn’t,atequilibriumconcentra8onsareconstantb)Doescondensa8onoccur?YES

c)Doesvaporiza8onoccur?YES,atthesameratethatcondensa8onoccursd)Whatcondi8onsmustbemetforequilibriumtooccur?Closedcontainer,stabletemperature,lowEa

Asystemisatequilibriumduetoabalancingofmanyfactors.

Changingthecondi8onsofasystematequilibriumwill“shiT”theequilibrium.

A“shiT”iswhenEITHERmoreproductsareformed

(forwardreac8onspeedsup)OR

morereactantsareformed(reversereac8onspeedsup)

LeChatelier’sPrinciple

WhenanequilibriumsystemisdisturbedtheequilibriumwillshiTtoundothedisturbance.

Changingconcentra8onsH2(g)+Cl2(g)↔2HCl(g)

IncreasingH2orCl2concentra8onwillshiTtheequilibriumtotheright(moreproducts)becausethiscounteractstheaddi8onofreactant.

EXAMPLE‐Increasing[HCl]willshiTtheequilibriumtotheleT(towardsreactants).GETSRIDOFextraHCl!

Whataboutdecreasingconcentra8ons?

LeChatelier’sPrinciple

Whateverisdonetoanequilibriumsystemwillbepartlyundone.

Changingpressure

N2O4(g)↔2NO2(g)

1moleofgas↔2molesofgas

UNDERPRESSURE‐SHIFTTOLESSMOLESOfgas!

Increasepressure–shiTsleT(lessmolesofgaswilldecreasepressure)

Decreasepressure–shiTsright(moremolesofgaswillincreasepressure)

Changingpressureonlyaffectsequilibriumifproductshavea

differentnumberofgasmolesthanreactants.

H2O(l) H2O(g)0 gas moles 1 gas mole

Changingtemperature

Writeequa8onwithenergyasaproductorreactant.

Endothermic

Energy+A+B↔C+D

Increasetemp–favorsforward(shiTtotheright)becausethatusesuptheaddedenergy

DecreaseTemp?

Changingtemperature

Exothermic

A+B↔C+D+Energy

Increasetemp–favorsreversereac8onandashiTtotheleTbecausethatusesuptheaddedenergy

Decreasetemp?Thesystemwilldowhatitcantogetmoreenergy.

A catalyst will not affect theequilibrium position (a.k.a. shiftthe equilibrium).A catalyst will increase the reversereaction rate as much as it increases theforward reaction rate.

The system will reach equilibrium faster,but the final concentrations of reactantsand products are not changed by theaddition of a catalyst.

Changingconcentra8ondoesnotaffectpureliquidsorsolids.

Changingpressureonlyaffectsgases.

Theequilibriumconstant(Keq)isara8oofproductconcentra8onstoreactantconcentra8onsatequilibrium.

18.2

Keq = [C]c[D]d

[A]a [B]b

For aA + bB cC + dD