Energetics and Thermodynamics: HL Topic 15 - Comprehensive Notes, Study notes of Chemistry

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15. Energetics and

Thermodynamics (HL)

Topic

15 : (^) Energetics HL: - standard enthalpy (^) of formations H : formation (^) of one (^) mole of a compound from its^ elements^ in^ their^ standard^ states^

at standard^ conditions

ex:^ -H2(g) +^ [02(g)

• H20(e) (^) AH-(H2O)e -^ Scs)^ +^ O^ <(g)^

SOx() DH6(02)^ g Average bond^ energy^ :^ energy^ needed (^) to break /^ mol^ of substance^ in^ its gaseous

state.

ex :^ - (^) Fz(g) -^2 f(g) B.^ E^ all^ must be^ in^ (g)

• (^) O(g)

e 20(g) B .E

Lattice (^) enthalpy(Ditat)^ :standard^ enthalpy (^) change that occurs on^ the formation

of 1 mol of

gaseous ions (^) from solid (^) latticecionic

compound)

eX :^ -^ MX(s)^

• (^) M(g)" + X- (^) (g)

Hiattice) O

ins (9)

jonic - >

-^ NaCI(s)^ - > (^) Na + (g) +^ ( - (g) AHatNaC^ wompish -Mg0()2Mg(g) +^ Og) DHlatMgO Alt at^ enthalpy of atomization^ : change that occurs on^ the formation (^) of 1 mol^ of (^) separate gaseous atoms in (^) an element in^ its

standard state

ex:^ -^ M(x)

M(g) DHat^

dement

• (g)

• EX2(g)
• Nacg) DHat(Na) in^ standard^ atims State

[02(g)2O(q)

Dat

• C2(g)e(l(g)^ Dat lonization (^) energy :^ standard^ enthalpy change^ that occurs on the

removal of 1 mol of

e-from 1 mol (^) of atom (^) fortion) in gaseous

state.

ex :^ - M(g) = > (^) M

(g) +^

1 - 1E

-M

(g) e^ Mq) +^ le^ IEza second IE

• M(q)
  • -Mg + (g) (^) + le -

IE

eX:

k

(q)

• (^) Bria) & IE

, EA

((g) (^) + Br(g)^

DHlat

N M

DHat

DHat(k)

W

k(s)

• EBr^

> kBrc)

DHof DH :^ DHat(k)^ +^ DHatBrz^ +Eick) +^ EABr-DHiatKBr

• NOTE- Au (^) bond (^) energy Lattice (^) enthalpy ·^ reactants^

and · reactants are in

product we in na

solid and

products are (^) in gaseous

state.

· forms free radicalsforms ions f2(q) +: +. (^) Mg0()-Mg2(g) +^ O^.

DH (^) Lattice (^) w/respect to^ charge of ions^ and^ ionic^ radius: lonic (^) charge: DH (^) ,at

-67 As

ionic

charge

, Alain

a

Mg2+, 82

• 3795

lonic radius^ :

Naf (^910) f NaCI (^769) Ch => As ionic^ radius^ ↑, Aflattice ↓

NaBr 732 Bu

Nal 682 3

greated ionic radius Electronegativity :

Dx(Naf) =^ 4-0.^9

= 3.

DX(NaCl) = 3.^ 2 - 0.^9

=> DX^ Monic^

character ↑^ Alia+* = 2.^3 DX(Naf)) DX(NacI So DHIatf)) DHlat (Nack)

Enthalpy of (^) hydration (DHnyd)^ is^ the (^) enthalpy change when^

Imol

of (^) gaseous ions^ is^ added^ to (^) water to form ageous^ solution. It is the (^) amount (^) of energy released (^) during solvation^ process. AHned (^) always (^) negative

M

(g) =^ M

(aq) (^) DHnyd

X (g) -^ >^ X-^ (aq) Alued

Altuya depends^ onChageotions : as (^) chargenea Examples : DHuyd Nat^ =^ -424^ kj/mol (^) DHnyd Cl =^ - (^359) Ijimol AHuyd (^) Mg2=^ - (^1963) kj/mol DHnyd I= -^287 IjImol as (^) charge &^ 19Hnyd/ *^ as ionic^ radius^ & (^) IDHnyd) + EnthalpyChangeinSolutionisenthalpy change (^) tha solvent NaCks)soNatcaa) +^ (a) NaOH (^) Natcaa) (^) + HOjaq) (s)

DHsol can^ be^ +or-

Nat +^ OH

DH (^) ,at AHnyd DHnd OH

NaOH()Nata) +O

a

DHid (^) = DHilat^ +^ DHined(Nat) +^ Dth(Ott NaOH(s)

Application : ~ Babigt 2(g) DHiat =^2069 kilmol DHhyd^ DHhyd = = 1346 = - 359 Kilmil (^) Kilma V W BaCI (^) z > Bataa)^

+ 2 Daq)

DH'sol AH'sol :^ Atliat +^ DHnydBal +^ 2DHnydc- = 2069 -^1346 - 2(359) DHosol =^ 5 Ilmal Entropy(Ds)^ and (^) spontaneity : A chemical (^) reaction that is^ said to^ be (^) spontaneous if it:

• is^ a^ complete reaction
• attains^ equilibrium under^ certain^ conditions:

can be^ exothermic^ or^

endothermic Exothermic reactions are^ always spontaneous (some^ exceptions A chemical^ reaction^ that^ does^ not^ occur^ under^ certain^ conditions^ is

non-spontaneous.

Entropy (AS)^ is^ the^ distribution^ of energy^ among the^ particles.The

more the energy is distributed^ the^

higher

the entropy

spontaneous reactions leads to (^) higher entropy. As values order =^ order^

disorder

(j)

-- 000 000 se :^888888 00.^ O ⑧ S ⑧

solid

liquid gas

disorder

s

from

solid

-gas

: (^) particles gain more (^) movement

• more

way

to distribute^ energy - higher entropy Note: the more^ elements^ in^ Gaseous^ state there is in^ reaction (^) - (^) higher As

DS[X(g) +Y(q)^

Xy(g)]) DS[X(g) +^ Y (1)^

• (^) XY(q)

Gib's free (^) energy (DG) : state (^) function (depends on initial &^ final states^ only(

DGixn =^ EDGip)-EDGir)

related to^ DH , DS ,T G = H - TS DG= DH^ :

TAS

In exothermic reaction:^ heat^ is^ released^ from the (^) system to^ the^ surrounding . entropy (^) surrounding ↑ ·^ A3)0^ ,^ DG^

<0 => spontaneous (1)

· AS[O,^ DG) O^ = (^) non-spontaneous (t)^ (note:^ rev^ reaction^ is (^) spontaneous

Gib's (^) free (^) energy (^) change of (^) formation:

Change

in (^) free energy during^ formation^ of (^1) mol (^) ofa substance (^) from its

elements in^ standard^ state^ from its^ elements^ in^ standard^ conditions^ ·T=^298 , P =100kPa

AGixn (^) =

EDGYP)-EDGjCR) AGjelement =O^ (like DHof)

combustion (^) of ethanol:

· DG ethanol^

(l) = (^) - Ijlmal · DG7(2(g)^ =^ -394 (^).^4 kilma · DGf^ Hz0(q)^ =^ -228^.^6 kj/mal CzHgOH(e) +^ 30 2(g)

2( 2(g)

• (^) 3 H20(q)

AGixn = EDG> (p) -

EDGCR)

• (^394). 4)^ +^ 3)-^228. 6)) - [ - 175] = -1299. (^6) /mol

~ J note:^ /S^

• G S

AS) AS

(^6) -> G S

A

high temp^

more likely to be spont . Lit Fi ca

f -

formationof

compoundIne

at standard^ conditions

AH-f = DHf(p)

• DHf(r) = (3(-^ 394)^ +^27 286))^
• (185 .4) =^ - 1182-572-^ . 4

= = 1939. 7 /mol

Since DH^ =-^ and^ product^

are (l)8(9)

As most^ likely^

OX+

↑