Thermochemistry SPM form 5

7/26/2019 Thermochemistry SPM form 5

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Thermo chemistryThermo chemistry

The study of changes in heatThe study of changes in heat

energy during chemicalenergy during chemical

reactionreaction

ExothermiExothermi

ccReactionReaction

EndothermiEndothermi

ccReactionReaction


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A chemical reaction that givesout or release of

heatenergy to the surroundings

Exothermic ReactionExothermic Reaction


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Physical Processes

MeltingBoiling

CondensationSublimation

Exothermic Endothermic

Dissolving an alkali or

concentrated acid in water

Dissolving ammonium salts,potassium salts or

thiosulphate salts in water

Dissolving anhydrous saltssuch as anhydrous copper(II)

sulphate in waterHeating of hydrated salt

Freezing


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Exothermic Endothermic

1. Comustion of fuel!. "urning of metal#. $eutralisation%. &espiration

'. &usting of iron. &eaction of reactive metal

with acid. &eaction of caronate with

acid*. &eaction of alkaline metal

with water+. Haer process

1. hermal decomposition of

nitrate salts!. hermal decomposition ofcaronate salts

#. &eaction of acid withhydrogen caronates

%. -hotosynthesis

Chemical Reactions


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Energy Change DuringEnergy Change During

Formation And Breaking OfFormation And Breaking Of

BondsBondsChemical Reaction

bond breaking and bond

formation!absorb energy" !release

energy"


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If heat absorb to break the bondshigherthan heat releasedduring

formation of bonds - endothermicendothermic

If heat absorb to break the bonds is

lo#erthan heat releasedduringformation of bonds - exothermicexothermic


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E$ER%& 'E(E' D)A%RA*E$ER%& 'E(E' D)A%RA*

Every chemical substances

have certain amount of chemicalenergyanddi+erentfor dierent

substances.

Symbol is,,The amount of heat energy released orabsorbed during chemical reaction heat of

reaction.

Symbol is --,,, unit./ mol./ mol0101

! " Total Energy Content 2roduct # Total EnergyContent Reactant

" ,3roducts

- ,reactants


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The Energy $evel %iagram &or

Exothermic Reaction EndothermicReaction

Reactants

Energy

2roducts

H = - xKJmol-

Reactants

Energy 2roduct

s

H = !"KJmol-


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A22')CAT)O$A22')CAT)O$

A 'lastic bag containing se'aratecom'artment (thin )lm* of +ater solidammonium nitrate 'laced in a 'lastic bag

Sueeed it, the com'artment broken andsolid ammonium nitrate dissolved in +ater

Endothermic4 'rovide instant coldness

COLD PACK

Other substance :Ammonium chloridePotassium nitrateSodium thiosulphate


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A 'lastic bag containing se'arate

com'artment (thin )lm* of +ater anhydrous calcium chloride 'laced in a'lastic bag

Sueeed it, the com'artment broken andanhydrous calcium chloride dissolved in +ater

Exothermic, release heat

HOT PACK

Other substance :Anhydrous magnesium sulphateAnhydrous copper(! sulphateCalcium o"ide


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5 ty3e of heat of5 ty3e of heat ofreactions reactions ,eat of 2reci3itation

,eat of$eutrali6ation

,eat of Dis3lacement,eat of Combustion


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H#AT O$ P%#CPTATO&H#AT O$ P%#CPTATO&

m

m#

D#$&ATO& :,eat of 3reci3itation is the energy change

'hen mole o) precipitate is )ormed'hen mole o) precipitate is )ormedfrom itsions7To calculate Heat of Precipitation

Ste$ find energy change , /

/ 0 mc

m = m1 + m2c = 4.2

= temp change

Ste$ # find mol, n oth solution n 0 231444

Ste$ % find H

H 0 /3 n 56 mol71

7- - -- - - -7- - -


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H#AT O$ DSPLAC#*#&TH#AT O$ DSPLAC#*#&T

D#$&ATO& :

!eat of dis'lacement is the energy change mole ofmole of

metal is displaced from its salt solutionmetal is displaced from its salt solutionb" moreb" moreelectro$ositi&e metalelectro$ositi&e metal

m

89cess metalTo calculate Heat of Displacement

Ste$ 'find energy change , /

/ 0 mc

m 0 m

c 0 %.!

0 temp change

Ste$ # 'find mol, n solution n 0 231444

Ste$ % 'find H

H 0 /3 n 56 mol71

7- - -

- - - -7- - -


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H#AT O$ +T%ALSATO&H#AT O$ +T%ALSATO&D#$&ATO& :

!eat of neutraliation is the energy change +hen

mole o) 'atermole o) 'ateris formed from the neutrali,ationbet+een mole o) H- ion )rom an acid and mole o) H- ion )rom an acid and

mole o) OH. ion )rom an al/alimole o) OH. ion )rom an al/ali

acid

m

(l)ali

m#

To calculate Heat of Neutralization

8te3 1 8te3 1 )nd energy change , / / " mc m " m0 m1

c " 2.1 " tem' change

8te3 9 8te3 9 )nd mol, n both solution n " mv30444

8te3 : 8te3 : )nd !

! " /3 n 56 mol-0


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H#AT O$ CO*0+STO&H#AT O$ CO*0+STO&D#$&ATO& :

!eat of combustion is the heat given o +hen

mole o) alcohol is burnt completelymole o) alcohol is burnt completelyin an e7cessof 81gas.

To calculate Heat of Combustion

8te3 1 )nd energy change , / / " mc

m " 1OL+*# O$ 2AT#%USED

c " 2.1 " tem' change

8te3 9 )nd mol, n(FOR F;E'< A'CO,O'*

n " 9ass 8f Alcohol

:sed9olar mass of

Thermochemistry SPM form 5

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