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HEAT of Reactions(Thermochemistry)

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Released heat vs. Absorbed heat

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• The energy value of food is indicated in calorie unit.

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• 'issolution of ammonium nitrate / endothermic rxn

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• 0nstant cold ac% in first aid %it

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E1TA234 CA15E O6 REACT0O17

• Examle8

C9(g) + O(g) ! CO(g) + O(l) :; /mol

• ,(ho? many coffees you can ma%e by a certain amount of gas used)

; follo? the reaction @

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•

The heat change at the end of a chemical reaction underconstant ressure is called entalpy change of the

reaction and indicated by :.

•

Entaly cannot be measured directlyB it can only beuantified by entahy change after the chemical

reactions.

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•  Problem #1

• CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) ΔH= -890k!"ol

Ans?er the follo?ing uestions for the reaction given above8

a) 0s it endothermic or exothermic

 b) o? many moles of C9 must be used to roduce "$*.%&

energyD

c) hen .g of CO is obtained ho? much heat ?ill be

releasedD F(CO); 99g>mol

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• 7tandard heat of formation (:f )

• :f value of free atoms and free samle molecules

acceted as (=)

• :f values for some molecules are given on tables.

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•  Problem #2

  #O2(g) + $!2O2(g) → #O%(g)

6ind the heat of reaction (:) for the given reaction byusing :f values of comounds from table...

  'ata8

•:f (7O) ; / #G %&>mol

• :f (7O") ; / "#* %&>mol

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• eat of combustion

(Combustion is a tye of chemical reaction in ?hich fuelsreact raidly ?ith oxygen to result in the roduction of light

and heat).

C9(g) + O(g) ! CO(g) + O(l):(combustion) ; / mol

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• eat of neutraliation

(The heat of neutraliation is the amount of heat roduced by neutraliation (acid/base) reactions).

  1aO(a) + Cl(a) ! 1aCl(a) + O(l)

: (neutraliation) ; / $*%&>mol

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•  Problem #3

hen $=ml of =.F Cl solution is neutralied ?ith

enough HO solution ho? much heat is roducedD

 1aO(a) + Cl(a) ! 1aCl(a) + O(l)

: (neutraliation) ; / $*%&>mol