notes equation stoich

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Stoichiometric Calculations

The coefcients in the balanced

equation i!e the ratio o" moles o"reactants and #roducts.



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Startin $ith themass o" Substance% &ou can use theratio o" thecoefcients o" %and ' to calculatethe mass o"

Substance '"ormed (i" it)s a#roduct* or used (i"it)s a reactant*.



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Startin $ith +.00 o" CH+2$e calculate the moles o" CH+2

use the coefcients to /nd the moles o" H2

and then turn the moles o" $ater to rams.

CH+2 2 → C2 H2



Sample Exercise 3.16 Calculating Amounts of Reactants and Products

Ho$ man& rams o" $ater are #roduced in the o1idation o" +.00 o" lucose, CH+2

CH+2(s* 2(g*3 C2(g* H2(l*SolutionPlan

4irst, the amount o" CH+2 must be con!erted "rom rams to

moles.Second, $e can use the balanced equation, $hich relates themoles o" CH+2 to the moles o" H2 5 + mol CH+2 5 mol H2.

Third, $e must con!ert the moles o" H2 to rams.




The decom#osition o" 6Cl7 is commonl& used to #re#are small

amounts o" 2 in the laborator&5

2 6Cl7(s* 3 2 6Cl(s* 7 2(g*. Ho$ man& rams o" 2 can be

#re#ared "rom 8.0 o" 6Cl7

Answer: +.::

Practice Exercise

Solution (continued)




Pro#ane, C7H=, is a common "uel used "or coo>in and homeheatin. ?hat mass o" 2 is consumed in the combustion o" +.00

o" #ro#ane Answer: 7.8

Practice Exercise



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;imitin

@eactants


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Ho$ Aan& Coo>ies Can I Aa>e

• Bou can ma>e coo>iesuntil &ou run out o"

one o" the inredients.• nce this "amil& runs

out o" suar, the& $illsto# ma>in coo>ies

(at least an& coo>ies&ou $ould $ant toeat*.

1 dozen cookies = 1/4 cup butter 1 cup sugar 1 cup flour 1 egg



Ho$ Aan& Coo>ies Can I Aa>e

• In this e1am#le thesuar $ould be the

limitin reactant,because it $ill limitthe amount o"coo>ies &ou can

ma>e.

1 dozen cookies = 1/4 cup butter 1 cup sugar 1 cup flour 1 egg



;imitin @eactants

• The limitin reactant is the reactant#resent in the smallest stoichiometricamount.

! In other $ords, it)s the reactant &ou)ll run out o"/rst (in this case, the H2*.



;imitin @eactants

In the e1am#le belo$, the 2 $ould be the

e1cess reaent.



Sample Exercise 3.18 Calculating t"e Amount of Product #ormed from

a $imiting Reactant

%"e most important commercial process for con&erting ' from t"e air into

nitrogencontaining compounds is based on t"e reaction of ' and *

to form

ammonia ('*+),

'(g ) + *(g )- '*+(g )

*o. man moles of '*+ can be formed from +0 mol of ' and 20 mol of

*3

Solution




a $imiting Reactant

Consider t"e reaction Al(s) + Cl(g ) - AlCl+(s)0 A miture of 105 mol of

Al and +0 mol of Cl is allo.ed to react0 (a) 6"ic" is t"e limiting reactant3

(b) *o. man moles of AlCl+ are formed3 (c) *o. man moles of t"e ecess

reactant remain at t"e end of t"e reaction3

Answers: (a) Al7 (b) 105 mol7 (c) 085 mol Cl

Practice Exercise





a $imiting Reactant

Consider t"e follo.ing reaction t"at occurs in a fuel cell,

*(g ) 9 (g ) - *9 (g )

%"is reaction7 properl done7 produces energ in t"e form of electricit and

.ater0 :uppose a fuel cell is set up .it" 15 g of "drogen gas and 15

grams of ogen gas (eac" measurement is gi&en .it" t.o significant

figures)0 *o. man grams of .ater can be formed3

Solution




a $imiting Reactant

A strip of zinc metal .it" a mass of 0 g is placed in an a;ueous solution

containing 05 g of sil&er nitrate7 causing t"e follo.ing reaction to occur,

<n(s) Ag'9+(aq) - Ag(s) <n('9+)(aq)

Practice Exercise





Theoretical Bield

• The theoretical &ield is the ma1imumamount o" #roduct that can be made.

! In other $ords it)s the amount o"

#roduct #ossible as calculated throuhthe stoichiometr& #roblem.

• This is dierent "rom the actual &ield,

$hich is the amount one actuall&#roduces and measures.




Percent Bield

ne /nds the #ercent &ield b&com#arin the amount actuall&obtained (actual &ield* to the

amount it $as #ossible to ma>e(theoretical &ield*.

%ctual Bield Theoretical

Bield

Percent Bield D1 +00



Sample Exercise 3.20 Calculating t"e %"eoretical ield and t"e Percent

ield for a Reaction

Adipic acid7 *C2*>947 is used to produce nlon0 %"e acid is made

commerciall b a controlled reaction bet.een cclo"eane (C2*1) and 9,

C2*1(l ) 5 9(g ) - *C2*>94(l ) *9(g )

(a) Assume t"at ou carr out t"is reaction starting .it" 50 g of

cclo"eane and t"at cclo"eane is t"e limiting reactant0 6"at is t"e

t"eoretical ield of adipic acid3(b) ?f ou obtain ++05 g of adipic acid from our reaction7 ."at is t"e percent

ield of adipic acid3Solution

g C2*1 - mol C2*1 - mol *C2*>94 - g *C2*>94



Sample Exercise 3.20 Calculating t"e %"eoretical ield and t"e Percent

ield for a Reaction

?magine t"at ou are .orking on .as to impro&e t"e process b ."ic" iron

ore containing #e9+ is con&erted into iron0 ?n our tests ou carr out t"e

follo.ing reaction on a small scale,

#e9+(s) + C9(g ) - #e(s) + C9(g )

(a) ?f ou start .it" 15 g of #e9+ as t"e limiting reagent7 ."at is t"e

t"eoretical ield of #e3 (b) ?f t"e actual ield of #e in our test .as >80@ g7

."at .as t"e percent ield3

Answers: (a) 15 g #e7 (b) >+08

Practice Exercise

notes equation stoich

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