ITT Chng Ch 03 Mass Relationships in Chemical Reactions

7/29/2019 ITT Chng Ch 03 Mass Relationships in Chemical Reactions

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Mass Relationships inChemical Reactions


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By definition:

1 atom 12C weighs 12 amu

On this scale

1H = 1!!" amu

1#

O = 1#!! amu

Atomic massis the mass of an atom in

atomic mass units $amu%

Mic&o 'o&ld

atoms ( molecules

Mac&o 'o&ld

g&ams

)1


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*atu&al lithium is:

+,2- #.i $#!1/ amu%

02/"- +.i $+!1# amu%

+,2 #!1/ 02/" +!1#

1!!= #0,1 amu

)1

Average atomic massof lithium:


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34e&age atomic mass $#0,1%


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5he mole (mol)is the amount of a su6stance that

contains as many elementa&y entities as the&e

a&e atoms in eactly 12!! g&ams of 12C

)2

1 mol = NA= #!221)#+ 1!2)

34ogad&o7s num6e& $NA)


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Molar massis the mass of 1 mole of in g&ams

eggsshoes

ma&6lesatoms

1 mole 12C atoms = #!22 1!2)atoms = 12!! g

1 12C atom = 12!! amu

1 mole 12C atoms = 12!! g 12C

1 mole lithium atoms = #0,1 g of .i

8o& any element

atomic mass $amu% = mola& mass $g&ams%

)2


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One Mole of:

C 9

Cu 8e

Hg

)2


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1 amu = 1## 1!2, g o& 1 g = #!22 1!2)amu

1 12C atom

12!! amu

12!! g

#!22 1!2)

12

C atoms

=1## 1!2,g

1 amu

)2

M = mola& mass in g;mol

NA= 34ogad&o7s num6e&


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#!22 1!2)atoms ou ?nde&stand Molecula& Mass@

How many H atoms a&e in +2/ g of C)H"O @

1 mol C)H"O = $) 12% $" 1% 1# = #! g C)H"O

1 mol H = #!22 1!2)atoms H

/"2 1!2,atoms H

))

1 mol C)H

"O molecules = " mol H atoms

+2/ g C)H"O1 mol C)H"O

#! g C)H"O

" mol H atoms

1 mol C)H"O

#!22 1!2)H atoms

1 mol H atoms

=


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Formula massis the sum of the atomic masses

$in amu% in a fo&mula unit of an ionic compound

1*a 2200 amu

1Cl )/,/ amu

*aCl /",, amu

8o& any ionic compound

fo&mula mass $amu% = mola& mass $g&ams%

1 fo&mula unit *aCl = /",, amu

1 mole *aCl = /",, g *aCl))

*aCl


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o >ou ?nde&stand 8o&mula Mass@

'hat is the fo&mula mass of Ca)$AO,%2@

))

1 fo&mula unit of Ca)$AO,%2

) Ca ) ,!!"

2 A 2 )!0+

" O " 1#!!

)1!1" amu


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Percent compositionof an element in a compound =

n mola& mass of elementmola& mass of compound 1!!-

nis the num6e& of moles of the element in 1 mole

of the compound

C2H#O

-C =2 $12!1 g%

,#!+ g 1!!- = /21,-

-H =# $1!!" g%

,#!+ g 1!!- = 1)1)-

-O =1 $1#!! g%

,#!+ g 1!!- = ),+)-

/21,- 1)1)- ),+)- = 1!!!-

)/


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Ae&cent Composition and mpi&ical 8o&mulas

ete&mine the empi&ical fo&mula of a

compound that has the following

pe&cent composition 6y mass:< 2,+/D Mn ),++D O ,!/1 pe&cent

n


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Ae&cent Composition and mpi&ical 8o&mulas

< : EE 1!!#))!

!#)20

Mn : !#)20!#)20

= 1!

O : EE ,!2/)2

!#)20

n


18/31 )#

g CO2 mol CO2 mol C g C

g H2O mol H2O mol H g H

g of O = g of sample F $g of C g of H%

Com6ust 11/ g ethanol

Collect 22! g CO2and 1)/ g H2O

#! g C = !/ mol C

1/ g H = 1/ mol H

,! g O = !2/ mol O

mpi&ical fo&mula C!/H1/O!2/

i4ide 6y smallest su6sc&ipt $!2/%

mpi&ical fo&mula C2H#O


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) ways of &ep&esenting the &eaction of H2with O2to fo&m H2O

3 p&ocess in which one o& mo&e su6stances is changed into one

o& mo&e new su6stances is a chemical reaction

3 chemical equationuses chemical sym6ols to show whathappens du&ing a chemical &eaction

&eactants p&oducts


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How to Read Chemical uations

2 Mg O2 2 MgO

2 atoms Mg 1 molecule O2maGes 2 fo&mula units MgO

2 moles Mg 1 mole O2maGes 2 moles MgO

,"# g&ams Mg )2! g&ams O2maGes "!# g MgO

IS NOT2 g&ams Mg 1 g&am O2maGes 2 g MgO

)+


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Balancing Chemical uations

1 '&ite thecorrect

fo&mula$s% fo& the &eactants onthe left side and the correctfo&mula$s% fo& the

p&oduct$s% on the &ight side of the euation

thane &eacts with oygen to fo&m ca&6on dioide and wate&

C2H# O2 CO2 H2O

2 Change the num6e&s in f&ont of the fo&mulas

$coefficients% to maGe the num6e& of atoms ofeach element the same on 6oth sides of the

euation o not change the su6sc&ipts

)+

2C2H# NOT C,H12


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) 9ta&t 6y 6alancing those elements that appea& inonly one &eactant and one p&oduct

C2H# O2 CO2 H2O

)+

sta&t with C o& H 6ut not O

2 ca&6on

on left

1 ca&6on

on &ightmultiply CO26y 2

C2H# O2 2CO2 H2O

# hyd&ogen

on left

2 hyd&ogen

on &ightmultiply H2O 6y )

C2H# O2 2CO2 )H2O


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, Balance those elements that appea& in two o&mo&e &eactants o& p&oducts

)+

2 oygen

on left

, oygen

$22%

C2H# O2 2CO2 )H2O

) oygen

$)1%

multiply O26y+2

= + oygen

on &ight

C2

H#

O2

2CO2

)H2

O+

2

&emo4e f&action

multiply 6oth sides 6y 2

2C2H# +O2 ,CO2 #H2O


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/ ChecG to maGe su&e that you ha4e the samenum6e& of each type of atom on 6oth sides of the

euation

)+

2C2H# +O2 ,CO2 #H2O

Reactants A&oducts, C

12 H

1, O

, C

12 H

1, O

, C $2 2% , C

12 H $2 #% 12 H $# 2%

1, O $+ 2% 1, O $, 2 #%


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1 '&ite 6alanced chemical euation

2 Con4e&t uantities of Gnown su6stances into moles

) ?se coefficients in 6alanced euation to calculate the

num6e& of moles of the sought uantity

, Con4e&t moles of sought uantity into desi&ed units

3mounts of Reactants and A&oducts

)"


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Methanol 6u&ns in ai& acco&ding to the euation

2CH)OH )O2 2CO2 ,H2O

f 2!0 g of methanol a&e used up in the com6ustionDwhat mass of wate& is p&oduced@

g&ams CH)OH moles CH)OH moles H2O g&ams H2O

mola& massCH)OH

coefficientschemical euation

mola& massH2O

2!0 g CH)OH1 mol CH)OH

)2! g CH)OH

, mol H2O

2 mol CH)OH

1"! g H2O

1 mol H2O

=

2)/ g H2O

)"


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.imiting Reagents

)0

2*O 2O2 2*O2

*O is the limiting &eagent

O2is the ecess &eagent


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o >ou ?nde&stand .imiting Reagents@

n one p&ocessD 12, g of 3l a&e &eacted with #!1 g of 8e2O)23l 8e2O) 3l2O) 28e

Calculate the mass of 3l2O)fo&med

g 3l mol 3l mol 8e2

O)

needed g 8e2

O)

needed

OR

g 8e2O) mol 8e2O) mol 3l needed g 3l needed

12, g 3l 1 mol 3l2+! g 3l

1 mol 8e2O)2 mol 3l

1#! g 8e2O)1 mol 8e2O)

= )#+ g 8e2O)

9ta&t with 12, g 3l need )#+ g 8e2O)

Ha4e mo&e 8e2O) $#!1 g% so 3l is limiting &eagent )0


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?se limiting &eagent $3l% to calculate amount of p&oduct that

can 6e fo&med

g 3l mol 3l mol 3l2O) g 3l2O)

12, g 3l1 mol 3l

2+! g 3l1 mol 3l

2

O)

2 mol 3l1!2 g 3l

2

O)

1 mol 3l2O) = 2), g 3l2O)

23l 8e2O) 3l2O) 28e

)0


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Theoretical Yieldis the amount of p&oduct that would

&esult if all the limiting &eagent &eacted

Actual Yieldis the amount of p&oduct actually o6tainedf&om a &eaction

% Yield=

3ctual >ield

5heo&etical >ield 1!!

)1!

Reaction >ield

Ch i 3 i Ch i l 8 ili


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Chemist&y n 3ction: Chemical 8e&tiliIe&s

Alants need: *D AD

Documents

ITT Chng Ch 03 Mass Relationships in Chemical Reactions