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Chem
ical R
eact
ions
and
Qua
ntiti
esCh
apte
r 7Ch
emica
l Rea
ctio
ns o
ccur
Eve
ryw
here
…•
…w
hen
fuel
bur
ns w
ith o
xyge
n in
our
cars
to
mak
e th
e ca
r mov
e…•
…w
hen
we
cook
our
food
…•
…w
hen
we
dye
our h
air…
•…
in o
ur b
odie
s, ch
emica
l rea
ctio
ns co
nver
t fo
od in
to m
olec
ules
that
bui
ld a
nd m
ove
mus
cle…
•…
in le
aves
of t
rees
and
pla
nts,
carb
on d
ioxi
de
and
wat
er a
re co
nver
ted
to ca
rboh
ydra
tes…
Som
e ch
emica
l rea
ctio
ns a
re si
mpl
e,
whe
reas
oth
ers a
re q
uite
com
plex
…•
How
ever
, the
y ca
n al
l be
writ
ten
by ch
emica
l eq
uatio
ns th
at ch
emist
s use
to d
escr
ibe
chem
ical
reac
tions
.
•In
eve
ry ch
emica
l rea
ctio
n, a
tom
s are
rear
rang
ed to
gi
ve n
ew su
bsta
nces
.–
Just
like
follo
win
g a
recip
e, ce
rtai
n in
gred
ient
s are
co
mbi
ned
(and
ofte
n he
ated
) to
form
som
ethi
ng n
ew.
Chap
ter S
even
7.1
–Eq
uatio
ns fo
r Che
mica
l Rea
ctio
ns7.
2 –
Type
s of R
eact
ions
7.3
–Ox
idat
ion-
Redu
ctio
n Re
actio
ns7.
4 –
The
Mol
e7.
5 –
Mol
ar M
ass a
nd C
alcu
latio
ns7.
6 –
Mol
e Re
latio
nshi
ps in
Che
mica
l Equ
atio
ns7.
7 –
Mas
s Cal
cula
tions
for R
eact
ions
7.8
–Lim
iting
Rea
ctan
ts a
nd P
erce
nt Y
ield
7.
9 –
Ener
gy in
Che
mica
l Rea
ctio
ns
7.1
Equa
tions
for C
hem
ical R
eact
ions
Writ
e a
bala
nced
equ
atio
n fro
m fo
rmul
as o
f the
reac
tant
s and
pro
duct
s for
a
reac
tion;
det
erm
ine
the
num
ber o
f ato
ms i
n th
e re
acta
nts a
nd p
rodu
cts.
Chem
ical C
hang
e
•A
chem
ical c
hang
eoc
curs
whe
n a
subs
tanc
e is
conv
erte
d in
to o
ne o
r m
ore
new
subs
tanc
es th
at h
ave
diffe
rent
form
ulas
and
pro
pert
ies.
•Fo
r exa
mpl
e, w
hen
silve
r tar
nish
es,
the
shin
y, sil
ver m
etal
(Ag)
reac
ts
with
sulfu
r (S)
to b
ecom
e th
e du
ll,
blac
k su
bsta
nce
we
call
tarn
ish
(Ag 2
S).
Chem
ical R
eact
ion
•A
chem
ical r
eact
ion
alw
ays
invo
lves
a ch
emica
l cha
nge
beca
use
atom
s of t
he re
actin
g su
bsta
nces
form
new
co
mbi
natio
ns w
ith n
ew p
rope
rtie
s.
•Fo
r exa
mpl
e, a
chem
ical r
eact
ion
(and
chem
ical c
hang
e) ta
kes p
lace
w
hen
a pi
ece
of ir
on (F
e)
com
bine
s with
oxy
gen
(O2)
in th
e ai
r to
prod
uce
a ne
w su
bsta
nce,
ru
st (F
e 2O
3), w
hich
has
a re
ddish
-br
own
colo
r.
Evid
ence
of a
Che
mica
l Rea
ctio
n
Durin
g a
chem
ical c
hang
e, n
ew
prop
ertie
s are
ofte
n vi
sible
, whi
ch
indi
cate
s tha
t a ch
emica
l rea
ctio
n to
ok p
lace
.
Chem
ical E
quat
ion
Whe
n yo
u bu
ild a
mod
el
airp
lane
or p
repa
re a
new
recip
e,
you
follo
w a
set o
f dire
ctio
n.
Thes
e di
rect
ions
tell
you
wha
t m
ater
ials
to u
se a
nd th
e pr
oduc
ts yo
u w
ill o
btai
n.
In ch
emist
ry, a
chem
ical r
eact
ion
tells
us t
he
mat
eria
ls w
e ne
ed a
nd th
e pr
oduc
ts th
at w
ill fo
rm.
Writ
ing
a ch
emica
l equ
atio
n
Supp
ose
you
wor
k in
a b
icycle
shop
ass
embl
ing
whe
els a
nd fr
ames
into
bicy
cles.
You
coul
d re
pres
ent t
his b
y a
simpl
e eq
uatio
n:
Writ
ing
a ch
emica
l equ
atio
n
Retu
rn to
the
silve
r exa
mpl
e:
Whe
n sil
ver t
arni
shes
, the
shin
y, sil
ver
met
al (A
g) re
acts
with
sulfu
r (S)
to
beco
me
the
dull,
bla
ck su
bsta
nce
we
call
tarn
ish (A
g 2S)
.
* Un
bala
nced
equ
atio
n
Writ
ing
a ch
emica
l equ
atio
n
Retu
rn to
the
iron
exam
ple:
A ch
emica
l rea
ctio
n ta
kes p
lace
whe
n a
piec
e of
iro
n (F
e) c
ombi
nes w
ith o
xyge
n (O
2) in
the
air t
o pr
oduc
e a
new
subs
tanc
e, ru
st (F
e 2O
3), w
hich
ha
s a re
ddish
-bro
wn
colo
r.
* Un
bala
nced
equ
atio
n
Gene
rally
, eac
h fo
rmul
a is
follo
wed
by
an a
bbre
viat
ion,
in p
aren
thes
es, t
hat
give
s the
phy
sical
stat
e of
the
subs
tanc
e.so
lid (s
)liq
uid
(l)ga
s (g)
aque
ous (
aq) d
issol
ved
in w
ater
Writ
ing
a ch
emica
l equ
atio
n
Som
e re
actio
ns re
quire
hea
t to
be
adde
d in
ord
er fo
r the
chan
ge to
oc
cur.
For e
xam
ple,
whe
n yo
u bu
rn
char
coal
in a
gril
l, th
e ca
rbon
(C) i
n th
e ch
arco
al co
mbi
nes w
ith th
e ox
ygen
(O2)
to fo
rm ca
rbon
dio
xide
.
* Un
bala
nced
equ
atio
n
Chem
ical e
quat
ion
sym
bols
Cu(s
) + S
(s) →CuS
(s)
CaCO
3(s)
→CaO(s
) + C
O2(
g)
Na2S
O4(
aq) +
BaC
l 2(aq
)→BaSO
4(s)
+ 2N
aCl (a
q)
Iden
tifyi
ng a
bal
ance
d ch
emica
l equ
atio
n
Whe
n a
chem
ical r
eact
ion
take
s pla
ce,
the
bond
s bet
wee
n th
e at
oms o
f the
re
acta
nts a
re b
roke
n an
d ne
w b
onds
ar
e fo
rmed
to g
ive
the
prod
ucts
.
Iden
tifyi
ng a
bal
ance
d ch
emica
l equ
atio
n
All a
tom
s are
cons
erve
dw
hich
mea
ns th
at a
tom
s can
not b
e ga
ined
, los
t, or
chan
ged
into
ano
ther
type
of e
lem
ent d
urin
g th
e ch
emica
l rea
ctio
ns
Ever
y ch
emica
l rea
ctio
n m
ust b
e w
ritte
n as
a b
alan
ced
reac
tion,
whi
ch
show
s the
sam
e nu
mbe
r of a
tom
s for
eac
h el
emen
t for
the
reac
tant
s an
d in
the
prod
ucts
.
Bala
nced
chem
ical e
quat
ion
Cons
ider
the
follo
win
g in
whi
ch h
ydro
gen
(H2)
reac
ts w
ith o
xyge
n (O
2) to
form
wat
er:
H 2(g
) + O
2(g)
H 2
O(g
) un
bala
nced
ther
e ar
e th
e sa
me
num
ber o
f hyd
roge
nson
bot
h sid
es (2
) but
di
ffere
nt n
umbe
rs o
f oxy
gen
atom
s (2
and
1) so
it is
unb
alan
ced.
Bala
nced
chem
ical e
quat
ion
H 2(g
) + O
2(g)
H 2
O(g
) un
bala
nced
We
use
who
le n
umbe
rs ca
lled
coef
ficie
ntsi
n fro
nt o
f for
mul
as.
Coef
ficie
nts i
ndica
te h
ow m
any
of e
ach
mol
ecul
e ar
e in
an
equa
tion.
In th
e ba
lanc
edeq
uatio
n, th
ere
are
two
H 2m
olec
ules
and
two
H 2O
m
olec
ules
:
This
illus
trat
es th
e La
w o
f Con
serv
atio
n of
Mat
ter w
hich
stat
es th
at m
atte
r ca
nnot
be
crea
ted
or d
estr
oyed
dur
ing
a ch
emica
l rea
ctio
n.
Prac
tice
coun
ting
atom
s
Indi
cate
the
num
ber o
f eac
h ty
pe o
f ato
m in
the
follo
win
g ba
lanc
ed
chem
ical e
quat
ion:
Fe2S
3(s)
+ 6H
Cl(a
q)
2FeC
l 3(aq
) + 3
H 2S (
g)
reac
tant
spr
oduc
tsFe S H Cl
Prac
tice
coun
ting
atom
s
Indi
cate
the
num
ber o
f eac
h ty
pe o
f ato
m in
the
follo
win
g ba
lanc
ed
chem
ical e
quat
ion: 2C
2H6(
g) +
7O2(
g) →4CO
2(g)
+ 6H
2O(g
)
reac
tant
spr
oduc
tsC H O
Bala
ncin
g ch
emica
l equ
atio
ns
Whe
n sil
ver t
arni
shes
, the
shin
y, sil
ver m
etal
(Ag)
reac
ts w
ith
sulfu
r (S)
to b
ecom
e th
e du
ll, b
lack
subs
tanc
e w
e ca
ll ta
rnish
(A
g 2S)
. Wha
t is t
he b
alan
ced
chem
ical e
quat
ions
des
crib
ing
this
reac
tion?
Bala
ncin
g ch
emica
l equ
atio
ns
A ch
emica
l rea
ctio
n ta
kes p
lace
whe
n a
piec
e of
iron
(Fe)
co
mbi
nes w
ith o
xyge
n (O
2) in
the
air t
o pr
oduc
e a
new
subs
tanc
e,
rust
(Fe 2
O3),
whi
ch h
as a
redd
ish-b
row
n co
lor.
Wha
t is t
he
bala
nced
chem
ical e
quat
ion
desc
ribin
g th
is re
actio
n?
Bala
ncin
g ch
emica
l equ
atio
ns
Bala
nce
the
follo
win
g ch
emica
l rea
ctio
n:Na
3PO 4
(aq)
+ M
gCl 2(
aq)
Mg 3
(PO
4) 2(s
) + N
aCl (a
q)
Chap
ter S
even
7.1
–Eq
uatio
ns fo
r Che
mica
l Rea
ctio
ns7.
2 –
Type
s of R
eact
ions
7.3
–Ox
idat
ion-
Redu
ctio
n Re
actio
ns7.
4 –
The
Mol
e7.
5 –
Mol
ar M
ass a
nd C
alcu
latio
ns7.
6 –
Mol
e Re
latio
nshi
ps in
Che
mica
l Equ
atio
ns7.
7 –
Mas
s Cal
cula
tions
for R
eact
ions
7.8
–Lim
iting
Rea
ctan
ts a
nd P
erce
nt Y
ield
7.
9 –
Ener
gy in
Che
mica
l Rea
ctio
ns
7.2
Type
s of R
eact
ions
Iden
tify
a re
actio
n as
a co
mbi
natio
n, d
ecom
posit
ion,
sing
le re
plac
emen
t, do
uble
repl
acem
ent,
or co
mbu
stio
n.A
grea
t num
ber o
f rea
ctio
ns o
ccur
in n
atur
e, in
bi
olog
ical s
yste
ms,
and
in th
e la
bora
tory
.
How
ever
, the
re a
re so
me
gene
ral p
atte
rns a
mon
g al
l rea
ctio
ns th
at h
elp
us cl
assif
y rea
ctio
ns.
* no
te –
som
e re
actio
ns m
ay fi
t in
mor
eth
an o
ne ca
tego
ry.
Com
bina
tion
Reac
tions
•In
a co
mbi
natio
n re
actio
n, tw
o or
mor
e el
emen
ts o
r co
mpo
unds
bon
d to
form
one
pro
duct
.
•Fo
r exa
mpl
e, su
lfur a
nd o
xyge
n co
mbi
ne to
form
the
prod
uct
sulfu
r dio
xide
.
Com
bina
tion
Reac
tions
2Mg (
s) +
O2(
g)
2MgO
(s)
N 2(g
) + 3
H 2(g
) 2N
H 3(g
)
Cu(s
) + S
(s)
CuS (
s)
MgO
(s) +
CO
2(g)
M
gCO
3(s)
Deco
mpo
sitio
n Re
actio
ns
In a
dec
ompo
sitio
n re
actio
n, a
reac
tant
split
s int
o tw
o or
mor
e sim
pler
pro
duct
s.
For e
xam
ple,
whe
n m
ercu
ry (I
I) ox
ide
is he
ated
, the
com
poun
d br
eaks
apa
rt in
to m
ercu
ry a
tom
s and
oxy
gen.
2HgO
(s) →2Hg
(l) +
O2(
g)
Deco
mpo
sitio
n Re
actio
ns
CaCO
3(s)
→CaO(s
) + C
O2(
g)
Fe2S
3(s)
2F
e (s)
+ 3S
(s)
Repl
acem
ent R
eact
ions
In a
repl
acem
ent r
eact
ion,
ele
men
ts in
a co
mpo
und
are
repl
aced
by
oth
er e
lem
ents
.
In a
sing
le re
plac
emen
t rea
ctio
n,on
e el
emen
t sw
itche
s pla
ces
with
ano
ther
ele
men
t in
the
reac
tant
s.
*A a
nd B
switc
h pl
aces
.
Repl
acem
ent R
eact
ions
Zn(s
) + 2
HCl (a
q)
H 2(g
) + Z
nCl 2(
aq)
Cl2(
g) +
2KBr
(s)
2KCl
(s) +
Br 2
(l)
Repl
acem
ent R
eact
ions
In a
dou
ble
repl
acem
ent r
eact
ion,
the
posit
ive
ions
in th
e re
actin
g co
mpo
unds
switc
h pl
aces
.
Repl
acem
ent R
eact
ions
BaCl
2(aq
) + N
a 2SO
4(aq
)
NaO
H (aq
) + H
Cl(a
q)
Com
bust
ion
Reac
tions
The
burn
ing
of a
cand
le a
nd th
e bu
rnin
g of
fuel
in th
e en
gine
of a
car a
re e
xam
ples
of c
ombu
stio
n re
actio
ns.
In a
com
bust
ion
reac
tion,
a ca
rbon
-con
tain
ing
com
poun
d bu
rns i
n ox
ygen
(O2)
to p
rodu
ce ca
rbon
di
oxid
e (C
O2)
and
wat
er (H
2O) a
nd e
nerg
y in
the
form
of
hea
t or f
lam
e.
Fuel
+ O
2CO
2+
H 2O
*unb
alan
ced
Fuel
ofte
n: m
etha
ne (C
H 4),
prop
ane
(C3H
8), o
r sim
ilar.
Som
etim
es a
lso h
as o
xyge
n at
oms i
n th
e fo
rmul
a: C
3H7O
Com
bust
ion
Reac
tions
Fuel
+ O
2CO
2+
H 2O
unba
lanc
ed
Met
hane
gas
(CH 4
) aka
nat
ural
gas
und
ergo
es co
mbu
stio
n w
hen
used
to co
ok fo
od o
n a
gas s
tove
:
CH4(
g) +
2O
2(g)
→CO 2(g
) + 2
H 2O
(g) +
ene
rgy
Com
bust
ion
of p
ropa
ne (C
3H8):
C 3H 8
(g) +
5O
2(g)
→3CO2(
g) +
4H2O
(g) +
ene
rgy
Sum
mar
y of
Rea
ctio
n Ty
pes
Prac
tice
Clas
sify
as co
mbi
natio
n, d
ecom
posit
ion,
sing
le re
plac
emen
t, do
uble
repl
acem
ent,
or co
mbu
stio
n re
actio
n.
2Fe 2
O 3(s
) + 3
C (s)
3C
O 2(g
)+ 4
Fe(s
)
Prac
tice
Clas
sify
as co
mbi
natio
n, d
ecom
posit
ion,
sing
le re
plac
emen
t, do
uble
repl
acem
ent,
or co
mbu
stio
n re
actio
n.
2KCl
O3(
s) →2KC
l (s) +
3O 2
(g)
Prac
tice
Clas
sify
as co
mbi
natio
n, d
ecom
posit
ion,
sing
le re
plac
emen
t, do
uble
repl
acem
ent,
or co
mbu
stio
n re
actio
n.
C 2H 4
(g) +
3O 2
(g)
→2CO2(
g) +
2H2O
(g) +
ene
rgy
Chap
ter S
even
7.1
–Eq
uatio
ns fo
r Che
mica
l Rea
ctio
ns7.
2 –
Type
s of R
eact
ions
7.3
–Ox
idat
ion-
Redu
ctio
n Re
actio
ns7.
4 –
The
Mol
e7.
5 –
Mol
ar M
ass a
nd C
alcu
latio
ns7.
6 –
Mol
e Re
latio
nshi
ps in
Che
mica
l Equ
atio
ns7.
7 –
Mas
s Cal
cula
tions
for R
eact
ions
7.8
–Lim
iting
Rea
ctan
ts a
nd P
erce
nt Y
ield
7.
9 –
Ener
gy in
Che
mica
l Rea
ctio
ns
7.3
Oxid
atio
n-Re
duct
ion
Reac
tions
Defin
e th
e te
rms o
xida
tion
and
redu
ctio
n, id
entif
y th
e re
acta
nts a
s oxi
dize
dan
d re
duce
d.
Anot
her t
ype
of re
actio
n is
the:
oxid
atio
n-re
duct
ion
reac
tion
This
is a
cont
inua
tion
of th
e pr
evio
us se
ctio
n Ty
pes o
f Rea
ctio
ns.
The
oxid
atio
n-re
duct
ion
reac
tion
is ar
guab
ly o
ne o
f the
mos
t im
port
ant a
nd u
nden
iabl
y the
mos
t com
plica
ted
of th
e ty
pes w
e w
ill d
iscus
s in
this
chap
ter.
Beca
use
of th
is, o
xida
tion-
redu
ctio
n re
actio
ns h
as it
’s ow
n se
ctio
n in
this
chap
ter.
Perh
aps y
ou h
ave
neve
r hea
rd o
f an
oxid
atio
n an
d re
duct
ion
reac
tion.
How
ever
, th
is ty
pe o
f rea
ctio
n ha
s man
y im
port
ant a
pplic
atio
ns in
you
r eve
ryda
y lif
e.
Rust
y na
il
Tarn
ish o
n a
silve
r spo
on
Corr
osio
n on
met
al
Whe
n yo
u tu
rn o
n th
e lig
hts i
n yo
ur ca
r, an
oxi
datio
n-re
duct
ion
reac
tion
with
in
the
car b
atte
ry p
rovi
des t
he e
lect
ricity
.
Whe
n yo
u lig
ht a
cam
pfire
, as t
he w
ood
burn
s, ox
ygen
com
bine
s with
carb
on a
nd
hydr
ogen
to p
rodu
ce ca
rbon
dio
xide
, wat
er, a
nd h
eat.
-In
sect
ion
7.2
we
calle
d th
is a
com
bust
ion
reac
tion.
It is
. It’s
also
a ox
idat
ion-
redu
ctio
n re
actio
n.
Whe
n yo
u ea
t sta
rchy
food
, the
star
ches
bre
ak d
own
to g
ive
gluc
ose
whi
ch is
ox
idize
d in
our
cells
to g
ive
you
ener
gy.
Oxi
datio
n-Re
duct
ion
Reac
tions
In a
n ox
idat
ion-
redu
ctio
n re
actio
n(re
dox)
, ele
ctro
ns a
re
tran
sfer
red
from
one
subs
tanc
e to
ano
ther
.
Oxi
datio
n-Re
duct
ion
Reac
tions
If on
e su
bsta
nce
lose
s an
elec
tron
, ano
ther
subs
tanc
e m
ust g
ain
the
elec
tron
.
The
subs
tanc
e th
at lo
st e
lect
rons
was
oxi
dize
dan
d w
e de
fine
oxid
atio
nas
the
loss
of e
lect
rons
The
subs
tanc
e th
at g
aine
d el
ectr
ons w
as re
duce
dan
d w
e de
fine
redu
ctio
nas
the
gain
of e
lect
rons
Oxi
datio
n-Re
duct
ion
Reac
tions
The
subs
tanc
e th
at lo
st e
lect
rons
was
oxi
dize
dan
d w
e de
fine
oxid
atio
nas
the
loss
of e
lect
rons
The
subs
tanc
e th
at g
aine
d el
ectr
ons w
as re
duce
dan
d w
e de
fine
redu
ctio
nas
the
gain
of e
lect
rons
Redo
x –Ex
ampl
e 1
The
gree
n co
lor t
hat a
ppea
rs o
n co
pper
surfa
ces i
s due
par
tly to
:
2Cu (
s) +
O2(
g)
2CuO
(s)
This
is a
redo
x rea
ctio
n, a
nd w
e ca
n br
eak
the
equa
tion
up to
show
this.
Redo
x –Ex
ampl
e 1
Brea
k th
e eq
uatio
n in
to o
xida
tion
and
redu
ctio
n.
2Cu (
s) +
O2(
g)
2CuO
(s)
Oxid
atio
nGo
ing
from
cha
rge
0 to
+2,
Cu
lost
two
elec
tron
s and
Cu
was
ox
idize
d.
OIL
RIG
Redo
x –Ex
ampl
e 1
Brea
k th
e eq
uatio
n in
to o
xida
tion
and
redu
ctio
n.
2Cu (
s) +
O2(
g)
2CuO
(s)
Redu
ctio
nGo
ing
from
cha
rge
0 to
-2, O
2ga
ined
four
ele
ctro
ns a
nd O
2w
as re
duce
d.(E
ach
O w
ent f
rom
0 to
-2 a
nd g
aine
d 2
elec
tron
s. Be
caus
e th
ere
are
two
oxyg
en a
tom
s in
O2,
that
’s a
tota
l of f
our e
lect
rons
.)
OIL
RIG
Redo
x –Ex
ampl
e 1
To su
mm
arize
:
2Cu (
s)
2Cu2+
(s)
+ 4e
-ox
idat
ion
O2(
g) +
4e-
2O2-
(s)
redu
ctio
n
In a
redo
x rea
ctio
n, th
ere’
s alw
ays t
wo
piec
es th
at o
ccur
. One
su
bsta
nce
is ox
idize
d (lo
ses e
lect
rons
) and
ano
ther
subs
tanc
e is
redu
ced
(gai
ns th
e lo
st e
lect
rons
).
Redo
x –Ex
ampl
e 1
Orig
inal
equ
atio
n:2C
u (s)
+ O
2(g)
2C
uO(s
)
The
two
half
reac
tions
can
be a
dded
bac
k to
geth
er to
giv
e th
e or
igin
al e
quat
ion.
2Cu (
s)2C
u2+(s
) +
4e-
oxid
atio
n
O2(
g) +
4e-
2O2-
(s)
redu
ctio
n
Redo
x –Ex
ampl
e 2
Zn(s
) + C
uSO
4(aq
) Zn
SO4(
aq) +
Cu (
s)
Oxi
datio
n ha
lf-re
actio
n:
Redu
ctio
n ha
lf-re
actio
n:
____
____
___
was
oxid
ized
____
____
___
was
redu
ced
OIL
RIG
Redo
x –Ex
ampl
e 3
Zn(s
) + C
l 2(g)
Zn
Cl2(
s)
Oxi
datio
n ha
lf-re
actio
n:
Redu
ctio
n ha
lf-re
actio
n:
____
____
___
was
oxid
ized
____
____
___
was
redu
ced
OIL
RIG
Chap
ter S
even
7.1
–Eq
uatio
ns fo
r Che
mica
l Rea
ctio
ns7.
2 –
Type
s of R
eact
ions
7.3
–Ox
idat
ion-
Redu
ctio
n Re
actio
ns7.
4 –
The
Mol
e7.
5 –
Mol
ar M
ass a
nd C
alcu
latio
ns7.
6 –
Mol
e Re
latio
nshi
ps in
Che
mica
l Equ
atio
ns7.
7 –
Mas
s Cal
cula
tions
for R
eact
ions
7.8
–Lim
iting
Rea
ctan
ts a
nd P
erce
nt Y
ield
7.
9 –
Ener
gy in
Che
mica
l Rea
ctio
ns
7.4
The
Mol
eUs
e Av
ogad
ro’s
num
bert
o de
term
ine
the
num
ber o
f pa
rticl
es in
a g
iven
num
ber o
f mol
es.
At th
e gr
ocer
y st
ore,
you
buy
eggs
by
the
doze
n, o
r sod
a by
the
case
. At
Sta
ples
, pen
cils a
re o
rder
ed b
y th
e gr
oss a
nd p
aper
by
the
ream
.
The
term
s doz
en, c
ase,
gro
ss, a
nd re
am a
re u
sed
to co
unt t
he n
umbe
r of
item
s pre
sent
.
Chem
ists
doth
esa
me
thin
g,an
dth
eyca
llit
the
mol
e.
The
mol
e
In ch
emist
ry, p
artic
les (
such
as a
tom
s, m
olec
ules
, and
ions
) are
co
unte
d by
the
mol
ew
hich
cont
ains
6.0
2 x 1
023ite
ms.
Avog
adro
’s nu
mbe
r
6.02
x 1
023 is
kno
wn
as A
voga
dro’
s num
ber.
602
000
000
000
000
000
000
000
= 6.
02 x
1023
It is
a ve
ryla
rge
num
ber a
nd w
e us
e it
beca
use
atom
s are
so sm
all t
hat
it ta
kes a
n ex
trem
ely
larg
e nu
mbe
r of a
tom
s to
prov
ide
a us
able
am
ount
to
use
in ch
emica
l rea
ctio
ns in
a la
bora
tory
.
The
mol
e an
d Av
ogad
ro’s
num
ber
1 m
ole
of a
ny e
lem
ent a
lway
s con
tain
s Avo
gadr
o’s n
umbe
r of a
tom
s.
1 m
ole
of ca
rbon
ato
ms c
onta
ins 6
.02
x 1023
carb
on a
tom
s.1
mol
e of
alu
min
um a
tom
s con
tain
s 6.0
2 x
1023
alum
inum
ato
ms.
1 m
ole
of a
ny e
lem
ent =
6.0
2 x 1
023at
oms o
f tha
t ele
men
t.1
mol
e of
any
com
poun
d =
6.02
x 10
23of
that
com
poun
d
1 m
ole
of C
O2
cont
ains
6.0
2 x
1023
mol
ecul
es o
f CO
2.1
mol
e of
NaC
lcon
tain
s 6.0
2 x 1
023 m
olec
ules
of N
aCl.
Conv
ertin
g m
ole ↔
par
ticle
s
We
use
Avog
adro
’s nu
mbe
r as a
conv
ersio
n fa
ctor
to co
nver
t be
twee
n th
e m
oles
of a
subs
tanc
e an
d th
e nu
mbe
r of p
artic
les i
t co
ntai
ns. .
.Th
e pa
rtic
lesc
an b
e at
oms,
mol
ecul
es, i
ons,
or a
nyth
ing.
Rep
lace
pa
rticl
esw
ith it
emsi
f tha
t hel
ps.
Prac
tice
Conv
ert 4
.00
mol
es o
f sul
fur t
o at
oms o
f sul
fur.
Prac
tice
Conv
ert 3
.01
x 1024
mol
ecul
es o
f CO
2to
mol
es o
f CO
2
mol
es in
chem
ical f
orm
ulas
We
have
seen
in p
ast c
hapt
ers t
hat t
he su
bscr
ipts
in th
e ch
emica
l for
mul
a of
a co
mpo
und
indi
cate
the
num
ber o
f ato
ms
of e
ach
type
of e
lem
ent i
n th
e co
mpo
und.
For e
xam
ple,
asp
irin,
C9H
8O4
mol
es in
chem
ical f
orm
ulas
The
subs
crip
ts a
lso te
ll us
the
num
ber o
f mol
es o
f eac
h el
emen
t in
1 m
ole
of a
spiri
n.
mol
es in
chem
ical f
orm
ulas
And
beca
use
1 m
ole
aspi
rin =
6.0
2 x 1
023m
olec
ules
of a
spiri
n
mol
es in
chem
ical f
orm
ulas
We
can
also
use
subs
crip
ts fr
om th
e fo
rmul
a, C
9H8O
4, w
e ca
n w
rite
the
conv
ersio
n fa
ctor
s for
eac
h of
the
elem
ents
in 1
mol
e of
asp
irin.
Prac
tice
Prop
yl a
ceta
te, C
5H10
O2,
give
s the
odo
r and
ta
ste
of p
ears
. How
man
y m
oles
of C
are
pr
esen
t in
1.50
mol
es o
f pro
pyl a
ceta
te?
Chap
ter S
even
7.1
–Eq
uatio
ns fo
r Che
mica
l Rea
ctio
ns7.
2 –
Type
s of R
eact
ions
7.3
–Ox
idat
ion-
Redu
ctio
n Re
actio
ns7.
4 –
The
Mol
e7.
5 –
Mol
ar M
ass a
nd C
alcu
latio
ns7.
6 –
Mol
e Re
latio
nshi
ps in
Che
mica
l Equ
atio
ns7.
7 –
Mas
s Cal
cula
tions
for R
eact
ions
7.8
–Lim
iting
Rea
ctan
ts a
nd P
erce
nt Y
ield
7.
9 –
Ener
gy in
Che
mica
l Rea
ctio
ns
7.5
Mol
ar M
ass a
nd C
alcu
latio
nsCa
lcula
te th
e m
olar
mas
sfor
a su
bsta
nce
give
n its
che
mica
l fo
rmul
a; u
se m
olar
mas
s to
conv
ert b
etw
een
gram
sand
mol
es.
A sin
gle
atom
or m
olec
ule
is m
uch
too
smal
l to
wei
gh, e
ven
usin
g th
e be
st sc
ale.
In fa
ct, i
t tak
es a
hug
e nu
mbe
r of a
tom
s or m
olec
ules
to m
ake
enou
gh o
f a su
bsta
nce
for y
ou to
see.
An a
mou
nt o
f wat
er th
at co
ntai
ns A
voga
dro’
s num
ber o
f wat
er
mol
ecul
es (6
.02
x 1023
) is o
nly
a fe
w si
ps!
So in
a la
b, w
e us
e a
scal
e to
wei
gh o
ut su
bsta
nces
in m
oles
.
Mol
ar M
ass
For a
ny e
lem
ent,
the
quan
tity c
alle
d m
olar
mas
sis t
he q
uant
ity
in g
ram
s tha
t equ
als t
he a
tom
ic m
ass o
f tha
t ele
men
t.
Mol
ar M
ass
We
are
coun
ting
6.02
x 1
023at
oms o
f an
elem
ent w
hen
we
wei
gh o
ut th
e nu
mbe
r of g
ram
s equ
al to
the
mol
ar m
ass.
For e
xam
ple,
car
bon
has a
n at
omic
mas
s of 1
2.01
on
the
perio
dic t
able
. Thi
s m
eans
1 m
ole
of ca
rbon
ato
ms h
as th
e m
ass o
f 12.
01g.
Then
to o
btai
n 1
mol
e of
carb
on
atom
s, w
e w
ould
wei
gh o
ut 1
2.01
g of
carb
on.
Atom
ic m
ass o
f Car
bon:
12.
01 a
mu
Mol
ar m
ass o
f Car
bon:
12.
01 g
/mol
Usin
g M
olar
Mas
s
The
mol
ar m
ass o
f an
elem
ent i
s use
ful t
o co
nver
t mol
es o
f an
elem
ent t
o gr
ams (
or g
ram
s to
mol
es).
For e
xam
ple,
1 m
ole
of su
lfur a
s a m
ass o
f 32.
066g
1 m
ole
S =
32.0
66g
of S
Mol
ar M
ass o
f a C
ompo
und
We
can
calcu
late
the
mol
ar m
ass o
f a co
mpo
und
by a
ddin
g up
the
mol
ar m
ass
of e
ach
atom
.
Exam
ple:
Cal
cula
te th
e m
olar
mas
s of l
ithiu
m ca
rbon
ate
(Li 2C
O3)
Prac
tice
Calcu
late
the
mol
ar m
ass f
or sa
licyc
licac
id, C
7H6O
3.
Exam
ples
of 1
mol
e
Calcu
latio
ns u
sing
Mol
ar M
ass
We
can
now
chan
ge fr
om m
oles
to g
ram
s (or
gra
ms t
o m
oles
) us
ing
the
mol
ar m
ass a
s a co
nver
sion
fact
or.
Exam
ple:
Con
vert
0.7
50 m
oles
of s
ilver
to g
ram
s of s
ilver
.
Calcu
latio
ns u
sing
Mol
ar M
ass
We
can
chan
ge m
oles
to g
ram
s (or
vice
ver
sa) f
or a
com
poun
d us
ing
the
com
poun
d’s m
olar
mas
s.
Exam
ple:
A b
ox o
f sal
t con
tain
s 737
g o
f NaC
l. Ho
w m
any
mol
es o
f NaC
lar
e pr
esen
t?
Sum
mar
yCh
apte
r Sev
en
7.1
–Eq
uatio
ns fo
r Che
mica
l Rea
ctio
ns7.
2 –
Type
s of R
eact
ions
7.3
–Ox
idat
ion-
Redu
ctio
n Re
actio
ns7.
4 –
The
Mol
e7.
5 –
Mol
ar M
ass a
nd C
alcu
latio
ns7.
6 –
Mol
e Re
latio
nshi
ps in
Che
mica
l Equ
atio
ns7.
7 –
Mas
s Cal
cula
tions
for R
eact
ions
7.8
–Lim
iting
Rea
ctan
ts a
nd P
erce
nt Y
ield
7.
9 –
Ener
gy in
Che
mica
l Rea
ctio
ns
7.6
Mol
e Re
latio
nshi
ps in
Chem
ical E
quat
ions
Give
a q
uant
ity in
mol
es o
f rea
ctan
t or p
rodu
ct, u
se a
mol
e-m
ole
fact
orfro
m th
e ba
lanc
ed ch
emica
l equ
atio
n to
calcu
late
the
num
ber o
f mol
esof
ano
ther
subs
tanc
e in
the
reac
tion.
Law
of C
onse
rvat
ion
of M
ass
In a
ny ch
emica
l rea
ctio
n, th
e to
tal a
mou
nt o
f mat
ter i
n th
e re
acta
nts i
s equ
al to
the
tota
l am
ount
of m
atte
r in
the
prod
ucts
. -a
n ap
plica
tion
of th
e La
w o
f Con
serv
atio
n of
Mas
s
Thus
no
mat
eria
l is l
ost o
r gai
ned
as o
rigin
al su
bsta
nces
are
ch
ange
d in
to n
ew su
bsta
nces
.
For e
xam
ple,
tarn
ish (A
g 2S)
, for
ms w
hen
silve
r rea
cts w
ith su
lfur t
o fo
rm si
lver
sulfi
de:
2Ag (
s) +
S (s)
Ag
2S(s
)
For e
very
2 si
lver
ato
ms,
1 su
lfur a
tom
is re
quire
dO
rFo
r eve
ry 2
mol
es o
f silv
er a
tom
s, 1
mol
e of
sulfu
r ato
ms i
s req
uire
d.
Beca
use
the
mol
ar m
ass c
an b
e de
term
ined
, the
mol
es o
f Ag,
S, a
nd
Ag2S
can
also
be
stat
ed in
term
s of m
ass (
gram
s) o
f eac
h…
Thus
215
.8 g
of A
g an
d 32
.1 g
of S
reac
ts to
form
247
.9 g
of A
g 2S.
215.
8g +
32.
1g =
249
.9g
The
tota
l mas
s of r
eact
ants
(249
.9 g)
equ
als t
he to
tal m
ass o
f the
pr
oduc
ts (2
49.9
g).
Info
in a
bal
ance
d eq
uatio
n
The
vario
us w
ays i
n w
hich
a ch
emica
l equ
atio
n ca
n be
inte
rpre
ted:
Mol
e-m
ole
fact
ors
Whe
n iro
n re
acts
with
sulfu
r, th
e pr
oduc
t is i
ron(
III) s
ulfid
e:2F
e (s)
+ 3S
(s)
Fe2S
3(s)
From
the
bala
nced
equ
atio
n, w
e se
e th
at 2
mol
es o
f iro
n re
acts
with
3 m
oles
of
sulfu
r to
form
mol
e of
iron
(II) s
ulfid
e.
(Act
ually
, any
am
ount
of i
ron
or su
lfur m
ay b
e us
ed, b
ut th
e ra
tioof
iro
n re
actin
g w
ith
sulfu
r will
alw
ays b
e th
e sa
me.
)
Mol
e-m
ole
fact
ors
From
the
coef
ficie
nts,
we
can
writ
e m
ole-
mol
e fa
ctor
sbet
wee
n an
y tw
o co
mpo
unds
in a
n eq
uatio
n.2F
e (s)
+ 3S
(s)
Fe2S
3(s)
Fe a
nd S
:
Fe a
nd F
e 2S:
S an
d Fe
2S:
Mol
e-m
ole
fact
ors i
n ca
lcula
tions
Whe
neve
r you
pre
pare
a re
cipe,
you
ne
ed to
kno
w th
e pr
oper
am
ount
s of
ingr
edie
nts a
nd h
ow m
uch
the
recip
e w
ill m
ake.
The
sam
e is
true
for c
hem
istry
.
Now
that
we
have
writ
ten
all t
he p
ossib
le m
ole-
mol
e fa
ctor
s for
2Fe (
s) +
3S(s
) Fe
2S3(
s)
we
will
use
thos
e m
ole-
mol
e fa
ctor
s in
a ch
emica
l cal
cula
tion.
Prac
tice
#1
How
man
y m
oles
of s
ulfu
r are
nee
ded
to re
act w
ith 1
.42
mol
es
of ir
on?
2Fe (
s) +
3S(s
) Fe
2S3(
s)
2molesFe 3molesS
2molesFe
1moleFe 2S 3
3molesS
1moleFe 2S 3
Prac
tice
#2
How
man
y m
oles
of i
ron
are
need
ed to
reac
t with
2.7
5 m
oles
of
sulfu
r?2F
e (s)
+ 3S
(s)
Fe2S
3(s)
2molesFe 3molesS
2molesFe
1moleFe 2S 3
3molesS
1moleFe 2S 3
Chap
ter S
even
7.1
–Eq
uatio
ns fo
r Che
mica
l Rea
ctio
ns7.
2 –
Type
s of R
eact
ions
7.3
–Ox
idat
ion-
Redu
ctio
n Re
actio
ns7.
4 –
The
Mol
e7.
5 –
Mol
ar M
ass a
nd C
alcu
latio
ns7.
6 –
Mol
e Re
latio
nshi
ps in
Che
mica
l Equ
atio
ns7.
7 –
Mas
s Cal
cula
tions
for R
eact
ions
7.8
–Lim
iting
Rea
ctan
ts a
nd P
erce
nt Y
ield
7.
9 –
Ener
gy in
Che
mica
l Rea
ctio
ns
7.7
Mas
s Cal
cula
tions
for R
eact
ions
Give
n th
e m
ass i
n gr
ams o
f a su
bsta
nce
in a
reac
tion,
calcu
late
the
mas
s in
gra
ms o
f ano
ther
subs
tanc
e in
the
reac
tion.
Whe
n w
e ha
ve th
e ba
lanc
ed ch
emica
l equ
atio
n fo
r a re
actio
n,
we
can
use
the
mas
s of o
ne o
f the
subs
tanc
es (A
) to
calcu
late
the
mas
s of a
seco
nd (B
).
How
ever
, the
calcu
latio
ns re
quire
us t
o co
nver
t the
mas
s of A
to
the
mol
es o
f A (u
sing
A’s m
olar
mas
s). T
hen
we
use
the
mol
e-m
ole
fact
or to
conv
ert m
oles
A to
mol
es B
. The
n fin
ally
use
B’s
mol
ar m
ass t
o co
nver
t mol
es B
to g
ram
s B.
gram
s A
m
oles
A
m
ole
B
g
ram
s Bm
olar
mas
s Am
olar
mas
s Bm
ole-
mol
efa
ctor
Prac
tice
How
man
y gr
ams o
f CO
2ar
epr
oduc
edw
hen
54.6
gof
C 2H 2
isbu
rned
?
2C2H
2(g)
+ 5O
2(g)
→4CO2(
g) +
2H2O
(g)
Prac
tice
Calcu
late
gra
ms C
O2
prod
uced
whe
n 25
g o
f O2
reac
ts.
2C2H
2(g)
+ 5O
2(g)
→4CO
2(g)
+ 2H
2O(g
)
Chap
ter S
even
7.1
–Eq
uatio
ns fo
r Che
mica
l Rea
ctio
ns7.
2 –
Type
s of R
eact
ions
7.3
–Ox
idat
ion-
Redu
ctio
n Re
actio
ns7.
4 –
The
Mol
e7.
5 –
Mol
ar M
ass a
nd C
alcu
latio
ns7.
6 –
Mol
e Re
latio
nshi
ps in
Che
mica
l Equ
atio
ns7.
7 –
Mas
s Cal
cula
tions
for R
eact
ions
7.8
–Lim
iting
Rea
ctan
ts a
nd P
erce
nt Y
ield
7.
9 –
Ener
gy in
Che
mica
l Rea
ctio
ns
7.8
Limiti
ng R
eact
ants
and
Pe
rcen
t Yie
ldId
entif
y th
e lim
iting
reac
tant
and
calcu
late
the
amou
nt o
f pro
duct
fo
rmed
from
the
limiti
ng re
acta
nt. G
iven
the
actu
al q
uant
ity o
f pro
duct
, de
term
ine
the
perc
ent y
ield
for a
reac
tion.
Whe
n yo
u m
ake
pean
ut b
utte
r san
dwich
es fo
r lun
ch, y
ou n
eed
2 sli
ces o
f br
ead
and
1 ta
bles
poon
of p
eanu
t but
ter f
or e
ach
sand
wich
.
+
If yo
u ha
ve 8
slice
s of b
read
and
a fu
ll ja
r of p
eanu
t but
ter,
you
will
run
out o
f br
ead
afte
r you
mak
e 4
pean
ut b
utte
r san
dwich
es o
nce
the
brea
d is
used
up,
ev
en th
ough
ther
e is
a lo
t of p
eanu
t but
ter l
eft i
n th
e ja
r. Th
e nu
mbe
r of s
lices
of
bre
ad h
as li
mite
d th
e nu
mbe
r of s
andw
iches
you
can
mak
e.
Limiti
ng R
eact
ant
1 pe
anut
but
ter
sand
wich
1 Tb
l. pe
anut
butte
r
2 sli
ces
brea
d
On
a di
ffere
nt d
ay, y
ou m
ight
hav
e 8
slice
s of b
read
but
onl
y a
tabl
espo
onof
pean
utbu
tterl
efti
nth
epe
anut
butte
rjar
.You
will
run
outo
fpea
nutb
utte
raf
tery
oum
ake
just
1 sa
ndw
ich a
nd h
ave
6 sli
ces o
f bre
ad le
ft ov
er. T
he
smal
ler a
mou
nt o
f pea
nut b
utte
r ava
ilabl
e ha
s the
lim
ited
the
num
ber o
f sa
ndw
iches
you
can
mak
e.
Limiti
ng R
eact
ant
Limiti
ng R
eact
ant
The
reac
tant
that
is co
mpl
etel
y us
ed u
p is
the
limiti
ng re
acta
nt.
The
reac
tant
that
does
notc
ompl
etel
yre
acta
ndis
left
over
isca
lled
the
exce
ssre
acta
nt.
In th
e sa
me
way
, the
reac
tant
s in
a ch
emica
l rea
ctio
ns d
o no
t al
way
s com
bine
in q
uant
ities
that
allo
w e
ach
to b
e us
ed u
p at
ex
actly
the
sam
e tim
e.
In m
any
reac
tions
, the
re is
a li
miti
ng re
acta
nt th
at d
eter
min
es
the
amou
nt o
f pro
duct
that
can
be fo
rmed
.
Mol
es fr
om Li
miti
ng R
eact
ant
Whe
n w
e kn
ow th
e qu
antit
ies o
f the
reac
tant
sofa
chem
ical
reac
tion
we
calcu
late
the
amou
nt o
f pro
duct
that
is p
ossib
le
from
eac
h re
acta
nt if
it w
ere
com
plet
ely
cons
umed
. The
lim
iting
re
acta
nt is
the
one
that
runs
out
firs
t and
pro
duce
s the
smal
ler
amou
nt o
f pro
duct
.
Iden
tifyi
ng Li
miti
ng R
eact
ant
If 3.
00 m
oles
of C
O a
nd 5
.00
mol
es o
f H2
are
the
initi
al re
acta
nts,
wha
t is t
he
limiti
ng re
acta
nt?
And
how
man
y m
oles
of C
H 3O
H ca
n be
pro
duce
d.
CO(g
) + 2
H 2(g
) CH
3OH (
g)
Prac
tice
#1
If 4.
00 m
oles
of C
O a
nd 4
.00
mol
es o
f H2
are
the
initi
al re
acta
nts,
wha
t is t
he
limiti
ng re
acta
nt?
And
how
man
y m
oles
of C
H 3O
H ca
n be
pro
duce
d.
CO(g
) + 2
H 2(g
) CH
3OH (
g)
Prac
tice
#2
The
quan
titie
s of t
he re
acta
nts c
an a
lso b
e gi
ven
in g
ram
s. W
e co
mbi
ne k
now
ledg
e fro
m se
ctio
ns 7
and
8 to
find
the
limiti
ng
reac
tant
.
The
calcu
latio
n to
find
the
limiti
ng re
acta
nt is
the
sam
e as
the
last
two
Prac
tice
slide
s. Bu
t bef
ore
we
can
do it
, we
mus
t con
vert
gr
ams t
o m
oles
.-S
ubsc
ripts
in ch
emica
l equ
atio
ns a
re n
otgr
ams!
!-Y
ou n
eed
to u
se m
oles
to co
mpa
re su
bscr
ipts
!!
Mas
s fro
m Li
miti
ng R
eact
ant
How
man
y gr
ams o
f CO
are
form
ed fr
om 7
0.0
g of
SiO
2an
d 50
.0 g
of C
?
SiO
2(s)
+3C
(s) →SiC (s
)+2C
O(g
)
Prac
tice
In o
ur re
actio
ns so
far w
e ha
ve a
ssum
ed 1
00%
effi
cienc
y, m
eani
ng a
ll of
the
reac
tant
s cha
nged
com
plet
ely
to p
rodu
cts.
Whi
le th
is is
idea
l, it’
s har
dly
real
ity. O
ften,
reac
tant
is lo
st w
hen
mov
ing
from
co
ntai
ner t
o co
ntai
ner,
chem
icals
aren
’t 10
0% p
ure,
and
unw
ante
d sid
e re
actio
ns
use
up re
acta
nt m
akin
g un
wan
ted
prod
ucts
. Thu
s 100
% o
f the
des
ired
prod
uct i
s no
t act
ually
obt
aine
d.
Whe
n w
e do
a ch
emica
l rea
ctio
n in
the
lab,
we
mea
sure
outs
pecif
icqu
antit
ieso
fth
ere
acta
nts.
We
then
calcu
late
the
theo
retic
al y
ield
for t
he re
actio
n. W
hich
is
the
amou
nt o
f pro
duct
(100
%) w
e w
ould
exp
ect i
f all
the
reac
tant
s wer
e co
nver
ted
to th
e de
sired
pro
duct
s.
Whe
n th
e re
actio
n en
ds, w
e co
llect
and
mea
sure
the
mas
s of t
he p
rodu
ct th
at
was
act
ually
mad
e. T
his i
s cal
led
the
actu
al y
ield
.
Beca
use
the
reac
tion
is ha
rdly
eve
r 100
% e
fficie
nt th
e ac
tual
yie
ld is
less
than
the
theo
retic
al y
ield
.
Perc
ent Y
ield
We
can
repr
esen
t the
ratio
of a
ctua
l yie
ld to
theo
retic
al y
ield
in
one
num
ber c
alle
d pe
rcen
t yie
ld.
%yield=ac
tualyield
theoreticalyi
eldx100
Perc
ent Y
ield
Wha
tist
he%
yiel
d of
LiHC
O3
for t
he re
actio
n if
50.0
g o
f LiO
Hgi
ves 7
2.8
g LiH
CO3.
LiOH (
s) +
CO
2(g)
LiHCO
3(s)
Prac
tice
Chap
ter S
even
7.1
–Eq
uatio
ns fo
r Che
mica
l Rea
ctio
ns7.
2 –
Type
s of R
eact
ions
7.3
–Ox
idat
ion-
Redu
ctio
n Re
actio
ns7.
4 –
The
Mol
e7.
5 –
Mol
ar M
ass a
nd C
alcu
latio
ns7.
6 –
Mol
e Re
latio
nshi
ps in
Che
mica
l Equ
atio
ns7.
7 –
Mas
s Cal
cula
tions
for R
eact
ions
7.8
–Lim
iting
Rea
ctan
ts a
nd P
erce
nt Y
ield
7.
9 –
Ener
gy in
Che
mica
l Rea
ctio
ns
7.9
Ener
gy in
Che
mica
l Rea
ctio
nsGi
ven
the
heat
of r
eact
ion,
calcu
late
the
loss
or g
ain
of
heat
for a
n ex
othe
rmic
or e
ndot
herm
icre
actio
n.Al
mos
t eve
ry ch
emica
l rea
ctio
n in
volv
es a
loss
or g
ain
of e
nerg
y.
To d
iscus
s ene
rgy
chan
ge fo
r a re
actio
n, w
e lo
ok a
t the
ene
rgy
of
the
reac
tant
s bef
ore
the
reac
tion
and
the
ener
gy o
f the
pro
duct
s af
ter t
he re
actio
n.
The
SI u
nit f
or e
nerg
y is
the
joul
e (J)
1ki
lojo
ule
(kJ)
=10
00 jo
ules
(J)
Ener
gy in
Che
mica
l Rea
ctio
ns
Ener
gy is
ofte
n pr
esen
t as h
eat.
The
heat
ofre
actio
nis
the
amou
ntof
heat
abso
rbed
orre
leas
eddu
ring
are
actio
nth
atta
kesp
lace
atco
nsta
ntpr
essu
re.
Ach
ange
of e
nerg
y oc
curs
as r
eact
ants
inte
ract
, bon
ds b
reak
ap
art,
and
prod
ucts
form
.
Anot
hern
ame
forh
eato
frea
ctio
nis
enth
alpy
chan
ge.
ΔH =
Hpr
oduc
ts-H
reac
tant
s
Heat
of R
eact
ion
In a
n ex
othe
rmic
reac
tion
the
ener
gy o
f the
pro
duct
s is l
ower
than
that
of t
he
reac
tant
s.-
Heat
isre
leas
ed a
long
with
the
prod
ucts
that
form
.
Fore
xam
ple
whe
n1
mol
eof
H 2an
d1
mol
eof
Cl2
reac
t,2
mol
eHC
lfor
m.T
heen
ergy
ofth
eHC
lis1
85kJ
less
than
the
H 2an
dCl
2
Exot
herm
ic Re
actio
ns
Beca
use
prod
ucts
are
low
eren
ergy
,tha
ten
ergy
diffe
renc
eis
rele
ased
ashe
at.
We
writ
eΔH
with
a n
egat
ive
sign
to in
dica
te
exot
herm
ic.
Hot p
acks
are
use
d in
med
icine
, cam
ping
gea
r, em
erge
ncy
kits
, etc
.In
side
the
hot p
ack
are
two
pouc
hes.
One
pou
ch h
as w
ater
, the
ot
her h
as C
aCl 2
Whe
n th
e bo
unda
ry is
bro
ken
betw
een
pouc
hes a
n ex
othe
rmic
reac
tion
take
s pla
ce a
nd re
leas
es h
eat.
CaCl
2(s)
CaCl
2(aq
)
Tem
pera
ture
s ca
n in
crea
se a
s muc
h as
66C
Exo
exam
ple:
Hot
Pac
ks
In a
n en
doth
erm
ic re
actio
n, th
e en
ergy
of t
he p
rodu
cts i
s hig
her
than
that
of t
he re
acta
nts.
-He
at is
requ
ired
to b
egin
the
reac
tion
and
conv
ert r
eact
ants
to
pro
duct
s. Fo
r exa
mpl
e: 1
mol
e N
2an
d 1
mol
e O
2re
act t
o fo
rm 2
mol
es N
O o
nly
whe
nat
le
ast 1
80 k
J of h
eat i
s add
ed.
Endo
ther
mic
Reac
tions
We
writ
eΔH
with
a p
ositi
ve si
gn to
indi
cate
en
doth
erm
ic.
Cold
pac
ks w
ork
the
sam
e w
ay w
ith tw
o po
uche
s. O
ne p
ouch
as
wat
er, t
heot
herh
asNH
4NO
3. Th
e te
mpe
ratu
re ca
n dr
op to
4-5
C.
NH4N
O3(
s) +
26kJ
NH4N
O3(
aq)
Endo
exa
mpl
e: C
old
Pack
s
The
valu
e of
ΔH
refe
rs to
the
heat
chan
ge fo
r eac
h su
bsta
nce
in th
e ba
lanc
ed
equa
tion.
2H2O
(l)
2H2(
g) +
O2(
g)Δ
H =
+572
kJ
mea
ns th
atfo
rthi
srea
ctio
n,+5
72kJ
are
abs
orbe
d by
2 m
oles
of H
2O to
pr
oduc
e 2
mol
es o
f H2
an 1
mol
e of
O2.
We
can
use
ΔH to
writ
e co
nver
sion
fact
ors j
ust l
ike th
e m
ole-
mol
e fa
ctor
s fro
m se
ctio
n 7.
6.Calcu
latio
ns o
f Hea
t in
Reac
tions
Supp
ose
that
9.0
0 g
H 2O
und
ergo
es th
e re
actio
n. C
alcu
late
the
heat
abs
orbe
d.
2H2O
(l)
2H2(
g) +
O2(
g)Δ
H =
+572
kJ
Calcu
latio
ns o
f Hea
t in
Reac
tions
How
muc
h he
at, i
n kJ
, is r
elea
sed
whe
n ni
trog
en a
nd h
ydro
gen
reac
t to
form
50
.0g
of a
mm
onia
(NH 3
)?
N 2(g
) + 3
H 2(g
) 2N
H 3(g
)Δ
H =
-92.
2 kJ
Prac
tice
Chap
ter S
even
7.1
–Eq
uatio
ns fo
r Che
mica
l Rea
ctio
ns7.
2 –
Type
s of R
eact
ions
7.3
–Ox
idat
ion-
Redu
ctio
n Re
actio
ns7.
4 –
The
Mol
e7.
5 –
Mol
ar M
ass a
nd C
alcu
latio
ns7.
6 –
Mol
e Re
latio
nshi
ps in
Che
mica
l Equ
atio
ns7.
7 –
Mas
s Cal
cula
tions
for R
eact
ions
7.8
–Lim
iting
Rea
ctan
ts a
nd P
erce
nt Y
ield
7.
9 –
Ener
gy in
Che
mica
l Rea
ctio
ns
