csec rates of reaction 2014.pptx
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RATES OF REACTION
CSEC Chemistry
Prepared by M. J. McNeil, MPhil.
Departmet !" C!ti#i$ %Ed#cati!& St#dies
P!rtm!re C!mm#ity C!lle$e
Mai Camp#s
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'ECT(RE O)JECTI*ES I
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+AT DOES TE
RATE OF A REACTION MEAN-
What is the rate of these reactions?
Chemical reactions require varying le$ths !" time
for completion.
The speed of different chemical reactions varies
h#$ely.
Some reactions are ery "ast and others are ery
sl!/.
Reaction rate is the rate or speed at which pr!d#cts
are "!rmed or reactats are c!s#med.
A reacti! rate depends on the characteristics !" the
reactats ad pr!d#cts and the c!diti!s under
which the reaction is run.
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slow fast very fast
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This is the area of chemistry concerned with the speeds, or rates, at which a
chemical reaction occurs and the path ta0e y the reaction.
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CEMICA' 1INETICS
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A B
time
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+2 ST(D2 REACTION RATES-
!y understanding how the rate !" a reacti! is affected y cha$i$
c!diti!s, one can learn the details of what is happening at the m!lec#larleel.
The length of time it ta"es to ba0e ch!c!late chip c!!0ies depends on the
rate at which ba0i$ s!da #s!di#m bicarb!ate or hydr!$e carb!ate$
decomposes at %&& oC.
'anufacture of Ammonia %aber Pr!cess& 3 specific conditions
#temperat#re ad press#re$ to aid the reaction to proceed in a c!mmercially
"easible length of time.
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MEAS(RIN4 RATES OF REACTION
Rate !" reacti! is a meas#red cha$ed in the am!#t !" a speci"ic reactat
!r pr!d#ct as a function of time.
Rate ( meas#red cha$e in a $ie pr!perty
time ta0e for change to occur
)uring any chemical reaction, it has een found that the c!cetrati! of reactats
decreases at the same rate as the c!cetrati! !" the pr!d#ct icreases. *owever,
the change in concentration per unit time is sometimes challenging to measure directly.
+ther property changes which are often used are
%i& !l#me !" a $ase!#s pr!d#ct
%ii& c!l!#r itesity
%iii& am!#t !" a precipitate "!rmed
%i& decrease i mass %i" $as is liberated& 7
Measuring the rate of a reaction means measuring the change in the amount of a reactant or
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+2 ARE SOME REACTIONS
FASTER TAN OTERS-
Some people can r# "ast, others
r# m!re sl!/ly, and still others
d! !t r# at all. 'olecules are
the same- some are ery reactie,
others react less rapidly, and still
others react ery sl#$$ishly.
The CO''ISION TEOR2
eplains this.
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CO''ISION TEOR2 OF REACTION
/n order for a chemical reaction to occur, the
following TREE c!diti!s M(ST e
met
#i$ The particles of the reacti$
s#bstaces must c!llide with each other
to brea0 !ld b!ds in the reactats, and
"!rm e/ b!ds in the pr!d#cts.
The more c!llisi!s in a system, the
more li"ely c!mbiati! of molecules
will happen.
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CO''ISION TEOR2 OF REACTION
/n order to react the following conditions must
e met
#ii$ The colliding particles must produced
s#""iciet eer$y to brea0 the !ld b!ds in
the reactats. This energy is termed the
actiati! eer$y5, #to e discussed in
details later$.
N!t all c!llisi!s produce the required
energy, therefore !t all c!llisi!s results in
a reacti! !cc#rri$.
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CO''ISION TEOR2 OF REACTION
/n order to react the following conditions
must e met
#iii$ Reactant particles m#st c!llide with
the c!rrect !rietati! so that the
energy produced y the collision can
e passed on to the onds to e ro"en.
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FACTORS TAT AFFECT
REACTION RATES
Through etensive e6perimets, chemists have determined that the rate of a
reaction depends on si6 variales
C!cetrati! !" reactats
Temperat#re
Catalyst S#r"ace Area %Particle Si7e&
Press#re
'i$ht
'ET8S 'OO1 AT TEM IN DETAI'.
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EFFECT OF CONCENTRATION ON
TE RATE OF A REACTION
'ore often than not, the rate of a reaction
icreases when the c!cetrati! of a reactant
is icreased and ice3ersa.
Why increasing the concentration increases the
rate of reaction and vice0versa?
At a hi$her c!cetrati!, there are m!re
particles in the same am!#t of space. Thismeans that the particles are more li"ely to
react.
*ence, increasing the p!p#lati! of reactants
increases the li"elihood of a s#ccess"#l
c!llisi!. The converse of this statement is also
true.
/n some reactions, however, the rate is
#a""ected y the concentration of a
particular reactant, as long as it is
present at some concentration.
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highlower concentration
IN*ESTI4ATION OF TE EFFECT OF
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IN*ESTI4ATION OF TE EFFECT OF
CONCENTRATION ON REACTION RATE
Add the Cl to the Na9S9O: in the flas".
Record the time ta0e for the ; to disappear.
Repeat with di""eret c!cetrati!s of Na9S9O:
The ierse the time #
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The formation of a pale yell!/ %c!ll!idal& precipitate !" s#lph#r can e used to monitor the progress of the reaction.
1lease visit http://www.youtube.com/watch?v=r4IZDp!"b# to view this expt. (7 mins
The rate !" a chemical reacti! is NOT affected y a cha$e i !l#me of the reacting solut
provided that the c!cetrati! remains the same.
HCl Na2S2O3 H2O+NaCl
IN*ESTI4ATIN4 TE EFFECT OF
CONCENTRATION ON RATE
+ ++ SO2
1%
http://www.youtube.com/watch?v=r4IZDPpN-bkhttp://www.youtube.com/watch?v=r4IZDPpN-bkhttp://www.youtube.com/watch?v=r4IZDPpN-bkhttp://www.youtube.com/watch?v=r4IZDPpN-bkhttp://www.youtube.com/watch?v=r4IZDPpN-bk
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IN*ESTI4ATIN4 TE EFFECT OF
CONCENTRATION ON RATE
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TE EFFECT OF CONCENTRATION ON RATE
R
A
T
E
CONCENTRATION
Conclusion
?
Rate is directly
proportional to
concentration
1
Time
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SETTIN4 (P TE RATES E;PERIMENT
What e>#ipmet is needed to iesti$ate the rate !" hydr!$e e!led?
gas syringe
ruer ung
ruer connecter glass tue
conical
flas!
magnesium
hydrochloric
acid
DETERMININ4 REACTION
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h y d
r o g e n p r o d u c e d
( c m 3 )
time (seconds)10 20 30 40 50
10
20
30
40
50
60
70
00
"
y
DETERMININ4 REACTION
RATES FROM 4RAPS
rate of reaction
"
y
rate of reaction (
45 s
67 cm2 rate of reaction ( 9.9? cm:=s
The gradient of the graph is equal to the initial rate of reaction
at that time.
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EFFECT OF TEMPERAT(RE ON RATE
The hi$her the temperat#re, the "aster the
rate !" a reacti! and ice3ersa.
/n many chemical reactions, a rise in
temperature of
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TEMEPAT(RE )ATTERIES
Why are batteries more li"ely to r#d!/ m!re >#ic0ly in c!ld /eather?
At l!/ temperat#res the
reaction that generates the
electric current proceeds m!re
sl!/ly than at hi$her
temperat#res.
This means atteries are less
li"ely to deliver enough
c#rret to meet demand.
O+ DOES TEMEPERAT(RE AFFECT RATE-
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O+ DOES TEMEPERAT(RE AFFECT RATE-
The reacti! etween s!di#m thi!s#l"ate and hydr!chl!ric
acid produces s#l"#r.
S#l"#r is s!lid and so it turns the s!l#ti! cl!#dy.
*ow can this fact e used to meas#re the e""ect !"
temperat#re on rate !" reacti!?
hydrochloric
acid
sodium
chloridesulfur
sodium
thiosulfate + +sulfur
dio"ide ++
Na#$#O%(a!)
#&Cl
(a!)
#NaCl
(a!)
$
(s)++ $O#(g)
+ +
IN*ESTI4ATIN4 TE EFFECT OF
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IN*ESTI4ATIN4 TE EFFECT OF
TEMPERAT(RE ON RATE
Add the Cl to the Na9S9O: in the flas".
Record the time ta0e for the ; to disappear.
Record the temperat#re after mi6i$.
The ierse the time %
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"e#t
REPEAT AT DIFFERENT TEMPERAT(RES
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EFFECT OF TEMPERAT(RE ON RATE
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EFFECT OF TEMPERAT(RE ON RATE
R
A
T
E
TEMPERATURE
Conclusion ?
Rate increases
with increasingtemperature
1 Time
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EFFECT OF CATA'2ST ON RATE
A catalyst is a s#bstace that
icreases the rate !" a reacti!
/ith!#t bei$ c!s#med i the
!erall reacti!.
The catalyst generally d!es !t
appear in the !erall balacedchemical e>#ati! #although its
presence may e indicated y
writing its formula over the arrow$.
The presence of a s!lid catalyst #finely divided$ provides a s#r"ace area over
which gas molecules react #c!tact catalyst$, resulting in m!re c!llisi!s and
hence icrease the reacti! rate.
The gases must e dried #CaO$ and purified efore passing them over thecatalyst to prevent 8p!is!i$9 of the catalyst.
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Catalysts NE*ER produce more product 0 they :ust produce the same amount more quic"ly.
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Ay reacti! ! a s!lid ca !ly ta0e place
! the s#r"ace !" the s!lid.
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EFFECT OF CONCENTRATION
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EFFECT OF CONCENTRATION
OF A CATA'2ST ON RATE
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Di""eret catalysts /
di""eret /ays, b#t
reacti!8s actiati!
&$%9&l%9
&a>%,)r
&a>%99 OO,9O,9
Catalysts NE*ER produce more product 0 they :ust produce the same amount more quic"ly.
5T/! mai "#cti!s of a catalyst
$ A catalyst speeds up reactions y
red#ci$ the Bactiati!
eer$y needed for successfulreaction.
$ A catalyst may also provide an
alteratie mechaism, or
path/ay, that results in a faster
rate.
A catalyst is a substance that increases the rate o
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A catalyst is a substance that increases the rate o
chemical reaction without itself being consumed.
ratecataly%ed & rateuncataly%ed
E*ER2DA2 CATA'2ST
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E*ER2DA2 CATA'2ST
Nic0el is a catalyst in the production of margarine
#hydrogenation of vegetale oils$.
'any catalysts are trasiti! metals or their compounds.
;or eample
Plati#m is a catalyst in the catalytic
c!erters of car e6ha#sts. /t cataly
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EFFECT OF S(RFACE AREA
%PARTIC'E SIE& ON RATE
!ecause the reaction occurs at the s#r"ace ofthe s!lid reactat or catalyst, the rate
icreases with icreasi$ s#r"ace area
#state !" s#b3diisi!$ of the solid and ice3
ersa.
*ence, the reacti! is directly pr!p!rti!al
to the s#r"ace area of s!lid reactat.
/n such a reaction, c!llisi! occurs etween
the m!i$ particles and the s!lid reactat,
hence the larger the surface area, the greater
the opportunities for collisions and the
greater the rate of reaction.
The c!erse of this condition is
also tr#e.
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EFFECT OF SURFACE AREA ON
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EFFECT OF SURFACE AREA ON
RATE
3%
Repeat using the sam
p!/dered CaCO:
and the same !l#m
and the same c!ce
Rec!rd the time ta0e "!r
CO9 t! ed
% N! "#rther ma
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RESULTS
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IN*ESTI4ATIN4 TE EFFECT OF
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The rate !" release !" CO9 $as can e used to
monitor the pr!$ress of the reaction.
1lease visit http://
www youtube com/watch?v=&'tw#um )*
HCl CaCO3 H2O +
IN*ESTI4ATIN4 TE EFFECT OF
PARTIC'E SIE ON RATE
+ + CCaCl2
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Add the Cl t! a lar$e chips !" CaCO i the "las0
http://www.youtube.com/watch?v=FJtwkum_QAYhttp://www.youtube.com/watch?v=FJtwkum_QAYhttp://www.youtube.com/watch?v=FJtwkum_QAYhttp://www.youtube.com/watch?v=FJtwkum_QAYhttp://www.youtube.com/watch?v=FJtwkum_QAYhttp://www.youtube.com/watch?v=FJtwkum_QAY
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Add the Cl t! a lar$e chips !" CaCO: i the "las0
As C+4 is released the mass of the flas" drops
"e
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Res#lt
Fiely diided particles react "aster tha lar$e particle40
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EFFECT OF PRESS(RE ON RATE
Why does icreasi$ the press#re on$ase!#s reactats icrease the rate of
reaction and ice3ersa?
As press#re icreases, the space in
which the particles are moving
ecomes smaller.
The gas particles bec!me cl!ser
together, icreasi$ the "re>#ecy of
c!llisi!s. This means that the particles
are more li"ely to react.
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lower 'ressure h
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EFFECT OF 'I4T ON RATE
'i$ht eer$y of a s#""icietly high frequency can brea0 some chemical b!ds and sospeed #p chemical reaction.
=amples of li$ht sesitie reactions are
Reactions of hydr!$e with hal!$es.
#i$ *4 > Cl4 4*Cl #e6pl!sie$. This reaction is slow and fast in diffused and
direct sunlight$.
#ii$ 1hotosynthesis construct the equation for this reaction.
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4'OSSAR2
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actiati! eer$y 3 The amount of energy needed to start a
reaction #for ond rea"ing to occur$.
catalyst 3 A sustance that increases the rate of a chemical
reaction without eing used up.
c!cetrati! 3 The numer of molecules of a sustance in agiven volume.
rate !" reacti! 3 The change in the concentration over a
certain period of time.
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THE END
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THE END
NOT SO QUICK!
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JUNE 2013, Q4
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