1.2 notes - measuring reaction rates · chemistry i2-unit i-reaction kinetics--notes ~,\\ t.)
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Chemistry I2-Unit I-Reaction Kinetics--Notes
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1.)
1.2 Notes - Measuring Reaction Rates
- different methods for different reactions.- some changes are easier to measure than others!
Monitoring Reaction Rates
- properties which can be monitored (measured at specific time intervals) inorder to determine rx. rate.
We must consider: ~ !1,'1l u~ 1".fo o.hou+- p.-ofl2.l4i ~J \lJ~• -subscripts (s) (1) (g) (aq) CtAA \ A t(\ {A S '
, • coefficients of gases U.(..(,. .
f' • heat (endo or exo?)
Here are the properties that we often measure experimentally:(1) Colour change(2) Temp changes(3) Volume changes(4) Mass changes(5) Change in Concentration (Molarity)(6) Change in Acidity, lH1
Colour changes- good choice if a coloured reactant is consumed or new coloured product is formed.
eg.) CU(s)+ 4HN03(aq) -7copper clear
- in this case could measure: r0.k - b CO\C\k( "(\4os\ ~£) +, ("()~
Rate= ~ 13\",<. \(\-knsi~().nm<...,
or Rate = ~ Brow(\ \(\-\{nsi ~b tfM("
- colour intensity can be measured quantitatively using a spectrophotometer(see p. 4 in Hebden.)
Chemistry I2-Unit l-Reacuon Kinetics-Notes Page 7of 17 pages
Chemistry J 2-Unit J -Reaction Kinetics-Notes2.) Temp changes -E~() : net'1- e}<.i+S- in exothermic reaction temperature of surroundings will iDci fASL
- in endothermic reaction temperature of surroundings will d<-L" UlS ~- measured in insulated container (with a thermometer)
rate = L\ tempL\ time -
3.) Pressure changes (when gases are involved)
~]SPAcE.~ .
*must be at constant volume or sealed container 'N e.. lA-\\-a c.h 0. pres Sur.(( ~a~e., .(m.o'9) ,
• if more moles of gas (coefficient) in products pressure will \ n CJ{ ~& ~less pre.S(\A.f-(. m~'{<'f('~S~\.I.(0Zn(s) + 2HCl(aq) ~ \ H2(g) + ZnCh(aq)
C m.o·S· \ .0\.0 ..9If more MOG in reactants - pressure wil1_----'dV-!-e""'--"'(J{~~=o.."-=->!!!!S_.t-_=__
rate = L\ pressure (constant volume)L\ time
• If equal MOG, pressure will not change:
*Must be at constant pressure (example: in a balloon)
nb Lh 0(\8 t \()Pr~~Su{€;.
'* '('(\-e.C\~U(\~ ~ f ~( c\--h\sr-eClC~O(\ \s- a..
'OJ\-£> <..h<H 'ce, .
\ N02(g) +\ cO(g) ~ IC02(g) + \NO(g)'- Y '" '-.----v-----/
;). rrv-o. .9 :l en.~.:;
Volume change (when GASES are involved)4.)
5.)
• if more gas is produced, volume of balloon will increase )
\.\- mOte.. m.o8 If)rro.CTCA(\~ ... pY~SS\A.(~'NO) o.(.<i.{A~~
rate = 8 volume8 time
(constant pressure)
Mass changes* we can measure mass if a solid is being used up/produced. Also when a gas is escaping(measure the change in mass of container and contents).
rak=- t f(\ ().S~c+.- \J\i-----t -h'Mv• if only one solid is used up
- could remove Mg solid periodically and weigh it:
Chemistryi2-Unit I-Reacti n Kinetics-Notes Page 8 of 17pages
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Chemistry i2-Unit I-Reaction Kinetics=Notes
• if one gas is produced and escapes, measure mass of what's left in container(mass of container and contents) , 8a (' Pihc\\A..(.-t-
eg) heat + CaC03(s) ~ CaO(s) C02(g) -<t:::~i
rate = L1 mass of container & contentsL1 time of6NL-------------~~S~$r~M\
Note: it's not practical to measure masses of (aq) substances separately since they are mostly
water. eg) ClI(S) E<;J-7orH2(g) ~3h;)A mass ofHNOJ~ .• fngtia~cePtaPIFj
A time~ \\\.ea~U(ema s s O~L..'\ -\OY- So\\ dS }(9 as
piOau(;~.6.) Changes in Concentration (for specific ions)
Note: Does the [Br -] change? _ND Explain.\ije S-(.l eqU.ll\ am(.)\l\\-ts of- B-;- on r~t-\-£\(\+ a~ pvotA.uvt-sr cA<.~· I.+ \~ t\. SeE"G-rfr'1"o~ \ t)rJ 1
The concentration ola specific ion can be measured:- using spectrophotometer ~f- t.t. \ ou c~ .- periodic samples taken and titrated to measure cone.
Chemistry I2-Unit l-Reaction Kinetics-Notes Page 9 of 17pages
~liIJIJ-[/!l/I j-j(eoClion Kinetics-Notes
7.) Changes \n Ac~~tW
_ special case of #6rat~ = 1:1 (H+l
~tim~
~; Q~~~ ~-fJeasure of acidityv Ij \o\M [J.\"tl 'pH Q 7 J_ 14 \ \< > ~n Sea \-G .
more acidic more basic -(less basic) (less acidic) -W-( '('(IO{-l It 1- PV..Q ~.((\-\- ; II.- ~
• iCM-' SC>\\A HoA .. .. +1iI... \A"D/ /J
H' is a reactant ( II ••, v+ ..l or any acid nci, HN03
etc.) ,,(J0\ (,. f' \ 0 \AI P H '\ .[H 1will aery.fA':./.... \, , • J
(~ SOPHWill==6D uO ,
8l-ts USld \.\.0) -r (+0 J,- __ :::!......___ \" (Ie;; acidic) . Wd..-...~ ItJ.)rate = .1 pH -t=~~
A time
Do Hebden Q' #7Do Worksheet S1.2 - 9 on page 5.
Chemistry 12 .=Unit 1-Reactio .n Kmetics-7.T«otesPagelOof17 pages