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