how fast, how far ? (module 5 first bit )

Question 1

units of k

Answer 1

mol dm3 s^-1

Question 2

units of concentrations

Answer 2

moldm^-3

Question 3

conc time graphs vs conc rate graphs

Answer 3

conc rate- incorporates ZAT FINE SURF

conc time graphs - dont incorporate the 3 shapes

Question 4

what changes the value of the rate constant

Answer 4

change in temeprature - increase= higher rate constant

Question 5

arhenius equation

Answer 5

K= A * E ^ -ea/RT

GRAPH: x axis = 1/T, gradient= -Ea /R, y axis= ln (Rate)

thus Ea= - gradient * R

this is derived from rearranged version of arheniu equation

Question 6

rearranged version of arhenius equation

Answer 6

lnk= -Ea/RT + ln(A)

ln (A) , the preexponential factor , is calculated from y intercept

Question 7

green box: analysing by colorimetry

Answer 7

. reactio nbetween propane and iodine in presence of acid atalyst

as reaction proceeds, iodine sued and and orange colour fades . absorbance of colour measured by colorimeter

1. prepare standard solutions of known conc of iodine
2. get filter w complementary colour of coloured cheical for iodine ( green / blue filter)
3. zero colorimeter
4. measure absorbance readings of standard iodine solutions
5. plot callibration curve of absorbance agaisnt iodine concentration ( to convert absorbance to conc of iodine )
6. carry out reaction between propanone and iodine. tae absorbance readings of reacting mixture at time intervals
7. use callibration curve to get concentration from absorbance reading
8. plot second graph of conc of iodine against time.
9. from conc time grpah, get the order of reaction with respect to iodine
   .

Question 8

green box : determining kc from experimental results

Answer 8

. reaction of cawrb acid with alchohol- reversible reaction

1. mix 0.1 mol ch3cooh and 0.1 mol c2h5oh . add 0.05 mol hcl ( catalyst)
2. add 0.05 mol hcl to second conical flask ( control )
3. stopper both flasks and leave for week to reach equillibrium
4. carry out titration on equillibrium mixture using sodium hydroxide standard solution
5. repeat tiration w control- to determine amount of acid catalyst added .

Question 9

2 types of graphs

Answer 9

concentration, time (ZINE FURVE )

rate, concentration (used for initial rates ) (ZAT FINE SURF) ( k is the gradient of this graph )

Question 10

initial rates method

Answer 10

instantaneous rate at start of reaction where time is zero. found by measuring tangent draw and t=0

clcok reaction- obtain initial rate of reaction by taking single measurement . tiem for visual change to occur ( colour )

.assumptionP average rate of reaction over this time = initial rate

.initial rate proportional to 1/t

.clock reaction repeated several times w different concentrations and values of 1/t calculated for each experimental run

Question 11

most common initial rates method: iodine clock reaction

Answer 11

relies on formation of iodine as aq iiodine coloured orange brown. time from start of reaction and appearnace of iodine colour measured.

starch usually added since it forms blue black solution with iodine

1. one of the reactants concentrations vary and the other is kept constant
2. sodium thiosulfate added to delay colourc change ( Removes iodine as it forms and after this chemical is used up; the blue black colour appears)

. in each epxperiemtn, soltion oclourless at start and time , t i measured for blue black colour of starch- iodine to appear

.initial rate is proportional to 1/6t

. graph fof 1/t agaisnt concentration plotted and shapes are matched to known order shapes

.further experiemnts carried out hwere conc of one of other eactants changed

.from result, order with respect tok each reactant determined + rate equation written - rrate cosntant then calculated

(`1/t = y axis…… cocnentration = x axis _ ( 1/t is proportional to rate therefore orders can be derived jsut like the rate concentration graph )

(the reactant that is usually changing is hydrogen peroxide, and we plot graphs based on this

Question 12

accuracy of clock reactions

Answer 12

clock reaction , gets average rate for “initial rate” (rate at the beginning )

hence… shorter the periood of time over which averager ate is measured, the less the rate changes over that time period ( LOOK AT PAGE 286 )

.initial rate is approixmation but kinda ccurate provided that less that 15 percent of the reaction has taken place. if over 50 percent of the reactant has been used up like grapoh 2 on figure 8 page 286… then it wont be accurate