Rate equations Flashcards
Explain qualitatively why doubling the temp has a much greater effect on the rate of the reaction than doubling the conc of E
More molecules Ea<E
Doubling T by 10C causes many more molecules to have this E
Whereas doubling [E] only doubles number with this E
Rearrange Lnk = LnA - Ea/RT for Ea
Ea = RT(LnA-Lnk)/1000
Suggest why the 1cm portions of the reaction mixture are added to an excess of NaHCO3 solution
Neutralised the acid
So stops the reaction
Suggest why the order of this reaction with respect to propanone can be ignored in this experiment
Conc of propanone is constant
Conc of propanone much larger than conc of iodine
Explain how the graph shows that the reaction is zero order with respect to iodine in the reaction between propanone and iodine
Constant gradient
So rate of reaction does not change as conc changes
So zero order
When working out Ea, does it have - or + at the end
POSITIVE!
Define the term overall order of reaction
The sum of powers
Explain how graphical methods can be used to process the measured results to confirm that the reaction is first order
Plot graph of concentration against time and take tangents
Plot rate against conc
Straight line through origin means first order
A general equation for a reaction is shown.
A(aq) + B(aq) + C(aq) → D(aq) + E(aq)
In aqueous solution, A, B, C and D are all colourless but E is dark blue.
A reagent (X) is available that reacts rapidly with E. This means that, if a
small amount of X is included in the initial reaction mixture, it will react with
any E produced until all of the X has been used up.
Explain, giving brief experimental details, how you could use a series of
experiments to determine the order of this reaction with respect to A. In
each experiment you should obtain a measure of the initial rate of reaction.
Stage 1 Preparation
1a Measure known volumes of A, B and C
1b Use of colorimeter
1c into separate container(s)
Stage 2 Procedure
2a Start clock at the point of mixing
2b Take series of colorimeter readings at regular time intervals
2c Use of same concentration of B and C / same total volume
2d Same temperature
2e Repeat with different concentrations of A
Stage 3 Use of Results
3a Plot absorbance vs time and calculate gradient at time=0
3b plot of gradient against volumes/concentrations of A or plot
log(1/time) vs log(volume or concentration of A)
3c description of interpreting order from shape of 1/time vs volume or
concentration graph / gradient of log plot gives order
Inital rates 6 marker:
Describe an experiment to investigate the order or reaction with respect to thiosulphate.
Describe the prep u will make before u begin to record data. The procedure for obtaining ur results and process to interpret the results
Prep!
Measure 50cm3 of HCl (3noldm-3 conc) using measuring cylinder
Measure 50cm3 of 1moldm-3 Na2S2O3 into 250cm3 conical flask
Place X under the Na2S2O3 flask
Obtaining!
Add HCl to conical flask, start the timer immediately
Stop timer once x disappears and record the time taken
Repeat experiment changing vol of Na2S2O3
Ensure to keep total volume constant by adding water
Results!
Rate is proportional to 1/time
Volume is proportional to concentration
Calculate 1/time for each conc of Na2S2O3
Plot graph of 1/time vs volume
Control variables of inital rates reaction?
Volume
Temperature <- Thermometer or using water bath
Volume and concentration of HCl
(Leaving it still/no swirl)
Describe continuous monitoring
Prep, obtaining, results
Prep!
Measure 50cm3 of Na2S2O3 into conical flask (1moldm-3)
Measure 50cm3 of 3moldm-3 HCl using a measuring cylinder
Gas syringe prepared
Obtaining!
Add HCl into conical flask, start timer immediately and place bung into conical flask immediately
Record volume of gas produced every 5 seconds for 2 minutes
Add 25cm of Na2S2O3 to 25cm3 of water to create a conc of 0.5moldm-3
Repeat experiment for new conc of Na2S2O3
Results
Plot 2 graphs of volume of SO2 vs time
Calculate gradient for a tangent drawn at t=0
Conc 1 Conc 2 x2
Rate 1 rate 2 x2 (1 order) x4 (second order)
same (zero order)
