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Experiment 7. Reaction Kinetics (Work Sheet).docx

Experiment 7. Reaction Kinetics (Worksheet)

Student name (Print):_______________________
I. Suggestion of Use (1) This is a dry lab. (2) Instructors may assign different problems for different students in the same group to work on in the lab. (3) If preferred, instructors may randomize those numbers in the given problems and then assign to students.
II. Objectives (1) Interpret reaction order based on provided experimental data of reactant concentrations at different times; (2) Calculate reaction rate constant value and derive the unit; (3) Figure out activation energy using Arrhenius equation based on provided rate constant values at different temperatures.
III. Principles, Procedures, and Practices
There are two ways to interpret reaction order. The first way is based on initial reaction rates at different initial reactant concentrations. This method has been practiced in the first experiment of reaction kinetics. The second way is based of the change of reactant concentration with reaction time. In this experiment, we will practice on the second way with provided experiment data. III.1 Relationship of reactant concentration (Ct) and time (t) For a reaction, aAproducts, its reaction order can be interpreted by investigating the relationship between reactant concentration (Ct) and reaction time (t).
Zero-order					First-order								Second-order
Ct=C0-kt slope=-k					lnCt=lnC0-kt slope=-k								1Ct=1C0+kt slope=k
III.2 Practice-Reaction Order and Rae Constant
Your instructor will select a problem for you to work on. (Different problems may be assigned to different students in the same group.)
Problem 1				Problem 2					Problem 3					Problem 4
Reaction temperature, T = 25.0 C
t (s)	Ct (M)			t (s)		Ct (M)			t (s)			Ct (M)		t (s)				Ct (M)
0	1.00			0		0.900			0			0.950		0				0.960
100	0.89			100		0.699			100			0.868		100				0.895
200	0.79			200		0.571			200			0.786		200				0.835
300	0.70			300		0.483			300			0.704		300				0.778
400	0.62			400		0.418			400			0.622		400				0.726
500	0.55			500		0.369			500			0.540		500				0.677
600	0.49			600		0.330			600			0.458		600				0.631
700	0.43			700		0.298			700			0.376		700				0.588
800	0.38			800		0.272			800			0.294		800				0.548
900	0.34			900		0.251			900			0.212		900				0.511
Step 1: Based on data from your chosen problem, finish the following calculation.
Ct and t					lnCt and t								1/Ct and t
t		Ct			t				lnCt				t				1/Ct
Step 2: Use obtained data to plot
Plot Ct ~ t					Plot lnCt ~ t								Plot 1/Ct ~ t
Step 3: Answer questions (determining reaction order):
Is plot Ct ~ t linear? yes, no. Is the reaction the zero-order? yes, no.					Is plot lnCt ~ t linear? yes, no. Is the reaction the first-order? yes, no.								Is plot 1/Ct ~ t linear? yes, no. Is the reaction the second-order? yes, no.
Step 4: Calculate slope for the linear line shown above and figure out rate constant k value and unit:
Example of slope calculation: slope=y2-y1x2-x1								Calculate the slope of the linear line shown in your above three plots. Slope =_______________ _________ value unit Hence, rate constant k = ________________ ________ at 25 C. value unit
III.3 Reaction Activation Energy At different temperatures, the reaction rate constant varies. The Arrhenius Equation is used to describe the relationship between temperature and rate constant. k=Ae-EaRT , hence lnk=lnA-EaR1T Based on the above equation, lnk and 1/T is linear. The slope equals to -Ea/R.
III.4 Practice-Reaction Activation Energy
Continue with the same problem your instructor selected for you in III.2
Temperature (C)					25.0						35.0				45.0
Rate constant, k (unit omitted purposely)					__________________ (copy result from III.2 step 4.)						0.00203				0.00332
Problem 2
Temperature (C)					25.0						35.0				45.0
Rate constant, k (unit omitted purposely)					__________________ (copy result from III.2 step 4.)						2.30				1.06103
Problem 3
Temperature (C)					25.0						35.0				45.0
Rate constant, k (unit omitted purposely)					__________________ (copy result from III.2 step 4.)						9.3510-4				1.0610-3
Problem 4
Temperature (C)					25.0						35.0				45.0
Rate constant, k (unit omitted purposely)					__________________ (copy result from III.2 step 4.)						0.00201				0.00535
Step 1. Based on data from your problem, finish the following calculation.
Your problem #______
T (C)			T (K)				1/T (K-1)			Rate const, k						lnk
25.0
35.0
45.0
Step 2. Using data obtained in step 1, plot lnk against 1/T.
Based on the range of your obtained lnk, selected the most appropriate chart to plot lnk against 1/T.
Most appropriate for problem 1.									Most appropriate for problem 2.
Most appropriate for problem 3.									Most appropriate for problem 4.
Step 3. Calculate linear line slope and figure out activation energy.
Hint: slope=-EaR Ea=-slopeR , in which R=8.314J/(molK) Slope = _______________ ________ value unit Activation energy =________________ _____ value unit