CHEM 172 Kinetics Computer Lab Max. 15 points Purpose The purpose of this lab is
ID: 536088 • Letter: C
Question
CHEM 172 Kinetics Computer Lab Max. 15 points
Purpose
The purpose of this lab is to determine the order of reaction and the activation energy using Excel spread sheet with its plotting feature.
Background
X-Y plot of the data generated from Excel spreadsheet provides, through regression, the value of the slope (i.e. the ratio of Y to X) when the data show a significant linear correlation. Excel also provides the R value, the significance of the correlation. The R value being greater than 0.9 means that the correlation between X and Y variables are significant at the confidence level greater than 90 percent.
In this lab you will exploit slope values from linear correlations between X and Y variables to determine reaction order and activation energy. You have learned at least three different kinds of reaction order kinetics represented as follows:
[A]t = -kt + [A]o (zero order reaction kinetics)
ln[A]t = -kt + ln[A]o (1st order reaction kinetics)
1/[A]t = kt + 1/[A]o (2nd order reaction kinetics)
(the above three can fit to the linear equation pattern below)
Y = (slope) X + b
Each of the three kinetic equations can have a linear correlation between time t and one of the variables of [A]t, ln[A]t, and1/[A]t for zero order, 1st order and 2nd order, respectively. The slope of each correlation is all the same as k, except the sign, thereby providing the rate constant from the value of the slope.
How to approach this lab?
Using Excel spread sheet, you simply plot three different correlations And compare the R2 values from those three correlations to determine the correct order of reaction.
1. Identification of reaction order (10 points)
Nitrogen dioxide gas decomposes to nitrogen monoxide gas and oxygen gas,
NO2(g) NO(g) + O2(g)
The following data were collected from the reaction at 300 oC:
Time, X (second) [NO2], Y (M)
0.0 0.01000
50 .0 0.00787
100.0 0.00649
200.0 0.00481
300.0 0.00380
(1-1) Recreate a table by adding to the given table two data columns of ln[NO2] and 1/[NO2] (show this table by printing it out)
(1-2) Generate three plots: [NO2] vs time; ln[NO2] vs time; 1/[NO2] vs time
(Show these plots by printing them out. When you draw the trend line for each plot, which is the 5th step and the step 6th in the previous exercise, do not choose the box of “set intercept=0”. Choose only the two boxes: “display equation on chart”, and “display R-squared value on chart.”)
(1-3) Now by comparing the three trendlines in the plots, decide what reaction order this
is. (Hint: refer to the equations of zero, first, and second order reactions on the plots along with their R-squared values.)
(1-4) Write down the rate law expression for the reaction.
(1-5) Determine the magnitude of the rate constant with its exact unit.
(Hint: find the slope)
(1-6) Determine the rate of reaction at [NO2] of 0.00500 M.
(1-7) Recreate a table by adding to the given table a data column of reaction rate.
Each rate in the column must respond to each NO2 concentration in the given table.
(1-8) Generate two plots: the reactions rates vs time and the reaction rates vs [NO2].
Interpret the plots. (show these plots by printing them out)
Explanation / Answer
for zero order reaction, [NO2] vs time is straight line , for 1st order, ln[NO2] vs time is straight line for 2nd order, 1/[NO2] vs time is straight line.
the data of plot of [NO2] vs time ( Zero order), ln [NO2] vs time (1st order), 1/[NO2] vs time (2nd order ) is shown below in a single plot
which ever gives straight line with higest R2 value that will be the order of reaction,
since highest R2 value is obtained for the plot of 1/[NO2] vs t, the reaction is 2nd order.
the equation of best fit is 1/[NO2] =0.543*time+99.83 (1)
the rate constant is the slope K=0.543/M.sec
the rate expression -rA= K[NO2]2,
since -dNO2/dt= K[NO2]2
at 0.005M
-d(NO2/dt)= rate= 0.543*(0.005)2= 0.000013575 M/sec
the plot of reaction rate vs time and reaction rate vs concentration of NO2 are given below
the rate is calculated as rA= -dCA/dt= K[NO2]2