Question

In: Chemistry

Consider the decomposition of acetaldehyde (CH3CHO) into methane (CH4) and carbon monoxide (CO).


Consider the decomposition of acetaldehyde (CH3CHO) into methane (CH4) and carbon monoxide (CO).

CH3CHO → CH4 + CO

An experiment is performed where the concentration of acetaldehyde is measured at various time intervals, resulting in the following data.

Time (s)[CH3CHO] (M)
0.00.242
20.00.168
40.00.129
60.00.104


(a) Using Excel (or similar software), graph the three types of plots outlined below and enter the slope, y-intercept, and R2 for each graph). Use the graph with the best linear fit to determine the order of the reaction with respect to CH3CHO. (Enter your answer to three significant figures.)

graph (1):    [CH3CHO]tvs. time

slope=
y-intercept=
R2=



graph (2):    ln [CH3CHO]t vs. time

slope=
y-intercept=
R2=



graph (3):    1/[CH3CHO]tvs. time

slope=
y-intercept=
R2=


Recall that for a  ---Select--- zero order first order second order reaction, a plot of [CH3CHO] vs. time will yield a straight line. For a  ---Select--- zero order first order second order reaction, a plot of ln[CH3CHO] vs. time will yield a straight line. For a  ---Select--- zero order first order second order reaction, a plot of 1/[CH3CHO] vs. time will yield a straight line. The graph of 1/[CH3CHO] vs. time has the best fit to a straight line, so this reaction is  ---Select--- zero order first order second order .

(b) Calculate the rate constant for this reaction.
1/M·s

(c) Determine the rate law for this reaction. (Rate expressions take the general form: rate = k . [A]a . [B]b.)

Solutions

Expert Solution

(a) Graph 1:

[CH3CHO] vs. time

equation: y= -0.0023x + 0.223

slope = -0.0023
y-intercept = 0.2283
R2 = 0.9428

Graph 2:

ln[CH3CHO] vs. time

Equation: y= -0.014x - 1.4588

slope =  -0.014
y-intercept = 1.4588
R2 = 0.9856

Graph 3:

1/[CH3CHO] vs. time

Equation: y= 0.0912x + 4.1256

slope =  0.0912
y-intercept = 4.1256
R2 = 0.9999 = 1

From the above plot, for a second order reaction, a plot of 1/[CH3CHO] vs time will yield a straight line. The graph of 1/[CH3CHO] vs. time has the best fit to a straight line, so this reaction is second order. .
(b)The rate constant for this reaction.1/M·s

For a second order reaction the slope of 1/[CH3CHO] vs time gives the rate constant. Since the slope of the plot is  0.0912. The rate constant = 0.0912.1/M·s

(c) The rate law for this reaction.

The rate law for second order reaction can be expressed as below

queen_honey_blossom answered 3 years ago
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