The decomposition of nitrosyl bromide is followed by measuring total pressure
because the number of moles of gas changes; it cannot be followed
colorimetrically because both NOBr and Br2 are reddish brown:
2 NOBr(g) ® 2 NO(g) + Br2(g)
Use the data in the table to answer the following:
a) Determine the average rate over the entire experiment.
b) Determine the average rate between 2.00 and 4.00 s.
c) Use graphical methods to estimate the initial reaction rate.
d) Use graphical methods to estimate the rate at 7.00 s.
e) At what time does the instantaneous rate equal the average rate over
the entire experiment?
Time (s) [NOBr] (mol/L)
0.00 0.0100
2.00 0.0071
4.00 0.0055
6.00 0.0045
8.00 0.0038
To solve this problem, we need to use the given data to calculate the average rate of the reaction over different time intervals and estimate the initial reaction rate and rate at a specific time using graphical methods.
a) To determine the average rate over the entire experiment, we can use the following formula:
Average rate = (change in concentration)/(change in time)
Here, the change in concentration is the difference in [NOBr] between the initial and final time, and the change in time is the difference in time between the initial and final measurements.
Initial [NOBr] = 0.0100 mol/L
Final [NOBr] = 0.0038 mol/L
Initial time = 0.00 s
Final time = 8.00 s
Now, apply the average rate formula:
Average rate = (0.0038 - 0.0100 mol/L) / (8.00 s - 0.00 s)
b) To determine the average rate between 2.00 and 4.00 s, we use the same formula but consider the change in concentration and time only between those specific times.
Change in [NOBr] = [NOBr] at 4.00 s - [NOBr] at 2.00 s
Change in time = 4.00 - 2.00 s
c) To estimate the initial reaction rate graphically, we can plot a graph of [NOBr] vs. time and draw a tangent line at the initial time point (0.00 s). The slope of this tangent line represents the initial reaction rate.
d) To estimate the rate at 7.00 s graphically, repeat the same procedure as in part c) but draw a tangent line at the time point 7.00 s.
e) To find the time at which the instantaneous rate equals the average rate over the entire experiment, we need to find the point on the graph where the tangent line (representing the instantaneous rate) is parallel to the line connecting the initial and final concentration points.
Using the given data, you can calculate the desired rates and find the time at which the instantaneous rate equals the average rate by following the steps described above.