[Ryco]

Hi, I have two problems that I think I am setting up right, yet I do not seem to be able to come to the correct answer.

1.  In a set of experiments, NO2 was in large excess, at a concentration of 1.0e13 molecules/cm3 with the following data collected. Find the value of the rate constant. The reaction is 1st order with an overall rate law   of k[NO2][ O]


Time (s)   Concentration of O (atoms/cm3)

 0           5.0e9
 1.0e-2    1.9e9
 2.0e-2    6.8e8
 3.0e-2    2.5e8


Here do I use ln[1.9e9]= -k(1e-2) + ln[5e9] to find k?



2. The reaction given below is known to be zero order in A and to have a rate constant of 3.8e-2 mol/L·s at 25°C.      A-> B + C

An experiment was run at 25°C where [A]0 = 1.0e-3 M. Calculate the concentration of B after 6.0e-3 s has elapsed.

I used       [A] = -( 3.8e-2 mol/Ls )(6.0e-3) + 1.0e-3 mol/L    to solve for the concentration of A, but from there how do I find the concentration of B? By a 1/1 mol ratio?

[DevaDevil]

1.) reaction rate v = k * [NO2] * [O2]
k can be found from the plot of ln[O2] vs time (which should be a linear plot. -k is the slope.)

2.) stoechiometry indeed shows just as much B as C is formed, however it also shows that for every mole A reacted, 1 mole B AND 1 mole C is formed.