The following data were obtained for the concentration vs.time for a certain che

Question

The following data were obtained for the concentration vs.time

for a certain chemical reaction. Values were measured at1.00s

intervals, beginning at 0.00s and ending at 20.00s. Concentrations

in mM are:

   10.00, 6.91, 4.98, 4.32, 3.55, 3.21,

2.61,2.50, 2.22, 1.91, 1.80, 1.65, 1.52, 1.36, 1.42, 1.23, 1.20,

1.13,1.09, 1.00, 0,92.

A) Plot concentration (c) vs time, ln c vs time, and 1/c

vstime.

B) Is the data 0th, 1st, or 2nd order? Calculate the

rate constant for the reaction

C) What might be an experiment method which might be used to measure the concentrations that are changing so rapidly? The reaction is over in 20 s

Explanation / Answer

Initial conc. Final conc Tine consumed Change in moles/time in sec

10.00 3.21 5 sec 6.79 mM / 5 secc = 1.358 mM/sec

10.00 1.80 10 sec 8.2 mM / 10 sec = 0.82 mM/sec

10.00 1.23 15 sec 8.77 mM/ 15 sec = 0.584 mM/sec

10.00 0.92 20 sec 9.08 mM/20 sec = 0.454 mM/sec

Change in concentrations at 5 and 10 sec Rates at 5 and 10 sec

3.21 =1.78 1.358 mM/sec = 1.65

1.80   0.82 mM/sec

So the rate is changing more or less as much concentration is chnaging. So its first order reaction

Flash photolysis combined with absorption spectroscopy can study reactions on a microsecond time scale. Laser induced fluorescence extends the measurements to nanosecond time scales

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