Hint: It is not necessary to graph these data. (1) The observed half life for th

Question

Hint: It is not necessary to graph these data.

(1)
The observed half life for this reaction when the starting concentration is 1.45×10-2 M is s and when the starting concentration is7.25×10-3 M is ______s.

(2)
The average rate of disappearance of NH3 from t = 0 s to t = 999 s is ___________ M s-1.

(3)
The average rate of disappearance of NH3 from t = 999 s to t = 1.50×103 s is _________M s-1.

(4)
Based on these data, the rate constant for this _______(zerofirstsecond) order reaction is _______M s-1.

Explanation / Answer

1. The half life is defined as the time required for the concentration to drop to 50% of its inital value. When the starting concentration is 1.45*10-2 and 50% of this becomes 7.25*10-3M and hence half life is 999 sec

when the intial concentration is 7.25/1000 and the 50% of it is 3.63*10-5 and hence half life is 1500 seconds

2. the rate of disappearance from t= 0 to t= 999 sec is (1.45*10-2- 7.25*10-3)/999=7.3*10-7M/s

3. The rate of disappearance from t=0 and t=1500 sec,rate = (1.45/100- 3.63/1000)/ 1500= 7.25*10-7 M/s, same as the rate of disapearance from 0 to 999 sec

The rate is zero order since it is independent of concentration

for zero order -dCNH3/dt= K

and hence K= rate constant= 7.25*10-7M/s

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