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| | | Message 1 of 4 in Discussion |
| From:  2122101234 (Original Message) | Sent: 1/11/2005 3:01 AM |
Hey everyone! I’m a bit confused on a rate of chemical reaction calculation�?This is from Petrucci’s “General Chemistry�?textbook:
There’s an example question in the book that is as follows:
A + 3B -> 2C + 2D
[B]= 0.9986 M and 13.20 min later [B]=0.9746 M. What is the average rate of reaction during this time period, expressed in Ms-1.
The answer given is 1.01x 10-5 Ms-1
Since the rate of reaction = (-1/3 )([B]/t)= -(1/3)((0.9746M- 0.9986)/ 792s) = 1.01 X10 -5Ms-1.
Alright, so I understood this question and attempted one of the practice this question:
2A+ B-> C+ D
[A]= 0.3629 M. At a time 8.25 min later {A}= 0.3187M. What is the average rate of the reaction?
I did this question the exact same way as the practice example and I got 4.46X 10 -5Ms-1.
Rate of reaction= -(1/2)( [A]/t) = - (1/2)((0.3187M-0.3629M)/ 495s) = 4.46X 10 -5Ms-1
But it turned out my answer was wrong. According the answer book:
Rate of reaction= -�?[A]/ t = - (0. 3187M-0.3629M)/ 8.25 min x 1 min/60s = 8.93X 10 -5Ms-1
I’m confused. When am I supposed to use the ratio and when do I not use it? Or is this a text book error?
Sorry for the long post! Thanks
Note: I had problems putting up this post, sorry.The "�? are supposed to be deltas.
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