SOLUTION: A substance in a chemical reaction is used up at a rate that is proportional to the amount of the substance present at any time. If ½ of the substance is used up in 2 hours, h

Question 1187683: A substance in a chemical reaction is used up at a rate that is proportional to the
amount of the substance present at any time. If ½ of the substance is used up in 2
hours, how much of the substance is left at the end of 2 hours and 30 minutes?
Answer by ikleyn(52858) (Show Source): You can put this solution on YOUR website!
.
A substance in a chemical reaction is used up at a rate that is proportional to the
amount of the substance present at any time. If ½ of the substance is used up in 2
hours, how much of the substance is left at the end of 2 hours and 30 minutes?
~~~~~~~~~~~~~~~

Since the substance in a chemical reaction is used up at a rate that is proportional 
to the amount of the substance present at any time, we have classical exponential decay of the substance.



We also are given that the half-life time of this substance decay is 2 hours.



Since  2 hours and 30 minutes is   = 1.25 half-periods,  the remaining mass 
at the end of 2 hours and 30 minutes will be


     = 0.420448 = 0.420  (rounded)  


of the original amount of the substance in the reaction.

Solved, answered and explained in all details.

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