Asked by Bob

A substance undergoes a first-order decomposition. After 40.0 min at 500 degrees C, only 12.5% of the original sample remains. What is the half-life of the decomposition? If the original sample weighted 243 g, how much would remain after 2 hours?
Answered by College Hacker
).5^n = 0.125
n = 3
t 1/2 = 40 mins / 3
t 1/2 = 13.3 mins

Hope that helps
Answered by College Hacker
n * t1/2 = mass/(2^n)
n * t1/2 = 2 hrs = 120 mins
n = 120/13.3
n = 9.02 (n = number of half-cycles)
remaining mass = 243/(2^9.02)
= 0.467g
0.467g is remaining after 2 hrs
Answered by Writeacher
Is Bob going to trust someone who calls himself "College Hacker"? Hmmm!
Answered by College Hacker
It's up to Bob. If you find anything wrong with the solution, please correct it :)
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