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### half-life

Posted: Sat Mar 03, 2018 2:51 pm
What is the purpose of determining a half life?

### Re: half-life

Posted: Sat Mar 03, 2018 3:08 pm
Half life is the time (represented in equations by t1/2) required for the concentration of a reactant to reduce to half of its initial value

### Re: half-life

Posted: Sat Mar 03, 2018 9:27 pm
Half life can also tell you how fast a substance decays.

ie. A substance that has a half life of 10 seconds has a faster rate of decay in comparison to a substance that has a half life of 10 days.

### Re: half-life

Posted: Sat Mar 03, 2018 9:49 pm
The greater the rate constant, the shorter is the half life. You can use half life to calculate the amount of reactant remaining in a reaction.
At any stage of a reaction, the concentration of A remaining after n half-lives is: (1/2)^n * [A]

### Re: half-life

Posted: Sat Mar 03, 2018 9:54 pm
A half- life tells you how long it takes for the reactants to reach half of their initial concentrations. It can be used to predict the concentration of a substance in a reaction over time.

### Re: half-life

Posted: Sat Mar 03, 2018 9:58 pm
Also, going off of finding the half-life, remember that you can also find the "one-third" life or "one-fourth" life, etc.

### Re: half-life

Posted: Sat Mar 03, 2018 10:53 pm
In regards to applications, half lives can be very useful in determining the approximate age of organic objects via radiometric dating!

### Re: half-life

Posted: Sun Mar 04, 2018 12:25 pm
Half-life can be used to approximate how much of a substance decayed or still remains. For instance, if you start with 100 mol of a substance with a half-life of 10 years then you can determine the following:

50% of the 100 mol, that is 50 moles, will have decayed in 10 years
50% of the 100 mol, that is 50 moles, still remain in 10 years
25% of the 100 moles, that is 25 moles, remain after 20 years

### Re: half-life

Posted: Sun Mar 04, 2018 1:47 pm
Adding on to the possible applications of half-life, you can use the half-life to determine how much of a given drug is in a bloodstream x hours after it was initially administered. I think this is actually how the frequency with which you take certain medicines is determined!