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March 6, 2015

March 6, 2015

Posted by **Jay** on Friday, May 6, 2011 at 10:18am.

- Chemistry -
**DrBob222**, Friday, May 6, 2011 at 7:06pmLet's start with 100 atoms of U238. Suppose x atoms of U238 decompose to Pb. Then there must be 100-x atoms U238 not yet decomposed. We know the ratio is 0.1462; therefore,

(x/100-x) = 0.1462 and solve for x which is the amount of Pb formed and 100-x is the amount of U left.

So No = 100 and N = 100-x, whatever that value is. Substitute into

ln(No/N) = kt

You know No and N. You want to find t. k = 0.693/t_{1/2}and you have the half life. Solve for k and substitute into the equation above.

- Chemistry -
**Jude**, Friday, May 6, 2011 at 8:20pmThank you so much DrBob222. You are the best

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