推 Tuba:謝謝大大,我會好好研究的...m(_ _)m 03/14 23:07
※ 編輯: Aesop 來自: 163.26.149.26 (03/15 11:25)
※ 引述《Tuba (Walk the line)》之銘言：
: 1.年級：高中 (不確定是高二或高三)
: 2.科目：化學
: 3.章節：C 14的半衰期
: 4.題目：
: The half-life for the radioactive decay of C-14 is 5730 years.
: How long will it take for 20% of the C-14 atoms in a sample of C-14 to decay?
: Ans:1800year
(1/2)^(t/5730) = 8/10 = 4/5
(t/5730)log2=log(5/4)=log5-log4=log5-2log2
t=5730x[(log5-2log2)/log2]=5730x[(log5/log2)-2]
=5730x0.321928094=1844.6(years)
: 接著題目問
: If a sample of C-14 initially contains 1.3 mmol of C-14, how many millimoles
: will be left after 2245 years?
: Ans:0.99 mmol
(1/2)^(2245/5730)=x/1.3
x=1.3 x (1/2)^(2245/5730)=0.9908( mmole )
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