A radioactive element gets ... -Eduinfy.com
MCQ Solution: Chemical Kinetics

A radioactive element gets spilled over the floor of a room. Its half-life period is 30 days. If the initial velocity is ten times the permissible value, after how many days will it be safe to enter the room?

1) 100 days
2) 1000 days
3) .300 days
4) 10 days

 

Solution

Say Permissible rate is $$\vartheta$$

then $$\vartheta _{2}=100$$
$$\vartheta =kA$$
     $$=kA_{0}e^{-kt}$$
      $$kA_{0}e^{\frac{-0.693t}{t_{\frac{1}{2}}}}
$$\vartheta =\vartheta _{0}e^{\frac{-0.693t}{t_{\frac{1}{2}}}}$$
$$\vartheta =10\vartheta e^{\frac{-0.693t}{t_{\frac{1}{2}}}}$$
$$l_{n}(10)=\frac{-0.693}{t_{\frac{1}{2}}}t$$
$$t=\frac{t_{\frac{1}{2}}*2.303}{0.693}*10$$
     $$=1000$$days
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