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Zinaida [17]
3 years ago
9

A radioisotope has a half-life of 12 days. If a sample is measured to contain 5 grams of radioisotope, how much time has passed

if the sample originally measured 160 grams of radioisotope?​
Chemistry
1 answer:
Sophie [7]3 years ago
7 0
60 days have passed. In every 12 days the radioisotope loses half of its life. So in the first 12 days, from 160 grams it decreases to half so it becomes 80 grams. The second 12 days, from 80 grams, it decreases to half and becomes 40 g. The third 12 days, from 40 it becomes half to 20 g. The fourth 12 days, from 20 g it becomes half to 10 g. And in the fifth 12 days, from 10 g it becomes half to 5 grams. So 5 times it became half.
5 x 12 ( days)= 60 days
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When 20.0 g of KI are dissolved in 50.0 mL of distilled water in a calorimeter, the temperature drops from 24.0 °C to 19.0 °C. C
Reil [10]
<h2>Answer:</h2>

<em>8.67kJ/mol</em>

<h2>Explanations</h2>

The formula for calculating the amount of heat absorbed by the water is given as:

\begin{gathered} q=mc\triangle t \\ q=50\times4.18\frac{J}{g^oC}\times(19-24) \\ q=50\times4.18\times(-5) \\ q=-1045Joules \\ q=-1.045kJ \end{gathered}

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Since heat is lost, hence the enthalpy change of the solution will be negative that is:

\begin{gathered} \triangle H=-q \\ \triangle H=-(-1.045kJ) \\ \triangle H=1.045kJ \end{gathered}

Determine the enthalpy of solution in kJ•mol-1

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Hence the enthalpy of solution in kJ•mol-1 for KI is 8.67kJ/mol

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