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Lelu [443]
3 years ago
9

What is the half-life of an isotope that decays to 6.25% of its original activity in 18.9 hours?

Chemistry
1 answer:
inessss [21]3 years ago
8 0
Radioactive material obeys 1st order decay kinetics,
For 1st order reaction, we have 
k = \frac{2.303}{t}Xlog \frac{\text{initial conc.}}{\text{final conc.}}
where, k = rate constant of reaction

Given: Initial conc. 100, Final conc. = 6.25, t = 18.9 hours

∴ k = \frac{2.303}{18.9} X log \frac{100}{6.25} = 0.1467 hours^(-1)

Now, for 1st order reactions: half life = \frac{0.693}{k} =  \frac{0.693}{0.1467} = 4.723 hours.


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How many formula units are in 239.2g of <br> Br2<br> MgCl2<br> H2O<br> Fe
Oksana_A [137]

The formula units in the substances are as follows:

  • Br2 = 8.99 × 10^23 formula units
  • MgCl2 = 1.51 × 10^24 formula units
  • H2O = 2.57 × 10^24 formula units
  • Fe = 2.57 × 10^24 formula units

<h3>How many moles are in 239.2 g of the given substances?</h3>

The moles of the substances are determined from their molar mass.

Molar mass of the substances is given as follows:

  • Br2 = 160 g/mol
  • MgCl2 = 95 g/mol
  • H2O = 18 g/mol
  • Fe = 56 g/mol

Formula units = mass/molar mass × 6.02 × 10^23

The formula units in the substances are as follows:

  • Br2 = 239.2/160 × 6.02 × 10^23 = 8.99 × 10^23 formula units
  • MgCl2 = 239.2/95 × 6.02 × 10^23 = 1.51 × 10^24 formula units
  • H2O = 239.2/18 × 6.02 × 10^23 = 2.57 × 10^24 formula units
  • Fe = 239.2/56 × 6.02 × 10^23 = 2.57 × 10^24 formula units

In conclusion, the number of formula units is derived from the moles and Avogadro number.

Learn more about formula units at: brainly.com/question/24529075

#SPJ1

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How many molecules of glucose are in 5. 72 grams of glucose c6h12o6?.
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