Respuesta :

emilyro
half-life means you divide by 2 
21.6 / 3.6 = 6 hf (hf = half-life) 
then you divide by 2^6 
6.02 x 10^23 / 2^6 = 9.40625 x 10^21 atoms 
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26 
3hf ===> 2^3 
10.0 / 2^3 = 1.25 gram (remaining) 
answer : 10 - 1.25 = 8.75g 
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27 
128 / 2^n = 2 
64 = 2^n 
n = 6 
24 /6 = 4  
4 days is the half-live of the sample 
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28 
2.5/4.46 of 50% initial mass 
(2.5/4.46) x 0.5 x 2 = 0.5605 g 
answer: 2 - 0.5605 = 1.4395 g 
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29 
2^7 = 128 
so 7 half-lifes 
7* 8040 = 56200 days 
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30 
the time of 10 half-lifes 
= 10 x 0.334s = 3.34s 
raphealnwobi

128 × 10²⁰ atoms would be present after 20.0 days

The half life of an element is the time taken for the element to decay to half of its initial value. It is given by:

[tex]N(t)=N_o(\frac{1}{2} )^\frac{t}{t_\frac{1}{2} }[/tex]

N(t) is the quantity of substance after t days, N₀ is the initial value and t₁₋₂ = half life

Given N₀ = 6.02 x 10²³ atoms, t = 20 days, t₁₋₂ = 3.6 days, hence:

[tex]N(20)=6.02*10^{23}*(\frac{1}{2} )^\frac{20}{3.6 }=128 * 10^{20}[/tex]

Therefore 128 × 10²⁰ atoms would be present after 20.0 days

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