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kvv77 [185]
3 years ago
11

How many half-lives must elapse until 84 % of a radioactive sample of atoms has decayed? -g?

Chemistry
1 answer:
Ivahew [28]3 years ago
4 0
Half-life is the time required for decay of 50% of radio-active nuclei.

Thus, when radio-active material crosses 1st half-life, 100/2 = 50% radio-active material is left and remaining 50% is elapsed.

When, when radio-active material crosses 2nd half-life, 50/2 = 25% radio-active material is left and remaining 75% is elapsed.

When radio-active material crosses 3rd half-life, 25/2 = 12.5% radio-active material is left and remaining 87.5% is elapsed.

Thus, 2 <span>half-lives must elapse until 84 % of a radioactive sample of atoms has decayed.</span>
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A piece of unknown metal with mass 68.6 g is heated to an initial temperature of 100 °C and dropped into 42 g of water (with an
kogti [31]

The piece of unknown metal is in thermal equilibrium with water such that Q of metal is equal to Q of the water. We write this equality as follows:

-Qm = Qw

Mass of metal (Cm)(ΔT) = Mass of water (Cw) (ΔT)

where C is the specific heat capacities of the materials.

We calculate as follows:

-(Mass of metal (Cm)(ΔT)) = Mass of water (Cw) (ΔT)

-68.6 (Cm)(52.1 - 100) = 42 (4.184) (52.1 - 20)

Cm = 1.717 -----> OPTION C

8 0
3 years ago
Calculate the wavelength, in nanometers, of the light emitted by a hydrogen atom when its electron fallsfrom the n = 7 to the n
Helga [31]

Answer:

λ=2167.6 nm

The wavelength of light emitted is 2167.6 nm.

Explanation:

We recall that Eₙ=\frac{-2.18*10^{-18} J}{n^{2} }

since there was transition from n7 to n=4 we will first calculate the change in the energy i.e ΔE

ΔE=E₄-E₇

ΔE=-2.18*10^{-18} J(\frac{1}{4^{2} } -\frac{1}{7^{2} } )

ΔE=-9.1760*10^-20 J

Now:

|ΔE|=Energy of photon=h*v=h*c/λ

λ=h*c/|ΔE|

λ=\frac{6.63*10^{-34}J.s*3.00*10^{8}m/s  }{9.1760*10^{-20} J }

λ=2.1676*10^-6 m

λ=2167.6*10^-9 m

λ=2167.6 nm

The wavelength of light emitted is 2167.6 nm.

5 0
3 years ago
What is the mass of 6.14x10^25 atoms of gold
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3452.6^15 atoms of gold.

3 0
3 years ago
Can anyone answer this?? Thanks in advance <br><br> AlCl3 + Cu = ?
Kazeer [188]
Reaction won't occur
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3 0
2 years ago
The number of neutrons in an atom can be found by subtracting the atomic number from the what?
Svetradugi [14.3K]

Answer:

This approximation of mass can be used to easily calculate how many neutrons an element has by simply subtracting the number of protons from the mass number. Protons and neutrons both weigh about one atomic mass unit or amu. Isotopes of the same element will have the same atomic number but different mass numbers.

Explanation:

3 0
3 years ago
Read 2 more answers
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