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Andre45 [30]
3 years ago
8

The half-life of Radium-226 is 1590 years. If a sample contains 100 mg, how many mg will remain after 4000 years?

Chemistry
1 answer:
guajiro [1.7K]3 years ago
4 0
We can calculate the amount left after 4000 years by using the half-life equation. It is expressed as:

A = Ao e^-kt

where A is the amount left at t years, Ao is the initial concentration, and k is a constant.

From the half-life data, we can calculate for k.

1/2(Ao) = Ao e^-k(1590)
k = 4.36 x 10^-4

A = 100 e^-<span> 4.36 x 10^-4(4000)
</span>A = 17.48 mg
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Hen solid kbr is dissoved in water, the solution gets colder. this is an example of a(n) ________ reaction.
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Endothermic reactions. These are reactionsthat take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder
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What are the symbols for the elements with the following valence electron configurations? List all.a. s2d1b. s2p3c. s2p
maria [59]

Answer:

Sc : 4s 2 3d 1

 Y : l 5s 2 4d 1

La : 6s 2 5d 1

Ce : 6s 2 4f 1 5d 1

Gd : 6s 2 4f 7 5d 1

Lu : 6s 2 4f 14 5d 1

Ac : 7s 2 6d 1

Pa : 7s 2 5f 2 6d 1

U : l 7s 2 5f 3 6d 1

Np : 7s 2 5f 4 6d 1

Cm : 7s 2 5f 7 6d 1

b. s2p3

he pnictogens:

N l : 2s 2 2p 3

P l : 3s 2 3p 3

As : 4s 2 3d 10 4p 3

Sb : 5s 2 4d 10 5p 3

Bi : 6s 2 4f 14 5d 10 6p 3

Mc : 7s 2 5f 14 6d 10 7p 3

c.The noble gases:

Ne : 2s 2 2p 6

Ar : 3s 2 3p 6

Kr : 4s 2 3d 10 4p 6

Xe : 5s 2 4d 10 5p 6

Rn : 6s 2 4f 14 5d 10 6p 6

Og : 7s 2 5f 14 6d 10 7p 6

Explanation: From the periodic tables we can drive elements with the electronic configuration

Sc : 4s 2 3d 1

 Y : l 5s 2 4d 1

La : 6s 2 5d 1

Ce : 6s 2 4f 1 5d 1

Gd : 6s 2 4f 7 5d 1

Lu : 6s 2 4f 14 5d 1

Ac : 7s 2 6d 1

Pa : 7s 2 5f 2 6d 1

U : l 7s 2 5f 3 6d 1

Np : 7s 2 5f 4 6d 1

Cm : 7s 2 5f 7 6d 1

b. s2p3

he pnictogens:

N l : 2s 2 2p 3

P l : 3s 2 3p 3

As : 4s 2 3d 10 4p 3

Sb : 5s 2 4d 10 5p 3

Bi : 6s 2 4f 14 5d 10 6p 3

Mc : 7s 2 5f 14 6d 10 7p 3

c.The noble gases:

Ne : 2s 2 2p 6

Ar : 3s 2 3p 6

Kr : 4s 2 3d 10 4p 6

Xe : 5s 2 4d 10 5p 6

Rn : 6s 2 4f 14 5d 10 6p 6

Og : 7s 2 5f 14 6d 10 7p 6

3 0
3 years ago
For a particular reaction at 235.8 °C, ΔG=−936.92 kJ/mol , and ΔS=513.79 J/(mol⋅K) . Calculate ΔG for this reaction at −9.9 °C.
Rudik [331]

Answer:

-138.9 kJ/mol

Explanation:

Step 1: Convert 235.8°C to the Kelvin scale

We will use the following expression.

K = °C + 273.15 = 235.8°C + 273.15 = 509.0 K

Step 2: Calculate the standard enthalpy of reaction (ΔH°)

We will use the following expression.

ΔG° = ΔH° - T.ΔS°

ΔH° = ΔG° / T.ΔS°

ΔH° = (-936.92kJ/mol) / 509.0K × 0.51379 kJ/mol.K

ΔH° = -3.583 kJ (for 1 mole of balanced reaction)

Step 3: Convert -9.9°C to the Kelvin scale

K = °C + 273.15 = -9.9°C + 273.15 = 263.3 K

Step 4: Calculate ΔG° at 263.3 K

ΔG° = ΔH° - T.ΔS°

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ΔG° = -138.9 kJ/mol

8 0
3 years ago
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