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Elden [556K]
3 years ago
10

What is the number of electrons in a completely filled second shell of an atom?(1) 32 (2) 2 (3) 18 (4) 8

Chemistry
1 answer:
Sphinxa [80]3 years ago
7 0
The number of electrons in a completely filled second shell of an atom is 8.
Hope this helped. 
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The entropy of an exothermic reaction decreases. This reaction will be spontaneous under which of the following temperatures?
kakasveta [241]

Answer:Low temperatures

Explanation:

∆G= ∆H-T∆S

If ∆H is negative (exothermic reaction), then in order to maintain ∆G<0 which is the condition for spontaneity; T must decrease. This is because, decrease in T will keep the difference of ∆H and T∆S at a negative value in order to satisfy the above stated condition for spontaneity.

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Explain the difference between an endothermic and an exothermic reaction using the concepts of potential energy, stability, and
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An Exothermic reaction releases energy into the surroundings and so the products have more potential energy then the reactants. The enthalpy change is a negative value. Whereas, an endothermic reaction involves the absorption of energy into the system and so the reactants have more potential energy than the products. The enthalpy change is a positive value. This is clearly represented in energy profile diagrams.
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I think it’s salt water
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Lead(II) nitrate is added slowly to a solution that is 0.0800 M in Cl− ions. Calculate the concentration of Pb2+ ions (in mol /
barxatty [35]

Answer:

[Pb^{2+}]=3.9 \times 10^{-2}M

this is the concentration required to initiate precipitation

Explanation:

PbCl_2  ⇄ Pb^{2+}+2Cl^-

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Ip>Ksp

Precipitation starts only when solution is supersaturated because solution become supersaturated then it does not stay in this form and precipitation starts itself only solution become saturated.

This usually happens when two solutions containing separate sources of cation and anion are mixed together and here also we are mixing lead (||)nitrate solution(source of lead(||)) into the Cl- solution.

Ip=[Pb^{2}][2Cl^-]^2=Ksp

Ksp=2.4\times 10^{-4}

lets solubility=S

[Pb^{2+}] = S

[Cl^-]=2S

Ksp=[Pb^{2+}]\times [Cl^-]^2

Ksp=S \times (2S)^2

Ksp=4S^3

S=\sqrt[3]{\frac{Ksp}{4} }

S=3.9\times 10^{-2}

[Pb^{2+}]=3.9 \times 10^{-2}M this is the concentration required to initiate precipitation

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What is the hardest mineral listed here? <br> A. quartz B. calcite C. gypsum D. corundum
a_sh-v [17]
The answer would be D. The only minerals harder than corundum is diamond.
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