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Blizzard [7]
3 years ago
7

Magnesium has an atomic mass of 24.3. there are two isotopes of magnesium - one contains 12 neutrons and the other contains 13 n

eutrons in the nucleus. what is the fractional abundance of the one that contains 12 neutrons?
Chemistry
1 answer:
Juli2301 [7.4K]3 years ago
3 0
So what we know:
-Atomic Mass = Protons + Neutrons
-Atomic Number is the number of protons

Magnesium's atomic number is 12, so the natural occurring isotope for magnesium is Mg-12 (12 protons and 12 neutrons). Added up we have an atomic mass of 24 amu. Which means if we added one neutron in Mg-13, our atomic mass would be 25 amu.

We can use the equation:
(amu of isotope 1)x + (amu of isotop 2)(x-1) = Average atomic mass
where isotope 1 is the fractional abundance we're solving for.

Plugged in it looks like this:
24x + 25(1-x) = 24.3

Now to solve for x:
24x + 25 - 25x = 24.3
   -x + 25 = 24.3
        -x = -.7
         x = .7

So in this case, the fractional abundance of Mg-12 would be .7, or 70%.<span />
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d) 0.1835 mol/MJ

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The enthalpy of formation (ΔH°f) is the enthalpy of a reaction to form a compound by its constituents. For CO₂, ΔH°f = - 393.5 kJ/mol.

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b) The combustion reaction is:

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ΔH°rxn = [2*(-285.3 ) + 1*(-393.5)] - [1*(-74.8)]

ΔH°rxn = -889.3 kJ/mol = -889.3x10⁻³ MJ/mol

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c) C₃H₈(g) + 10O₂(g) → 3CO₂(g) + 4H₂O(l)

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ΔH°rxn = -2,296.5 kJ/mol = -2.2965 MJ/mol

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d) C₈H₁₈(l) + (25/2)O₂(g) → 8CO₂(g) + 9H₂O(l)

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