3. What is the atomic mass of phosphorous if phosphorous-29 has a percent abundance of 35.5%, phosphorous-30 has a percent abundance of 42.6%, and phosphorous-31 has a percent abundance of 21.9%?

The atomic mass is the mass of an atom. Although the SI unit of mass is the kilogram, atomic mass is often expressed in the non-SI unit atomic mass unit or unified mass or dalton.

To calculate the atomic mass the step we should follow is as follows:-

Hence, the atomic mass of the phosphorus is:-

After solving it,

=

Hence, the atomic mass of the Phosphorus is 29.864amu

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The atomic mass of phosphorus is 29.864 amu.

Explanation:

Given data:

Atomic mass of phosphorus = ?

Percent abundance of P-29 = 35.5%

percent abundance of P-30 = 42.6%

Percent abundance of P-31 = 21.9%

Solution:

Average atomic mass = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass) + (abundance of 3rd isotope × its atomic mass  / 100

Average atomic mass  = (29×35.5)+(30×42.6) + (31×21.9) /100

Average atomic mass =  1029.5 + 1278 + 678.9/ 100

Average atomic mass  = 2986.4 / 100

Average atomic mass = 29.864 amu.

The atomic mass of phosphorus is 29.864 amu.

answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.

according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.

δh(reaction) = ∑nδh(products) - ∑nδh(reactants)

δh(reaction) = [δh +δh] - [δh]

δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj

here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj

therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.