"a sample of silicon has an average atomic mass of 28.084amu. in the sample, there are three isotopic forms of silicon. about 92.22% of silicon atoms are 27.9769amu, which have the mass of 28si; about 4.68% are 28.9764amu, which have the mass of 29si, and the remaining isotope, 30si, has a mass of 29.9737amu. calculate the percent isotopic composition of 30si."

The percentage abundance for isotope is 3.09 %.

Explanation:

Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

   .....(1)

We are given:

Let the fractional abundance for isotope be 'x'

Mass of isotope = 27.9769 amu

Percentage abundance of isotope = 92.22 %

Fractional abundance of isotope = 0.9222

Mass of isotope = 28.9764 amu

Percentage abundance of isotope = 4.68%

Fractional abundance of isotope = 0.0468

Mass of isotope = 29.9737 amu

Fractional abundance of isotope = x

Putting values in equation 1, we get:

Converting this fractional abundance into percentage abundance by multiplying it by 100, we get:

Hence, the percentage abundance for isotope is 3.09 %.

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"