Why is a weighted average used to calculate the average atomic mass of an element

No rated answer for this but, have an Explanation Down

Explanation:

The mass written on the periodic table is an average atomic mass taken from all known isotopes of an element. This average is a weighted average, meaning the isotopes relative abundance changes its impact on the final average. The reason this is done is because there is no set mass for an element.

"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"

it means there are 3 atoms of oxygen