- published: 06 Aug 2015
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The abundance of a chemical element is a measure of the occurrence of the element relative to all other elements in a given environment. Abundance is measured in one of three ways: by the mass-fraction (the same as weight fraction); by the mole-fraction (fraction of atoms by numerical count, or sometimes fraction of molecules in gases); or by the volume-fraction. Volume-fraction is a common abundance measure in mixed gases such as planetary atmospheres, and is similar in value to molecular mole-fraction for gas mixtures at relatively low densities and pressures, and ideal gas mixtures. Most abundance values in this article are given as mass-fractions.
For example, the abundance of oxygen in pure water can be measured in two ways: the mass fraction is about 89%, because that is the fraction of water's mass which is oxygen. However, the mole-fraction is 33.3333...% because only 1 atom of 3 in water, H2O, is oxygen.
As another example, looking at the mass-fraction abundance of hydrogen and helium in both the Universe as a whole and in the atmospheres of gas-giant planets such as Jupiter, it is 74% for hydrogen and 23-25% for helium; while the (atomic) mole-fraction for hydrogen is 92%, and for helium is 8%, in these environments. Changing the given environment to Jupiter's outer atmosphere, where hydrogen is diatomic while helium is not, changes the molecular mole-fraction (fraction of total gas molecules), as well as the fraction of atmosphere by volume, of hydrogen to about 86%, and of helium to 13%.
You have always lived like this
You have always lived like this
The ice blue chill
The dark gray sky
The frozen ground
And the helpless feeling of insignificance
You have always lived like this
You have always lived like this
Yeah
The day's routine
The day's unsure
The day is done
And the dreams of being somewhere you can't be
The ice blue chill
The dark gray sky
The frozen ground
And the helpless feeling of insignificance
You have always lived like this
You have always lived like this
You have always fought the elements
They take on different forms
There has always been a struggle
With the things you can't perform
You will always fight the elements
They are not in your hands
You will always fight the elements
Unless you understand
Unless you understand
Unless you understand that
You have always lived like this