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Welcome to our Physics lesson on The Meaning of Mole. Avogadro's Number, this is the first lesson of our suite of physics lessons covering the topic of The Kinetic Theory of Gases. Ideal Gases, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
When you go to buy rice, you take pockets of 1 kg from the shelves. Everybody would laugh if hears you saying to the seller: "Please, give me 7432 grains of rice."
Similarly, it is meaningless to consider the gas molecules individually; they always are taken as "pockets" of particles. In tutorial 1.1 "Units. Systems of Units. Fundamental and Derived SI Units", it was explained that the standard (SI) unit of amount of matter is not kilogram but mole (mol) instead. It represents a determined number of particles used as a standard of measurement for all materials.
By definition, one mole (in short mol) of a substance represents the mass of 6.02 × 1023 particles of that substance.
The number 6.02 × 1023 is known as Avogadro's number (NA) and it represents the number of particles contained in 12 g of Carbon - 12.
In other words, 1 mol of carbon-12 has a mass of 12 grams and contains 6.022140857 x 1023 of carbon atoms (written in 10 significant figures). We say molar mass M of carbon-12 is 12 g/mol = 0.012 kg/mol.
Mole is one of the seven fundamental quantities in science. It differs from mass as for the same number of particles (for example for one mole) different materials have different masses. Therefore, mole represents better than mass the number of particles contained in a sample of material.
We can calculate the number of moles n in a certain amount of a known substance of mass m and molar mass M through the equation
The molar mass of oxygen O2 is 32 g/mol. How many molecules are there in 160 g O2?
First, we must calculate the number of moles n contained in 160 g oxygen O2. We have M = 32 g/mol and m = 160 g. Thus,
Hence, the number N of O2 molecules contained in 160 g oxygen O2 is:
You have reached the end of Physics lesson 13.6.1 The Meaning of Mole. Avogadro's Number. There are 6 lessons in this physics tutorial covering The Kinetic Theory of Gases. Ideal Gases, you can access all the lessons from this tutorial below.
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