What is a mole and why is it useful?

The number of moles is related to the amount of a substance we have. If we were to use the number of particles, the numbers would be huge and impractical to use. So, Avagadro's number provides us a link with the number of moles of something, and the number of particles.

n = N x NA

Where, n = number of moles N = number of particles NA = avagadro's number (6.022 x 10^23)

Particles can be anything - atoms, molecules, electrons, ions etc. Avagadro's number relates them all to one quantity.

Ratios of moles are very handy:

C + O2 -> CO2

1 mole of carbon + 1 mole of oxygen -> 1 mole of carbon dioxide

2Mg + O2 -> 2MgO

2 moles of magnesium + 1 mole of oxygen -> 1 mole of magnesium oxide

Even though in the above equations, carbon and magnesium are atoms and oxygen is a molecule, it is only the ratio of the two that matters.

Number of moles, n, is also used in many calculations, so it is useful to know where it originates from!

Answered by Michael L. Chemistry tutor

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