Avogadro Number Calculator
Calculate the number of atoms or molecules in any substance using Avogadro's number. Free online Avogadro's constant calculator for chemistry.
What is Avogadro's Number?
Avogadro's number, also known as Avogadro's constant, is the number of particles (atoms, molecules, ions, or other entities) in one mole of a substance. Its value is exactly $6.02214076 \times 10^{23}$ particles per mole. Named after the Italian scientist Amedeo Avogadro, this constant is fundamental to chemistry and provides the bridge between the microscopic world of atoms and the macroscopic world of grams and kilograms.
One mole of any substance always contains exactly Avogadro's number of particles. For example, one mole of water ($H_2O$) contains $6.022 \times 10^{23}$ water molecules, and one mole of carbon contains $6.022 \times 10^{23}$ carbon atoms.
How to Use Avogadro's Number
The key relationships involving Avogadro's number are:
$$n = \frac{m}{M}$$
$$N = n \times N_A$$
where $n$ is the amount of substance in moles, $m$ is the mass in grams, $M$ is the molar mass in g/mol, $N$ is the number of particles, and $N_A$ is Avogadro's constant ($6.022 \times 10^{23}$ mol⁻¹).
For example, to find the number of molecules in 18 grams of water:
$$n = \frac{18.015 \text{ g}}{18.015 \text{ g/mol}} = 1 \text{ mol}$$
$$N = 1 \times 6.022 \times 10^{23} = 6.022 \times 10^{23} \text{ molecules}$$
Frequently Asked Questions
What is Avogadro's number used for?
Avogadro's number is used to convert between the number of particles (atoms, molecules, ions) and the amount of substance in moles. It is essential for stoichiometric calculations, determining the mass of individual atoms or molecules, and understanding the scale of chemical reactions.
Why is Avogadro's number 6.022 x 10²³?
Avogadro's number is defined as the number of atoms in exactly 12 grams of carbon-12. This value was experimentally determined to be approximately $6.02214076 \times 10^{23}$ and is now an exactly defined constant in the International System of Units (SI).
How do I calculate the number of atoms from moles?
To calculate the number of atoms from moles, simply multiply the number of moles by Avogadro's number: atoms = moles × $6.022 \times 10^{23}$. For example, 2 moles of carbon contain $2 \times 6.022 \times 10^{23} = 1.2044 \times 10^{24}$ atoms.
What is the difference between a mole and a molecule?
A molecule is a single particle made of two or more atoms bonded together. A mole is a unit of measurement that represents $6.022 \times 10^{23}$ particles. So one mole of water contains $6.022 \times 10^{23}$ water molecules.
How do I convert mass to number of atoms?
First, divide the mass by the molar mass to get the number of moles. Then multiply by Avogadro's number to get the number of atoms. For example, 12 g of carbon (molar mass 12 g/mol) equals 1 mole, which contains $6.022 \times 10^{23}$ atoms.
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