Chemistry
Mole, mass, volume: basic calculations
What is a mole
Mole: the unit of amount of substance.
1 mole contains 6,02·10²³ particles. This is the Avogadro constant, NA.
Molar mass M (g/mol) is numerically equal to the relative molecular mass. M(H₂O) = 18 g/mol. M(CO₂) = 44 g/mol.
At standard conditions Vm = 22,4 L/mol.
Basic formulas
| Quantity | Formula |
|---|---|
| n (mol) | n = m / M |
| n (mol) | For a gas n = V / 22,4 |
| n (mol) | n = N / 6,02·10²³ |
| D (density) | M₁ / M₂ |
Relative density of a gas D = M₁ / M₂. M(gas) = 29·D (relative to air).
Avogadro's law: under the same conditions, equal volumes of gases contain equal numbers of molecules.
Key facts
- Standard conditions (STP): 0 °C (273 K) and 101,325 kPa.
- Ideal gas equation: PV = nRT.
- Mass fraction: ω(E) = Ar·n / Mr · 100%.
- In a mixture: ω = m(component) / m(mixture).
- m ⇄ n ⇄ V. Number of particles: N = n · NA.
- 1 mole of any gas occupies a volume of 22,4 L at STP. 22,4 L applies only to gases.
- 1 mole of H₂O contains 3·6,02·10²³ atoms, while the number of molecules is 6,02·10²³.