Avogadro's law - higher tier
Avogadro's lawAt a given temperature and pressure, equal volumes of different gases contain an equal number of molecules. states:
- equal volumes of different gases contain an equal number of particles under the same conditions of temperature and pressure
This means that equal numbers of moleThe amount of substance that contains the same number of particles as there are atoms in 12 g of carbon-12 (contains the Avogadro's constant 6.0 Ă10ÂČÂł number of particles). of gases occupy the same volume under the same conditions of temperature and pressure. For example:
- 1 mol of hydrogen gas occupies the same volume as 1 mol of methane gas
- 10 mol of nitrogen monoxide gas occupy the same volume as 10 mol of argon gas
- the volume of 1 mol of any gas under these conditions is 24 dm3
Avogadro's law can be used to calculate the volumes of gases involved in reactions.
Using Avogadro's law
Hydrogen reacts with chlorine to form hydrogen chloride:
H2(g) + Cl2(g) â 2HCl(g)
The mole ratio of hydrogen to chlorine is 1:1. This means, for example, that in terms of volume:
- 1 cm3 of hydrogen reacts with excess chlorine to produce 2 cm 3 of hydrogen chloride
- 250 cm3 of hydrogen reacts with excess chlorine to produce 250 cm3 of hydrogen chloride
The mole ratio of hydrogen to hydrogen chloride is 1:2. This means, for example:
- 1 cm3 of hydrogen produces 2 cm3 of hydrogen chloride
- 250 cm3 of hydrogen produces 500 cm3 of hydrogen chloride
Question
Nitrogen reacts with hydrogen to produce ammonia:
N2(g) + 3H2(g) â 2NH3(g)
Calculate the volume of ammonia that can be produced from 150 cm3 of hydrogen and an excess of nitrogen.
The mole ratio of hydrogen to ammonia is 3:2
Volume of ammonia = \(\frac{150}{3}\times{2}\)
Volume = 100 cm3
Question
Hydrogen reacts with oxygen to produce steam: 2H2(g) + O2(g) â 2H2O(g)
Calculate the volume of steam that can be produced from 50 cm3 of oxygen and an excess of hydrogen.
The mole ratio of oxygen to steam is 1:2
Volume of steam = \(\frac{50}{1}\times2\)
Volume = 100 cm3