Avogadro's law - Higher
Avogadro's lawAt a given temperature and pressure, equal volumes of different gases contain an equal number of molecules. states that when the temperature and pressureForce exerted over an area. The greater the pressure, the greater the force exerted over the same area. stay the same:
- equal volumeThe volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 ml. of different gases contain an equal number of moleculeA collection of two or more atoms held together by chemical bonds.
This means that equal amounts in moles 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
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) → 2HCl(g)
The mole ratioThe ratio of the amounts of two substances as shown in a balanced equation. of hydrogen to chlorine is 1:1. This means, for example, that in terms of volume:
- 1 cm3 of hydrogen reacts exactly with 1 cm3 of chlorine
- 250 cm3 of hydrogen reacts exactly with 250 cm3 of chlorine
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) → 2NH3(g)
Calculate the volume of ammonia that can be produced from 150 cm3 of hydrogen and an excessIn chemistry, a substance is in excess if there is more than enough of it to react with another reactant. 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) → 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