大象传媒

More chemical calculations - Higher - EdexcelAvogadro's law

Calculations involving the mole can be used to determine unknown concentrations, volumes and masses in reactions. One mole of any gas occupies 24 cubic decimetres at room temperature and pressure.

Part of Chemistry (Single Science)Separate chemistry 1

Avogadro's law

states that equal of different gases contain an equal number of .

This applies when the temperature and stay the same.

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) 鈫 2HCl(g)

The of hydrogen to chlorine is 1:1. This means, for example:

  • 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) 鈫 2NH3(g)

Calculate the volume of ammonia that can be produced from 150 cm3 of hydrogen and an of nitrogen.

Question

Hydrogen reacts with oxygen to produce steam: 2H2(g) + O2(g) 鈫 2H2O(g)

Calculate the volume of steam that can be produced from 50 cm3 of oxygen and an excess of hydrogen.