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.
Avogadro's lawAt a given temperature and pressure, equal volumes of different gases contain an equal number of molecules. states that 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 applies 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.
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:
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.
