1.0 Introduction

  Eudiometry

Eudiometry or gas analysis involves the calculations based on gaseous reactions in which at least two components are gaseous, in which the amounts of gases are represented by their volume, measured at the same pressure and temperature. Some basic assumptions related to calculations are:

1. Gay-Lussac's law of volume combination holds good. According to this law, the volumes of gaseous reactants reacted and the volumes of gaseous product formed, all measured at the same temperature and pressure, bear a simple ratio. $${N_2}\left( g \right) + 3{H_2}\left( g \right) \to 2N{H_3}\left( g \right)$$$$1\;Vol.\quad \;\;3\;Vol.\quad \quad \;\;2\;Vol.$$ The problem may be solved directly in terms of volume, in place of a mole.

2. The volumes of solids or liquids are considered to be negligible in comparison to the volume of gas. It is due to the fact that the volume occupied by any substance in the gaseous state is even more than thousand times the volume occupied by any substance in solid or liquid states. $$2{H_2}\left( g \right) + {O_2}\left( g \right) \to 2{H_2}O\left( l \right)$$$$2\;mole\quad \;\;1\;mole\quad \;2\;mole$$$$2\;Vol.\quad \quad 1\;Vol.\quad \quad 0\;Vol.$$

3. Air is considered as a mixture of oxygen and nitrogen gases only. It is due to the fact that about 99% volume of air is composed of oxygen and nitrogen gases only.

4. Nitrogen gas is considered as non-reactive gas. It is due to the fact that nitrogen gas reacts only at the very high temperature due to is very high thermal stability. Eudiometry is performed in a eudiometer tube and the tube cannot withstand very high temperature. This is why nitrogen gas cannot participate in the reactions occurring in the eudiometer tube.

For the reaction involving gaseous reactants and products

The stoichiometric coefficient of balanced chemical reactions also gives the ratio of volumes in which gaseous reactants are reacting and products are formed at same temperature and pressure.

The volume of gases produced is often given by mentioning certain solvent which absorbs contain gases.