Explain Gay Lussac's law by means of a particle diagram?

1 Answer
Jan 9, 2016


Gay-Lussac's Law of Combining Volumes states that when gases combine in chemical reactions, their volumes are always in the ratio of small whole numbers.


Gay-Lussac found that 1 volume of nitrogen and 3 volumes of hydrogen always reacted to form 2 volumes of ammonia.

(from www.molechemistry.info)

The volume ratios were always nitrogen:hydrogen:ammonia = 1:3:2.

Based on Gay-Lussac's results, Amedeo Avogadro theorized that equal volumes of gases at the same temperature and pressure contained equal numbers of molecules (Avogadro's law).

This meant that Gay-Lussac's results could be expressed as

#underbrace("nitrogen")_color(red)("1 molecule") + underbrace("hydrogen")_color(red)("3 molecules") → underbrace("ammonia")_color(red)("2 molecules")#

If this were true, the results made sense only if nitrogen and hydrogen were diatomic molecules and ammonia had the formula #"NH"_3"#.

(from molechemistry.info)

Suddenly, chemical reactions became understandable.

Chemists could write the reaction as

#underbrace("N"_2)_color(red)("1 Vol.") +underbrace color(black)("3H"_2)_color(red)("3 Vol.") → underbrace("2NH"_3)_color(red)("2 Vol.")#

It all made sense!