What is the missing factor? What do the N20, NH4Cl,
and evaporation processes have in common with most exothermic reactions
that X makes them take place spontaneously, even though these reactions
The answer is that all of these reactions create disorder NO2
and O2 gas molecules are more disordered than crystals
of N206. Hydrated ammonium and chloride ions
in solution are more disordered than the regular array of NH4Cl
ions in a crystal. H20 molecules moving about freely
as water vapor are more disordered than the closely packed molecules
of the liquid, or the frozen molecules of the solid .
Most explosions are destructive precisely because they convert
solids or liquids into gases that push out against their surroundings.
(The expansion of the gases when they are heated by the reaction
is another destructive factor.) A decrease in energy or enthalpy
certainly is an important component in determining spontaneity,
but the other aspect is the production of disorder.
Disorder increases from ice
to liquid to vapour, as more Hydrogen bonds are broken and as water
molecules begin to move past one another.