How can an explosion be explained by the different ways molecules are packed together in solids, liquids and gases?

a) Gases tend to occupy a much larger volume than solids and liquids, since intermolecular forces are much weaker. b) Explosives are very unstable molecules: in this context, unstable means “full of potential energy about to be readily released”. By combining concepts a) and b) together, the answer follows. Explosives are solids or liquids and they occupy a very small volume. The chemical reaction involves breaking up the explosive molecules into many gas molecules, commonly CO2, CO, N2, O2 and H2. For example, 2 moles of solid TNT become 5 moles of H2, 12 moles of CO and 3 moles of N2 (plus two moles of solid carbon) upon reaction: each mL of TNT is instantaneously expanded over 1600 times, so make sure you decline to carry out any experiment that involves TNT.