Clathrate hydrates (or
gas clathrates,
gas hydrates,
clathrates,
hydrates, etc.) are
crystalline water-based
solids physically resembling
ice, in which small
non-polar molecules (typically
gases) or
polar molecules with large hydrophobic
moieties are trapped inside "cages" of
hydrogen bonded, frozen
water molecules. In other words, clathrate hydrates are
clathrate compounds in which the host molecule is
water and the guest molecule is typically a gas or liquid. Without the support of the trapped molecules, the
lattice structure of hydrate clathrates would collapse into conventional ice crystal structure or liquid water. Most low molecular weight gases, including O
2, H
2, N
2,
CO2,
CH4,
H2S, , , and , as well as some higher
hydrocarbons and
freons, will form
hydrates at suitable temperatures and pressures. Clathrate hydrates are not officially chemical compounds, as the sequestered molecules are never bonded to the lattice. The formation and decomposition of clathrate hydrates are first order phase transitions, not chemical reactions. Their detailed formation and decomposition mechanisms on a molecular level are still not well understood. Clathrate hydrates were first documented in 1810 by Sir
Humphry Davy who found that water was a primary component of what was earlier thought to be solidified chlorine.