For gas dissolved in liquid at low concentrations: $P_{gas}$ = $K_H$ * $x_{gas}$. $K_H$ = Henry's constant (units: same as pressure). Higher $K_H$ = lower gas solubility (gas escapes more easily). $K_H$ increases with temperature (gases are less soluble at higher T — unlike most solids). Applications: (1) Carbonated beverages — CO2 dissolved under pressure, escapes when opened (P decreases). (2) Deep-sea diving — N2 dissolves under high pressure (narcosis), released as bubbles during rapid ascent $\frac{decompression sickness}{bends}$. Solution: use He/O2 mixture (He has very high $K_H$, low solubility). (3) Oxygen transport — blood absorbs O2 proportional to its partial pressure in lungs. Henry's law is the limiting case of Raoult's law for the solute in very dilute solutions.