Why do gases always tend to be less soluble in liquids as the temperature is raised?
The solubility of gases in liquids decreases with rise in temperature because the dissolution of gas in a liquid is an exothermic process. When gas molecules dissolve in a liquid, the process is similar to condensation and heat is evolved.
Since the dissolution process involves a dynamic equilibrium, it follows Le Chatelier's Principle. According to this principle, when temperature is increased for an exothermic process, the equilibrium shifts in the direction that absorbs heat. Therefore, the equilibrium shifts towards the reverse direction (gaseous phase), resulting in decreased solubility of the gas in the liquid.
Explanation
The textbook explains that dissolution of gases is an exothermic process (similar to condensation) where heat is evolved. Following Le Chatelier's Principle, increasing temperature for an exothermic equilibrium shifts the equilibrium to favor the endothermic direction (reverse process), thus reducing solubility.