Question

1Q-How solubility of gases in liquids increases on decreasing the temperature?
2Q-
How solubility of gases in liquids increases on increasing pressure?

Answer 1

Solubility of Gases vs. Temperature:
The variation of solubility for a gas with temperature can be determined as follows.
As the temperature increases, the solubility of a gas decreases.
More gas is present in a solution with a lower temperature compared to a solution with a higher temperature.
The reason for this gas solubility relationship with temperature is very similar to the reason that vapor pressure increases with temperature. Increased temperature causes an increase in kinetic energy. The higher kinetic energy causes more motion in molecules which break intermolecular bonds and escape from solution.
This gas solubility relationship can be remembered if you think about what happens to a "soda pop" as it stands around for awhile at room temperature. The taste is very "flat" since more of the "tangy" carbon dioxide bubbles have escaped. Boiled water also tastes "flat" because all of the oxygen gas has been removed by heating.
Gas Pressure and Solubility:
Liquids and solids exhibit practically no change of solubility with changes in pressure. Gases as might be expected, increase in solubility with an increase in pressure. Henry's Law states that: The solubility of a gas in a liquid is directly proportional to the pressure of that gas above the surface of the solution.
If the pressure is increased, the gas molecules are "forced" into the
solution since this will best relieve the pressure that has been applied.
The number of gas molecules decreases. The number of gas molecules
dissolved in solution increases.
Carbonated beverages provide the best example of this phenomena. All carbonated beverages are bottled under pressure to increase the carbon dioxide dissolved in solution. When the bottle is opened, the pressure above the solution decreases. As a result, the solution effervesces and some of the carbon dioxide bubbles off.