The effect of increasing pressure on solubility depends significantly on the state of matter of the substance being dissolved (the solute).
For gases dissolved in liquids, increasing the pressure absolutely increases their solubility. However, for solids and liquids dissolved in liquids, pressure has very little effect on solubility.
Pressure's Effect on Solubility
Solubility is the maximum amount of a substance (solute) that can dissolve in a given amount of solvent at a specific temperature and pressure. While temperature is a major factor for all types of solutions, pressure primarily influences the solubility of gases.
Solubility of Gases
When considering gases dissolving in liquids, the relationship between pressure and solubility is quite direct and significant.
According to the provided reference: Solubility of gases increases with increase in pressure.
This principle is described by Henry's Law, which states that the amount of a gas dissolved in a liquid is directly proportional to the partial pressure of the gas above the liquid.
Why does this happen?
- Imagine a gas in a closed container above a liquid. Gas molecules are constantly moving, some entering the liquid (dissolving), and some leaving the liquid back into the gas phase (coming out of solution).
- At a specific pressure, a state of equilibrium is reached where the rate of gas molecules dissolving equals the rate of them coming out of solution.
- If you increase the pressure, you force more gas molecules into the space above the liquid. This increases the frequency of gas molecules colliding with the liquid surface and entering the solution.
- The rate of dissolving increases, while initially, the rate of molecules leaving the solution remains the same. To re-establish equilibrium, more gas dissolves in the liquid, leading to higher solubility.
Practical Examples:
- Carbonated Drinks: Soda and sparkling water contain carbon dioxide gas dissolved under high pressure. When you open the container, the pressure above the liquid decreases to atmospheric pressure, and the solubility of CO₂ drops sharply, causing bubbles of gas to escape from the solution.
- Deep-Sea Diving: Divers breathe compressed air. As they descend, the pressure increases, causing more nitrogen from the air to dissolve in their blood and tissues. If they ascend too quickly, the pressure decreases rapidly, and the excess dissolved nitrogen comes out of solution as bubbles, leading to decompression sickness, or "the bends."
Solubility of Solids and Liquids
For solid or liquid solutes dissolved in a liquid solvent, changes in pressure typically have a negligible effect on their solubility.
This is because:
- Solids and liquids are largely incompressible. Changes in pressure do not significantly affect their volume or the intermolecular distances within the solute or solvent.
- The process of dissolving solids or liquids usually involves relatively small volume changes compared to dissolving gases.
Therefore, while technically there might be a tiny change in solubility with extreme pressure variations, for most practical purposes, the solubility of solids and liquids in liquids is considered independent of pressure.
Summary of Pressure's Effect on Solubility
To clarify the impact of pressure on solubility based on the solute type:
| Solute Type | Effect of Increasing Pressure on Solubility | Reason | Example |
|---|---|---|---|
| Gas | Increases | More gas molecules forced into solution (Henry's Law) | Carbonated beverages |
| Solid | Minimal to negligible effect | Solids are largely incompressible | Salt in water |
| Liquid | Minimal to negligible effect | Liquids are largely incompressible | Alcohol in water |
In conclusion, increasing pressure primarily increases the solubility of gases, as supported by the principle that Solubility of gases increases with increase in pressure. Its effect on solid and liquid solubility is insignificant under typical conditions.
