Why does solubility increase with pressure

Underwater, our bodies are similar to a soda bottle under pressure. Imagine dropping the bottle and trying to open it. In order to prevent the soda from fizzing out, you open the cap slowly to let the pressure decrease.

On land, we breathe about 78 percent nitrogen and 21 percent oxygen, but our bodies use mostly the oxygen. Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:. If the pressure is decreased, the converse is true. Gas molecules will actually come out of solution. This is why carbonated beverages are pressurized. It should be noted that changes in pressure will only effect the solubility of a gas solute.

If the solute is a liquid or solid, there will be no change in solubility. Does solubility change with pressure? Experimentally it is found that the solubility of most compounds depends strongly on temperature and, if a gas, on pressure as well. As we shall see, the ability to manipulate the solubility by changing the temperature and pressure has several important consequences.

Figure Although the solubility of a solid generally increases with increasing temperature, there is no simple relationship between the structure of a substance and the temperature dependence of its solubility.

Many compounds such as glucose and CH 3 CO 2 Na exhibit a dramatic increase in solubility with increasing temperature. Solubility may increase or decrease with temperature; the magnitude of this temperature dependence varies widely among compounds. In fact, the magnitudes of the changes in both enthalpy and entropy for dissolution are temperature dependent.

Because the solubility of a compound is ultimately determined by relatively small differences between large numbers, there is generally no good way to predict how the solubility will vary with temperature. The variation of solubility with temperature has been measured for a wide range of compounds, and the results are published in many standard reference books.

Chemists are often able to use this information to separate the components of a mixture by fractional crystallization The separation of compounds based on their relative solubilities in a given solvent. According to the temperature curves in Figure The crystals can then be separated by filtration. Fractional crystallization is a common technique for purifying compounds as diverse as those shown in Figure For the technique to work properly, the compound of interest must be more soluble at high temperature than at low temperature, so that lowering the temperature causes it to crystallize out of solution.

In addition, the impurities must be more soluble than the compound of interest as was KBr in this example and preferably present in relatively small amounts. The solubility of gases in liquids decreases with increasing temperature, as shown in Figure Attractive intermolecular interactions in the gas phase are essentially zero for most substances.

When a gas dissolves, it does so because its molecules interact with solvent molecules. Conversely, adding heat to the solution provides thermal energy that overcomes the attractive forces between the gas and the solvent molecules, thereby decreasing the solubility of the gas. The phenomenon is similar to that involved in the increase in vapor pressure of a pure liquid with increasing temperature, as discussed in Chapter 11 "Liquids". In the case of vapor pressure, however, it is attractive forces between solvent molecules that are being overcome by the added thermal energy when the temperature is increased.

The decrease in the solubilities of gases at higher temperatures has both practical and environmental implications. Anyone who routinely boils water in a teapot or electric kettle knows that a white or gray deposit builds up on the inside and must eventually be removed.

The problem is not a uniquely modern one: aqueducts that were built by the Romans years ago to carry cold water from alpine regions to warmer, drier regions in southern France were clogged by similar deposits. This decrease in the solubility of oxygen as temperature goes up is one of the reasons cold water fish like trout can not live in warm water.

There are a wide range of dependencies on the temperature and although most compounds increase their solubility as heated, some actually show a decrease. We will revisit this material when we get to chapter 18 and cover entropy and Gibb's free energy. Some of the molecules in the gas phase condense when they contact the liquid and some in the liquid evaporate into the gas.

Thus the molecules can be considered to be partioned across both phases, with some in the liquid and some in the gas phase. For a system at equilibrium the rate they enter the gas phase equals the rate at which they enter the liquid, and so the concentration in both phases is constant. Robert E. The breadth, depth and veracity of this work is the responsibility of Robert E. Belford, rebelford ualr. You should contact him if you have any concerns.

This material has both original contributions, and content built upon prior contributions of the LibreTexts Community and other resources, including but not limited to:. Introduction In this section we will look at how the pressure and temperature effect solubility. Pressure Effects on Solubility When a gas phase molecule hits the surface of a liquid it may be deflected back into the gas or dissolved into the solution, in the latter case becoming a solute particle.

Answer The solubility would decrease because there would be less molecules hitting the surface. Henry's Law Henry's law states that the concentration of a gaseous solute in a liquid is proportional to the absolute pressure.