http://www.ck12.org Chapter 16. Solutions
Each liter of solution can hold a maximum of 2.0 millimoles of that particular gas at the indicated temperature and
pressure.
Temperature Effects
As with all substances, the solubility of gases is temperature dependent. However, in contrast to the situation for
most solids and liquids, higher temperatures will decrease the solubility of a gaseous solute.Figure16.7 shows this
relationship with several common gases.
FIGURE 16.7
Solubility-temperature curves for various
common gases.This inverse relationship between solubility and temperature can be understood by looking at a molecular model.
Recall that higher temperatures are associated with faster particles. Gas particles are held in solution by attractive
interactions with the solvent molecules. If the particles are moving slowly, these attractive forces will pull back any
particles that try to escape the surface of the solution and re-enter the gas phase. However, if the gas particles are
moving fast enough, these interactions will not be sufficiently strong to prevent this process from occurring. As
a result, more particles are able to escape, and the amount of dissolved solute is less than it would be at a lower
temperature.
Pressure Effects
At a constant temperature, the amount a given gas that dissolves in a given type and volume of liquid is directly
proportional to the partial pressure of that gas in the area immediately adjacent to the solution. This principle is
calledHenry’s Lawand is illustrated inFigure16.8.
Mathematically, Henry’s Law is expressed as follows:
ρ=kHc
whereρis the partial pressure of the gas,cis its molar solubility at the given temperature and pressure, andkHis
a constant that depends on the temperature and the identities of both the solute and solvent. Some kHvalues for
various gases dissolved in water at 298 K are presented in theTable16.2.
TABLE16.2:kH Values for Various Gases Dissolved in Water at 298 K
Gas Constant (Pa•mol−^1 •L) Constant (atm•mol−^1 •L)
He 282.7× 106 2865
O 2 74.68× 106 756.7
N 2 155.× 106 1600.