Comparison To Raoult's Law
For a dilute solution, the concentration of the solute is approximately proportional to its mole fraction x, and Henry's law can be written as:
This can be compared with Raoult's law:
where p* is the vapor pressure of the pure component.
At first sight, Raoult's law appears to be a special case of Henry's law where kH = p*. This is true for pairs of closely related substances, such as benzene and toluene, which obey Raoult's law over the entire composition range: such mixtures are called "ideal mixtures".
The general case is that both laws are limit laws, and they apply at opposite ends of the composition range. The vapor pressure of the component in large excess, such as the solvent for a dilute solution, is proportional to its mole fraction, and the constant of proportionality is the vapor pressure of the pure substance (Raoult's law). The vapor pressure of the solute is also proportional to the solute's mole fraction, but the constant of proportionality is different and must be determined experimentally (Henry's law). In mathematical terms:
- Raoult's law:
- Henry's law:
Raoult's law can also be related to non-gas solutes.
Read more about this topic: Henry's Law
Famous quotes containing the words comparison and/or law:
“I have travelled a good deal in Concord; and everywhere, in shops, and offices, and fields, the inhabitants have appeared to me to be doing penance in a thousand remarkable ways.... The twelve labors of Hercules were trifling in comparison with those which my neighbors have undertaken; for they were only twelve, and had an end; but I could never see that these men slew or captured any monster or finished any labor.”
—Henry David Thoreau (1817–1862)
“The great King of kings
Hath in the table of his law commanded
That thou shalt do no murder. Will you then
Spurn at his edict, and fulfill a man’s?
Take heed; for he holds vengeance in his hand
To hurl upon their heads that break his law.”
—William Shakespeare (1564–1616)