If the partial pressure of a gas above a liquid is doubled, according to Henry's law, how does the concentration of dissolved gas change (assume constant temperature)?

• A. It remains unchanged.
• B. It increases by a factor of 4.
• C. It increases in direct proportion to the partial pressure, i.e., doubles if P doubles.
• D. It decreases with increasing pressure.

Answer: (C)

Henry's law says that, at a fixed temperature, the amount of gas dissolved in a liquid is proportional to the partial pressure of that gas above the liquid. The constant of proportionality is specific to the gas–solvent pair and to the temperature. Because the relationship is linear, increasing the partial pressure by a factor directly increases the dissolved concentration by the same factor. So if the partial pressure doubles, the concentration of dissolved gas also doubles. This holds as long as the temperature stays constant and the solution remains in the dilute regime where Henry's law applies.