Henry's Law is for a gas dissolved in a liquid and states P = kC where P is the partial pressure of the gas above the solution and C is the concentration of the gas dissolved in the liquid. The k is a "constant", that is, it is independent of P, C and time but depends on the type of gas and the type of liquid. According to Pickover, page 184 (reference below), Henry's Law assumes:

A1. the gas/liquid system has reached equilibrium, and A2. the gas does not chemically react with the liquid, and A3. the concentration of gas in the liquid is low, and A4. the gas pressure is low.

I would be grateful for any help in answering the following:

Q1. Is the list of assumptions, A1 to A4, correct and complete? I have no reason to doubt it but I would like to confirm it.

Q2. Some authors (e.g. Dickinson E.J., Road Materials and Pavement Design, 2000, 1(3), 255-280) have applied Henry's Law to the diffusion of oxygen in air at atmospheric pressure into bitumen which is a semi-solid at room temperature. Is there any experimental evidence that Henry's Law can be extended to such a system?

Reference Pickover, C., "Archimedes to Hawking", Oxford University Press 2008


Regarding Q1, Henry's law states:

At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

  • A1 is answered by the definition itself: the system should be at equilibrium.
  • A2 is straightforward: if the gas reacted, you would not have a constant pressure as a certain (if not all) quantity of it would be removed from the system[1]. This would also keep your system from being at equilibrium, defying the previous assumption.
  • A3 and A4 both depend on the fact that – as the concentration or the partial pressure rise – the system deviates from an ideal model where the solute is infinite-diluted and in such system Raoult's Law should be used instead[2]. So you need a low concentration and partial pressure of your gas.

To answer to Q2, Henry's Law can be applied to any solvent, whether liquid, vapour or solid[3], [4]. It has been used, within certain limits, to study absorption of gas in zeolites[5] or hydrogels, but I couldn't find any precise experimental data on it. Only that in such systems it is only a limited law, adequate at low mole fractions, but useful for practical purposes when high precision is not required.

    1 Henry's Law, UC Davis University ChemWiki
    2 North Carolina State University, CH 431 / Lecture 14
    3 Francis L. Smith and Allan H. Harvey (September 2007). "Avoid Common Pitfalls When Using Henry's Law".
    4 Rosenberg, Robert M., Peticolas, Warner L., Journal of Chemical Education, Volume 81, 11, pp 1647-1652
    5 Eric G. Derouane, Zeolites as solid solvents, Journal of Molecular Catalysis A: Chemical, Volume 134, 1–3, pp 29-45

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the gas/liquid system has reached equilibrium,beacause pressure is defined only when gas is in equilibrium otherwise gas will not have same pressure throughout gas.A3. the concentration of gas in the liquid is low, and A4. the gas pressure is low.because gas will deviate from ideal nature and there will be more collisions which will deviate it from following Henry's LAw.A2,the gas does not chemically react with the liquid because laws in chemistry that relates physical properties assumes that the interaction between particles is zero or negligible which is not possible in chemical reaction

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    $\begingroup$ Can you cite your source for this? Also, the formatting is a bit garbled. $\endgroup$ – jonsca Jul 19 '14 at 22:59

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