Question

State Henry’s Law.

Answer 1

In 1805, an English Chemist William Henry gave an important generalisation called Henry's law on the basis of a series of observations about the effect he had observed of pressure on the solubility of gases. The law relates the solubility of a gas at a given temperature and shows proportionality to the pressure at which it is dissolved.

Complete step by step solution:
If we take mole fraction of gas (${{x}_{b}}$) at a given temperature as a measure of its solubility and p is the partial pressure of the gas in equilibrium with the solution, then according to Henry's law,
or p = ${{K}_{H}}\times {{x}_{b}}$.
where KH is constant of proportionality and is called Henry law constant.
If a mixture of gases is brought in contact with solvent each participating gas dissolves in proportion in order to its partial pressure. This means that Henry's law applies to each gas independent of the presence of other gases.
The knowledge of the K value of a gas at given temperature can help us in calculation of its solubility at that temperature. It is important to note that solubility of gas decreases as the temperature is increased. This implies that higher the value of K of a gas is, lower H will be its solubility and vice versa.
Partial pressure of a gas is a linear function of its mole fraction as is clear from the equation . It means that the plot of ${{x}_{B}}$ is a straight line passing through the origin The slope of the line is equal to ${{K}_{H}}$.

Note: LIMITATIONS OF HENRY'S LAW
Henry law is valid only under following conditions:
(i)The pressure of the gas is not too high.
(ii) The temperature is not too low.
(iii) The gas should not undergo any chemical reaction with the solvent.
(iv) The gas should not undergo dissociation in solution.