Laws of Solutions

Henry’s Law

Henry’s Law states that at a constant temperature, the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of that gas above the liquid. Mathematically, it can be expressed as:

C=kH⋅PC = k_H \cdot PC=kH​⋅P

where:

• CCC is the concentration of the gas in the liquid.
• kHk_HkH​ is Henry’s Law constant for the gas in a particular solvent.
• PPP is the partial pressure of the gas above the liquid.

This law is particularly useful in understanding the behavior of gases in solutions, such as the dissolution of carbon dioxide in water to form carbonated beverages.

Raoult’s Law

Raoult’s Law describes the vapor pressure of an ideal solution as a function of the vapor pressures of the pure components and their mole fractions in the solution. It states that the partial vapor pressure of each volatile component in the solution is equal to the vapor pressure of the pure component multiplied by its mole fraction in the solution. Mathematically, it can be expressed as:

Pi=Xi⋅Pi∗P_i = X_i \cdot P_i^*Pi​=Xi​⋅Pi∗​

where:

• PiP_iPi​ is the partial vapor pressure of component iii in the solution.
• XiX_iXi​ is the mole fraction of component iii in the solution.
• Pi∗P_i^*Pi∗​ is the vapor pressure of the pure component iii.

For a solution with multiple volatile components, the total vapor pressure is the sum of the partial pressures of all components:

Ptotal=∑iPi=∑iXi⋅Pi∗P_{total} = \sum_{i} P_i = \sum_{i} X_i \cdot P_i^*Ptotal​=∑i​Pi​=∑i​Xi​⋅Pi∗​

Raoult’s Law is applicable to ideal solutions, where the interactions between different molecules are similar to those between like molecules.

Both Henry’s Law and Raoult’s Law are fundamental principles in physical chemistry, particularly in the study of solutions and their behaviors.