What is Henry's law? Define each term in the equa. tion, and give its units. Explain the law in terms of the kinetic molecular theory of gases.

Henry's Law, named after the English scientist William Henry, is a gas solubility law. It states that: '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.' This can be mathematically expressed as \[ P = kH.c \], where P stands for the partial pressure of the gas, kH is Henry's law constant, and c refers to the concentration of the dissolved gas.

In the equation \[ P = kH.c \], the terms are defined as follows: \n1. \( P \): This stands for the partial pressure of the gas. It's a measure of the thermodynamic activity of the gas molecules in the air above the liquid. It is generally expressed in units of pressure such as atmospheres (atm), millimeters of mercury (mmHg), or pascals (Pa).\n2. \( kH \): This is Henry's law constant and it depends on the substance and the temperature. It can be different units, such as M/atm, mol/L·atm, or other depending on the context. \n3. \( c \): This is the concentration of the gas in the liquid. It's often given in terms of molar concentration (such as mol/L), but can also be given in terms of molality, mol/kg.

From the perspective of the kinetic molecular theory of gases, the molecules of a gas are in constant, random motion and frequently collide with each other and with the walls of any container. When gas molecules come in contact with the surface of a liquid, some are 'captured' by the liquid and dissolve. At the same time, molecules of the gas dissolved in the liquid escape into the gas-phase at the liquid's surface. When the rate at which the molecules dissolve equals the rate at which they escape, an equilibrium is reached. The more gas molecules there are in the air above the liquid (i.e., the higher their partial pressure), the more frequently collisions occur between gas molecules and the liquid surface, resulting in a greater amount of dissolved gas. This basic molecular-level picture is what lies behind Henry's Law.

In conclusion, Henry's Law provides the explanation of why the amount of gas in a liquid solution increases as the pressure of the gas increases. The pressurized gas molecules knock the liquid molecules and enter into the liquid phase. The proportionality is given by Henry's Law constant. Its applications range from scuba diving to carbonated drinks and gas absorption in industry.