What is Henry’s law?

What is Henry’s law?

Henry’s law is a gas law which says that at the amount of gas that is dissolved in a liquid is exactly proportional to the partial pressure of that gas above the liquid while the temperature is held constant. Henry’s law constant (typically represented by ‘kH‘) is the proportionality constant for this connection. The mathematical formula for Henry’s law is as follows:

P C (or) P = kH.C


  • ‘P’ refers to the partial gas pressure above the liquid in the atmosphere.
  • ‘C’ indicates the dissolved gas concentration.
  • ‘kH‘ is the constant Henry’s gas law.

The English chemist William Henry established this concept in the early 19th century. It is notable that the constant rule of Henry may be stated in two ways. If the constant is specified as solubility/pressure, it is called the solution solubility constant in the Henry law (referred to as ‘H’). On the other hand, if the constant proportionality is determined by pressure/solubility, the volatility constant of the law of Henry is (referred to as the ‘kH‘).

Henry law constant

The Henry law constant (KH) is the ratio of the compound’s partial air pressure to the compound in water concepts at a certain temperature. It is also termed the air-water partition coefficient. Values for law-standards of Henry are expressed in atmospheric air units to moles per cm for water (atm-m3/mol) or in a size less unit, which is described as the Henry Law Constant (atm-m3/mol), whereby KH is the Henry Law Konstant (atm-m3/mol), R is the ideal gas constant (8.20575 x 10−5 atm-m3/mol-K) and T is the water temperature constant (K).As a rule, compounds having a Henry law constant larger than 10−3 atm-m3/mol and less than 200 g molecular weight are considered volatile per mole compounds.

Examples of Henry’s Law

Pepsi and other Carbonated Drinks

Every time a pepsi bottle (or any carbonated beverage) is opened, the law of Henry comes into effect. The gas above the closed carbonated drink is normally pure carbon dioxide and is kept under a pressure slightly exceeding the normal air pressure. The carbon dioxidesolubility in the unopened beverage is likewise high in consequence of Henry’s rule.

The pressurized CO2 flows into the atmosphere when the container is opened (which is usually accompanied by a hissing sound). The solubility of the carbon dioxide in the drink likewise drops (as Henry’s Law requires) because of partial pressure of CO2 in the environment above the drink.This leads to little bubbles and to the surface of the dissolved CO2 in the form of small bubbles.

If the carbonated drink remains open enough, the carbon dioxide concentration in the drink reaches a balance with the carbon dioxide concentration in the air (~0.05 percent), which causes the drink to go flat (the drink is losing its ‘fizzy’ taste).

Respiration and the Oxygenation of Blood

Inhalation is accompanied by a rise in the alveoli’s partial oxygen pressure during the breathing. The following gas exchanges occur as a result of Henry law when deoxygenated blood interacts with the oxygen-rich air in the alvéols:

  • Since the alvéol’s partial oxygen pressure in the alvéoles and the dissolves oxygen level in the deoxygenated blood are low, oxygen flows from the alvéols in the blood deoxygenated.
  • The alveoli are quite low in partial carbon dioxide pressure (CO2constitutes approximately 0.05 percent of the atmosphere). Because the deoxygenated blood has a very high percentage of dissolved CO2, gas is moving from the blood to the blood alveoli. The carbon dioxide is removed through exhalation from the body.

Thus, Henry’s law plays an integral role in the respiration of many organisms.

Factors that affect the law of Henry

The value of the gas constant in the law of Henry depends on the following factors:

  • The solvent’s nature
  • The gas’s nature
  • Pressure and temperature

Limitations of Henry’s Law

This rule is only valid when the system’s molecules are in equilibrium. When gases are under extremely high pressure, Henry’s law doesn’t hold true. The rule does not apply when the gas and the solution interact with each other in chemical reactions.

Here you must understand that, to grasp the advanced ideas, you must first master the fundamentals of chemistry. For example, before you can comprehend isomerism, you must first understand the concepts of molecular weight and molecular number. Before delving into these areas, I recommend that you review your basics from 10th and 11th grade. To enhance your foundations, you can use numerous online platforms such as doubtnut.com. Revision is also an essential component of chemistry. Reread the Chemistry chapters as much as possible. It will keep everything in your mind fresh.