What Is Henry's Law?
Henry's law is one of the basic laws of physical chemistry. Discovered by Henry of the United Kingdom in 1803 when studying the law of the solubility of gases in liquids. It can be expressed as: in a sealed container at a certain temperature, the partial pressure of the gas is proportional to the molar concentration of the gas dissolved in the solution.
- Chinese name
- Henry 's Law
- Foreign name
- Henry's law
- expression
- Pg = Hx
- Presenter
- Henry
- Presentation time
- 1803
- Applied discipline
- Physical Chemistry
- Henry's law is one of the basic laws of physical chemistry. Discovered by Henry of the United Kingdom in 1803 when studying the law of the solubility of gases in liquids. It can be expressed as: in a sealed container at a certain temperature, the partial pressure of the gas is proportional to the molar concentration of the gas dissolved in the solution.
Introduction to Henry's Law
- Henry's law, one of the basic laws of physical chemistry, was discovered by Henry of the United Kingdom in 1803 when he studied the solubility of gas in liquids. The solubility of a solute (usually a gas) in solution is directly proportional to the equilibrium pressure of the solute on the liquid surface. "Its formula is
- Pg = Hx
- In the formula: H is the Henry constant, x is the solubility of the gas mole fraction, and Pg is the partial pressure of the gas. H can well represent the dissolved amount of gas, but Henry's law is only applicable to systems with very low solubility. Strictly speaking, Henry's law is only an approximate rule and cannot be used in systems with high pressure. In this sense, the Henry constant is only a function of temperature and has nothing to do with pressure.
Details of Henry's Law
- In the experiment of volatile solutes in dilute solutions, the experiment shows that the law is correct only when the solubility of the gas in the liquid is not very high. At this time, the gas is actually a volatile solute in the dilute solution, and the gas pressure It is the vapor pressure of the solute. So Henry's Law can also be expressed as: at a certain temperature, the partial vapor pressure of the solute in the dilute solution is directly proportional to the solution concentration.
- Generally, the solubility of the gas in the solvent is small, and the resulting solution belongs to the range of dilute solutions. The composition of the solution of the gas B in the solvent A is approximately proportional to the pressure of the gas solute B when it is represented by the molar fraction of B x B , the molar mass concentration b B , and the concentration c B. Henry's law can take many forms when expressed in formulas. Such as:
- P B = K x, B x B
- P B = K b, B · b B
- P B = K c, B · c B
- Where p B is the vapor partial pressure of the solute in the dilute solution; x B is the mass fraction of the solute substance; k is the Henry's constant, and its value is related to the nature of the temperature, solute and solvent, and the Henry coefficient is basically not affected by pressure. Due to the different scales of the solution composition in Henry's Law, the units of Henry's coefficient are different, and the same solute in the same solvent at a certain temperature is also different. X B (mole fraction of solute B), b B (mass) (Molar concentration) or c B (substance concentration) will change with the k value. The units of K x , K b , and K c are Pa, P a · mol ^ -1 · , and P a · mo ^ l-1 · dm ^ 3, respectively.
- Henry's law applies only if the solutes have the same molecular state in the gas and liquid phases. If the solute molecules are dissociated or associated in the solution, xB (or m B , c B, etc.) in the above formula should refer to the content of the same part as the molecular state in the gas phase; when the total pressure is not large, If multiple gases are dissolved in the same liquid at the same time, Henry's Law can be applied to any one of them; in general, the thinner the solution, the more accurate Henry's Law is, and the solute can strictly obey the Law when x B 0.
Examples of Henry's Law
- Different temperatures have different Henry coefficients. As the temperature rises, the volatile capacity of volatile solutes increases, and the Henry coefficient increases. In other words, as the temperature increases at the same partial pressure, the solubility of the gas decreases.
- If several gases are dissolved in the same solvent at the same time to form a dilute solution, the equilibrium partial pressure of each gas and its solubility relationship apply to Henry's Law, respectively. An example is the dissolution of N2 and O2 in air in water. Table 1 shows the Henry's coefficients of several gases in water and in benzene at 25 ° C.
- Table 1 Henry coefficients Kx (25 ° C) of several gases in water and benzene.
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- * 1GPa = 10 ^ 9Pa