Solutions Henry’s law

The standard state of an electrolyte is the hypothetical ideally dilute solution (Henry s law) at a molarity of 1 mol kg (Actually, as will be seen, electrolyte data are conventionally reported as for the fonnation of mdividual ions.) Standard states for non-electrolytes in dilute solution are rarely invoked. 

The equihbrium partitioning of a chemical solute between a Hquid and vapor phase is governed by Henry s law when the Hquid mixture is very dilute in the solute. Henry s law generally is vaHd at concentrations below 0.01 mol/L of solution, although the upper limit can sometimes extend to 0.1 mol/L or higher (10). Over this concentration range, a direct proportionaHty, ie, Henry s constant, is observed between the partial pressure of the chemical in the gas phase and its mole fraction in the Hquid phase. Henry s constant, when expressed in this way, has units of pressure (3). 

If followed in experimenrtally accessible dilute solutions, Henry s law would be manifested as a horizontal asymptote in a plot such as Figure 19.3 as the square of the molality ratio goes to zero. We do not observe such an asymptote. Thus, the modified form of Henry s law is not followed over the concentration range that has been examined. However, the ratio of activity to the square of the molality ratio does extrapolate to 1, so that the data does satisfy the definition of activity [Equations (16.1) and (16.2)]. Thus, the activity clearly becomes equal to the square of the molality ratio in the limit of infinite dilution. Henry s law is a limiting law, which is valid precisely at infinite dilution, as expressed in Equation (16.19). No reliable extrapolation of the curve in Figure 19.2 exists to a hypothetical unit molality ratio standard state, but as we have a finite limiting slope at = 0, we can use... 

Another factor that differentiates the solubility of gases from solids and liquids is the effect of pressure. The effect of pressure on gas solubility was studied extensively by a contemporary and close associate of John Dalton named William Henry (1775-1836). Henry s Law states that the solubility of a gas is directly proportional to the partial pressure of that gas over the solution. Stated mathematically, Henry s Law is c = kP, where c is the concentration of the dissolved gas in moles per liter, k is Henry s law constant for the solution, and P is the partial pressure of the gas above the solution. Henry s Law is demonstrated every time a carbonated beverage is opened. During the carbonation process, carbon dioxide is dis-... 

For the concentration dependence of /jla, we can employ the dilute-solution Henry s law limit (fiA = /jla H rinxA) to obtain... 

For dilute non-reacting solutions, Henry s Law is used to describe the linear equilibrium distribution of a compound between the bulk liquid and gas phases (Figure 3-3) ... 

The method determines the partial pressure of methane in the gas phase above the solution (Henry s law). Methane catalytically oxidizes on a heated platinum filament, that is part of a Wheatstone bridge. The heat generated increases the electrical resistance of the filament which is measured and compared against calibrated standards. 

Figure 4 Acetone-chloroform solution Henry s law activity coefficients solid curve for chloroform with acetone as the solvent, dashed curve for acetone with chloroform as the solvent.

Construct the equilibrium line. For dilute solutions, Henry s law will apply. In general, it will be applicable for pressures under 2 atm and liquid mole fractions less than 0.01. For this example, the liquid mole fraction x is (100 lb TCE/106 lb soln) (18/132) = 1.37 x 1CT5, where 18 and 132 are the molecular weights of water and trichloroethylene, respectively. Therefore, Henry s law will apply. 

This shows that the vapour pressure of the dissolved substances are proportional to their mole fractions in an ideal solution. Henry s law). Equation (21.10) can be rewritten... 

As shown by Rault s law and Henry s law, the partial vapor pressure of a solution component is always proportional to its mole fraction. If the component predominates as Hie solvent, Rault s law says that the partial vapor pressure is proportional to the pure vapor pressure. If the component represents a tiny amount of solution. Henry s law says that the vapor partial pressure is proportional to Benny s irw constant. 

If a gas phase is present, chemical species may volatilize from the liquid or solid phase, which is an important partitioning process in a variety of circumstances (e.g., transport in the unsaturated zone, or for treatment processes). The equilibrium vapor pressure can be used with the ideal gas law to estimate the mass in a given volume and temperature under equilibrium conditions. For solutions with more than one component, Raoult s law can be used to quantify the vapor pressure of each component. For dilute aqueous solutions, Henry s law describes the equilibrium relationship between dissolved chemicals and their vapor pressure ... 

For dilute solutions, Henry s law is usually a good choice for an equilibrium relationship. In this case, = mx, which is defined in relation to the overall mass transfer by Eq. (19). For a dilute solution... 

Also, for sufficiently dilute solutions, Henry s law always applies so that y = mx... 

The p -process. This is the process of transferring one s molecule from an ideal-gas phase into a dilute ideal solution (Henry s law) at fixed temperature... 

The Henry s law constant depends on the temperature, the volatility, and the pressure. It is not valid for substances such as electrolytes, which dissociate in solution. For ideal solutions, Henry s law is valid over the entire range of concentrations (0-100%), and the Henry s law constant equals the vapor pressure of that component. 

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