electrolyte solutionThe concentration that actually plays a role in is called effective concentration, namely activity.Activity coefficient refers to the ratio coefficient between activity and concentration.Due to the interaction between ions in the electrolyte solution, the total concentration of the electrolyte cannot represent its effective concentration. It is necessary to introduce an empirical correction coefficient γ (activity coefficient) to represent the deviation between the actual solution and the ideal solution.[1]
Chinese name
activity coefficient
Foreign name
Activity coefficient
Introduction
Proportional coefficient of activity and concentration
In physical chemistry,activity(Activity)“Effective concentration”, or "effective mole fraction" of the substance.This concept was first proposed by Gilbert Newton Lewis.[2]
The chemical potential of component B in an ideal mixture can be expressed as
According to Raoult's law, for a non ideal liquid mixture, it can be expressed as
Therefore, the chemical potential of component B of non ideal liquid mixture can be expressed as
A is the activity of component B expressed by mole fraction, γ is the activity factor of component expressed by mole fraction, also known as activity coefficient, which represents the deviation between the mole fraction of component B and the ideal liquid mixture in the actual mixture.
electrolyteThe activity coefficient of is usually determined byemf, solubility andfreezing pointAnd so on.The activity coefficient is affected by temperature, dielectric constant of water, ion concentration and valence.In order to make the thermodynamic formula of ideal solution (or extremely dilute solution) applicable to real solution, it is used to replace a physical quantity of concentration.
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Non ideal dilute solution
1. Chemical potential form of solute concentration expressed by mole fraction
3. The chemical potential form of solute concentration expressed by the amount and concentration of the substance
Calculation of activity and activity factor
1. Vapor pressure method
For solvents,
, where pA is the measured value of steam pressure.For solutes,
, where pB is the measured value of steam pressure.
The activity coefficient can be obtained by plotting cB.
2. Graphical integration
Gibbs Duhem formula can be used to calculate the activity of solvent (substance) from the activity of solute (agent).If the activity of component A is calculated from the actual activity of component A, and the measured activity value of component B is consistent with the calculated value, they are said to meetThermodynamic consistency。
For example, according to Gibbs Duhem formula, under isothermal and isobaric conditions:
It can be obtained that,
If you use
yes
Draw a diagram, which can be obtained by graphical integration
。[1]
history
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Introduction and development of activity concept
The concept of activity was first proposed by G.N. Lewis in 1907, and was quickly applied to electrochemistry to measure the activity coefficient of electrolyte in aqueous solution.
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Mid 1930sChipmann(J. Chipman) introduced the concept of activity to metallurgical melt, and proposed that 1% concentration solution in metal solution is the activity standard state. This suggestion quickly becameMetallurgical Physical ChemistryIt is accepted by workers and popularized.C. Wagner recommended Ln in 1952γI is expanded according to McLaurin series, which lays the foundation for calculation of multi-component activity coefficient in metallurgical melt.In the 1950s and 1960s, the research work on the determination of activity and activity interaction coefficient was very active, mainly using chemical equilibrium and solubility methods. It has gradually developed into its own system and become a classic experimental method.Late 1960ssolid electrolyteThe oxygen cell has become a good means to measure the activity and interaction coefficient of oxygen in black and nonferrous metal melts.In the 1970s, many activity data of ferrous metal liquid and slag have been measured, but they are not complete.For non-ferrous metals, especially for matte andMolten saltMore work needs to be done for the activity data of etc.
development
Activity can not solve the structural problem of metallurgical melt.It can point out the deviation of thermodynamic action of components in real solution and ideal solution, but cannot provide the reason for the deviation.For a long time, many scholars have proposed the structural model of component phase interactionStatistical thermodynamicsA series of formulas are derived to predict the activity coefficient of components, which has achieved some success for some binary alloys. However, these semi empirical formulas are only applicable to the substances in a particular system, or the special concentration range of a system. So far, the general expressions applicable to different types of universal alloy systems have not been found.The attempt to obtain the linear relationship between activity parameters and concentration parameters for some binary alloy dilute solutions by proper conversion of concentration coordinates has not yet been successful.
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In a word, activity is applied to metallurgical process, so that metallurgical reaction can be carried out quantitativelyThermodynamic calculationAnd analysis have played and will continue to play their due roles in clarifying whether multiple reactions can be carried out selectively, in controlling and adjusting whether the product can reach the maximum yield, and in controlling how smelting operations can be carried out under optimal conditions.The determination of the activity of components in metallurgical solution (including solid solution and aqueous solution), the exploration of melt structure by using activity, and the prediction of the activity of components and other thermodynamic properties from the envisaged structure will remain more important research topics in the future.[3]
