What is the difference between concentration and activity? Relationship between activity and concent

Concentration generally refers to the amount of solute in a solution or solvent, which is like a unit used to measure the quantity of a substance. For example, the amount of salt in a glass of salted water can be expressed by the concept of concentration. The focus of the concept of liveness is the word "live", which reflects the decay in matter.

For example, food contains a variety of substances, and not all of these substances are absorbed by the body.

For the sake of activity, the human body absorbs these substances. For example, the effective collision of substances in the reaction can cause the reaction to occur, and the number of particles in the effective collision is the activity, so the activity is a measure of the likelihood of the reaction.

Activity refers to a physical quantity used to replace concentration in order to make the thermodynamic formula of an ideal solution (or extremely dilute solution) applicable to a real solution, and the concept of activity was first proposed by Lewis. For ideal liquid mixtures, Raoult's law pb xb is conformed to, and for non-ideal liquid mixtures, Raoult's law is modified to pb fbxb ab, so fb indicates the degree of deviation between the non-ideal and ideal liquid mixtures, which is actually the deviation coefficient of Raoult's law. For the ideal liquid mixture ab xb, fb 1, while for non-ideal ab≠xb, fb can be greater than less than 1, so the activity is dimensionless in relation to the composition x.

Activity is generally less than concentration and has an activity coefficient. It is expressed by the formula: activity = concentration activity coefficient.

For example, CH3COOH has 1mol L, but it is a weak electrolyte, so the ionized H+ is less than 1mol L, and the H+ concentration ionized by CH3COOH is related to activity.

The concentration at which the electrolyte solution actually works becomes the effective concentration. The activity coefficient refers to the ratio coefficient of activity to concentration.

Relationship between activity and concentration: When concentration increases, activity increases accordingly.

Activity and concentration are important concepts in chemical reactions, which are related to the rate and equilibrium of chemical reactions. The activity of a substance in solution refers to the level of activity it exhibits relative to a pure substance when it interacts with other substances. Concentration, on the other hand, describes the mass or relative amount of a substance contained in a unit volume or mass.

The link between activity and concentration is affected by the composition of the solution, and different solutions have different effects on chemical reactions. At the same concentration, the activity coefficient of different ions is different. In general, for polar ions, the less dispersed, the greater the activity coefficient.

Changes in the composition of the solution also affect the activity of the mixture.

The relationship between concentration and activity not only plays an important role in chemical reactions, but also has a wide range of applications in other disciplines. For biologists, understanding the relationship between activity and concentration can lead to a better understanding of the principles of enzyme-catalyzed reactions, which is very important for drug preparation and gene research.

Calculation method and influencing factors of activity coefficient:

The activity coefficient is an important indicator to describe the solubility of a substance in solution, which is the ratio of the solute concentration in the solution to the pure solute concentration, also known as the solubility meniscus delay coefficient. The calculation methods of activity coefficient include theoretical calculation method, measurement method and fitting method.

The theoretical calculation method is based on the principle of the interaction force between the solute and the solvent in the solution and the chemical reaction, and the activity coefficient is calculated theoretically. The activity coefficient is calculated by experimentally measuring the parameters such as electromotive force, osmotic pressure, boiling point, etc. in the solution. The fitting method calculates the activity coefficient by fitting the experimental data into a certain equation.

The activity coefficient is affected by a variety of factors, among which the most influential factors include temperature, pressure, ionic strength, pH, hydration capacity of anions, and interaction forces between solutes and solvents in the solution. When the temperature increases or the pressure decreases, the activity coefficient decreases; When the ionic strength increases or the pH value changes, the activity coefficient also changes.

The concentration that actually plays a role in the electrolyte solution becomes the effective concentration, which is called activity. The activity coefficient refers to the ratio coefficient of activity to concentration. In electrolyte solutions, the total concentration of electrolytes is not representative of their effective concentration due to the interaction between ions, and an empirical correction factor (activity factor) needs to be introduced to represent the deviation of the actual solution from the ideal solution.

The formula for the relationship between the average activity coefficient and concentration in <> is: activity = activity coefficient * ion concentration. The coefficient is greater than or equal to 1, and the activity coefficient is 1 only if the ionic strength in the solution is close to 0.

Activity is a physical quantity used in place of concentration in order to make the thermodynamic formula of an ideal solution (or very dilute solution) applicable to a real solution.

The vast majority of metallurgical reactions involve solutions (solid solutions, metallurgical melts, and aqueous solutions), which are often not ideal. In order to carry out quantitative thermokinetic calculations and analysis, the concentration of each component in the solution must be replaced by activity. Activity is the effective concentration (or thermodynamic concentration) of a component.

The concentration of the component must be corrected by a coefficient to conform to certain physicochemical laws (e.g., the law of mass action, Raoeur's law, Henry's law, the law of distribution, etc.), and this correction factor is called the activity factor.

The activity coefficient refers to the ratio coefficient of activity to concentration. InElectrolyte solutionDue to the interaction between ions, the total concentration of the electrolyte is not representative of its effective concentration, and an empirical correction coefficient fi (activity coefficient) needs to be introduced to represent the deviation of the actual solution from the ideal solution.

Activity: In physical chemistry, activity is the activity of a substance"Effective concentration", or material"Valid molar fraction.

This concept was first proposed by Gilbert Newton Lewis.

Place the chemical potential of component I in the ideal mixture.

Replace the molar fraction (xi) in the expression with the activity (ai) to obtain the chemical potential of component i in the real mixture, as shown below

Ideally, XI is equal to AI.

Activity coefficient (i, or"Activity factor") is defined by the following formula, which is equivalent to the degree to which i in the real mixture deviates from the ideal situation.

The activity coefficient of the electrolyte can usually be determined by the electromotive force.

Solubility and freezing point, etc. The magnitude of the activity coefficient is determined by the temperature and the dielectric constant of the water.

Ions such as concentration and valence. In order to make the thermodynamic formula of an ideal solution (or a very dilute solution) applicable to a real solution, it is used as a substitute for a physical quantity of concentration.

Activity = Activity coefficient * concentration.

Activity factor < = 1

The activity coefficient is 1 only when the ionic strength in the solution is close to 0.

Activity = Activity coefficient * concentration, activity is the concentration representation used in theoretical calculation, concentration is the actual value, activity coefficient is the correction of the actual concentration in the theoretical calculation, because there is no theoretical calculation method with a good concentration at present, and it needs to be corrected.