Boiling point of the mixture

No, it’s not. . The boiling point of a mixture can be higher than that of each of its components. . Some are lower than each of them. . The boiling point of an azeotrope can be found in manuals, or it can be determined by creating a gas-liquid phase equilibrium diagram through experiments

No, different substances have different boiling points when mixed together; some form a maximum azeotrope, some form a minimum azeotrope, and most fall somewhere in between.

Obviously not. Generally, substances with lower boiling points evaporate first, which can lead to an azeotrope that slightly raises the boiling temperature. That’s my opinion; I’d appreciate guidance from experts. This post was last edited by jsabc007 on 2009-4-2 at 18:33.]

The boiling point of a mixture is related to its physical properties. The boiling point of an ideal solution is the bubble point (usually lying between the boiling points of the two components), whereas ideal liquids generally have a minimum or maximum azeotrope boiling point (lower than the lowest boiling point of the pure components or higher than their highest boiling point).

No. For example, one of the colligative properties of dilute solutions is that the increase in boiling point equals the mass molar concentration of the solute in the liquid phase multiplied by the boiling point elevation constant of the solvent

An azeotrope, also known as an equibubble, refers to a liquid mixture of two or more components in which, when boiling at a constant pressure, both the composition and the boiling point remain unchanged. This actually indicates that the steam generated by boiling at this point has exactly the same composition as the liquid itself. Azeotropes cannot be separated by conventional distillation or fractionation methods. Not all binary liquid mixtures can form azeotropes; Science Class lists in the table below some common compositions of azeotropes along with their boiling points. The temperature-component phase diagrams of such mixtures have a notable feature: their vapor line (the boundary between the gas-liquid mixture and the gaseous state) and the liquid line (the boundary between the liquid state and the gas-liquid mixture) share the same highest or lowest point. If such a point is the highest point, it is called a positive azeotrope ； If such a point is the lowest point, it is called a negative azeotrope. Most azeotropes are negative azeotropes, that is, they have the lowest boiling point. It is worth noting that any azeotrope is specific to a particular external pressure. For different pressures, their azeotrope components and boiling points will vary ； Practice has shown that it is difficult for two components with a boiling point difference of more than 30 K to form azeotropes (for example, water and propanone do not form an azeotrope).

Obviously not. The bubble point method is commonly used to determine the boiling point of a mixture. For a non-ideal solution, the activity coefficients of each component must be considered.

No, when different substances are mixed together, their boiling points vary; some are higher than the highest boiling point, while others are lower than the lowest boiling point, though most fall somewhere in between.

There is no such thing as a boiling point for mixtures; the point at which bubbling occurs in an open system is called the bubble point. The boiling point applies to pure components

For example: Ammonia dissolves in water to form an ammonia solution; what is its boiling point? I checked the tables, namely those showing the enthalpy values for different concentrations of ammonia solution. Data on the boiling point of ammonia is only available at pressures below 20 Kg/cm2; so what should I do if I want to find the boiling point of ammonia at a concentration of 25 Kg/cm2? Thank you, Instructor!

Generally, the low-boiling components evaporate first, which leads to an azeotrope that slightly raises the boiling temperature; this is certain. As for determining the boiling point of 25 KG/cm2 concentrated ammonia solution, is such a high concentration actually used?

Yes, if it can’t be found, how can it be calculated?

If no azeotrope is formed after mixing and the substances are only mutually soluble, they should boil at their respective boiling points； If an azeotrope can be formed, it should be the minimum azeotrope, right?

There is no boiling point; only a boiling range.

I think most people up above will understand it pretty well after reading it. I’ve forgotten what I studied in college too; it’s a good chance to learn it again anyway.

What everyone has said is correct: a mixture has only a boiling range when no azeotrope is formed, while it has an azeotrope temperature when an azeotrope is formed.

A mixture results in a boiling point that falls within a certain range. Pure alcohol boils at 78.5°C, while pure water boils at 100°C; when mixed, the boiling point lies between 78.5°C and 100°C. For example, a mixture of 80% water and 20% alcohol may boil and vaporize at temperatures ranging from 92°C to 98°C (this range is assumed). Below 92°C, the mixture is in a liquid state; above 98°C, it is in a gaseous state; in between, it exists as a mixture of both liquid and gas.

As I recall, the method for estimating the boiling point of a mixture can be found in books such as chemical process manuals; if that’s not possible, simulations can be carried out using software like ASPEN. There are likely various methods available—for example, passing the mixture through a simple equipment module, setting the feed vapor fraction to 1 and the pressure, and then determining the feed temperature, which would correspond to the boiling point (this is just my personal opinion; please feel free to point out any errors for discussion). This post was last edited by lujianfei79 on 2009-4-3 at 18:45

The mixture indeed cannot be analyzed using the boiling point; instead, the bubble point must be used!!! The calculation of the bubble point temperature is based on the following: for P, x1, x2……xc, and T, y1, y2……yc. In cases where both the gas and the liquid are ideal, the bubble point equation f(T) = ∑(ki*)^-1 = 0 is used, and trial and error is required for determining the values. For other situations, the calculations are more complex, involving the use of activity coefficients, as determined by thermodynamics.