For a pure solvent, is the higher the boiling point, the higher the freezing point?

Boiling point refers to the temperature at which the vapor pressure of a liquid (pure liquid or solution) is equal to the outside pressure. If no external pressure is indicated, it is considered to be kPa. For the solution of difficult volatile solutes, due to the drop in vapor pressure, in order to make the vapor pressure of the solution reach the external pressure, it is necessary to make the temperature exceed the boiling point of the pure solvent, so the boiling point of this kind of solution is always higher than the boiling point of the pure solvent, this phenomenon is called the boiling point of the solution, the greater the concentration of the solution, the more the boiling point rises.

The freezing point is the temperature at which the liquid and solid phases of a substance establish equilibrium. When the freezing point is reached, the vapor pressure of the liquid and solid phases must be equal, otherwise the two phases cannot coexist. Therefore, the freezing point is essentially the temperature of the solid, liquid and gas phases of the substance.

The freezing point of pure water is k(9), at which point the vapor pressure of both water and ice is Pa(mm Hg). The freezing point of a solution is the temperature at which the solvent crystals begin to precipitate from the solution. At this time, the system is composed of a solution (liquid phase), a solvent solid phase, and a solvent vapor phase.

For aqueous solutions, the solvent solid phase is pure ice. Due to the drop in the vapor pressure of the solution, when k, the vapor pressure of the ice is still Pa, and the vapor pressure of the solution must be lower than the Pa, in this way, the solution and the ice can not coexist, only at a certain temperature below k, the vapor pressure of the solution can be equal to the vapor pressure of the ice, and the temperature at this time is the freezing point of the solution, so the freezing point of the solution is always lower than that of the pure solvent, and this phenomenon is called the freezing point drop. The greater the concentration of the solution, the more the vapor pressure drops, and the more the freezing point drops.

In the same solution, as the solvent continues to crystallize and precipitate, the concentration of the solution will continue to increase, and the freezing point will continue to decrease.

Both the increase in the boiling point of the solution and the decrease in the freezing point are caused by the decrease in the vapor pressure of the solution. For dilute solutions with non-electrolytes that are difficult to volatile, since the vapor pressure drop dp is directly proportional to the mass molar concentration of the solution, the increase in boiling point and the decrease in freezing point of such solutions should also be related to the mass molar concentration. Raoult points out according to dependence:

For dilute solutions that are difficult to volatilize non-electrolytes, an increase in boiling point dtb or a decrease in freezing point dtf is directly proportional to the molar concentration of the solution mass. <>

The difference between boiling point and freezing point and pure solvent:

Boiling Point: Boiling is a violent vaporization phenomenon that occurs simultaneously inside and on the surface of a liquid at a certain temperature. The temperature at which a liquid boils is known as the boiling point.

Freezing point: Freezing point is the temperature at which a crystalline substance solidifies, and different crystals have different freezing points. At a certain pressure, the freezing point of any crystal is the same as its melting point.

With the same crystal, the freezing point is related to the pressure. The freezing point of crystals that expand in volume during solidification decreases with the increase of pressure. When solidifying, the freezing point of crystals that shrink in volume increases with increasing pressure. During the solidification process, the liquid transforms into a solid while emitting heat.

So the temperature of the substance will be in the liquid state when it is higher than the melting point; When it is below the melting point, it is in a solid state. Amorphous substances have no freezing point.

Pure solvent: Pure solvent is a term for a substance, not a specific substance. There is no solute, for example, sodium chloride solution, the solvent is water, and the solute is sodium chloride. The pure solvent is water.

The boiling point is the critical temperature at which a liquid becomes a gas, and the melting point is the freezing point at which a solid becomes a liquid.

It is a liquid that becomes a gas, and the numerical value is the same as the melting point.

The boiling point and the freezing point temperature are the same, but the angle of the station is different, and the solidification is said from the perspective of the liquid to the solid; The melting point refers to the point of view from solid to liquid, and we often say how much it is about iron, tungsten, etc., which are not easy to melt. For water, we also often say the melting point because the melting point is more written. As for adding to the water.

matter, then it becomes a mixture, and the prerequisite for the crystal is pure substance.

Not counting crystals. I think what you did was to add salt to the water, the questioner didn't think about it so much, you just look at it as a crystal, its melting point is lowered, you don't have to think about it.

Compare the mass molar concentration of particles actually present in solution. KCl is completely ionized, so actually m 2mol kg. Acetic acid partially ionized, m 1 2mol kg.

Glucose is completely non-ionizing, m 1mol kg. So, according to the dependence of the dilute solution. The freezing point of potassium chloride solution was the lowest, followed by acetic acid aqueous solution, and glucose aqueous solution was the highest.

It can be seen from the last column of the experiment ** that the water and alcohol did not solidify at the beginning, and when the volume ratio reached a certain value, the mixture could coagulate, but the water and alcohol were not separated, so the water and alcohol could not be separated from the mixture with Zhang Xiao's scheme.

Normally, the freezing point of water is 0, and it is not difficult to see from the last column of ** that after adding alcohol to water, the freezing point is lower than 0, so adding alcohol will cause the freezing point of water to decrease.

Composition of the solution:

1. Solubility: dissolved substances (e.g., salt and water are used to prepare brine, salt is the solute).

2. Solvent: a substance that can dissolve other substances (for example: salt and water are used to configure brine, and water is the solvent).

3. When two solutions are miscible with each other, the one with a large amount is generally called a solvent, and the one with a small amount is called a solute.

4. When two solutions are miscible with each other, if one of them is water, water is generally called a solvent.

5. Solids or gases are soluble in liquids, and liquids are usually called solvents.

The boiling point of a dilute solution is not necessarily higher than that of a pure solvent, and if it is a non-volatile solute, it is in line with the dependence of a dilute solution, then the boiling point of a dilute solution is higher than that of a pure solvent, but not necessarily if it is a volatile solute.

The molar fraction of the solute in the dilute solution tends to be close to zero, while the molar fraction of the solvent approaches 1, so the dilute solution is very close to the ideal solution, and the solvent in the dilute solution behaves the same as it behaves when it is in the ideal solution.

The solute in a dilute solution obeys Henry's law, and its solvent obeys Raoult's law, so a dilute solution can also be defined as follows: "A solution in which the solvent obeys Raoult's law and the solute obeys Henry's law at constant temperature and pressure."

Not necessarily. If it is a non-volatile solute, it conforms to the dependence of the dilute solution, so the boiling point of the dilute solution is higher than that of the pure solvent. However, this is not necessarily the case for volatile solutes.

Yes, there is a boiling point rise constant. The reason is that the solute particles in the dilute solution will attract the solvent, making it difficult for the particles on the surface of the solvent to leave the liquid surface due to the attraction, so that the balance of the particles on the surface of the solvent leaving the liquid is broken and becomes more difficult, and the boiling point is to describe such an equilibrium, so the boiling point will rise.

Determination of the melting and boiling point of substances of different crystal types: Atomic Crystals, Ion Crystals, Molecular Crystals (General). The melting and boiling points of metal crystals have a wide range and a large span.

Some are higher than atomic crystals, such as W melting point 3410, which is greater than Si. Silicon is lower than molecular crystals, such as Hg is liquid at room temperature.

The radius of the cation of the metal crystal and the number of free electrons. The smaller the cation radius and the more free electrons there are, the lower the melting and boiling point.

Boiling point Note: The boiling point of water is 100 under standard atmospheric pressure conditions, the lower the atmospheric pressure, the lower the boiling point, and the higher the atmospheric pressure, the higher the boiling point. When the pressure of the vapor is equal to the pressure of the outside, the vapor pressure has reached a saturated state, and the water will boil at this time, and the temperature of the water when it boils is the boiling point of the water.

Although the number of solute molecules in dilute solution is small, they still affect the movement of solvent molecules. In dilute solutions, solute molecules occupy the space around the solvent molecules, reducing the interaction forces between the solvent molecules. This makes the solvent molecules require more energy to get out of the liquid surface when boiling, so the boiling point of a dilute solution is higher than that of a pure solvent.

In addition, the solute molecules will also form hydrogen bonds, van der Waals forces and other interaction forces with solvent molecules, which will increase the surface tension of the solution, making the boiling point of the solution further increase.

In conclusion, the boiling point of a dilute solution is higher than that of a pure solvent due to the influence of the solute molecules on the interaction forces and surface tension between the solvent lifting and leakage molecules.