What are the two factors that affect the boiling point Please explain it to the masters

The boiling point is the temperature at which a liquid boils, that is, the temperature at which a substance changes from a liquid state to a gaseous state. The saturated vapor pressure in the bubbles formed inside the liquid as it boils.

The bubble must be equal to the pressure exerted by the outside world for the bubble to grow and rise, so the boiling point is the temperature at which the saturated vapor pressure of the liquid is equal to the outside pressure.

The two main factors that affect the boiling point are the external pressure and the liquid substance.

The boiling point of a liquid is related to the external pressure. When the pressure of the liquid increases, its boiling point increases; When the pressure decreases; The boiling point decreases. For example, the steam pressure in a steam boiler is about a few tens of atmospheres, and the boiling point of water in a boiler can be more than 200.

For another example, when cooking rice in a high mountain, the water is easy to boil, but the rice is not easy to cook. This is due to the fact that the atmospheric pressure decreases with the increase in the topography and the boiling point of water also gradually decreases with the increase in altitude. (At an altitude of 1,900 meters, the atmospheric pressure is about 79,800 Pa (600 mm Hg, the boiling point of water is.)

At the same atmospheric pressure, the boiling point of the liquid is also different. This is because the saturation vapor pressure is related to the type of liquid. At a certain temperature, the saturated vapor pressure of various liquids is also constant. For example, ether saturates air pressure at 20.

Pa (44 cm Hg) is below atmospheric pressure, and the temperature rises slightly, making the saturated vapor pressure of ether and atmospheric pressure stronger.

Equally, heat the ether to 35 to boil. If the liquid contains impurities, it will also affect the boiling point of the liquid. The boiling point of a liquid containing solute is higher than that of a pure liquid, which is due to the fact that the gravitational force between the liquid molecules increases after the presence of a solute, the liquid is not easy to vaporize, and the saturated vapor pressure is also smaller.

To make the saturation vapor pressure the same as the atmospheric pressure, the boiling point must be raised. Different liquids have different boiling points under the same external pressure. The relationship between boiling point and pressure can be explained by the Clausius equation. Get.

Are you talking about intermolecular forces? (Relative molecular mass and molecular polarity?) ）

The greater the polarity and relative molecular weight, the greater the intermolecular interaction, and the higher the corresponding boiling point.

The boiling point of different liquids is different.

The higher the concentration of the same substance, the higher the boiling point.

The lower the pressure, the lower the boiling point. So the two factors you want are concentration and pressure.

The boiling point rise constant is the boiling point increase value after adding 1mol of solute to 1000g of pure solvent.

Molar boiling point elevation constant The boiling point increase value of 1mol solute added to 1000g of pure solvent, which is a constant only related to the properties of the solvent, and is often expressed in kb.

Introduction

Due to non-volatile, non-electrolyte.

The vapor pressure of the solution.

It is lower than the vapor pressure of the pure solvent, so when the temperature rises to the normal boiling point tb, the vapor pressure of the solvent is still lower than the atmospheric pressure of the 760mmHg column.

Only when the temperature continues to rise to Tb does the vapor pressure of the solution equal to the outside atmospheric pressure and the solution boils. The difference between Tb and Tb is expressed as Tb, which is called the increase in the boiling point of the solution.

The above content reference: Encyclopedia - Molar boiling point rise constant.

Question 1: What is the melting and boiling point related to 1. For substances with different crystal types, generally speaking: atomic crystals, ionic crystals, molecular crystals, and metal crystals have a wide range of melting points.

2. Atomic crystal: the shorter the bond length and the greater the bond energy of the atomic crystal, the more stable the covalent bond is, the higher the melting and boiling point of the substance, and vice versa. Such as:

Diamond (C C) Silicon Carbide (Si C) Crystalline Silicon (Si Si).

3. Ion crystal: The smaller the anion and cation radius and the higher the charge number in the ion crystal, the stronger the ionic bond, the higher the melting and boiling point, and vice versa.

Such as kf kcl kbr ki, cao kcl.

4. Metal crystal: the more the number of valence electrons of the metal atom in the metal crystal, the smaller the atomic radius, and the more the electrostatic interaction between the metal cation and the free electron.

Strong, the stronger the metallic bond, the higher the melting boiling point, and vice versa. Such as: na mg al.

The melting and boiling point of an alloy is generally lower than that of the pure metals of its components. Such as aluminum-silicon alloy pure aluminum (or pure silicon).

5. Molecular crystals: The greater the intermolecular force of molecular crystals, the higher the melting and boiling point of the substance, and vice versa. (Molecular crystals with hydrogen bonds, melting boiling point.)

abnormally high) e.g. h2o h2te h2se h2s, c2h5oh ch3och3.

1) For molecular crystals with similar composition and structure, the larger the relative molecular mass, the stronger the intermolecular force, and the higher the melting and boiling point of the substance.

Such as: CH4 SIH4 GEH4 SNH4.

2) For substances with different composition and structure (similar relative molecular mass), the greater the molecular polarity, the higher its melting and boiling point, such as melting boiling point.

co＞n2，ch3oh＞ch3ch3。

3) In the oils formed by higher fatty acids, the greater the degree of unsaturation, the lower the melting and boiling point. Such as:

c17h35cooh＞c17h33cooh；

4) Hydrocarbons, halogenated hydrocarbons, alcohols, aldehydes, carboxylic acids and other organic substances generally increase with the increase of the number of carbon atoms in the molecule, such as C2H6 CH4, C2H5Cl Ch3Cl, CH3COOH HCOOH.

5) Isomers: The isomers of chain hydrocarbons and their derivatives decrease with the increase of branching. Such as:

ch3(ch2)3 ch3 (positive) ch3ch2ch(ch3)2(heterogeneous) (ch3)4c (new). When the isomer of aromatic hydrocarbons has two substituents, the melting point decreases according to pair, ortho and meta. (The boiling point decreases according to the proximal, intermediate, and para-position.)

The reason why the lowest constant boiling point occurs is because the substances in the liquid mixture have mutual influence, if the ideal mixture, that is, there is no interference between the substances, then there is no minimum constant boiling point, so 1 is the mutual interference of its own factors, and its degree, 2 is the pressure, the pressure rises to a certain value, and the constant boiling point disappears.

The shape of the phase diagram is closely related to the interaction between the molecules in the mixture. If the attraction between two molecules of different components is less than that between molecules of pure components, after the formation of a liquid mixture, the molecules are easy to overflow the liquid surface and produce positive deviations. In the same way, when the pressure is constant, the gravitational force of the molecule decreases, and the required heating temperature does not need to be too high, which is lower than the heating temperature of the pure component, resulting in the lowest constant boiling point.

Uses:

For multiphase systems, the mutual transformation of each phase, the formation of new phases, and the disappearance of old phases are related to temperature, pressure, and composition. The various geometries that represent the laws of phase transitions given according to the experimental data are called phase diagrams. From this geometry, it is possible to directly identify the various aggregation states in the multiphase system and the conditions under which they are located (temperature, pressure, composition).

The strength of the chemical bond or intermolecular force determines the melting and boiling point.

General: atomic crystals, ionic crystals, intramolecular crystals, and the melting and boiling points of gold-tolerant crystals vary greatly (such as tungsten, mercury).

For atomic crystals, the smaller the bonding atomic radius, the shorter the bond length, the greater the bond energy, the stronger the covalent bond, and the higher the melting and boiling point of the atomic crystal.

For ionic crystals, the size of the ionic charge number (the main factor) and the size of the ionic radius determine the strength of the ionic bond and determine the melting and boiling point. In general, ionic bonds increase with the increase of ionic charge number and decrease of ionic radius.

For molecular crystals, the stronger the van der Waals force, the higher the melting boiling point.

1.For molecules with similar composition and structure, the larger the relative molecular mass, the stronger the intermolecular interaction, and the higher the melting and boiling point of the molecular crystal.

2.For molecules of the same relative mass, as in isomers, in general, the higher the number of branches, the lower the boiling point, and the more symmetrical the molecule, the higher the melting point. Note: The effect of external conditions on the melting and boiling point of a substance is not always consistent. The melting point is often related to the symmetry of the spatial structure of the crystal.

3.If there are hydrogen bonds between molecules, the intermolecular force is stronger than that of other crystals of the same kind with similar structures, so the melting and boiling point is relatively high).

For metal crystals, the size of the ionic charge number (the main factor) and the size of the ionic radius determine the strength of the metal bond and determine the melting and boiling point. In general, metallic bonds increase with the increase of the number of metal cation charges, the decrease of ionic radius electricity, and the atmospheric pressure is also affected.

Comparison of substances in different states under the same conditions.

1. Under the same conditions, the melting and boiling points of substances in different states are different, generally including: solid, liquid, and gas. For example: NABR (solid) > BR2> HBR (gas).