# Freezing point and boiling relationship

### Raoult's Law; boiling point elevation; freezing point depression — CSSAC

For a solution with a liquid as solvent, the temperature at which it freezes to a One valuable use of these relationships is to determine the molecular mass of. Solutes in the liquid phase also raise the equilibrium boiling temperature. Pressure also affects freezing temperature (a little) and boiling temperatures (a lot). Freezing point depression is a colligative property observed in solutions, brought on . The Relationship Between Boiling Point Elevation and Vapor Pressure.

Indicate what happens to the boiling point and the freezing point of a solvent when a solute is added to it. Calculate boiling point elevations and freezing point depressions for a solution.

Boiling point elevation and freezing point depression - Chemistry - Khan Academy

People who live in colder climates have seen the trucks put salt on the roads when snow or ice is forecast. Why do they do that?

## Freezing and Boiling Points

As a result of the information you will explore in this section you will understand why these events occur. You will also learn to calculate exactly how much of an effect a specific solute can have on the boiling point or freezing point of a solution. The example given in the introduction is an example of a colligative property. What this means for the example above is that people in colder climates don't necessarily need salt to get the same effect on the roads - any solute will work.

However, the higher the concentration of solute, the more these properties will change. When table salt is added to water the resulting solution has a higher boiling point than the water did by itself.

The ions form an attraction with the solvent particles that then prevent the water molecules from going into the gas phase. A liquid can become supercooled because the particles in a solid are packed in a regular structure that is characteristic of that particular substance. Some of these solids form very easily; others do not. Some need a particle of dust, or a seed crystal, to act as a site on which the crystal can grow.

### Melting Point, Freezing Point, Boiling Point

It is difficult for these particles to organize themselves, but a seed crystal can provide the framework on which the proper arrangement of ions and water molecules can grow. Because it is difficult to heat solids to temperatures above their melting points, and because pure solids tend to melt over a very small temperature range, melting points are often used to help identify compounds. Measurements of the melting point of a solid can also provide information about the purity of the substance.

Pure, crystalline solids melt over a very narrow range of temperatures, whereas mixtures melt over a broad temperature range.

Mixtures also tend to melt at temperatures below the melting points of the pure solids. Boiling Point When a liquid is heated, it eventually reaches a temperature at which the vapor pressure is large enough that bubbles form inside the body of the liquid. This temperature is called the boiling point.

### Freezing and Boiling Points

Once the liquid starts to boil, the temperature remains constant until all of the liquid has been converted to a gas. The normal boiling point of water is oC. But if you try to cook an egg in boiling water while camping in the Rocky Mountains at an elevation of 10, feet, you will find that it takes longer for the egg to cook because water boils at only 90oC at this elevation.

In theory, you shouldn't be able to heat a liquid to temperatures above its normal boiling point. Before microwave ovens became popular, however, pressure cookers were used to decrease the amount of time it took to cook food.

## Boiling point elevation and freezing point depression

In a typical pressure cooker, water can remain a liquid at temperatures as high as oC, and food cooks in as little as one-third the normal time. To explain why water boils at 90oC in the mountains and oC in a pressure cooker, even though the normal boiling point of water is oC, we have to understand why a liquid boils.

By definition, a liquid boils when the vapor pressure of the gas escaping from the liquid is equal to the pressure exerted on the liquid by its surroundings, as shown in the figure below.

Liquids boil when their vapor pressure is equal to the pressure exerted on the liquid by its surroundings. The normal boiling point of water is oC because this is the temperature at which the vapor pressure of water is mmHg, or 1 atm. Under normal conditions, when the pressure of the atmosphere is approximately mmHg, water boils at oC.