File Name: boiling points questions and answers .zip
Boiling point , temperature at which the pressure exerted by the surroundings upon a liquid is equaled by the pressure exerted by the vapour of the liquid; under this condition, addition of heat results in the transformation of the liquid into its vapour without raising the temperature. At any temperature a liquid partly vaporizes into the space above it until the pressure exerted by the vapour reaches a characteristic value called the vapour pressure of the liquid at that temperature.
Melting Point and Freezing Point. Pure, crystalline solids have a characteristic melting point , the temperature at which the solid melts to become a liquid.
The transition between the solid and the liquid is so sharp for small samples of a pure substance that melting points can be measured to 0. The melting point of solid oxygen, for example, is Liquids have a characteristic temperature at which they turn into solids, known as their freezing point. In theory, the melting point of a solid should be the same as the freezing point of the liquid.
In practice, small differences between these quantities can be observed. It is difficult, if not impossible, to heat a solid above its melting point because the heat that enters the solid at its melting point is used to convert the solid into a liquid. It is possible, however, to cool some liquids to temperatures below their freezing points without forming a solid.
When this is done, the liquid is said to be supercooled. When this solid melts, the sodium acetate dissolves in the water that was trapped in the crystal to form a solution.
When the solution cools to room temperature, it should solidify. But it often doesn't. If a small crystal of sodium acetate trihydrate is added to the liquid, however, the contents of the flask solidify within seconds. 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. 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. 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. 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 o C. 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 90 o C 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. In a typical pressure cooker, water can remain a liquid at temperatures as high as o C, and food cooks in as little as one-third the normal time. To explain why water boils at 90 o C in the mountains and o C in a pressure cooker, even though the normal boiling point of water is o C, 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. The normal boiling point of water is o C 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 o C.
At 10, feet above sea level, the pressure of the atmosphere is only mmHg. At these elevations, water boils when its vapor pressure is mmHg, which occurs at a temperature of 90 o C. Pressure cookers are equipped with a valve that lets gas escape when the pressure inside the pot exceeds some fixed value. This valve is often set at 15 psi, which means that the water vapor inside the pot must reach a pressure of 2 atm before it can escape.
Because water doesn't reach a vapor pressure of 2 atm until the temperature is o C, it boils in this container at o C. Liquids often boil in an uneven fashion, or bump. They tend to bump when there aren't any scratches on the walls of the container where bubbles can form. Bumping is easily prevented by adding a few boiling chips to the liquid, which provide a rough surface upon which bubbles can form.
When boiling chips are used, essentially all of the bubbles that rise through the solution form on the surface of these chips. Liquids boil when their vapor pressure is equal to the pressure exerted on the liquid by its surroundings.
The particles making up solids and liquids are held together by intermolecular forces and these forces affect a number of the physical properties of mater in these two states. In the mean time we talk about What Darwin Never Knew Worksheet Answer Key, below we can see particular related images to add more info. Intermolecular Forces Worksheet 2 Answers 1 Using your knowledge of molecular structure, identify the main intermolecular force in the following compounds. This is the result of the large difference in electronegativity between oxygen and hydrogen. Use your knowledge of intermolecular forces to discover the properties of solutions and mixtures.
Melting Point and Freezing Point. Pure, crystalline solids have a characteristic melting point , the temperature at which the solid melts to become a liquid. The transition between the solid and the liquid is so sharp for small samples of a pure substance that melting points can be measured to 0. The melting point of solid oxygen, for example, is Liquids have a characteristic temperature at which they turn into solids, known as their freezing point.
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For a solution with a liquid as solvent, the temperature at which it freezes to a solid is slightly lower than the freezing point of the pure solvent. This phenomenon is known as freezing point depression and is related in a simple manner to the concentration of the solute. The lowering of the freezing point is given by. Table 1 gives data for several common solvents. A similar property of solutions is boiling point elevation.
Intramolecular forces bonding forces exist within molecules and influence the chemical properties. Topic can be quite a complete lesson in one maybe a small sub-topic. Intermolecular force - or physical force - is the attraction between molecules.
Intermolecular forces IMFs can be used to predict relative boiling points. The stronger the IMFs, the lower the vapor pressure of the substance and the higher the boiling point. Therefore, we can compare the relative strengths of the IMFs of the compounds to predict their relative boiling points. When comparing compounds with the same IMFs, we use size and shape as tie breakers since the London dispersion forces increase as the surface area increases. Since all compounds exhibit some level of London dispersion forces and compounds capable of H-bonding also exhibit dipole-dipole, we will use the phrase "dominant IMF" to communicate the IMF most responsible for the physical properties of the compound. In the table below, we see examples of these relationships.
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