Effect of pressure on melting point. Regelation

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Effect of pressure on melting point. Regelation If a substance expands on solidifying, then the application of pressure lowers the melting point. Conversely, substances which contract in volume on solidifying have their melting points raised by pressure. Thus, the freezing point of water is lowered by just over 0.007 K per atmosphere increase in pressure, while the […]

Change of volume on solidification

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Change of volume on solidification When water freezes to form ice expansion occurs and the ice takes up a bigger volume than the water. For this reason, water pipes are liable to burst during very cold weather, although the leaks do not occur until a thaw sets in. Sometimes the expansion of a substance on solidification serves […]

The refrigerator

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The refrigerator Cooling in a domestic refrigerator takes place when a volatile liquid, Freon, evaporates inside a copper coil surrounding the freezing box (Fig. 19.5). As fast as the vapour is formed it is removed by an electric pump, and so under the reduced pressure the liquid evaporates rapidly and may even boil. The necessary latent heat of […]

Vaporization when heat is supplied

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Vaporization when heat is supplied  When vaporization occurs the vapour occupies a much larger volume than the liquid so that energy is required to separate the molecules against their mutual attractions (internal work). In addition extra energy is required to enable the vapour to expand against the atmospheric pressure (externcl work). The heat required to provide the sum […]

Fusion and vaporization in relation to the kinetic theory of matter

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Fusion and vaporization in relation to the kinetic theory of matter Fusion We explained on page 138 that the molecules of solids vibrate to and fro alternately attracting and repelling one another. Their total energy can be looked on as consisting of two parts: kinetic energy which depends on the temperature; and potential energy which depends on the […]

Cooling by evaporation explained by the kinetic theory

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Cooling by evaporation explained by the kinetic theory The molecules of a liquid have an average kinetic energy which increases with temperature. Molecules near the surface which happen to be moving faster than average can escape from the attraction of their neighbours and escape out of the liquid. Some of these may collide with other molecules above the […]

To make ice by the evaporation of ether

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To make ice by the evaporation of ether A beaker about one-third full of ether is stood in a small pool of water on a of wood (Fig. 19.4). A current of air is then bubbled through the ether by rubber tube attached to bellows. The ether evaporates into the bubbles, and the vapour is carried quickly away […]

Cooling produced by evaporation

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Cooling produced by evaporation Some liquids have a low boiling-point, and thus change from liquid to vapour quite easily at ordinary temperatures. These are called volatile liquids. Methylated spirit and ether are examples. If a little methylated spirit or eau-de-Cologne is spilt on the hand it evaporates rapidly and the hand feels very cold. To change from liquid […]

To measure melting point from a cooling curve

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To measure melting point from a cooling curve The latent heat given out when a molten substance freezes to the solid state may be shown by the following experiment with naphthalene. Naphthalene is a white crystalline solid obtained from coal-tar. It has a pungent smell and is often used by gardeners as a soil fumigant. A test-tube containing naphthalene […]

Latent heat calculations

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Latent heat calculations Fig. 19.1 is a self-explanatory illustration of the heat required at various stages when 2 g of ice at – 6 °C are completely converted into steam at 100°C., I ( , The following data are used: