Latent heat

Effect of pressure on melting point. Regelation

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 …

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The refrigerator

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 …

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Vaporization when heat is supplied

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 …

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Fusion and vaporization in relation to the kinetic theory of matter

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 …

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Cooling by evaporation explained by the kinetic theory

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 …

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To measure melting point from a cooling curve

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 …

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Latent heat calculations

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: