Heat of Transformation

Heat of Transformation - The heat required to change the...

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Heat of Transformation When heat is added to a solid or a liquid, the temperature of the sample does not necessarily rise. During a phase change (melting, boiling) heat is added to the sample without an increase in temperature. The amount of heat transferred per mass unit during a phase change is called the heat of transformation (symbol L) for the process. The amount of heat needed/released is given by where m is the mass of the sample. Problem 28P What mass of steam of 100 ϒ C must be mixed with 150 g of ice at 0 ϒ C, in a thermally insulated container, to produce liquid water at 50 ϒ C ? We start with calculating the heat required to transform 150 g of ice at 0 ϒ C to 150 g of liquid at 0 ϒ C. The heat of transformation of water is 333 kJ/kg (see Table 20-2, page 555). The transformation of ice into water therefore requires a total heat given by
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Unformatted text preview: The heat required to change the temperature of 150 g of water from 0 ϒ C to 50 ϒ C is given by The total heat that needs to be added to the system is therefore equal to 81.5 kJ. This heat must be supplied by the steam. Heat will be released when the steam is transformed into liquid, The heat of transformation for this process is 2260 kJ/kg. Suppose the mass of the steam is m. The total heat released in the conversion of steam into water is given by The heat released when the steam cools down from 100 ϒ C to 50 ϒ C is given by The total heat released by the cooling of the steam is therefore equal to 2470 m kJ. The total heat required is 81.5 kJ, and we therefore conclude that the mass of the steam must be equal to 33 g....
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