Question

Practice example a b

531 12-2 Some Properties of Liquids when ydrogen bonds;: and when to increase with the molecular and the of a gas neverse of uid is called condensation s always negative. Condensation is is always positive bums produced by a given mass c ster) are much mone severe than burns produced by the same Hot water cens by releasing heat as it cools. Steam antity of heat when it condenses to liquid water, followed by e liquid mol e molecules rgetic than of heat as the hot water cools. Estimating the Heat Evolved in the Condensation of Steam of steam obtained at the normal boiling point of water was allowed to condense on a slightly ases. The uegdata from Table 124 estimate the quanity of heat evolved Why is the result only an estimate? iquid at describe the steam sample a bit more precisely. Steam is water vapor, H:O(g): and when in equilit- ist liquid water at its normal boiling point, the steam is at 1.000 atm pressure. seen in a volume of gas (0.750 L) at a fixed temperature (100.00 C) and pressure (1,000 atm), and so we 1.000 atm x 0.750L uation to calculate the number of moles of H:0(g). That is, in the each gen nds PV RT 0.08206 L atm mol K1 x (273.15 +100.00) K - 0.0245 mol condensation of the H,O(g) to be the negative of the value of AvapH Ona molar basis HO given basis, estimate the enthalpy of in st en in Table 12.4, that is, -44.0kj mol"1, For the 0.0245 mol sample of steam, AzndH-0.0245 mol × (-44.0 kJ morりー -1.08 kJ he result is only an estimate for two reasons: (1) Δο๐ndH, like Δ sed was for 298 K, whereas it should have been for 373 K, a value that was not given. (2) The condensed d water was at a temperature lower than 373 K ("slightly cooler surface"). An additional small quantity of hat was liberated as the condensed steam cooled to that lower temperature. vapH, is temperature dependent. The value RACTICE EXAMPLE A: How much heat is required to vaporize a 2.35 g sample of diethyl ether at 298 K? ACTICE EXAMPLE B: Calculate a more accurate answer to Example 12-2 by using AvapH 40.7 k) mol" for aterat 100。C, 85.0°C as the temperature of the surface on which the steam condenses, and 421 J g-1 oCi as deaverage specific heat of H 0(1) in the temperature range 85 to 100 °C Pressure

Answer 1

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