Freezing molar heat

Using these data for water, the molar heat capacity is 18.02 cal/mol K (approximately 75.40 J/mol K). Note that the deviations from this average are all less than 1 percent between the freezing and boiling points. The point being made is that the heat capacity may depend (slightly) on temperature, but is a reasonably stable value making it possible to consider heat capacity as a constant, as it is in this book. 

By means of equation (38.12), it is possible to determine the activity of the solvent ai in any solution, from a knowledge of the depression of the freezing point, and certain other properties. The procedure may be illustrated by a consideration of aqueous solutions. With water as solvent, Lo is the molar heat of fusion of ice at 0 C and 1 atm. pressure, viz., 1438 cal. mole further, Cp)i for water may be taken with sufficient accuracy as 18 and (Cp). for ice as 9 cal. deg. mole S so that ACp is 9 cal. deg. " mole Inserting these values into equation (38.12), with To equal to 273.16 K,... 

Since Lo is the molar heat of fusion of the pure solvent at its fi-cczing point, at 1 atm., ijroMi/lOOOZ/o is exactly equivalent to the molal freezing point depression constant X, as defined by equation (36.12) hence equation... 

Heat of soHdification The amount of heat that must be removed from a specific amount of a liquid at its freezing point to freeze it with no change in temperature usually expressed in J/g or kJ/mol in the latter case it is called the molar heat of solidification. 

How much heat is evolved if 225 g of liquid water freeze at 0°C The molar heat of fusion... 

How much heat energy is evolved as 250 g of liquid ammonia freeze to form solid ammonia at its normal freezing point The molar heat of fusion of ammonia is 5.65 kj/mole. The molar mass of ammonia is 17.0 g. State the answer in terms of a change in heat energy, AH. 

Another application of a power series in physical chemistry is in the discussion of colligative properties (freezing-point depression, boiling-point elevation, and osmotic pressure). If is the mole fraction of solvent, AyapHm is the molar heat of vaporization of the solvent, Tq is the pure solvent s boiling temperature, and T is the solution s boiling temperature, it is shown in physical chemistry textbooks that... 

Intermolecular forces Intramolecular forces Dipole-dipole attraction Hydrogen bonding London dispersion forces Normal boiling point Heating/cooling curve Normal freezing point Molar heat of fusion Molar heat of vaporization... 

A similar analysis with L/ replaced by L , the molar heat of vaporization of the pure solvent, relates the boiling-point elevation for nonvolatile solutes to the activity coefficients and the solution molecular weight of the solute. Although more accurate results are obtained by use of freezing-point determination, the boiling-point method is often used when only a small quantity of the solution is available. 

Consider the following facts Water freezes spontaneously at — 5°C and 1 atm, and ice has a more ordered structure than liquid water. Explain how a spontaneous process can lead to a decrease in entropy. Ammonium nitrate (NH4NO3) dissolves spontaneously and endothermically in water. What can you deduce about the sign of A5 for the solution process Calculate the equilibrium pressure of CO2 due to the decomposition of barium carbonate (BaC03) at 25°C. (a) Trouton s rule states that the ratio of the molar heat of vaporization of a liquid (AT/yap) to its boiling point in kelvins is approximately 90 J/K mol. Use the following data to show that this is the case and explain why Trouton s rule holds tme ... 

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