inal tem- capacity I,O(l) to 14-58. Calcium hydroxide, Ca(OH) (s), is prepared y

Question

inal tem- capacity I,O(l) to 14-58. Calcium hydroxide, Ca(OH) (s), is prepared y by adding calcium oxide (lime), CaO(s), to water It is important to know how much energy is as heat in order to provide for adequate cooling. A 10.0-gram sample of Cao () is added to 1.00 liter of water in a calorimeter with a total heat capacity of to It is importa evolved m metal contact 4.37 k.K1. -1.mol) is 2.70 K. e of the the sur- The observed increase in temperature is 270 K. Calculate the value of Hoxn for the pro- duction of 1.00 mole of Ca(OH)2 (s). The equation describing the reaction is CaO (s) + H20 (l) Ca (OH)2(s) t 25.0°C C. The 14-59. A 5.00-gram sample of potassium chloride is 48.1°C. dissolved in 1.00 liter of water in a calorimeter that has a total heat capacity of 4.51 kJ·K". The tempera-

Explanation / Answer

14-58 : dHorxn = dT x Cp/moles

moles of CaO = 10 g/56.0774 g/mol = 0.178 mols

dT = 2.70 K

Cp = 4.37 kJ/K

So,

dHorxn = 2.70 x 4.37/0.178 = 66.286 kJ/mol

14-59 : molar heat of solution of KCl = dT x Cp/moles

moles of KCl = 5 g/74.5513 g/mol = 0.067 mol

dT = 0.256 K

Cp = 4.51 kJ/K

So,

molar heat of solution = 0.256 x 4.51/0.067 = 17.232 kJ/mol

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