Lime is a term that includes calcium oxide (CaO, also

Chapter 10, Problem 136AP

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Problem 136AP

Lime is a term that includes calcium oxide (CaO, also called quicklime) and calcium hydroxide [Ca(OH)2, also called slaked lime]. It is used in the steel industry to remove acidic impurities, in air-pollution control to remove acidic oxides such as SO2, and in water treatment. Quicklime is made industrially by heating limestone (CaCO3) above 2000°C:

Slaked lime is produced by treating quicklime with water:

The exothermic reaction of quicklime with water and the rather small specific heats of both quicklime [0 946 J/(g • ºC)] and slaked lime [1.20 J/(g • °C)] make it hazardous to store and transport lime in vessels made of wood. Wooden sailing ships carrying lime would occasionally catch fire when water leaked into the hold, (a) If a 500.0-g sample of water reacts with an equimolar amount of CaO (both at an initial temperature of 25°C), what is the final temperature of the product, Ca(OH)2? Assume that the product absorbs all the heat released in the reaction, (b) Given that the standard enthalpies of formation of CaO and H2O are −635.6 and −285.8 kJ/mol, respectively, calculate the standard enthalpy of formation of Ca(OH)2.