To find the final temperature of the product, Ca(OH)2, we can use the principle of conservation of energy.
First, let's calculate the heat released in the reaction:
1 mol of CaO reacts with 1 mol of H2O to produce 1 mol of Ca(OH)2.
The molar heat of reaction for the formation of Ca(OH)2 is -65.2 kJ.
Since the reaction is exothermic, the heat released in the reaction is -65.2 kJ.
Next, we need to calculate the heat absorbed by the water:
q = mcΔT
where q is the heat absorbed, m is the mass of water (500 g), c is the specific heat capacity of water (4.18 J/gC), and ΔT is the change in temperature.
Since the initial temperature of both the water and CaO is 25°C, and assuming the final temperature is T°C, the change in temperature for both substances is T - 25.
Setting the heat released equal to the heat absorbed:
-65.2 kJ = (500 g)(4.18 J/gC)(T - 25)
-65,200 J = (2090 J/C)(T - 25)
Now, solve for T:
T - 25 = -65,200 J / 2090 J/C
T - 25 = -31.25
T = -6.25°C
Therefore, the final temperature of the product, Ca(OH)2, is -6.25°C.
Lime is a term that includes both calcium oxide (CaO, also called quicklime) and calcium
hydroxide [Ca(OH)2, also called slaked lime]. It ranked 6th among the top 50 industrial chemicals
produced in the United States in 1988 (32.3 billion pounds). Lime is one of the oldest chemicals
know. It has been used as a building material since 1500 B.C. The largest consumer of lime is
the steel industry, which uses the basic properties of lime to remove acidic impurities in iron ores. Lime is also used in air-pollution control and water treatment (to neutralize acids) and to alesser extent in the food industry.
Industrially quicklime is prepared by by heating limestone (CaCO3) above 2000oC:
CaCO3(s) CaO(s) + CO2(g) ΔHo = 177.8 kJ
Slaked lime is produced by treating quicklime with water:
CaO(s) + H2O(s) Ca(OH)2(s) ΔHo = -65.2 kJ
Quicklime is a white solid that melts at 2570 oC. 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.oC) made the storage and transport of the substance hazardous in the old days. Wooden
sailing ships would occasionally catch fire when water leaked into the hold containing lime.
A 500 g sample of water is reacted with an equimolar amount of CaO (both at an initial
temperature of 25oC). What is the final temperature of the product, Ca(OH)2?
Assume that the product absorbs all the heat released in the reaction.
1 answer