{20} Calcium oxide reacts with water to yield calcium hydroxide: CaO(s) + H 2 O

Question

{20} Calcium oxide reacts with water to yield calcium hydroxide:

CaO(s) + H2O (l) à Ca(OH)2 (aq)    H = - 83.4 kJ/mol

What will be the temperature of solution if 5.60 g of CaO is dissolved in 100.0 mL of water in a coffee-cup calorimeter with initial temperature of 21.0 oC?

Assume that specific heat of the solution in calorimeter is the same as for water, 4.184 J/g oC, density of solution is 1.00 g/mL, and calorimeter itself absorbs negligible amount of heat.

Atomic mass of Ca is 40.0 amu, atomic mass of O is 16.0 amu.

Explanation / Answer

m = 5.6 g of CaO

MW of CaO = 56.0774 g/mol

mol of CaO = mass/MW = 5.6/56.0774 = 0.0998619

now

mass of waer = 100 mL * 1 g/mL = 100 g

so:

total mol reacting:

0.0998619 mol of CaO reacts... find Q:

Q = 0.0998619*83.4 = 8.3284 kJ = 8328.4 J

Now...

Q = m*C*(Tf-Ti)

total mass = 100 g + 5.6 = 105.6 g

8328.4 = 105.6 * 4.184* (Tf-21)

Tf = 8328.4 / (105.6 * 4.184 )+ 21

Tf = 39.8497 °C

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