When 0.500 g CaO(s) is added to 140. g H2O at 23.1 °C in a coffee cup calorimeter, this reaction occurs.
CaO(s)+H2O(l)-->Ca(OH)2 (aq) and enthalpy = -81.9 kj/mol
Calculate the final temperature of the solution. The specific heat capacity of water is 4.184
Hrxn = -81.9 kJ/mol
mol of CaO = mass/MW = 0.5/56.0774 = 0.0089162479 mol of CaO
mol of H2O = mass/MW = 140/18 = 7.777 mol of H2O
since CaO is limiting
then
0.0089162479 mol should be used
Q = nHRxn = 0.0089162479 *-81.9 = -0.73024070301kJ = -730.240 kJ
note that this is EXOthermic, meaning this will increase the temperature of the system (i.e.calorimeter)
then
Q = m*Cp*dT
Q = 730.240 J
mT = 0.5+140 = 140.5 g
Cp = 4.184J/gC (approx of water)
dT = Tf- 23.1
Q = m*Cp*dT = (140.5)(4.184)(Tf-23.1) = 730.240
(140.5)(4.184)(Tf-23.1) = 730.240
Tf = 730.240 /(140.5*4.184) + 23.1 = 24.3422
Tf = 24.3422 °C
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