Given the following information help a CHEM 102 student determine the initial te

Question

Given the following information help a CHEM 102 student determine the initial temperature, arn important piece of data they forgot to write down during the Calorimetry lab. Reaction: H2SO4(aq) + Ba(OH)2(aq) 2H2O(l) + BaSO4(s) 50.0 mL of 0.100 M sulfuric acid and 50.0 mL of 0.100 M barium hydroxide at the same initial temperature was mixed in a coffee cup calorimeter coming to a final temperature of 19.2C Assume density of solutions to be 1.00 g/mL and specific heat that of water. Also, assume sulfuric acid is limiting reactant. Grxn at 25°C =-100 kJ/mol H2SO4 Ba(OH)2 H20 BaSO4 20 123 70 132 Grxn.as-R7/nQ -100

Explanation / Answer

Neutralization reaction,

Ba(OH)2 + H2SO4 ---> BaSO4 + 2H2O

H2SO4 is the limiting reactant

From the given data,

dSo = dSo(products) - dSo(reactants)

       = (132 + 2 x 70) - (123 + 20)

       = 129 J/K-mol

Given,

dGo = -100 kJ/mol

using,

dGo = dHo - TdSo

with, T = 298 K

we get,

dHo = -100 + 298 x 0.129 = -61.56 kJ/mol

dH in J,

moles H2SO4 = 0.1 M x 0.05 L

so,

dHo = -61.56 x 1000 x 0.1 M x 0.05 L = -308 J

we know,

dH = -q = -mCpdT

let Ti be the initial temperature which the experimentalist forgot to note down, so-

-308 = -100 x 4.18 x (19.2 - Ti)

Ti = 18.5 oC  

The initial temperature of the system was 18.5 oC

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