Question

When 10.0 g KOH is dissolved in 100.0 g of water in a coffee-cup calorimeter, the temperature rises from 25.18 ˚C to 47.53 ˚C. Calculate the ∆Hrxn for the dissolution process. Assume that the solution has a specific heat capacity of 4.184 J/gK

Answer #1

∆Hrxn = -10.29kJ

∆Hsol= -57.74kJ/mol

Explanation

Heat absorbed by water is q

q = m × ∆T × C

m= mass of solution,100gm

∆T = temperature raise , 47.53℃ - 25.18℃ = 22.35℃

C = Heat capacity of solution , 4.184J/K mol

q = 110g × 22.35℃ × 4.184J/K mol

= 10286J

Heat absorbed by water =- Heat relaesed by dissolution

Therefore,

∆Hrxn = -10286J = -10.29kJ

Mass of KOH = 10.00g

Molar mass of KOH = 56.11g/mol

No of mole of KOH = 10g/56.11g/mol = 0.17822

∆Hsol = -10.29kJ/0.17822mol = -57.74kJ/mol

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H of this reaction. (Assume that the total
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