When pure sulphuric acid dissolves in water, a large amount of energy is release
ID: 537437 • Letter: W
Question
When pure sulphuric acid dissolves in water, a large amount of energy is released. To measure it, 175 grams of water was placed in a coffee-cup calorimeter and chilled to 10.0C. Then 4.90 grams of sulphuric acid (H2SO4; mm=98 g/mol) also at 10.0C was added to it and rapidly mixed. The temperature rose rapidly to 14.9C. Assume that the specific heat is the same as the water and that all the heat evolved is absorbed by water.
A) Determien the q value for this reaction in kJ. Answer: 3.6 kJ
B) Determine the Hdissolution in kJ/mole of H2SO4. Answer: -71 kJ/mol
I know how to do part A but I'm not sure what the formula for part B is. I got a positive answer.
Explanation / Answer
(a) m, mass of water = 175 g = 0.175 Kg
Cp = 4.185 Kg/Kg. K
T1 = 10°C = 283 K
T2 = 14.9 °C = 287.9 K
q = m * Cp * T = m * Cp *(T2 - T1) = 0.175 * 4.185 * (287.9 - 283) = 3.59 KJ = 3.6 KJ
(b) mass of sulphuric acid = 4.9 g
molar mass of sulphuric acid = 98 g/mol
no of moles = 4.9/98 = 0.05 mol of sulphuric acid
q = -H'diss = -3.59 KJ
Hdiss = H'diss/ no of moles = 3.59 /0.05 = 71.8 KJ/mol
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