Question

A coffee cup calorimeter is prepared, containing 100.000 g of water (specific heat capacity = 4.184 J/g K) at initial temperature 80.000 C. A salt weighing 5.556 g is quickly added. The salt has a molar mass of 470.659 g/mol. The final temperature of the solution is 11.517 C. Assume no heat loss to the surroundings. Assume the specific heat capacity of the solution is equal to that of pure water, and that the mass of the solution is equal to the mass of the solid plus the mass of water in the calorimeter. What is the molar heat of solution for the salt, in kJ/mol?

Answer 1

Answer:  Molar heat of solution for the salt is 2563 kJ/mol

Explanation:

Let the heat absorbed during reaction be q.

$q=m\times c\times \Delta T$

q = Heat gained by solution = ?

m = Mass of water + mass of salt = 100.000 g + 5.556 g = 105.556 g

c = Heat capacity of solution =  Heat capacity of water = 4.184 J/g°C

Change in temperature = ΔT = (80.000°C-11.517°C) = 68.483°C

$q=105.556g\times 4.184J/g^0C\times 68.483^0C=30245.3J$

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}=\frac{5.556g}{470.659g/mol}=0.01180moles$

0.01180 moles of salt absorbs = 30245.3 J

1 mole of salt absorbs  =$\frac{30245.3J}{0.01180}\times 1=2563161.02J=2563kJ$ of heat

Thus molar heat of solution for the salt in kJ/mol is 2563