Question

What is the heat of dissolution in kj/g of an unknown salt if 1.300g raises the temperature of 51.055 g if purified water by 0.452 C. Assume the specific heat of the solution is 4.18j/c *g.

Answer 1

Ans. Given,

            Mass of salt used = 1.300 g

            Mass of water = 51.055 g

            Increase in temperature = 0.452⁰C

# The amount of energy required to raise water’s temperature is given by-

q = m s dT                           - equation 1

Where,

q = heat gained

m = mass

s = specific heat of water

dT = Final temperature – Initial temperature

Putting the values in equation 1-

            q = 51.055 g x (4.18 J g^-10C^-1) x 0.452⁰C

            Hence, q = 96.4612748 J = 0.09646 kJ

Therefore, dissolution of 1.300 g salt is associated with release of 0.09646 kJ energy. This energy was absorbed by water sample to increase its temperature by 0.452⁰C.

# Now,

Heat of dissolution of salt = Heat released in kJ / Mass of salt in kg

                                                = 0.09646 kJ / 1.300 g

                                                = 0.0742 kJ / g

Since, heat is being released during dissolution, a (-ve) sign shall be prefixed with the value to denote the same.

Hence, heat of dissolution of salt = - 0.0742 kJ / g