chemistry/calorimetry (please help if you can)

Question

A generic solid, X, has a molar mass of  69.6 g/mol. In a constant‑pressure calorimeter, 18.8 g of X is dissolved in 401 g of water at 23.00 °C.

X(s) → X (aq)

The temperature of the resulting solution rises to 27.80°C. Assume the solution has the same specific heat as water, 4.184 J/(g·°C), and that there is negligible heat loss to the surroundings.

a. How much heat was absorbed by the solution? (in kJ)

b. What is the enthalpy of the reaction? (in kJ/mol)

Answer 1

As the temperature of the water increased, you can calculate the heat evolved by the dissolving of X by using the relation Q = c x m x Δt where c is specific heat of water (4.184 J/g-deg), m is mass of water in grams, Δt is change in temperature of the water in ºC.

Q = 4.184J/g-ºC x 401 g x (27.80 - 23.00) ºC = 8050 J or 8.05 kJ

moles of x = 1/69.6 mol/g x 18.8 g X = 0.270 mol X

ΔH = 8.05 kJ/0.270 mol = 29.8 kJ/mol