Chemistry -- Enthalpy?

Question

15.3g NaNO3 dissolved in 256g Water in a coffee-cup calorimeter. Temperature of water falls from 25.00 degrees C to 21.56 degrees C. What is the enthalpy change when one mol sodium nitrate is dissolved in water. Specfic Heat capacity of water = 4.184J/g*k

Please explain thanks!

Answer 1

Q = mc(Tf-Ti)
Delta H = kj / mol

Q = (256 g)(4.184 j/gC)(25.00 C -21.56 C)

This will give the amount of heat absorbed in joules.
Convert from j to kj by dividing the above answer by 1000.

Delta H is calculated by taking the kj from above and dividing by the number of moles of NaNO3 present.

NaNO3 = 23 + 14 + 48
Divide 15.3 g by the total from above to get moles NaNO3.