Calcium chloride dihydrate, CaCl₂·2H₂O, is a common component of one-time chemical heaters because it dissolves exothermically in water:
CaCl2⋅2H2O(s)→Ca2+(aq)+2Cl−(aq)+2H2O(l)
The enthalpy of dissolution under the conditions of interest is ΔHdiss=−81.3kJ mol−1.
A foil packet contains a 30.0g granular mixture that is 70.0% by mass CaCl₂·2H₂O, the remainder being inert material that does not dissolve.
Immediately after activation, the mixture is poured into 150g of water initially at 25.0∘C in an insulated container. Assume the specific heat capacity of the resulting solution is the same as that of pure water, 4.18J g−1∘C−1, and that no heat is lost to the container or surroundings.
(a) Determine the mass (in grams) and the amount (in moles) of CaCl₂·2H₂O that actually dissolves.
(b) Calculate the heat q (in kilojoules) released by the dissolution process.
(c) Using your result from part (b), compute the final temperature of the water after the salt has completely dissolved.
(d) Discuss two realistic experimental factors that could cause the actual observed temperature change to differ from the value calculated in part (c).