A reusable commercial cold pack relies on the dissolution of sodium thiosulfate pentahydrate, Na₂S₂O₃·5H₂O, in water. The enthalpy of dissolution for this compound at the temperature of use is reported as ΔHdiss=+20.0kJ mol−1.
A particular cold-pack pouch contains 0.250kg of solid Na₂S₂O₃·5H₂O sealed in a thin plastic bag that is broken just before use, allowing the solid to mix completely with liquid water in an insulated outer packet.
(a) Calculate the number of moles of Na₂S₂O₃·5H₂O present in the pouch.
(b) Determine the quantity of heat q (in kilojoules) absorbed or released by the dissolution of this mass of Na₂S₂O₃·5H₂O. State clearly whether the surroundings become warmer or cooler.
(c) Suppose the heat calculated in part (b) is drawn entirely from 200g of water initially at 25.0∘C. Using cH2O=4.18J g−1∘C−1, estimate the final temperature of the water. Assume no energy loss to the surroundings.