A hand-warmer contains a supersaturated aqueous solution of sodium acetate. When a metal disk inside the pouch is flexed, the sodium acetate crystallizes rapidly, and the temperature of the pouch rises from 20.0∘C to 54.0∘C within 30 s. Assume the mass of the solution is 75.0g and its specific heat capacity is 3.7Jg−1∘C−1. Heat losses to the environment are negligible during the 30 s interval.
(1) Calculate the quantity of heat transferred between the crystallizing system and the surroundings during the 30 s interval. Include units and the correct sign.
(2) Classify the crystallization process as endothermic or exothermic and justify your answer with reference to both the calculated heat and the temperature change.
(3) Suppose the hand-warmer is now activated inside an insulated mitten rather than in open air. Predict qualitatively (no calculation required) how the final recorded temperature change of the pouch would compare with the 34∘C change observed in open air. Explain your reasoning in terms of heat exchange with the surroundings.