Phase change hand warmer. Sodium acetate in solution has a freezing point at 58°C and a...

Phase change hand warmer. Sodium acetate in solution has a freezing point at 58°C and a latent heat of freezing of 210 kJ/kg, but a solution of this compound can remain in liquid form at much lower temperatures. This condition, known as super cooling, occurs in substances that form specific crystalline structures when in solid form. Such systems need a seed crystal to start the solidification process. Reusable hand warmers like that in Figure P14.63 are sold in sporting goods stores and contain about 60 g of sodium acetate solution. Clicking a piece of metal in the solution generates sound waves. The resulting increase in pressure causes a seed crystal to form, leading to full crystallization of the hand warmer within 4 s. Suppose a hand warmer is activated on a particularly cold morning when the solution was at a temperature of 10°C. Phase transitions occur at constant temperature, and the liquid is mostly water. (a) Calculate the heat generated by the phase transition. (b) What is the fi nal temperature of the hand warmer?