A sealed, well-insulated calorimeter contains 50.0 g of ice at 0 °C. An electric…
PHYSICS · Multi-part · A Level · Physics · Further mechanics and thermal physics · Further mechanics and thermal physics
Problem
A sealed, well-insulated calorimeter contains 50.0 g of ice at 0 °C. An electric heater is briefly switched on, supplying enough energy to convert all of the ice to liquid water at 0 °C. After the heater is turned off, the calorimeter is placed in contact with a refrigerated bath held at 0 °C until the same 50.0 g of water has completely frozen back to ice at 0 °C.
(a) For the melting step, state the algebraic sign of q for the water system and justify your answer in terms of the direction of energy transfer.
(b) Explain why the temperature of the water remains constant at 0 °C while the phase change occurs even though energy is being transferred.
(c) The molar enthalpy of fusion of water at 0 °C is 6.01 kJ mol−1, and the molar mass of water is 18.0 g mol−1. Calculate the numerical value (magnitude only) of q for the melting of the 50.0 g sample. Include appropriate units in your answer.
(d) Determine both the sign and the numerical value of q for the subsequent freezing step. Compare this quantity with the value obtained in part (c) and account for any similarities or differences.