Question

A student made a copper bracelet by hammering a small copper bar into the desired shape. The bracelet has a mass of 30.1 grams and was at a temperature of 21°C in the classroom. After the student wore the bracelet, the bracelet reached a temperature of 33°C. Later, the student removed the bracelet and placed it on a desk at home, where it cooled from 33°C to 19°C. The specific heat capacity of copper is 0.385 J/g•K.
69 Explain, in terms of heat flow, the change in the temperature of the bracelet when the student wore the bracelet. [1]

70 Determine the number of moles of copper in the bracelet. [1]

71 Show a numerical setup for calculating the amount of heat released by the bracelet as it cooled on the desk. [1]

72 Explain, in terms of chemical activity, why copper is a better choice than iron to make the bracelet. [1]

Answer 1

69. The student's skin was obviously warmer than the initial temperature of the bracelet. According to the second law of thermodynamics, heat transfers from a higher temperature to a lower temperature hence heat transfers from the student's skin to the bracelet warming up the bracelet. 

70. moles of copper=mass of copper/molar mass of copper
=30.1g/(63.55g/mol)= 0.4736 moles Cu

71. Delta H( heat released) = mCp(deltaT) = 30.1g(0.385 J/gK)(33-19)K = 162.23J

72. Copper is chemically less active than iron.