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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]

Verified Answer :

vince876
  1. 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.

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. To determine number of moles of copper:

Given mass=30.1 grams

Molar mass= 63.55 g/mol

\(\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}\\\\ \text{Number of moles}=\frac{30.1}{63.55} =0.4736 \text { moles}\)

Thus, the number of moles of copper is 0.4736.


71. Calculating the amount of heat released:

ΔH( heat released) = m Cp(ΔT)

= 30.1g(0.385 J/g. K)(33-19)K

ΔH= 162.23J

Thus, the amount of heat released is 162.23 J.


72. Copper is chemically less active than iron.

Copper does not displace iron from its solution since it is less reactive than iron. A more reactive metal displaces a less reactive metal from its solution.

Learn more:

brainly.com/question/25548593

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