In an industrial Hall–Héroult cell used to produce aluminum

CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry

Problem

In an industrial Hall–Héroult cell used to produce aluminum, a steady current of

100\,\text{kA}

is maintained for a continuous

24.0\,\text{h}

period. The cell operates at an average potential difference of

4.50\,\text{V}

. At the end of the day,

6.50\times10^2\,\text{kg}

of aluminum metal is removed from the cell. (a) Calculate the theoretical mass of Al that should be produced during the

24.0\,\text{h}

interval. (b) Determine the percent yield based on the actual mass obtained. (c) Calculate the total electrical energy (in

\text{kWh}

) delivered to the cell during the

24.0\,\text{h}

period. (d) The standard energy required to reduce

\text{Al}^{3+}

\text{Al(l)}

under the operating conditions is

851\,\text{kJ}\,\text{mol}^{-1}

of Al produced. Using this value and your answer to part (a), calculate the percentage of the input electrical energy that is stored as chemical energy in the aluminum produced. (e) Discuss two operational factors that could account for the difference between the mass-based percent yield in part (b) and the energy efficiency calculated in part (d).

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