It takes 15 kWh (kilowatt-hours) of electrical energy to...

It takes $15 \mathrm{kWh}$ (kilowatt-hours) of electrical energy to produce 1.0 kg aluminum metal from aluminum oxide by the HallHeroult process. Compare this to the amount of energy necessary to melt $1.0 \mathrm{~kg}$ aluminum metal. Why is it economically feasible to recycle aluminum cans?

Key Concepts

Recycling Efficiency

Recycling aluminum, such as remelting used aluminum cans, requires much less energy than the electrolytic reduction process. The energy needed to change aluminum from its solid state to molten form is significantly lower than that required to extract aluminum from its ore, making the recycling process both economically and environmentally beneficial.

Energy Consumption in Metallurgy

A key consideration in metallurgy is the difference in energy input between producing metals from raw ores and processing recycled metals. By comparing these energy requirements, industries can identify cost-effective practices, with recycling offering major savings in energy consumption and reduced production costs.

Electrolytic Production (Hall?Héroult Process)

This process is used to produce aluminum from aluminum oxide and is extremely energy intensive because it relies on high-temperature electrolysis to break the strong ionic bonds in the oxide. The large amount of electrical energy required in this process makes the primary production of aluminum very costly in energy terms.

Transcript

00:01 We are told that it takes 15 kilowatt hours of electrical energy to produce 1 .0 kilograms of aluminum.

00:08 We want to compare this to the energy requirement to melt 1 .0 kilograms of aluminum.

00:13 We are given the value for the enthalpy of fusion for aluminum, which we use in order to determine the amount of energy required to melt 1 .0 kilograms of aluminum in units of kilojoules.

00:26 So in order to compare these two energy requirements, we should have them in the same units.

00:30 And so we should begin by converting the 15 kilowatts of energy that is required to produce 1 .0 kilograms of aluminum into kilojoules.

00:39 Once we have consistent units, we can compare the two energy requirements to help us explain why it is more economically feasible to recycle aluminum than it is to produce aluminum.

00:50 So we know that it takes 15 kilowatt hours of energy to produce 1 .0 kilograms of aluminum, so we can convert this into kilojoules of energy.

01:01 We know that one kilowatt is equal to 1 ,000 watts, and we know that 1 watt is equal to 1 jule per second.

01:14 We have units of hours in the numerator from kilowatt hours, and we have seconds in the denominator from converting watts to joules per second.

01:23 So we can cancel off those time units by saying that there are 3 ,600 seconds per hour.

01:30 And now we can convert that final energy unit from joules to kilojoules by dividing by a thousand joules...

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