   Chapter 18, Problem 131AE

Chapter
Section
Textbook Problem

# It takes 15 kWh (kilowatt-hours) of electrical energy to produce 1.0 kg aluminum metal from aluminum oxide by the Hall-Heroult process. Compare this to the amount of energy necessary to melt 1.0 kg aluminum metal. Why is it economically feasible to recycle aluminum cans? [The enthalpy of fusion for aluminum metal is 10.7 kJ/mol (1 watt = 1 J/s).]

Interpretation Introduction

Interpretation:

The requirement of electrical energy for the production of Aluminum from Aluminum oxide is given. The comparison between the energy required for producing Aluminum from Aluminum oxide and the energy for melting Aluminum and the reason behind the economical feasibility of recycling Aluminum cans is to be stated.

Concept introduction:

For melting of any substance some specific amount of heat is required. Therefore, the amount of heat that is required for melting one mole of substance and that too at its melting point is called the heat of fusion.

To determine: The comparison between the energy required for producing Aluminum from Aluminum oxide and the energy for melting Aluminum and the reason behind the economical feasibility of recycling Aluminum cans.

The amount of electrical energy required to produce Aluminum from Aluminum oxide is 54×106J .

The amount of energy required to melt Aluminum metal is 395.9×103J .

The energy for melting Aluminum is lower than the energy required for producing Aluminum from Aluminum oxide.

The requirement of lower energy for melting Aluminum than required to produce Aluminum from Aluminum oxide makes it an economically feasible process.

Explanation

Given,

The amount of electrical energy produced is 15kwh .

The enthalpy of fusion for Aluminum is 10.7kj/mol

The amount of metal produced is 1.0kg .

The conversion of kg to g is done as,

1kg=1000g

The conversion of kj to J is done as,

1kJ=1000J

Conversion of 10.7kJ to J is done as,

10.7kJ=10.7×1000J=10.7×103J

The conversion of kwh to wh is done as,

1kwh=1000w

Conversion of 15kwh to wh is done as,

15kwh=15×1000wh=15×103wh

The conversion of h to s is done as,

1h=3600s

The conversion of wh into J is done as,

1watt=1Js

Rearrange the equation to obtain the value of 1J ,

1J=1watts

The conversion of wh to ws is done as,

1wh=1w×3600s=3600ws

Conversion of 15kwh to ws is done as,

15×103wh=15×103w×3600s=54×1

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