1. Two manufacturing plants need 1.0x104 kg of Al each week. One plant produces the Al from bauxite (Al2O3) and the other produces Al from recycled cans. Recovering Al via recycling consumes only 5% of the energy it takes to manufacture aluminum from bauxite. What is the dollar difference in energy costs for the two plants? For this problem you should only consider the Al energy costs. Assume each company pays $0.04 per kWhr and ?Hf for Al2O3 is -1676 kJ/mole. Finally, you will need this conversion factor: 1 watt-hr = 3600 J.
A. $163,928.
B. $6,902.
C. $6,557.
D. $3,451.
E. $3,279.
2. Over the course of a month, a typical family uses approximately 100 gallons of hot water per day. Assume that a month has 30 days, the price of electricity is $0.06 per kWhr, the heat capacity of water is 4.18 J oC-1 g-1, the water is heated from 20 to 70 oC, and that the water heater is 100% efficient. What is the monthly expense for heating water? (You will need the conversion factor for watt-hours given in problem #1 and you may need to look up other conversion factors.)
A. $9.50
B. $22.06
C. $39.61
D. $158.33
E. $661.83