Chemistry and Chemical Reactivity - Solutions, summaries, and outlines. 2022 updated

INTERCHAPTER The Chemistry of Fuels and Energy Resources



The Chemistry of Fuels and Energy Resources
INSTRUCTOR’S NOTES

This section on fuels and energy sources is a natural progression from the study of thermodynamics applied to
chemistry in Chapter 5. The high degree of public interest in these topics should stimulate students to study the
topic. This section includes a wide range of subjects and multiple aspects of each. The content will give serious
students a great deal of authoritative information for them to consider.

SUGGESTED DEMONSTRATIONS
1. Fuel Cells
• Zerbinati, O. “A Direct Methanol Fuel Cell,” Journal of Chemical Education 2002, 79, 829.
2. Biosources of Energy
• Choi, M. M. F.; Wong, P. S.; Yiu, T. P. “Application of a Datalogger in Observing Photosynthesis,”
Journal of Chemical Education 2002, 79, 980.




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,INTERCHAPTER The Chemistry of Fuels and Energy Resources



SOLUTIONS TO STUDY QUESTIONS
1. CH4(g) + H2O(g) → 3 H2(g) + CO(g)
1 mol CH4 3 mol H2 2.016 g
100. g · · · = 37.7 g H2
16.04 g 1 mol CH4 1 mol H2

CH2(A) + H2O(g) → 2 H2(g) + CO(g)

1 mol CH2 2 mol H2 2.016 g
100. g · · · = 28.7 g H2
14.03 g 1 mol CH4 1 mol H2

C(s) + H2O(g) → H2(g) + CO(g)
1 mol C 1 mol H2 2.016 g
100. g · · · = 16.8 g H2
12.01 g 1 mol CH4 1 mol H2

2. Burning gasoline releases 47 kJ/g, burning C releases 32.8 kJ/g, and burning H2 releases 119.9 kJ/g.
fraction of C in gasoline + fraction of H in gasoline = 1
47 kJ/g = 32.8 kJ/g (fraction of C in gasoline) + 119.9 kJ/g (fraction of H in gasoline)
47 kJ/g = 32.8 kJ/g (x) + 119.9 kJ/g (1 – x)
x = 0.84
84% C and 16% H

453.6 g 33 kJ
3. 70. lb · · = 1.0 × 106 kJ
1 lb 1g

5.45 × 103 kJ 1 mol C8 H18
4. · = 47.7 kJ/g
1 mol C8 H18 114.2 g

5.45 × 103 kJ 1 mol C8 H18 0.688 g 1000 mL
· · · = 3.28 × 104 kJ/L
1 mol C8 H18 114.2 g 1 mL 1L

5. Burning 70. lb of coal produces 1.0 × 106 kJ/day (see problem 3).
4 qt 1L 1000 mL 0.8 g 43 kJ
7.0 gal · · · · · = 9 × 105 kJ
1 gal 1.06 qt 1L 1 mL 1 g

Burning 7.0 gal of oil produces about 14% less heat than burning 70. lb of coal.

6. Al2O3(s) → 2 Al(s) + 3/2 O2(g)
ΔHº = ΔfHº[Al2O3(s)] = –[1 mol · (–1675.7 kJ/mol)] = 1675.7 kJ
454 g 1 mol Al 1675.7 kJ
1.0 lb · · · = 1.4 × 104 kJ
1 lb 27.0 g 2 mol Al

Energy to recycle 1.0 lb aluminum = (1/3)(1.4 × 104 kJ) = 4.7 × 103 kJ
7. (a) Ethanol: C2H5OH(A) + 3 O2(g) → 3 H2O(A) + 2 CO2(g)

ΔfHº[O2(g)] = 0 kJ/mol


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,INTERCHAPTER The Chemistry of Fuels and Energy Resources



∆rH° = 2 ΔfHº[CO2(g)] + 3 ΔfHº[H2O(A)] – ΔfHº[C2H5OH(A)]

∆rH° = 2 mol (–393.509 kJ/mol) + 3 mol (–285.83 kJ/mol) – 1 mol (–277.0 kJ/mol)
∆rH° = –1367.5 kJ

–1367.5 kJ 1 mol C2 H5 OH 1000 g
· · = -29,684 kJ/kg
1 mol C2 H5 OH 46.0688 g 1 kg

Isooctane: C8H18(A) + 25/2 O2(g) → 9 H2O(A) + 8 CO2(g)

ΔfHº[O2(g)] = 0 kJ/mol
∆rH° = 8 ΔfHº[CO2(g)] + 9 ΔfHº[H2O(A)] – ΔfHº[C8H18(A)]

∆rH° = 8 mol (–393.509 kJ/mol) + 9 mol (–285.83 kJ/mol) – 1 mol (–259.3 kJ/mol)

∆rH° = -5461.2 kJ

-5461.2 kJ 1 mol C8 H18 1000 g
· · = -47,809 kJ/kg
1 mol C8 H18 114.230 g 1 kg

(b) (l000.0 g C2H5OH)(1 mol C2H5OH/46.0688 g C2H5OH)(2 mol CO2/mol C2H5OH) = 43.395 mol CO2

(1000.0 g C8H18)(1 mol C8H18/114.230 g C8H18)(8 mol CO2/mol C8H18) = 70.034 mol CO2

Isooctane produces more mol CO2 per kilogram.
(c) Isooctane produces more energy per kilogram and is better in terms of energy production, but it
produces more greenhouse gas per kilogram.

1 J/s 1 kJ 3600 s 24 hr
8. 100 W · · · · = 8640 kJ/day
1 W 1000 J 1 hr 1 day

8640 kJ 1 g coal
· = 260 g coal
1 day 33 kJ

940 kW-hr 1 kJ/s 3600 s
9. · · = 3.4 × 106 kJ/year
1 year 1 kW 1 hr

940 kW-hr 1 year $0.08
· · = $6.27/month
1 year 12 months 1 kW-hr

10. Non-renewable: The energy source is not replenished after it is consumed.
coal, natural gas
Renewable: The energy is derived in some way from the Sun’s energy, so it is replenished after use.
solar energy, geothermal energy, wind power

11. 2 CH3OH(A) + 3 O2(g) → 2 CO2(g) + 4 H2O(A)

∆rH° = 2 ΔfHº[CO2(g)] + 4 ΔfHº[H2O(A)] – 2 ΔfHº[CH3OH(A)]



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, INTERCHAPTER The Chemistry of Fuels and Energy Resources



∆rH° = 2 mol (–393.509 kJ/mol) + 4 mol (–285.83 kJ/mol) – 2 mol (–238.4 kJ/mol)
∆rH° = –1453.5 kJ
1453.5 kJ 1 mol CH3OH 0.787 g 1000 mL 1 kW 1 hr
· · · · · = 4.96 kW-hr/L
2 mol CH3OH 32.042 g 1 mL 1.0 L 1 kJ/s 3600 s

12. C8H18 (5.45 ×103 kJ/mol)(1 mol/114.23 g) = 47.7 kJ/g

CH4 (882 kJ/mol)(1 mol/ 16.04 g) = 55.0 kJ/g

C(s) (393.5 kJ/mol)(1 mol/12.011 g) = 32.8 kJ/g

H2 (241.83 kJ/mol)(1 mol/2.01594 g) = 119.96 kJ/g

H2 > CH4 > C8H18 >C(s)

2.6 × 107 J 1 kJ
13. 325 m · 50.0 m · 2
· = 4.2 × 108 kJ/day
m 1000 J

24 h 1.0 × 106 J 1 kJ
14. 1 day · · · 3 = 2.4 × 104 kJ/day
1 day 1h 10 J

103 J 1 kW-h
2.4 × 104 kJ/day · · = 6.7 kW-h/day
1 kJ 3.60 × 106 J

1 gal 4 qt 1L 1000 mL 1 cm3 0.737 g 48.0 kJ
15. 1.00 mile · · · · · · · = 2.43 ×103 kJ
55.0 miles 1 gal 1.057 qt 1L 1 mL 1 cm3 1g

16. Assume the density of water is 1.00 g/mL
qwater = (225 g)(4.184 J/g·K)(340. K – 293 K) = 4.4 × 104 J
1 J/s
1100 W · 90 s · = 9.9 × 104 J
1W

4.4 × 104 J
Efficiency = · 100% = 44% efficient
9.9 × 104 J




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