ANSWERS TO END-OF-CHAPTER QUESTIONS

55. If all of today’s technology presently based on fossil fuel combustion were replaced by
H2–O2 fuel cells, significantly more H2O would be released into the environment. Is this
effect a concern? Find out what other effects might be anticipated from switching to a
hydrogen economy.
Answer:
While water is not a criteria air pollutant, it is a greenhouse gas. Excess water in the
atmosphere could therefore contribute to global warming. Other effects include the release of
excess CO2 from the hydrogen production, and those listed in 56b below.
56. a. Hydrogen is generally considered as an environmentally friendly fuel, only
producing water after reacting with oxygen. What effect could the widespread use of
hydrogen have on urban air quality?
b. Some scientists are reporting concerns that leakage of hydrogen gas from cars, hydrogen
production plants, and fuel transportation could cause problems in Earth’s ozone layer. How
significant are these concerns? What is the mechanism by which hydrogen could destroy
ozone?
Answer:
a. The widespread use of hydrogen fuel could dramatically improve urban air quality by
reducing levels of particulate matter and SOx produced by internal combustion engines.
b. In June of 2003, geochemists at Caltech created a stir in the scientific community when
they published theoretical models in the journal Science that predicted hydrogen could leak
from production plants, transport systems, and hydrogen-powered cars in the future. They
predicted a large amount of hydrogen would reach the stratosphere assuming all current
fossil fuel combustion was replaced by hydrogen fuel cells and 10-20% of the hydrogen was
lost to leakage. The additional hydrogen in the stratosphere would react and significantly
increase the amount of water molecules found as ice in the stratosphere. Because ozone is
destroyed by reactions with chlorine radicals that take place on stratospheric ice, the
researchers proposed that the rate of ozone destruction would be enhanced. However, other
scientists in academic and industrial research claim the Caltech group’s hydrogen leakage
estimate is too high. One automobile executive argues that the industry would not allow such
a large amount of a valuable commodity (hydrogen) to go to waste. Another scientist points
out that the leaking hydrogen can be recovered. Others use the Caltech group’s research to
support the idea of on-site hydrogen production.
57. At the cutting edge of technology the line between science and science fiction often
blurs. Investigate the “futuristic” idea of putting mirrors in orbit around Earth to focus and
concentrate solar energy for use in generating electricity.
Answer:
Mirrors or lenses could be used to concentrate solar energy on a collection array in space and
send the electricity back to Earth. This technology would counteract one of the major
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