Section 6.7: Global Warming and Reaction Rates
Section 6.7 Questions, page 389
1. The 2 ºC limit to an increase in Earth’s average temperature is important because scientists
believe that an increase beyond the 2 °C mark would likely cause dramatic, irreversible climate
change that would have profound effects on the whole planet. Many different systems on Earth
are affected by temperature and a 2 °C change can affect the balance of these systems.
2. The three super greenhouse gases are new compounds that have only recently
been manufactured, and they were only recently detected in the atmosphere, so there was limited
scientific understanding of their potential impact in the atmosphere, and scientists believed that
sulfuryl fluoride and nitrogen trifluoride had environmental advantages in other areas. Sulfuryl
fluoride was believed to be more environmentally friendly than older fumigants. Nitrogen
trifluoride replaced perfluorocarbons, which damage Earth’s ozone layer. The source of
trifluoromethyl sulfur pentafluoride is not yet known, but it is likely released from electronic
devices and microchips as a by-product.
3. Answers may vary. Sample answer: Yes, I think that the people who approved the use of these
super gases should be held accountable for their potential effect on global warming. Earth has
become a toxic environment for all life due to the release of thousands of chemicals into the
environment before their potential for harm has been fully assessed. Although the development
of new compounds has brought many benefits, it has also proved a Pandora’s Box. At least as
much effort and money should go into testing new chemicals and researching and modelling
their potential impacts as goes into creating them.
4. Answers may vary. Sample answer: Yes, scientists are have made some progress in finding
ways to increase the decomposition rate of some greenhouse gases. For example, scientists have
developed a way to use beamed interfering radio frequency transmissions to decompose Arctic
atmospheric methane clouds. Methane can be decomposed by radio waves with a frequency of
13.56 MHz, which is equivalent to a wavelength of 22 m. Scientists have recommended that
several separated, low-frequency radio transmitters with large parabolic reflectors be set up to
transmit powerful radio transmissions into the methane-rich zone over the Siberian shelf, which
would cause the methane, almost immediately, to decompose.
Another set of researchers has now identified the structure of the enzyme that decomposes
nitrous oxide and the decomposition mechanism. The study demonstrated that the N2O-reductase
enzyme possesses active centres made up of four copper atoms and two sulfur atoms, which is
different than the structure scientists had assumed, which was a single sulfur atom only, Now
that the nitrous oxide decomposition mechanism is known, the reaction sequence of the enzyme
can be modelled much better. It is hoped that eventually it will be possible to use this knowledge
to prevent nitrous oxide from being released into the atmosphere.
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Chapter 6: Chemical Kinetics
6.7-1
Chemists are also working toward decomposing carbon dioxide into a form that is not harmful.
One group has devised the means to efficiently turn carbon dioxide into carbon monoxide with
the help of visible light, such as sunlight, have used an enzyme-modified titanium oxide
successfully to get carbon dioxide’s electrons excited. This helps in jumping the electrons into
the enzyme. After this enzyme starts its catalyst activity and helps in the reduction of carbon
dioxide to carbon monoxide. A photosensitizer is attached to the titanium. This photosensitizer
helps the utilization of visible light for the process. By performing this experiment, scientists
produced carbon monoxide from carbon dioxide. With the help of catalysts, carbon dioxide can
be converted into hydrocarbons or methanol. Next, they are hoping to either find or genetically
engineer an organism that uses light energy to activate carbon dioxide and reduce it to carbon
monoxide. However, they are proceeding with caution: carbon monoxide acts as toxin for
animals, so the risks in producing it must be given serious consideration.
Copyright © 2012 Nelson Education Ltd.
Chapter 6: Chemical Kinetics
6.7-2