CHEMISTRY 253
Spring, 2015 - Dixon
Group Assignment #10
Open Book – But 30 min. Time Limit
Group Names _________________________________________________
1. Various fossil fuel sources (natural gas, oil, or coal) can be used for combustion in domestic heating and for electricity generation. (8 pts)
a) Which of these fuels is not desirable for domestic heating? and for what reason is it not desirable?
b) Considering cost, energy release from combustion and generation of carbon dioxide, what measure (give example units) should one compare if looking at whether substitution of one fuel for another will be beneficial (lead to a decrease in CO2 emissions if energy production is constant)? Don’t consider secondary effects such as emission of other pollutants or variations in combustion efficiency.
2. Two environmental chemists at a barbecue are arguing over whether it is better to use charcoal or propane for grilling. Rather than arguing over which leads to tastier food, they are arguing over which heating method releases more greenhouse gases to the atmosphere. Charcoal typically is derived from heating wood under low oxygen conditions to produce mostly elemental carbon (essentially the same as coal although with fewer trace metals and sulfur) along with some CO, particulate matter, and water emissions. Propane is removed from natural gas sources at low temperatures (requiring energy for refrigeration cooling needed for the separation) where it remains a liquid for transport to customers. Propane’s lifetime is too short for it to be a significant greenhouse gas.
List three factors that the chemists should think about in determining which cooking method is “greener”. Explain how each factor could result in an increase (or decrease) in greenhouse gases. (9 pts)
3. Several pollution processes are linked to climate change where a reduction of pollution could limit near term warming of the Earth. Which of the following reductions would lead to a near term reduction in warming? Only one reduction will work. Explain your answer. (3 points)
a) reduction in sulfur emissions in burning coal
b) reduction of soot (light-absorbing particulates) from cleaner diesel engines
c) reduction of methyl bromine (a molecule only important for stratospheric ozone destruction).