氢氧燃料电池的突出优点是把化学能直接转变为电能,而不经过热能这一中间形式,已用于宇宙飞船及潜艇中,其电极反应为:
负极:2H2+4OH--4e-
4H2O
正极:O2+2H2O+4e-4OH-
所产生的水还可作为饮用水,今欲得常温下1 L水,则电池内电子转移的物质的量约为( )
A．8.9×10-3 mol
B．4.5×10-2 mol
C．1.1×102 mol
D．5.6×10 mol
答案：C
正负极反应合并得:2H2+O2
2H2O,若转移4 mol电子,则生成2 mol H2O,欲生成1 L水即 mol,转移电子为×2 mol≈1.1×102 mol。
Passage Two
| Cars account for half the oil consumed in the U.S. , about half the urban pollution and one fourth the greenhouse gases. They take a similar toll (损耗) of resources in other industrial nations and in the cities of the developing world．As vehicle use continues to increase in the coming decade, the U.S. and other countries will have to deal with these issues or else face unacceptable economic, health-related and political costs. It is unlikely that oil prices will remain at their cur- rent low level or that other nations will accept a large and growing U. S. contribution to global climatic change. Policymakers and industry have four options: reduce vehicle use, increase the efficiency and reduce the emissions of conventional gasoline-powered vehicles, switch to less harmful fuels, or find less polluting driving systems. The last of these—in particular, the introduction of vehicles powered by electricity-is ultimately the only sustainable (可持续的) option The other alternatives are attractive in theory but in practice are either impractical or offer only marginal improvements. For example, reduced vehicle use could solve traffic problems and a host of social and environmental problems, but evidence from around the world suggests that it is very difficult to make people give up their cars to any significant extent. In the U.S. mass-transit rider ship and carpooling (合伙用车) have declined since World War Ⅱ. Even in western Europe, with fuel prices averaging more than＄1 a liter (about ＄ 4 a gallon) and with easily accessible mass transit and dense populations, cars still account for 80 percent of all passenger travel. Improved energy efficiency is also appealing, but automotive fuel economy has barely made any progress in 10 years. Alternative fuels such as natural gas, burned in internal-combustion engines, could be introduced at relatively low cost, but they would lead to only marginal (边缘的最低限度的) reductions in pollution and greenhouse emissions (especially because oil companies are already spending billions of dollars every year to develop less polluting types of gasoline). |
The U.S. has to deal with the problems arising from vehicle use because______.
A．most Americans are reluctant to switch to public transportation systems
B．the present level of oil prices is considered unacceptable
C．other countries will protest its increasing greenhouse emissions
D．it should take a lead in conserving natural resources