- A nuclear reaction is different from a chemical reaction because it involves changes in the _nucleus__ rather than interactions of _electrons__ in an atom.
- The nuclei of atoms are held together by very _strong__ binding forces.
- The type of nuclear reaction used in commercial energy production is _fission___ which involves the splitting of a _large__ nuclei into two __smaller__ nuclei releasing large amounts of __energy____.
- The energy produced in nuclear reactions is due to mass defects resulting in small amounts of mass converting to larger amounts of energy. Identify the equation that represents this conversion. __E = mc2___
- The ideal fissionable fuel is __235U __. The balanced equation for decay is:
_1_235U + 1 1n → _1_141Ba + _1_92Kr + _3_1n + Energy
- Explain why this is considered a chain reaction and why it is difficult to control.
It is an exponential increase, for every one neutron in, three are released to initiate new reactions.
- Define critical mass. _____mass needed to initiate spontaneous fission of nuclei____
- When using fission to produce electricity, identify for each of the following the function of the part and the energy conversion that takes place:
- Fuel rods _contain fissionable material like 235U _ _mass → energy_
- Moderator __absorbs excess neutrons ____
- Control rods _high neutron absorbing materials that are raised and lowered to control the reaction_
- Shielding _prevents radiation from escaping into the environment__
- Coolant __prevents reactor form overheating (primary) and drives turbine (secondary)__
- Water _cooling and driving turbine_ __heat → mechanical__
- Turbine _water (steam) turns rotor___ __mech → mech___
- Generator _rotor turns wire coil in magnetic field__ _mech → electrical_
- Safety concerns with nuclear energy result from being able to control the chain reaction and the _spent_ fuel and byproducts.
- Radiation has three main forms. Summarize the characteristics of these by completing the following chart:
- The effects of radiation exposure are determined not only by the type of radiation but also the _half-life_ of the radioisotope undergoing decay and the length of exposure.
- Half-life is defined as: _amount of time it takes for half of the nuclei to decay_
- The main disadvantage to nuclear energy is the production of nuclear waste in the form of spent fuel and primary coolant. Give examples of how these materials are stored.
Buried in salt mines, encased in ceramic materials, stored in pools of water.
- What are the major advantages of nuclear energy? After large initial startup costs, fairly inexpensive to run. Large amount of energy for small amount of fuel. Relatively safe if safety and maintenance procedures are followed.
- What are the major disadvantages of nuclear energy? Disposal of radioactive waste, safety and possible terrorism.
- Nuclear fusion also produces extremely large amounts of energy. Fusion involves combining two __light__ nuclei to make a larger nuclei. Balance this fusion reaction; _2_ 2H → _1_3He + _1_1n + Energy
- Nuclear fusion is not currently feasible. What is the major technological problem that must be overcome? Containment, heat will melt most materials and magnetic containment requires a large amount of energy (currently more than they get out).
- What are the advantages to nuclear fusion? No radioactive waste and unlimited supply of fuel.
- What are the disadvantages to nuclear fusion? Can’t do it yet and very expensive.
- Explain how electricity is generated using hydroelectric power. Water falls down through turbines which drive generators.
- Identify what geological features must be present in order to build a hydroelectric dam.
River with high water volume and significant elevation drop in short area.
- Identify the advantages of hydroelectric power. Inexpensive to run (not to build), creates recreational lakes.
- Identify the disadvantages of hydroelectric power. Can disrupt ecosystems, expensive to build and pollution from recreational boaters
- Identify future technology that may harness hydroelectric power. Wave and tidal power.
- Solar power can be used in two different ways. Directly in _active_ & _passive__ systems or by conversion to electricity in _photovoltaic_ cells.
- Explain the difference between active and passive solar systems. Both use heat directly absorbed from the sun. Active systems use mechanical pumps or storage systems to redistribute this heat while passive systems simply reradiate heat directly.
- Identify the role that active and passive systems could play in reducing our dependence on other fuel sources. Reduces need to use more traditional heat sources like electricity and natural gas (fossil fuels)
- Briefly outline how photovoltaic cells convert solar energy to electricity. Solar cells contain layers of two different semiconductors (n-type and p-type). As sunlight strikes the surface, electrons are excited and jump from one type to the other. This movement of electrons results in an electric current.
- Explain why currently photovoltaics cannot make a major contribution to the power grid. Amount of electricity produced is small unless cells are very large and/or many are connected together in series. They are expensive and not easily used on a large scale.
- Explain why solar energy systems are considered the most environmentally friendly energy systems. No pollutants and very few mechanical systems.
- Write the equation for photosynthesis and explain how it can be used to convert to other forms of energy. Identify at least 3 different forms.
6CO2 + 6H2O → C6H12O6 + 6O2 Plants can be burned directly, converted to ethanol by fermentation and converted to methane by decomposition.
- Draw and label a diagram of a simple dry cell (Zn/C) battery labeling the anode and cathode. See study guide.
- Identify the half-reaction that occurs at each electrode.
Anode: (oxidation) Zn → Zn+2 + 2e-1
Cathode: (reduction) MnO2 + NH4+1 → NH3 + H2O + Mn2O3
- Explain why this battery is not rechargeable and has a short shelf-life. Reaction is not reversible, zinc electrode is consumed during the reaction. Out shell eventually is thin enough that it corrodes.
- Identify the advantages of alkaline dry cell over normal dry cells. Longer life and more stable power production.
- Draw and label a diagram of a lead/acid battery. See study guide.
- Identify the half-reaction that occurs at each electrode.
Anode: Pb → Pb+2 + 2e-1
Cathode; PbO2 + 4H2 + SO4-2 + 2e-1 → PBSO4 + 2H2O
- Explain why this battery is rechargeable. Neither electrodes are consumed so the reaction is easily reversible.
- Draw and label a hydrogen fuel cell. See study guide.
- Identify the half-reactions that occur at each electrode.
Anode: H2 → 2H+1 + 2e-1
Cathode; O2 +2e-1 → 2O-2
- Identify the applications, advantages and disadvantages of each battery.
- Identify the factors that affect the voltage and power available from a battery.
Voltage is determined by the nature of the reactants, the voltage difference between the two half-reactions. Power is the capacity to produce electrons and is related to both the voltage and current so the nature and size of the electodes/electrolytes.
- Why would it be difficult to produce commercial power from a battery? Voltage of a single cell is less than 3 volts. Many cells would need to be connected in series. This would make them too large and inefficient.
- Identify the advantages, disadvantages and limitations of each of the following as an energy resource.
- Even though alternative fuels play a small roll in overall energy production, why is it important to continue to promote their research and production? Anything that would reduce of power from the main power grid, and therefore our dependence on fossil fuels, will reduce pollutants and greenhouse gases. It would also allow countries to be more energy independent.
- Which energy sources are least polluting and environmentally friendly? Solar, wind and hydroelectric.
- Which energy sources produce electricity most efficiently? Nuclear and hydroelectric
- Which energy sources produce electricity most cheaply? Fossil fuels
- Why is it so difficult to reduce our dependence on fossil fuels? They are already in wide spread use so the technology is relatively inexpensive. There are large deposits around the world. Loss of jobs and political pressure.
- What is being done to offset the environmental issues with respect to fossil fuels? Industries are required to implement pollution reduction methods and alternative fuel sources and technologies are being explored.
- What more can/should we be doing?