# Essay topics

 Explain how a barometer works
 A tube filled with mercury is inverted into a pool of mercury. The mercury column falls until the weight of the mercury above the surface of the pool balances the force of the atmosphere on the open surface of the mercury in the pool. As air pressure changes, the height of the mercury column rises or falls.
 Explain Boyle’s pressure-volume relationship in terms of the kinetic-molecular theory
 The pressure of a gas is caused by collisions of the gas particles with the container walls. If the volume of a container is decreased, but the same quantity of gas is present at the same temperature, there will be more molecules per unit volume. This means that there will be more gas particle-wall collisions for a given unit of wall surface. In other words, there will be greater pressure (force/area on a surface).Conversely, if the volume of a container is increased, but the same quantity of gas is present at the same temperature, there will be fewer molecules per unit volume. This means that there will be fewer gas particle-wall collisions for a given unit of wall surface. In other words, there will be decreased pressure (force/area on a surface).
 Explain how hot-air balloonists use Charles’s law
 . When pressure is constant, gases expand when heated. So when the air inside of a balloon is heated, the volume of the fixed number of gas molecules inside of the balloon must increase. When at the higher temperature, the gas molecules move faster and collide with greater frequency and greater force with the balloon’s walls. Since the balloon is expandable, its volume must increase in order for the pressure to stay the same. Consequently, the hot-air balloon rises. This process is an illustration of Charles’s law: the volume of a fixed mass of gas at constant pressure varies directly with the Kelvin temperature.
 Explain the difference between a dilute strong electrolyte and a concentrated weak electrolyte in terms of number of dissolved ions and electrical conductivity
 The dilute strong electrolyte will have few ions in solution because of the low concentration, but all dissolved particles will be completely ionized or dissociated and the solution will carry electric current well. The concentrated weak electrolyte will have more molecules in solution, but because it only partially ionizes, will not carry electric current as well.
 How does temperature affect the free energy of a reaction?
 The formula  ΔG = ΔH – TΔS  shows that part of the energy change of a reaction is proportional to the temperature. Therefore, at higher temperatures, the contribution of the entropy change is more important in determining the free energy. At lower temperatures, the enthalpy change has more influence on the free energy.
 How does the free-energy equation predict the progress of a chemical reaction?
 The equation ΔG = ΔH – TΔS   shows that the free energy of a reaction depends on the enthalpy change, the entropy change, and the temperature of a reaction. If ΔG is negative, the change is spontaneous. If ΔG is positive, the change will not occur spontaneously. If ΔG is zero, neither the forward nor the reverse reaction is favored, so the result is a mixture of reactants and products.
 Explain why it is often necessary to start a campfire with many small pieces of kindling rather than with a few large logs
 Many small pieces of kindling have a greater amount of surface area than a few large logs. Fire is a surface reaction. One feature of surface reactions is that the amount of reaction that occurs is proportional to the amount of surface area. This feature is useful for starting the fire. Once the fire is burning well, the larger logs can be used to increase the heat output.
 Explain why lithium is a strong reducing agent, whereas fluorine is a strong oxidizing agent.
 Lithium has only one electron in its outer shell. To attain a stable, noble gas electron configuration, it must lose this electron.Fluorine, on the other hand, has seven outer shell electrons and so must gain one electron to attain a noble gas electron configuration.Since strong reducing agents are oxidized by loss of electrons and strong oxidizing agents gain electrons, lithium is a reducing agent and fluorine is an oxidizing agent.
 List two observations that would suggest that a chemical reaction is occurring in a voltaic cell
 Answers will vary. Some examples: electrical energy is produced, gas evolves at the electrodes, the color of the solution changes, and the masses of the electrodes change
 Is fractional distillation a chemical or physical process? Support your answer in your description of the process. Be as specific as possible
 Fractional distillation is a physical process used in the separation of the various components of petroleum on the basis of boiling point difference. Petroleum consists of many different alkanes of various molecular masses. They are separated physically in fractional distillation but undergo no change in chemical composition. (The latter is necessary for a chemical process.)The first group of alkanes to be collected is composed of low molecular mass hydrocarbons such as gasoline, followed by kerosene. These can have from 4-14 carbons each. Their boiling points are low. Then there are the “middle distillates” of moderate molecular mass with 12-20 carbons each. These include diesel fuel and heating oil. Their boiling points are higher. Then there are the “wide-cut” fractions with 20-36 carbons each. These include lubricating oils and waxes. Their boiling points are very high. Lastly, there is an asphalt residue.The large range of boiling points, increasing with molecular mass of the alkanes, permits the fractions to be boiled off then condensed separately in the distillation column. For example, alkanes that have higher boiling points have higher condensation temperatures and condense for collection lower in the tower.
 What is acid rain?
 The term "acid rain" is commonly used to mean the deposition of acidic components in rain, snow, fog, dew, or dry particles. The more accurate term is "acid precipitation." Distilled water, which contains no carbon dioxide, has a neutral pH of 7. Liquids with a pH less than 7 are acid, and those with a pH greater than 7 are alkaline (or basic). "Clean" or unpolluted rain has a slightly acidic pH of 5.6, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid.
 Describe the Effects of Acid Rain
 Acid rain causes acidification of lakes and streams and contributes to the damage of trees at high elevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation’s cultural heritage. Prior to falling to the earth, sulfur dioxide (SO2) and nitrogen oxide (NOx) gases and their particulate matter derivatives;sulfates and nitrates;contribute to visibility degradation and harm public health.
 How to Measuring Acid Rain
 The acidity of acid rain is measured using the pH scale. It ranges from 1 to 14.1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acid Neutral Alkali Substances like vinegar and lemon juice are acidic, and have a low pH. Distilled water is neutral with a pH of 7. Substances like blood and milk are alkaline and have a high pH.All rain is slightly acidic as it contains carbon dioxide, a gas found in air. Unpolluted rain usually has a pH of between 5 and 6. Acid rain has been found to have a pH as low as 3 and in some cases even lower.
 What you can do to help reduce acid rain emissions
 Sulphur dioxide and nitrogen oxides are the main pollutants that cause acid rain. These pollutants are emitted largely by the combustion of fossil fuels. Reducing the use of fossil fuels therefore, including the use of electricity generated by coal- and oil-fired power plants, will help reduce acid rain-causing emissions. In the home;;;;; Install a low-flow showerhead. ;;;;; Run the dishwasher only with a full load. ;;;;; Run the washing machine with a full load. In the yard;;;;; Consider changing to a low-maintenance landscape. ;;;;;;;;;;; If you have a pool, keep a cover over it when you are not using it.
 What effect does acid rain have on sea life?
 Acid rain is very harmful to the environment. Acid rain damages everything over a period of time because it makes the living things in the environment die. Acid rain affects the life in the water as well as the life on land. It is almost worse in water than on land because the fish that are in the water need the water to breathe. When the water gets polluted, then the fish get sick and end up dying. All rainwater contains some level of acidity. Acidity is measured by pH, which stands for potential of hydrogen. The pH scale measures the amount of acid in a substance. PH is measured on a scale from 0-14, with 7 being neutral. The lower the number is on the pH scale, the more acidic that substance is. Normal rainwater has a pH of 5.6. When the pH level of rainwater goes below 5.6, it is considered acid rain.All of the sea life will die when the water that they swim in gets to be too acidic. For example, all fish will die when the water goes below a pH of 4.5. Most of the frogs and insects that live around the water will also die when the water reaches a pH of 4.5. With a pH of 5.5, all of the bottom-dwelling bacterial decomposers, animals that eat the remains of the food that other animals don;t want, will begin to die. When these decomposers die, they leave the un-decomposed food on the bottom of the water. This pollutes the water by making the water dirty for all of the fish to swim in. All fresh water shrimp die when there gets to be a pH of 6.0. Aquatic plants will grow the best when the water is a pH between 7.0 and 9.2. If acid rain gets to be more of a problem, then all of the sea life will eventually be gone.Some of the lakes that were once acidic are recovering, but many more are not recovering. Of the 202 lakes that were chosen to be studied in the early 1980s; only 33% of them have become less acidic.
 What effect does acid rain have on the forests of the world?
 Trees are also harmed by acid rain. In Germany, the forests are believed to be dying because acid rain is harming them. Scientists say that acid rain damages the waxy outer coating that protectsthe leaves. When this happens, it allows the acid to seep into the tree. Instead of water changing from a liquid to a gas inside the leaves, gas is taking the place of the water. This prevents the plant from taking in carbon dioxide to perform photosynthesis, and the plant will eventually die.Acid rain, acid fog, and acid vapor also damage forests bydamaging the surface of the leaves and needles. This makes it harder for the trees to withstand the cold and will cause the tree to die. Acid rain also harms the soil that the trees are growing in by taking most of the valuable nutrients away from the soil. Acid rain also leaves a lot of aluminum in the soil, which can be harmful to the trees that grow there.The atmosphere deposits a lot of toxic metals into the forests because acid rain contains metal. Some of these metals are lead, zinc, copper, chromium, and aluminum. When there is acid rain, the rain releases these metals. This is believed to stunt the growth of many trees and plants. This also stunts the growth of mosses, algae, nitrogen-fixing bacteria, and fungi that are needed to help the forest grow. Forests need these because they eat the harmful things that will kill the trees, such as bad bacteria. Acid rain hurts trees because they cannot grow any more.
 What effect does acid rain have on the air, us, and our health?
Acid rain affects us in many different ways. One major way is our health. Breathing and lung problems in children and adults who have asthma and in children have been linked to acid air pollution. Everything that we eat, drink, and breathe has at one time come in contact with acid deposits. This could threaten our health by making us become sick. The following health problems occur each year in the U.S. and Canada due to acid rain:

 550 premature deaths 1,520 emergency room visits 210,070 asthma symptom days

 What can acid rain do to non-living things?
 Acid rain can also damage non-living things, such as buildings and statues. It can decay building materials and paints. Worst of all, it can damage non-replaceable buildings, statues, and sculptures that are part of our nation;s memories that we want to last for a very long time.
 What is acid rain caused by?
Acid rain is mainly caused by these substances that are being released into the air:

 ; Carbon dioxide: Carbon dioxide is released by burning coal, oil, and natural gas. If you inhale carbon dioxide, then since it is toxic, it can cause you to have to breathe more than usual, unconsciousness, and other serious health problems. Carbon monoxide: Carbon monoxide is released by burning gasoline, oil, and wood. When carbon monoxide enters your body, it goes into the bloodstream. When this happens, it will slow down the delivery of oxygen to the rest of the body, causing dizziness, headaches, and fatigue. Chlorofluorocarbons (CFCs): CFCs are the chemicals that are used in industry, refrigeration, air conditioning systems, and consumer products. Whenever CFCs are released into the air, they reduce the stratospheric ozone layer. The stratospheric ozone layer protects Earth;s surface from the harmful rays of the sun. Hazardous air pollutants (HAPS): HAPS are released into the air by sources such as chemical plants, dry cleaners, printing plants, and motor vehicles (cars, trucks, buses, and planes). HAPS can cause serious health problems like cancer, birth defects, nervous system problems, and deaths that are all due to people accidentally letting them go into the air. Lead: Lead is released by house and car paint as well as the manufacturing of lead batteries, fishing lures, certain parts of bullets, some ceramic ware, water pipes, and fixtures. In young children, lead can cause nervous system damage and learning problems. Nitrogen oxides: Nitrogen Oxides are released into the air by burning fuels such as gasoline and coal. When nitrogen oxides combine with VOCs, they can cause breathing difficulty in people who have asthma, coughs in children, and general illness in your respiratory system. Ozone: Ozone is released by motor vehicles, industries, burning coal, gasoline, and other fossil fuels, and in the chemicals that are in hairspray and paints. When ozone is close to the ground (ground level ozone) it can cause chest pain, irritated respiratory tract, or persistent cough, can make you unable to take deep breaths, and can make you more likely to get lung infections. Particulate matter (PM): PM, little particles of pollution, is released by cars, trucks, and buses that are burning diesel fuel, fertilizers, pesticides, road construction, steel making, mining, and turning on fire places and wood stoves. When PMs mix with air particles and get breathed in by something, they get stuck in the lung tissue. There they can cause increased respiratory disease and lung damage. Sulfur dioxides: Sulfur dioxides are released by burning coal, paper production, and melting metal. Sulfur dioxide can harm vegetation, harm metals, and cause lung problems, which include breathing problems and permanent lung damage. Volatile organic compounds (VOCs): VOCs are released into the air by burning gasoline, wood, coal, or natural gas, solvents, paints, glues, and other products that are used at work or at home.

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