Question 1. From personal experience, state whether these processes are endothermic or exothermic. Give a reason for each.

• A charcoal briquette burns.
• Water evaporates from your skin.
• Ice melts.

Answer:

1. Exothermic. Heat is released.
2. Endothermic. Heat is absorbed to break bonds.
3. Endothermic. Heat is absorbed to break the bonds.

Question 2. Chemical explosions are very exothermic reactions. Describe the relative bond strengths in the reactants and products that would make for a good explosion.

Answer: The relative bond strengths of the products are greater than that in the reactants, resulting in a very large exothermic reaction.

Question 3. How might you explain the difference between temperature and heat to a friend? Use some practical, everyday examples.

Answer:

1. Heat is the total energy of the molecular motion in a substance.
2. Temperature is the measure of the average energy of molecular motion of a substance.
3. Heat is a type of energy but temperature is not energy.
4. Heat cannot be directly measured with a device; temperature can be measured directly using devices such as thermometer.

For example, the hotness felt from a boiling kettle is the energy, and the degree of hotness can be measured using a thermometer.

Question 4. A premium gasoline available at most stations has an octane rating of 98. What does that tell you about:

• The knocking characteristics of this gasoline?
• Whether the fuel contains oxygenates?

Answer:

1. It has a knocking characteristics of 98% isooctane and 2% heptane.
2. No. Fuels that contains oxygenates would have octane rating over 100. Since the fuel has an octane rating of 98, it does not contain oxygenates.

Question 1. Understanding Earth’s energy balance is essential to understanding the issue of global warming. For example, the solar energy striking Earth’s surface averages 168 watts per square meter (W/m²), but the energy leaving Earth’s surface averages 390 W/m². Why isn’t Earth cooling rapidly?

Answer: The Earth does not cool rapidly because the atmosphere retains much of the emitted heat energy.

Question 2. Decide and explain whether the statement is correct or incorrect. Explain.

“This winter has lowered my concerns about global warming”

Answer: Incorrect. Global warming refers to an average increase in temperature of the Earth, and at the same time leads to erratic and more extreme weather conditions. Just because the a region of the Earth is experiencing a colder winter does not mean that the average global temperature has decreased.

Question 3. One of the first radar devices developed during World War II used microwave radiation of a specific wave range that triggers the rotation of water molecules. Why was the design not successful?

Answer: Absorption of microwave radiation by water in the atmosphere interferes with the detection of the intended objects.

Question 4. Now that you have studies air quality (Unit 1), stratospheric ozone depletion (Unit 2), and global warming (Unit 3), which do you believe poses the most serious problem for you in the short run (pick one and explain)? In the long run (Pick one and explain why)?

Answer:

1. Short run: Air quality poses the most serious problem in the short run because it directly affects our health conditions and immediate environment in which we live in.
2. Long run:  Global warming poses the most serious problem in the long run because there is no direct and effective solution for it. Also, we can only control limited amounts of CO2 emitted but can never fully reduce the amount of CO2 reduced by humans.
   

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Question 1. How can you purify your water when you are hiking? Name two or three possibilities. Compare these methods in terms of cost and effectiveness. Are any of these methods similar to those used to purify municipal water supplies? Explain.

Answer:

1. One method to purify water is to boil it. It disinfects the water by eliminating most microbes that can cause intestine-related diseases. Also, it does not affect the taste of the water. However, it cannot remove chemical toxins or impurities, and it requires time and fuel. In the event of incomplete combustion, it may even release soot and carbon monoxide to the environment.
2. Another method to purify water is to add iodine. It is easy and effective in twenty minutes, and cheap, but this method is not suitable for long-term use. Even though iodine is able to kill the bacteria present in water, it might be toxic if too much iodine is added. Furthermore, it does not remove chemicals such as fertilisers and poisons. Pregnant women and children should avoid purification with iodine.
3. The third method to purify water is to leave a clear water bottle in the sun for a day or two. Bacteria present in the water is destroyed via UV radiation and such method is cheap and convenient. However, this also depends on the weather conditions as the UV radiation from the Sun has to be strong enough for this method to work.

Question 2. Explain why desalination techniques, despite proven technological effectiveness, are not used more widely to produce potable drinking water.

Answer: Desalination techniques such as distillation and reverse osmosis are effective but very expensive and inconvenient due to high energy consumption and possible pollution to the environment. This is because large quantities of brine is released and has to be treated properly before being returned back to the ocean.

Question 3. Water quality in a chemical engineering building on campus was continuously monitored because testing indicated water from drinking fountains in the building had dissolved lead levels above those established by NEA.

• What is the likely major source of the lead in the drinking water?
• Do the research activities carried out in this chemistry building account for the elevated lead levels found in the drinking water? Explain.

Answer:

1. The likely major source of the lead in the drinking water is from the corrosion of lead pipes in the building.
2. Yes. Contaminated air, water, dust, food or consumer products due to exposure lead can all lead to an increase in lead levels found in the drinking water. It is also possible that the research activities involve lead as well.

Question 4. Some vitamins are water-soluble, whereas others are fat soluble. Would you expect either or both to be polar compounds. Explain.

Answer: No. Only vitamins that are water-soluble are polar compounds as it is able to form non-covalent bonds such as hydrogen bonding with water. Fat-soluble compounds are not soluble in water as it would form hydrophobic interactions with one another and would not form bonds with water molecules. Hence, it would repel from water as “like dissolves like”.