Q1: 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?

The amount of energy that Earth emitted (390W/m2) is more than twice the amount received (168W/m2). As the atmosphere absorbs quite a bit of the solar energy as heat energy, Earth does not cool rapidly (as seen from the yellow arrows in the picture below).

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Q2: Decide and explain where the statement is correct or incorrect. “This winter has lowered my concerns about global warming…”. Explain.

The statement is incorrect because global warming will not cause an immediate effect on the four seasons we have. There is a change in climate due to global warming but not a change in weather.

Image result for global warming winter harsher comic

The difference between climate and weather is that climate is the long term weather of a region, whereas weather is short term. In fact, due to global warming, we will have harsher winters due to the melting of artic ice. Hence, having winters does not improve the long term effects of global warming

Q3: 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?

The image below shows an example of a radar emission device used in World War I.

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Since the wavelength of radiation used triggers the rotation of water molecules, it means that the radiation can also be absorbed by the atmospheric water vapour. When this radiation is absorbed by water vapour around the radar, it makes the radar unable to detect the target objects and doesn’t reach the target object.

Q4: Now that you have studied 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)?

While the three problems are quite serious, they might affect us at different time intervals.

For example, air quality is a problem in the short run and can affect us on a daily basis, like the haze problem in Singapore. The stratospheric ozone depletion also affects us but is probably a major factor in the long run as the depletion process is relatively slow.

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Lastly, global warming and climate change are influential in the long run as these effects are gradual and usually felt over long periods of time. Some future effects include increase in daily temperature, increased frequency of wamr days and nights, more intense and frequent rainfall, potential increase in wind speed and rise in sea level (as seen from the picture below).

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Q1: From personal experience, state whether these processes are endothermic or exothermic. Give a reason for each.

a. A charcoal briquette burns.

This is an exothermic reaction. Heat is released when a charcoal briquette burns.

b. Water evaporates from your skin.

This is an endothermic reaction. When water evaporates from our skin, heat is absorbed, thus our skin feels cooler.

c. Ice melts.

This is an endothermic reaction. Heat is absorbed by the ice from the surrounding, allowing it to melt.

Q2: Chemical explosions are very exothermic reactions. Describe the relative bond strengths in the reactants and products that would make for a good explosion.Image result for chemical explosive example equation bond energy

Methane is a type of chemical explosive.

During a methane explosion,CH4 + 2 O2 -> CO2 + 2 H2O.

The bond energies involved are: 4 C-H single bonds (99kcal/mol*4), 2 O=O double bonds (119kcal/mol*2), 2 C=O double bonds (192kcal/mol*2) and 4 O-H single bonds (111kcal/mol*4).  The bond energies of the reactants should be lower than the bond energies of the products. The products has a higher bond energy as it releases more energy during bond formation, than give out energy during bond breaking of the reactants. Thus, leading to an exothermic reaction; net negative energy change.

Q3: How might you explain the difference between temperature and heat to a friend? Use some practical, everyday examples.

Heat is the total energy of the molecular movement, while temperature is a measurement of the average thermal energy of the molecule.Image result for heat and temperature cup water

A larger beaker of water (beaker A) will have more heat than a smaller beaker of water (beaker B), even though they are of the same temperature. Beaker B has lower energy, so it will take a shorter time to cool down.

It is similar to how a person with more mass has more kinetic energy than a person with less mass, even though they are travelling at the same velocity.

Q4: A premium gasoline available at most stations has an octane rating of 98. What does that tell you about:

a) the knocking characteristics of this gasoline?

The octane rating of gasoline is 98. This means that it has the knocking characteristics similar to a mixture composed of 98% isooctane and 2% n-heptane.

It is categorized as a premium gasoline as it has a higher octane rating than other blends sold at gasoline stations. This means that gasoline is more resistant to knocking than the other blends.

b) whether the fuel contains oxygenates?

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The octane rating does not tell us whether the fuel contains oxygenates (such as ethanol). Information on whether the fuel contains oxygenates may be available on other labels found around the pump.

The ozone layer can absorb some harmful UV rays and help to protect humans from its harmful effects. Unfortunately, some of the rays still penetrate through the ozone layer and enter the Earth’s atmosphere and harm us. This is why it is important to use sun protection such as sun block or sunscreens. The amount of sun protection factor recommended has been studied and mainly categorised by the time spent outdoors and the skin tone, as seen from the SPF selection guide below. Higher SPF required is usually for longer hours spent outdoors and for fairer skin tones.