AE 4

Unit 3- The Chemistry of Global Climate Change

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 energy leaving the Earth’s surface averages 390 W/m². Why isn’t the Earth cooling rapidly?

Considering the difference the Solar energy that strikes the Earth and the larger amount that is reflected, the temperature of the earth should be -18°C. However, because of various forcings, such as greenhouse gases and clouds, the temperature of the earth averages 16°C instead.

When solar radiation travels to the Earth, 29% of the radiation is reflected into space, after which, greenhouse gases in the atmosphere absorb 23% of what’s left. The rest of the 48% radiation is absorbed by the surface. After time, the surface of the Earth emits the radiation back into space. However, not all of the radiation is reflected back into space, again, greenhouse gases in the atmosphere (such as H2O and CO2) absorb some of what is reflected by the surface. Because of this, the greenhouse gases help to trap sufficient heat for the Earth to maintain a warmer average temperature.

https://www.nasa.gov/pdf/135642main_balance_trifold21.pdf

http://earthobservatory.nasa.gov/Features/EnergyBalance/page4.php

Question 2

Decide and explain whether the statement is correct or incorrect.

ae4

This statement is incorrect. Earth is not cooling down when winter is occurring. Winter is a season, and referred to as weather instead of climate. Climate and weather differ in terms of the time period. To understand the effects of global warming, meteorologists study the climate on earth instead of weather as climate refers to weather patterns over a long period of time and its statistics are more reliable while weather is over a short period of time and is unreliable. Furthermore, global warming does cause extreme weather events such as extreme winters and summers.  The cartoon may be depicting a scene of extreme winter caused by the effects of global warming.

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?

It was not successful because detection will fail due absorption of microwave by water. The microwave radiation will also result in the heating up of air around the radar resulting in sickness of the engineers of the radar.

Question 4

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 why)?

Air quality poses as the most serious problem in the short term as it can be easily be affected in a short period of time.  Short term health effects will also arise such as eye irritation, breathing difficulties etc. Over the long term, global warming poses the most serious problems. While the hole in the ozone layer will cause harmful radiation to leak, we should be able to pull through with sunblock. If the sea level continues to rise uncontrollably however, there is not much we can do about it and civilization in many parts of the world will be destroyed.

AE 3

  1. From personal experience, state whether these processes are endothermic or exothermic. Give a reason for each.
    • A charcoal briquette burns

Exothermic, as when charcoal briquette burns, heat is released.

    • Water evaporates from your skin

Endothermic. Water absorbs heat from my skin to break inter-molecular forces of attraction and evaporates.

    • Ice melts

Endothermic, for example when ice melts on my hand, my hand feels cooler as the ice absorbs heat energy from my hand.

 

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

Reactants should have weaker bonds while products should have stronger bonds.

ΔH = Bonds broken – bonds formed, so to have a good explosion, it should have a largely negative enthalpy change. Hence bonds formed for products should have large values, while bonds broken of reactants should have a smaller value.

 

3) How might you explain the difference between temperature and heat to a friend? Use a practical everyday example.

Heat refers to when energy moves from a warmer body to a colder body. In comparison temperature refers to the measure of the average speed of the heat flow (it can be measured in Celsius, Kelvin etcetera).

For example, when a hot cup of coffee is placed on a table, the cup of coffee may have a temperature of 80°C, and the table a temperature of 25°C. Heat will travel from the coffee cup to the table. Simultaneously, heat is being transferred to the surrounding air, over time, both the coffee cup and the table will return to room temperature.

 

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?

A gasoline’s octane rating is a measure of the gasoline’s resistance to causing knocking in a vehicle’s engine. It is able to burn with minimal knocking at a low octane rating of 98.

  • Whether the fuel contains oxygenates?

They are not oxygenates as the octane rating is at 98 while compounds with oxygenates have a octane rating of above 100.

Unit 2: Ozone Layer

Today, we learnt about the ozone layer. laughing

  • blue and purple – least ozone; green, yellow and red – more ozone 

 

  • 90% of ozone occurs in the stratosphere – measured in Dobson Unit (DU)
  • Isotopes
  • 1A – Alkali metals; 2A – Alkali earth metals; 7A – Halogens; 8A – Noble gases
  • Bonding
  • E=hv
  • Microwaves, Infrared, Visible, UV, X-rays, Gamma rays
  • UV radiation/light
  • CFCs – chlorine destroy ozone
  • Skin cancer
  • Ozone hole

Ozone layer or screen

Today we discussed the advantages and disadvantages of using the terms “ozone layer” and “ozone screen”. To a layman, the different associations with the word ‘layer’ and ‘screen’ will produce different preconceptions as to what the ozone is.

For example, an advantage of the term “layer” is that it is easily related to the idea of a layer amongst other layers in the atmosphere (stratosphere, troposphere, mesosphere). Conversely, it may imply something uniformly distributed across the globe, and thus lead to false visualisations of the layer.

For the term “screen”, the word directly relates to the function of the ozone in the atmosphere, which is, to sort of act as the earth’s sunscreen in absorbing UV rays. However, a disadvantage is the word “screen” being associated to something impermeable, blocking all UV radiation.