Ozone Depletion

Take care of our planet:

Ozone (O3) is found in two different parts of our atmosphere. Ground level ozone, a human health irritant and component of smog, is found in the lower atmosphere (troposphere) and has nothing to do with the "ozone hole." However, ozone in the stratosphere—the layer of atmosphere above the troposphere _ accounts for the vast majority of atmospheric ozone. Stratospheric ozone is protective for human health as it absorbs ultraviolet radiation from the sun, preventing the radiation from hitting Earth's surface and harming living organisms from this biologically dangerous radiation.




The stratospheric ozone layer shields life on Earth from the Sun’s harmful ultraviolet radiation. Chemicals that destroy ozone are formed by industrial and natural processes. With the exception of volcanic injection and aircraft exhaust, these chemicals are carried up into the stratosphere by strong upward-moving air currents in the tropics. Methane (CH₄), chlorofluorocarbons (CFCs), nitrous oxide (N₂O) and water are injected into the stratosphere through towering tropical cumulus clouds. These compounds are broken down by the ultraviolet radiation in the stratosphere. Byproducts of the breakdown of these chemicals form “radicals”—such as nitrogen dioxide (NO₂) and chlorine monoxide (ClO)—that play an active role in ozone destruction. Aerosols and clouds can accelerate ozone loss through reactions on cloud surfaces. Thus, volcanic clouds and polar stratospheric clouds can indirectly contribute to ozone loss.


 

(CFCs, freons, halons.) CFCs and other contributory substances are referred to as ozone-depleting substances (ODS).

Since the ozone layer prevents most harmful UVB wavelengths (280–315 nm) of ultraviolet light (UV light) from passing through the Earth's atmosphere, observed and projected decreases in ozone have generated worldwide concern leading to adoption of the Montreal Protocol that bans the production of CFCs, halogens  and other ozone-depleting chemicals such as carbon tetrachloride and trichloroethane. It is suspected that a variety of biological consequences such as increases in skin cancer, cataracts, damage to plants, and reduction of plankton populations in the ocean's photic zone may result from the increased UV exposure due to ozone depletion.




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Global Warming

Green house effect:

The greenhouse effect is the process by which absorption and emission of infrared radiation by gases in the atmosphere warm a planet's lower atmosphere and surface.Naturally occurring greenhouse gases have a mean warming effect of about 33 °C (59 °F).The major greenhouse gases are water vapor, which causes about 36–70 percent of the greenhouse effect; carbon dioxide (CO₂), which causes 9–26 percent; methane (CH₄), which causes 4–9 percent; and ozone (O₃), which causes 3–7 percent.

Human activity since the Industrial Revolution has increased the amount of greenhouse gases in the atmosphere, leading to increased radiative forcing from CO₂, methane, tropospheric ozone, CFCs and nitrous oxide.

Global warming is the increase in the average temperature of Earth's near-surface air and oceans since the mid-20th century and its projected continuation.
Most of the observed temperature increase since the middle of the 20th century has been caused by increasing concentrations of greenhouse gases, which result from human activities such as the burning of fossil fuel and deforestation.

Consequencies:An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, probably including expansion of subtropical deserts.

Warming is expected to be strongest in the Arctic and would be associated with continuing retreat of glaciers, permafrost and sea ice.



Other likely effects of the warming include more frequent and intense precipitation events, extreme weather events, species extinctions due to shifting isotherms, and changes in agricultural yields.

Balancing chemical reactions

1. Identify each element found in the equation. The number of atoms of each type of atom must be the same on each side of the equation once it has been balanced.
2. If possible, start with an element found in one compound on each side of the equation. Change the coefficients (the numbers in front of the compound or molecule) so that the number of atoms of the element is the same on each side of the equation. Remember! To balance an equation, you change the coefficients, not the subscripts in the formulas.
3. Once you have balanced one element, do the same thing with another element. Proceed until all elements have been balanced. It's easiest to leave elements found in pure form for last.
4. Check your work to make certain the charge on both sides of the equation is also balanced.

Example of Balancing a Chemical Equation

? CH₄ + ? O₂ → ? CO₂ + ? H₂O
Identify the elements in the equation: C, H, O
Identify the net charge: no net charge, which makes this one easy!

1. H is found in CH₄ and H₂O, so it's a good starting element.
2. You have 4 H in CH₄ yet only 2 H in H₂O, so you need to double the coeffient of H₂O to balance H. 1 CH₄ + ? O₂ → ? CO₂ + 2 H₂O
3. Looking at carbon, you can see that CH₄ and CO₂ must have the same coefficient. 1 CH₄ + ? O₂ → 1 CO₂ + 2 H₂O
4. Finally, determine the O coefficient. You can see you need to double the O₂ coefficient in order to get 4 O seen on the product side of the reaction. 1 CH₄ + 2 O₂ → 1 CO₂ + 2 H₂O
5. Check your work. It's standard to drop a coefficient of 1, so the final balanced equation would be written: CH₄ + 2 O₂ → CO₂ + 2 H₂O

 

Plastics for grade 9

An addition polymer is a polymer which is formed by an addition reaction, where many monomers bond together via rearrangement of bonds without the loss of any atom or molecule. This is in contrast to a condensation polymer which is formed by a condensation reaction where a molecule, usually water, is lost during the formation.The discharge of plastics after usage cause a pollution problem ,to decrease this problem we depend on recycling especially for thermoplastics.

To assist recycling of disposable items, the Plastic Bottle Institute of the Society of the Plastics Industry devised a now-familiar scheme to mark plastic bottles by plastic type. A plastic container using this scheme is marked with a triangle of three "chasing arrows", which encloses a number giving the plastic type:

1. PET (PETE), polyethylene terephthalate
2. HDPE, high-density polyethylene
3. PVC, polyvinyl chloride
4. LDPE, low-density polyethylene,
5. PP, polypropylene
6. PS, polystyrene

Plastics type marks: the resin identification code



Some products and the type of plastic they are manufactured from:

LDPE





Polyethylene bag





polystyrene



PVC pipes







PP



HDPE

Review on chemical reactions for Grade :7

A chemical reaction is defined as the process, wherein a set of chemical substances react with each other, which leads to their conversion into other different forms. The initial substances used the reaction are collectively called reactants, while the final substances formed after the reaction are known a products. In general, the chemical properties of the reactants and products are different from each other.

Aerobic Respiration
Do you know indulging in physical movements is associated with a chemical reaction? The process requires energy, which is yielded by aerobic respiration. Over here, respiration helps breaks down glucose (an energy source) into water, carbon dioxide and energy in form of ATP (adenosine triphosphate). The balancedcellular respiration equation is represented as:

C₆H₁₂O₆ + 6O₂ → 6CO₂+ 6H₂O + Energy

Photosynthesis
Photosynthesis is the process by which green plants manufacture their own food. This occurs in presence of sunlight and other raw materials, namely carbon dioxide and water. The chlorophyll pigment harvests the light energy from sunlight, which is then converted into glucose by the phenomenon of photosynthesis. In short, it is the opposite of aerobic respiration. Theequation for photosynthesis is:

6 CO₂+ 6 H₂O + Light energy → C₆H₁₂O₆ + 6 O

<sub>Propane Grill
Have you ever prepared meat in a propane grill? The meat placed over the burner is cooked with the help of heat energy released after burning of propane gas. Thus, propane is the reactant which when burnt with the help of oxygen gives heat energy and other byproducts. Check out the balanced equation for the combustion reaction that take place in a propane grill::

C3H8 + 5O2 → 4H2O + 3CO2 + energy</sub>

Look at the cases below indicate whether there is a chemical reaction taking place .

a-water is freezed ,melted ,then evaporated .

b-dissolve sugar in water.

CS tear gas

CS is a tear gas or chemical  forbidden since 1997.It was used in Iraq , Palestine ,Egypt,and Yemen ...... It caused the death of many innocent people .What is this gas? 




-chlorobenzalmalononitrile (also called o-chlorobenzylidene malononitrile) chemical formula: C₁₀H₅ClN₂is the defining component of a "tear gas" commonly referred to as CS gas.



 
This  chemical reacts with moisture on the skin and in the eyes, causing a burning sensation and the immediate forceful and uncontrollable shutting of the eyes. Effects usually include tears streaming from the eyes, coughing, running nose full of mucus, burning in the nose and throat areas, disorientation, dizziness and restricted breathing. It will also burn the skin where sweaty and or sunburned. In highly concentrated doses it can also induce severe coughing and vomiting. Almost all of the immediate effects wear off in a matter of minutes.As well as creating severe pulmonary damage, CS can also significantly damage the heart and liver.CS emits "very toxic fumes" when heated to decomposition, and at specified concentrations CS gas is an immediate danger to life and health. They also state that those exposed to CS gas should seek medical attention immediately.
In Israel, CS gas was reported to be the cause of death of Jawaher Abu Rahmah on December 31, 2010.^]
It has been noted that the solvent MiBK is itself harmful, and can cause inflammation, dermatitis, burns to the skin and liver damage.

video on types of chemical reactions