Photosynthesis occurs in all green plants and is the beginning of nearly all food chains therefore a source of life to all living organisms. It is the process where plants transform light energy from the sun into chemical energy. By using light energy trapped by chlorophyll (light absorbing pigment), plants combine carbon dioxide and water to form glucose and oxygen.

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As it absorbs energy from sunlight, this reaction is endothermic. Light energy is converted into chemical energy which is stored as glucose. When this occurs, most of the glucose is converted into complex carbohydrates such as starch which is used for energy and cellulose which makes up most of the plant wall which provides support and structure. .

Outline the role of the production of high energy carbohydrates from carbon dioxide as an important step in the stabilisation of the sun’s energy in a form that can be used by animals as well as plants.

Photosynthesis is essential for almost all living things on earth. It is clear that all life forms depend on sunlight for energy to live, to grow, to move, to gather food and to reproduce. Without the sun there would be no life as we know it and because animals have no method for harnessing energy directly from the sun, they rely on the production of carbohydrates in plants. Apart from absorption of heat, photosynthesis is the only way in which the natural environment can absorb soloar energy and use it to convert it into energy. In the process of photosynthesis, chlorophyll absorbs the energy from the suns rays to convert into oxygen and carbohydrates which is crucial for all animals to survive. These carbohydrates are considered to be high energy compounds because when they react (respiration or combustion) they release large amounts of energy.

Identify the photosynthetic origins of chemical energy in coal, petroleum and natural gas and on the location of deposits of the selected fossil fuels in Australia Coal, oil and natural gas come from decayed plant or animal remains. When a plant or animal dies, it decays and

Page 2 Year 11 Chemistry Research Assignment Essay

is broken down by bacteria mainly into carbon dioxide and water. But in some locations, and under certain conditions the decay process is interrupted which results in these dead plants and animals to form layers of energy rich compounds under the earth. These are known as fossil fuels. They are the remains of plants and animals the have been buried and subjected to extremely high temperature and intense pressure over millions of years.

Coal

clip_image004Most of the earth’s coal deposits were formed between 350 and 225 million years ago. When plant debris in low lying coastal and river areas subsided under water, the low oxygen environment inhibited the decay process so that the plant remains were in effect mummified. As successive layers of silt and sand forced the matter deeper and increased the pressure and temperature, coalification began. Initially, the organic matter is converted into a soft, spongy material called peat. With high temperature and pressure, the peat is converted into brown coal (lignite) then black coal (bituminous coal) and finally anthracite.

Coal contains a number of impurities particularly sulphur and sediments such as mud, deposited and buried with plant material. When the coal is burnt, it releases these impurities as pollutants into the atmosphere including sulphur dioxide and ash. In Australia, the sulphur levels are low therefore has a greater demand for use.

The Latrobe Valley in Victoria contains some of the worlds richest deposits of brown coal and huge deposits of black coal are found in the Sydney Basin (Hunter Valley, Woollongong and Lithgow)

Petroleum

Petroleum or crude oil consists of a mixture of hydrocarbons. Most of the petroleum comes from the buried remains of marine organisms, particularly plankton and bacteria. The oils and fats of these organisms are converted into hydrocarbons by high temperatures and pressures found deep underground. Due to its density, the oil tends to migrate upwards where it may seep out onto the earth’s surface or become trapped beneath rock.

Natural Gas
Natural gas also comes from marine organisms which accumulate as organic sediment in oceans or inland seas. Over long periods of time, the organic matter was covered by sediment and more sediment. The action of anaerobic bacteria, and the increasing temperature and pressure of being compacted and great depths turned organic material into hydrocarbons.

Describe the use of fractional distillation to separate the components of petroleum and identify the uses of each fraction obtained.
clip_image008Crude oil consists of a complex mixture of hydrocarbon compound molecules. This means that crude oil can be separated into many components by fractional distillation as these components have different boiling and condensation points. This is achieved using a fractionating tower. Firstly, the crude oil is heated to about 400 degrees to produce a hot liquid that goes into the fractionating tower. Inside there are horizontal trays each containing many bubble caps. As vapour rises, it forces up the bubble caps and bubbles through the condensed liquid in the trays.

The fractioning tower is designed so that the various fractions can be separated according to their boiling and condensation points. The higher boiling point components tend to condense to liquid while the lower boiling points continue to rise up the tower. The lower the boiling point of a component, the higher its vapour will rise in the fractioning tower before it condenses. The lighter hydrocarbons will condense towards the top of the tower while heavier ones will condense nearer the bottom.

Roofing tar, road bitumen (asphalt)

Identify the safety issues associated with the storage of alkanes
Alkanes are flammable, especially those with low molecular weights. Candle wax in principally paraffin, which is a high molecular weight alkane. Alkanes are non polar and the only attraction between their molecules being weak dispersion forces. Therefore they easily vaporise and mix with oxygen gas resulting vapour mixture is often explosive and always flammable. If any naked flames or sparks are close by, fires of explosion can occur.

Gaseous fuels such as methane, ethane and prophane must be stored in pressured, strong steel containers and kept cool. Make sure that all taps have a tight seal on them. LPG for example, is a mixture of propane and butane and is stored in this way. The cylinders are filled to less than 85% of their capacity to allow for thermal expansion.

Liquid hydrocarbons have a higher molecular weight but are still volatile. They must be stored in labelled metal containers with tight seals. The opening to the containers should be narrow to avoid vapour from forming as they are flammable. Store fuels in well ventilated areas and in small quantities in case it reacts to air and go into flames.

Describe the condition under which explosions occur and relate these to the importance of collisions between reacting particles.
The 3 requirements in which explosions occur are fuel, oxygen and heat. Explosive combustion occurs when a large amount of hot gas is produced in a very short period of time. This can happen when the fuel is finely divided and well mixed with oxygen, air or compound that act as oxidisers. The internal combustion engine works by vapourising petrol in air and then sparking the mixture, causing an explosion. Anything that increases the rate of reaction at which collisions occur will increase the rate of reaction. In gases react more readily than solids as gas particles collide with large numbers of other gas molecules, making reaction between them possible. Atoms in a solid can only react on the surfaces.

By this it is clear that substance in solution react better and more rapidly that as a solid. When you put two substances together and stir them, it keeps the solid suspended in the solution and exposes its maximum surface area. This also means there are more solids for the solution to react with. Mixing two substances together increases the rate of collision between reactant particles and so increases the rate of reaction. Analyse information and use the available evidence to relate the conditions under which explosions occur to the need for safety in environments where fine particles mix with air.

Explosions occur when the reactions become extremely rapid. This usually happens when there is good contact between reactant particles and when the reaction is highly exothermic with high activation energy.

Once the reaction is initiated, it liberates energy, which heats up the reaction mixture. This makes the reaction go faster, releasing energy more quickly, so there is an extremely rapid escalation in temperature and reaction rate, causing an explosion. In order for the rate to increase this way there must be a good supply of oxygen available to fuel, otherwise a limiting amount of oxygen will slow down the reaction.

Large lumps of fuel such as coal rarely explode because they rapidly use up the oxygen available ate their surfaces. However, very small particles of flammable material dispersed through a volume of air have great potential for causing explosions. The total surface area of the particles is large and each particle has a ready supply of oxygen.

Consequently, one aspect of providing safe working conditions is ensuring that there can be no build up of concentrations of flammable substances. Formation of flammable dust should be minimised, and what does form must be efficiently removed from the air.

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