7/29/2019 Chemistry Notes for Test

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1. Explain photosynthesis + photosynthesis is endothermic2. Carbohydrates are molecules made up of carbon, hydrogen and oxygen and include glucose, starch

and cellulose. They are formed by autotrophs through the process of photosynthesis, where

chlorophyll absorbs 2830kJ of energy per mole of glucose created. This energy is stored within the

bonds of the carbohydrate molecules and is released during the process of cellular respiration.During cellular respiration the potential energy of the carbohydrates is converted into ATP, which is

a form of energy more easily used by organisms. The amount of energy released is 2830 kJ per mole

(the same as is absorbed in photosynthesis. + how its necessary for all life

3. Normally, when an organism dies, it is decomposed and its energy returns to the biosphere throughthe carbon cycle, water, and nutrients, however if an organism is fossilised after it dies, the energy is

trapped within its body and under certain circumstances this energy can be converted into fossil fuels.

Different fossil fuels are formed depending on circumstances such as what mixture of plants and

animals was present, how long the material was buried and under what conditions of decomposition

and pressure the fossil fuels were forming. Oil and natural gas were formed by marine animalsburied by ocean or river sediments. Heat, pressure and bacteria combined to cook the organic

material. First this formed a thick liquid (oil) but in some of the hotter areas the process continued

and natural gas was formed. Eventually some of this natural gas and oil moved upwards and found

its way into cracks known as caprocks from which we mine these fossil fuels today. On the other

hand, while coal is created by the same types of forces, coal is formed from the remains of trees,

ferns and other plants that were living 300 to 400 million years ago.

4. Australia is the worlds largest exporter of coal and is ranked sixth in exports of liquefied natural gas,while in contrast most of Australias liquid energy needs are imported. Australia is estimated to hold

6% of the worlds coal resources and 2% of the worlds natural gas resources.

Australia is abundant in black and brown coal. Black: Bowen-Surat (Queensland) and the

Sydney basin (NSW). Brown: abundant and located in Gippsland Basin (Victoria). At the current

rate of production these brown coal reserves will last another 500 years.

Australia has large gas deposits found mostly in the Carnarvon, Browse and Bonaparte basins

off the northwest coast with smaller deposits in the Gippsland basin and the Cooper-Eromanga basin.

At current production these will last around 60 years.

Australias small oil resources are found mostly in the Carnarvon and Gippsland basins.

Coal, petroleum and natural gas are made up of compounds known as hydrocarbons. An

assortment of distinctly different compounds made with different proportions of these elements is

found in the fossil fuels. The fewer carbons in the compound, the lighter the compound and the morelikely the fossil fuel will be in a gaseous form.

Natural gas is defined as being made of hydrocarbons which remain in a gaseous form at

standard temperature and pressure and 20C and thus can be limited to hydrocarbons with four or

fewer carbon molecules: methane, ethane, propane and butane. Made up of methane and these

hydrocarbons, methane = 70-90% of total volume. It also contains impurities such as CO2, hydrogen

sulfide (H2S), hydrogen, nitrogen, helium, and argon which must be removed prior to sale.

Coal can contain as many as 76 of the 92 naturally occurring elements but most only in trace

amounts. There are 8 minerals found in coal enough to be major constituents: quartz, kaolinite, illite,

montmorillonite, chlorite, pyrite, calcite, and siderite. These minerals are made up mostly of oxygen,

aluminum, silicon, iron, sulfur, and calcium. The organic compounds in coal are made up of carbon,

hydrogen, oxygen, nitrogen, sulfur, and trace amounts of other elements.

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The key components of petroleum are carbon (93%97%), hydrogen (10% - 14%), nitrogen

(0.1% - 2%), oxygen (01.% - 1.5%) and sulphur (0.5% - 6%) along with a few trace metals. The

overall properties of different petroleum sources are determined by the percentages of the four main

hydrocarbons found in petroleum, which are typically present at these percentages: paraffins (15% -

60%), napthenes (30% - 60%), aromatics (3% to 30%), with asphaltics making up the remainder.

5. In order for two particles to react, they must collide (with the correct alignment and enough energy tobreak the bonds). Thus the rate of collision affects the rate of reaction, as with fewer collisions there

will be less chance that a reaction will occur.

Orientation of particles. Consider a reaction between ethene and hydrogen chloride:

As a result of the collision, the double bond is converted into a single bond, as a hydrogen atom gets

attached to one carbon, and a chlorine atom to the other. Can only happen if the hydrogen end of the

hydrogen chloride collides with the double bond between the carbons of ethene.

The double bond has a slight negative charge so the hydrogen (slight positive charge) is attracted.

There is a greater chance of correct alignment if the rate of collisions is greater, so in this way, the

higher the rate of collisions, the higher the rate of reactions.

Factors which increase the rate of collision (thus rate of reaction):o concentration (more particles of reactant per unit volume, increasing chances of collision)o state of division of a solid reactant (in smaller pieces, more surface area in contact)o stirring (keep solid suspended in solution maximising the surface area exposed, as well as

refreshing the solution, ensuring there is plenty of solvent for the solute to react with)

6. As the temperature increases the speed (kinetic energy) of the particles increases. This increases therate of collisions, increasing the reaction rate. Increasing the temperature increases the kinetic energy,

thus enabling particles to react now they have sufficient energy.

7. Explain activation energy + A catalyst increases the rate of reaction without being consumed byproviding an alternate pathway for the reaction that requires less activation energy.Homogeneous catalysts are in the same phase (there is no physical separation). Eg. nitrogen

dioxide is the catalyst for the reaction between sulphur dioxide and oxygen.

Heterogeneous catalysts are in a different phase. One or more of the reactants are adsorbed to

the catalyst at active sites where there is an interaction which makes them more reactive (may

involve a reaction with the surface or a weakening of the bonds). Once the reaction occurs the

product molecules are desorbed. Eg. finely divided platinum, which is used to catalyse the reaction

of carbon monoxide and oxygen to create carbon dioxide. This reaction is used in catalytic

converters in automobiles in order to remove carbon monoxide from the exhaust gases.

8. Explosions occur when reactions are occurring very rapidly, which often happens when there is goodcontact between particles, and the reaction is highly exothermic with a high activation energy. Once

the reaction is started, it releases energy as heat, which increases the temperature and speeds up the

reaction. Thus there is a rapid escalation in reaction rate and temperature causing an explosion.

Although large lumps of flammable substances arent likely to explode because there is less

surface area in contact with the air, smaller particles of flammable substances are dangerous and can

go up in flames, especially in a hot workplace. Thus an important component of workplace safety is

ensuring there is little build-up of flammable particles in the air.