A.S ChemUnit 2 Module 1 Definitions

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Section 1

Question Answer
Structural FormulaA structural formula shows the minimal detail for the arrangement of atoms in a molecule
Skeletal FormulaA skeletal formula is a simplified organic formula, with hydrogen atoms removed from alkyl chains, leaving just a carbon skeleton and associated functional groups
Displayed FormulaA displayed formula shows the relative positioning of all the atoms in a molecule and the bonds between them
General FormulaA general formula is the simplest algebraic formula for a member of a homologous series
Structural IsomersStructural isomers are molecules with the same molecular formula but with different structural arrangements of atoms
SteroisomersStereoisomers are compounEds with the same structural formula, but with a different arrangement of the atoms in space
E/Z isomerismE/Z isomerism is a type of stereoisomerism in which different groups attached to each carbon of a C=C double bond may be arranged differently in space because of the restricted rotation of the C=C bond
Cis/trans isomerismCis-trans isomerism is a special type of E/Z isomerism in which there is a non-hydrogen group and hydrogen on each C of a C=C double bond: the cis isomer (Z isomer) has the H atoms on each carbon on the same side; the trans isomer (E isomer) has the H atoms on each carbon on different sides.

Section 2

Question Answer
What is crude oil a mixture of and what are many of these?Crude oil is a mixture of over 150 different hydrocarbons, most of which are unbranched (straight-chain) alkanes
Why isn't crude oil very useful in its native state?Crude oil doesn't ignite easily, and so is not very useful in its native state
Where is crude oil refined?Crude oil is refined at a distillation plant
What is a hydrocarbon?A hydrocarbon is a compound of hydrogen and carbon only
Where does fractional distillation take place?In a fractionating column
What happens to the crude oil at the distillation plant?Mixture of hydrocarbons is first separated into fractions. Each fraction consists of a mixture of hydrocarbons with similar boiling points. Pure liquids have a fixed boiling point. A pure hydrocarbon can be obtained by further distillation of a crude oil fraction
Steps of crude oil distillation1.Crude oil is first vapourised by heating and is then passed into a fractionating column. 2. The column is hotter at the bottom than at the top, and the gases move through the column through a series of bubble caps. 3.Eventually, the gases reach a temperature that is lower than their boiling points, and here the vapour condenses to a liquid. 4.The liquid fractions are then tapped off into storage containers
Where do short chained hydrocarbons condense?Short-chained hydrocarbons with lower boiling points condense near the top of the column. Longer chained hydrocarbons with higher boiling points condense nearer to the bottom
What is residue from the process called and how is it removed?Residue from the process is bitumen, which is removed from the bottom of the column
Do gases condense in the fractionating column?Gases do not condense and pass through the outlet at the top of the column as petroleum gas

Section 3

Question Answer
What can fractions be used as?Fractions can be used as fuels or may be further processed to make petrochemicals
Why does boiling point increase as chain length increases?As chain length increases boiling point increases because the intermolecular forces between the molecules get stronger. In a longer-chained alkane, there are MORE POINTS OF CONTACT between the molecules leading to more Van der Waal's forces between the molecules. It therefore takes more energy and a higher temperature to separate the molecules.
What molecules does a crude oil fractiosn consist of and what forces of attraction act between these?In a crude oil fraction there are many different alkane molecules. There are weak intermolecular forces of attraction between the molecules called van der Waal's forces. In order to boil, these forces must be broken
Does a branches isomer have a lower or higher melting point than an unbranched isomer?A branched isomer has a lower boiling point than the unbranched isomer. In a branched alkane, there are fewer points of contact between molecules, leading to fewer van der Waal's forces between moleucles. Branched molecules can't get as close to each other as unbranched ones, thus decreasing the intermolecular forces between the molecules. Therefore less energy is required to separate the molecules.

Section 4

Question Answer
What are short-chain alkanes valuable as? What do they burn in and what do they produce?Short-chain alkanes are valuable as clean fuels. They burn in a plentiful supply of oxygen to form carbon dioxide and water.
Does methane burn cleanly in oxygen? What is it used for?Methane burns cleanly in oxygen to produce carbon dioxide and water. It is used for domestic heating and cooking.
What is octane used for?Octane is present in petrol, used to fuel the internal combustion engine.
What are propane and butane used for?Propane and butane are EASILY LIQUEFIED and are commonly known as LPG - they are used as fuels in BARBECUES and PORTABLE COOKING APPLIANCES.
What happens to octane in a limited supply of oxygen?In a limited supply of oxygen some of the octane will undergo incomplete combustion to form CARBON MONOXIDE rather than carbon dioxide.
What is carbon monoxide?Carbon monoxide is a colourless, odourless, poisonous, gas
How can carbon monoxide kill you?Carbon monoxide prevents the haemoglobin in red blood cells from binding with oxygen and the body's tissues become starved of oxygen - can be fatal.
How can carbon monoxide be formed in the home?Carbon monoxide can be formed in the home from faulty domestic heating systems, inadequate ventilation, blocked chimneys.
What can you do in the home to protect against carbon monoxide poisoning?Fit carbon monoxide detectors in the home

Section 5

Question Answer
Why are short chained hydrocarbons in high demand?For use as fuels (alkanes). For use in polymer production (alkenes).
What is cracking used for?Cracking is used to break down long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes.
What does catalytic cracking require and what happens during it?Catalytic cracking requires a catalyst. Long-chained alkanes are broken randomly - there are many different equations for cracking a starting material
Are the octane ratings of straight-chained alkanes high or low and what does this mean?Straight-chained octanes have low octane ratings (they don't burn very well)
What does the petroleum industry do?The petroleum industry processes straight-chain hydrocarbons into branched alkanes and cyclic hydrocarbons to promote efficient combustion
What is isomerisation?Isomerisation is the process that converts unbranched alkanes into branched alkanes
What is reforming?Reforming is the process by which aliphatic hydrocarbns can be converted into cyclic or aromatic hydrocarbons - involves the loss of a hydrogen molecule (or more than one)

Section 6

Question Answer
What i sover 90% of crude oil produced in the world used for?Over 90% of crude oil produced in the world is used as a source of fuel
What are petrochemicals made from?Petrochemicals such as plastics are made indirectly from crude oil.
Are the earth's known deposits of crude oil being replenished?The Earth's known deposits of crude oil are depleting at an alarming rate
What are the properties of a good fuel? e.g.? but?A good fuel needs to be readily available, easily transported and inexpensive, e.g. oil. But the price of oil has significantly increased in recent years
Do all hydrocarbons produce pollutants or not?All hydrocarbons produce pollutants
What do sulphur dioxide and nitrogen oxides do?Sulphur dioxide and nitrogen oxides contribute to acid rain.
What are increased co2 levels from combustion of fossil fuels leading to?Increased CO2 levels from combustion of fossil fuels is leading to global warming.
What do greenhouse gases do?Greenhouse gases prebent heat from escaping the atmosphere, and therefore lead to increased temperatures on earth.
What is biodiesel and what can it be used as?Biodiesel is a fuel oil derived from natural sources such as plants. Biodiesel can be used 100% pure, but its usually blended with diesel.
Problems with rich countries?Desirability of renewable fuels by 'rich' countries may lead to problems of food supply for countries supplying the 'crops for fuel'
How can ethanol be made?Ethanol can be made by fermenting sugar and other carbohydrates.
What happens to ethanol in a plentiful supply of oxygen? What can be done to make ethanol burn more efficiently?In a plentiful supply of oxygen ethanol burns efficiently to give carbon dioxide and water. It can be blended with petroleum, causing it to burn more efficiently - this significantly reduces harmful exhaust emissions and no major engine modifications are needed.

Section 7

Question Answer
Why is ethanol renewable?When made via fermentation, its raw material is sugar, which is renewable. The carbon dioxide given off when ethanol was burned was taken in by the plants from the atmosphere as they grew, so it's carbon neutral
Why isn't ethanol renewable?Crude oil takes millions of years to form and is finite. Ethanol obtained from the hydration of ethane is non-renewable, as ethane is derived from crude oil

Section 8

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