Chemistry Unit 2

What is Fractional Distillation?
The separation of the components in a liquid mixture into fractions which differ in boiling point.
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What are methane, heptane and dodecane used for?
Methane-natural gas, Heptane-petrol, dodecane-jet fuel
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How is crude oil formed?
through the action of heat and pressure on plant and animal remains
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What are fractions of crude oil used for?
Many are used as fuels, some processed to make plastics/medicines, some used for tar
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What is cracking?
The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter chain alkanes and alkenes
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Why do we use cracking?
Shorter than alkanes, high demand for petrol, can be used to make plastics, ethene is used to make ethanol
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What is isomerisation?
The conversion of a straight chain alkane into a branched chain isomer
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Isomerisation: How and why?
conditions:with a cataylst and fuel burns more efficiently
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What is reforming?
The conversion of an alkane into either a cyclic alkane or an arene
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Reforming: How and why?
condition: with a catalyst and fuel burns more efficiently
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What are the disadvantages of alkanes?
non renewable, produce atmospheric pollutants: Carbon Dioxide, Carbon monoxide, NOx(acid rain), Sulphur dioxide
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What is a biofuel?
A Biofuel is a fuel derived from recently living material eg. plant/animal waste
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Name 2 biofuels
Ethanol (fermenting sugars in plants) Biodiesel (from plant oils eg. **** seed oil)
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What is the greenhouse effect?
The greenhouse effect is the process in which absorption and subsequent emission of IR radiation by atmospheric gases warms the lower atmosphere and the planets surface
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What are greenhouse gases?
greenhouse gases absorb and re-emit infared (IR) radiation.
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Name 3 greenhouse gases
Water vapour (evaporation of ocean/lakes) Carbon Dioxide (Burning organic matter, volcanic eruptions, respiration of animals) methane (decaying organic matter, produced by animals, production of coal)
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Why do greenhouse gases absorb IR radiation?
the bonds absorb IR which causes bonds to vibrate so IR is re-emmited
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Name some effects of global warming
arctic ice is melting, hurricanes/storms are more frequent, sea levels rise
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What is the evidence for climate change?
ice core samples (carbon dioxide increase in samples since 1800's) temperature measurements (1995-2006 11 of 12 warmest years on record) concentration of carbon dioxide int he atmosphere has increased
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Explain carbon capture and storage
Storage in old geological formations such as old oil fields, injected (as a liquid) deep in the ocean, reacted to form carbonates
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What does a saturated hydrocarbon mean?
the hydrocarbons contain only single bonds
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What are structural isomers?
The same molecular formula but different structural formulas
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What happens when an alkane reacts with a halogen?
You replace one of the hydrogens with a halogen atom
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What is a mechanism?
its a sequence of steps that show the path taken by electrons in a reaction
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What do you call the breaking of covalent bonds?
often referred to as bond fission
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What are the 2 ways in which a covalent bond may break?
1. one electron from the shared pair goes to each atom, products are radicals (homolytic) 2. Both electrons from the bond go to the same atom, products are ions (Hetrolytic)
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What is a radical?
A radical is a species with an unpaired electron
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What are the 3 stages of radical substitution?
initiation, propagation and termination
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How is carbon monoxide formed?
formed via incomplete combustion of a hydrocarbon fuel and its toxic
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What are the concerns about nitrogen oxides?
they contribute to acid rain, can form photochemical smog
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What are the concerns about unburnt hydrocarbons?
can form photochemical smog, react with nitrogen oxides to produce low level ozone (in the atmosphere)
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How can we monitor air pollution?
IR spectroscopy (results can be compared)
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What are the 3 steps of the catalytic converters fitted in cars?
1. adsorption, reacting gases stick to the surface of the catalyst. 2. attraction between molecules and catalyst causes bonds in reaction to weaken (lower Ea) 3. products leave the surface of the catalyst
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Why is a catalytic converter an example of a heterogeneous catalyst?
this is because the catalyst is in a different state to the reactants
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Naturally what happens to the concentration of the ozone layer?
The formation of ozone and the breakdown of it happen at the same rate so the concentration remains constant
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What natural catalysts remove ozone?
Chlorine atoms and nitrogen oxide molecules
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What happens in exothermic reactions?
heat energy is given out to its surroundings so the temperature of the surrounds increase
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What happens in endothermic reactions?
Heat energy is taken in so the temperature of the surroundings decreases
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What is activation energy?
The activation energy is the minimum energy required to start a reaction by the breaking of bonds
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What is bond enthalpy?
the energy required to break, by homolytic fission, one mole of a given bond in the molecules in the gaseous state
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Why are bond enthalpy values always positive?
becuase breaking bonds requires the input of energy
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How do you calculate bond enthalpy?
enthalpy change = energy required to break bonds - energy released when new bonds form
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What are the limitations of bond enthalpy calculations?
Average bond enthalpy values are used rather than specific ones, only apply to the gaseous state
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What are the standard conditions?
temp: 298k and Pressure:1atm
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What is standard enthalpy of formation?
The enthalpy change that opccurs when one mole of a compound is formed from its constituent elements under standard conditions
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What is the standard enthalpy of combustion?
The enthalpy change that occurs when one mole of compound reacts completely with oxygen under standard conditions
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What are the conditions when its not possible to measure the enthalpy change of a reaction directly?
when the reaction is too slow or when the activation is too high
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What must happen for a collision to be successful?
the molecules must collide in the correct orientation and the molecules must collide with an energy greater than the activation energy
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How does concentration effect reaction rate?
the rate increases becuase there are more successful collisions per second, and there are more molecules per unit volume
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How does pressure effect reaction rate?
the rate increases so there are more successful collisions per second and more molecules per unit volume
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How does surface reaction effect reaction rate?
more molecules available to react so more successful collisions
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How does temperature effect reaction rate?
it increases the reaction rate as more molecules have energy greater than activation energy and so there are more successful collisions per second
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How does a catalyst effect the reaction rate?
the rate increases as a catalyst provides an alternative reaction pathway with a lover activation energy
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Why are catalysts important in the Chemical industry?
Lower temperature and pressures are required so the lower the energy demand the less carbon dioxide released, enable reactions with better atom economy (less waste products) to be used, they produce specific products at room temperature
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What is an unsaturated hydrocarbon?
It contains at least one C=C multiple bond
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Why do E/Z isomers occur?
they arise due to the fact that there is restricted rotation about the C=C
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What criteria must be fulfilled for a molecule to have E/Z isomers?
a C=C double bond, each carbon atom in the double bond must be bonded to 2 different groups
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What is an electrophile?
an electrophile is a species that accepts a pair of electrons
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What is a polymer?
a long chained molecular chain built up from monomer units
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What is a monomer?
a small molecule that combines with other monomers to form a polymer
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What is a repeat unit?
A repeat unit is a specific arrangement of atoms that occur in the structure over and over again
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Other cards in this set

Card 2


What are methane, heptane and dodecane used for?


Methane-natural gas, Heptane-petrol, dodecane-jet fuel

Card 3


How is crude oil formed?


Preview of the front of card 3

Card 4


What are fractions of crude oil used for?


Preview of the front of card 4

Card 5


What is cracking?


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