Developing Fuels AS Chemistry

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Define exothermic
Energy is released into surroundings, Delta-H is negative
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Define endothermic
Energy is absorbed, Delta-H is positive
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Define heterogeneous
a process involving substances in different phases
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Define Catalyst poisoning
refers to the effect a catalyst can be "poisoned" when it reacts with a compound that binds chemically to its active surface site
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Define catalysis
the process in which a chemical reaction is accelerated by catalyst
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Define catalyst
a chemical that speeds up a chemical reaction and can be recovered chemically unchanged at the end of a reaction
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In which state would a compound have its highest entropy?
Gas, then liquid,then aqueous solution then solid.
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Define entropy
the "number of ways" a chemical system can be arranged. The more ways, the higher the entropy.
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Is bond breaking endothermic or exothermic?
Endothermic
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Is bond making endothermic or exothermic?
exothermic
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Define bond enthalpy
the quantity of energy required to break the bonds of one mole of a gaseous compound. This is always endothermic therefore positive.
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Describe Hess' Law
The enthalpy change of a reaction is independent of the route it takes as long as the initial and final conditions are the same for each route.
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How do you calculate enthalpy change?
mass x specific heat capacity x temperature change. shortened version: (mcDelta-T)
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Define enthalpy change of reaction
the enthalpy change when one mole of matter is transformed by a chemical reaction in standard conditions
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Define enthalpy change of formation
the enthalpy change when one mole of substance is formed from its elements in their standard states under standard conditions
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Define enthalpy change of combustion
the enthalpy change when one mole of a substance in burned completely in oxygen in its standard states.
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What are standard conditions?
Pressure of 1 atmosphere, stated temperature usually 298K (25'C)
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1 mole has a volume of...
...24dm3
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What is the functional group of alcohols?
hydroxyl, -OH
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Describe a simple model to explain the function of a heterogeneous catalyst
1. Reactants get adsorbed on to catalyst surface. 2. Bonds break, new bonds form. 3.Products reabsorb off surface and diffuse away
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Why do we measure bond enthalpies indirectly in Hess cycles?
Because it is difficult to make measurements when everything is in its gaseous state and there also usually multiple bonds in compound
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Why is it that this is so far off the true value?
A bond enthalpy is the average energy needed to break that particular bond as is not specific to the molecule in an equation Bond enthalpies are for gaseous molecules and this may not be the molecules standard state.
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What is crude oil made up of?
a mixture of compounds, mainly hydrocarbons
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How can the components of crude oil be seperated?
fractional distillation, each compound has a different boiling point therefore can condense at different temps.
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What is fractional distillation?
Crude oil is evaporated, vapours condense at different temperatures in fractionating column.
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What are alkanes?
saturated hydrocarbons, general formula is CnH2n+2, they are aliphatic.
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What are cycloalkanes?
Have the general formula CnH2n. Are saturated. Are not aromatic! – They do not have a benzene ring but they aren’t aliphatic because they have a ring structure!
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What are alkenes?
Have the general formula CnH2n. Are unsaturated. Are aliphatic.
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What are arenes?
unsaturated aromatic hydrocarbons.
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What are ethers?
derived from alkanes by substituting an alyoxy group (-OR) for an H-atom. General formula R-O-R
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Define aliphatic
compounds that do not contain a benzene ring.
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Define aromatic
compounds that contain a benzene ring.
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Define saturated
contains maximum amount of hydrogen atoms (no double bonds)
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Define unsaturated
contain one or more double bond
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What is full structural formula?
shows all atoms and bonds
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What is shortened formula?
shows all atoms (but shortened)
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What is skeletal formula?
shows only the shape of carbon framework
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What affect do lone pairs have on bond angles?
-2.5' of what the angle would be
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What makes a linear molecule?
when there are only two groups of electrons of central atoms. 180'
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What are planar molecules?
when there are 3 groups of electrons around the central atom, 120'
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what are tetrahedral molecules?
when there are 4 groups of electrons around the central atom, 109.5'
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what are trigonal bipyramidal molecules?
5 groups of electrons around central atom 90' and 120'
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what are octahedral molecules?
6 groups of electrons around central atom, 90'
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What does a wedge represent in a 3D shape drawing?
a bond in front of the plane of paper
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what does a dotted line represent in a 3D shape drawing?
a bond behind the plane of paper
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Define isomers
same molecular formula but different structural formulas.
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What is chain isomerism?
as the number of carbons in an alkane increases, so do the possible isomers.
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what do the numbers in propon-1-ol and propon-2-ol represent?
the number of which carbon the functional group branches off from.
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what is position isomerism?
when the functional groups are situated in different posistions.
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what is functional group isomerism?
same molecular formula but different functional groups.
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what is meant by auto ignition?
the explosion of a fuel without spark
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define octane number
the tendency of a petrol based fuel to auto ignite.
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if a fuel has a high octane number, what does this mean?
low tendency to auto ignite
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What is meant by knocking?
when hydrocarbons auto-ignite, two explosions occur: one as the fuel-air mixture catches fire as its compressed and another when the spark occurs.
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The more branched an alkane the ______ the octane number
Higher
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the shorter the alkane, the _______ the octane number
Higher
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What happens in isomerisation?
Straight chain alkanes are heated in the presence of a catalyst,chains break, fragments join together again as branched chains,products pass over a zeolite (acts as a sieve) separating straight chains from branched ones,the straight ones are recycled
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What happens in reforming?
Naptha is passed over a catalyst which causes the alkanes to be converted into rings with the loss of hydrogen.Catalyst is Al2O3
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What happens in cracking?
breaking up large hydrocarbons into smaller more useful ones. Done under high temperatures in the presence of a catalyst.
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What does isomerisation, reforming and cracking all do?
Increase the octane number and consequently the performance quality.
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What are the 5 main pollutants?
Unburnt Hydrocarbons, Carbon Monoxide, Carbon Dioxide, Nitrogen Oxides, and Sulfur Oxides
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How are unburnt hydrocarbons produced?
incomplete combustion and evaporative emissions
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What do unburnt hydrocarbons contribute to?
formation of photochemical smog which causes respiratory problems
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How can unburnt hydrocarbon be reduced?
by catalytic converters and oxygenates
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Other cards in this set

Card 2

Front

Energy is absorbed, Delta-H is positive

Back

Define endothermic

Card 3

Front

a process involving substances in different phases

Back

Preview of the back of card 3

Card 4

Front

refers to the effect a catalyst can be "poisoned" when it reacts with a compound that binds chemically to its active surface site

Back

Preview of the back of card 4

Card 5

Front

the process in which a chemical reaction is accelerated by catalyst

Back

Preview of the back of card 5
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