2. developing fuels

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83 Terms

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gas volume

same for any one mole at room temperature and pressure

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number of moles

= volume in dm3 ÷ 24dm3

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room temperature and pressure

298k or 25 ˚c

100 kPa

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ideal gas equation

pV = nRT

p = pressure (Pa), V = volume (m3), n = moles, R = gas constant , t = temperature (K)

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pV÷RT =

moles, rearranged equation of pV = nRT

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gas syringe

used to measure gas volume produced

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enthalpy change

∆h is the heat energy transferred in reaction at constant pressure, kJ mol -1

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exothermic

gives out energy ∆H is negative, typically oxidation like combustion

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endothermic

absorbs energy ∆H is positive eg thermal decomposition or photosynthesis

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breaking bonds

energy is required so endothermic ∆H positive

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forming bonds

energy released so is exothermic ∆H negative

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average bond enthalpies

used to calculate enthalpy changes, for each individual bond , energy needed to break one mole of bonds in gas phase, averaged over many compounds

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enthalpy change of reaction

energy absorbed to break bonds - energy released in making bonds

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short bond length

means theres a higher bond enthalpy due to there been high attraction between atoms

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balanced forces

relation between repulsion between nuclei / electrons and attraction between nuclei and electrons are…

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standard enthalpy change of reaction

∆rHø, when as reaction occurs in molar quantities shown in equation

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standard enthalpy change of formation

∆fHø, when 1 mole of compound is from formed from its elements in standard states under standard condition

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standard enthalpy change of combustion

∆cHø, when 1 mole of substance is completely burnt in oxygen under standard conditions

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hess law

total enthalpy change of a reaction is always the same regardless of the route taken

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enthalpy of reaction

= enthalpy of formation (products) - enthalpy of formation (reactants)

drawn with elements going to reactants and products

<p>= enthalpy of formation (products) - enthalpy of formation (reactants)</p>
<p>drawn with elements going to reactants and products</p>
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enthalpy of formation

= enthalpy of combustion (products) - enthalpy of combustion (reactants)

drawn with products and reactants going to products of combustion

<p>= enthalpy of combustion (products) - enthalpy of combustion (reactants)</p>
<p>drawn with products and reactants going to products of combustion</p>
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reactant enthalpy

bond enthalpy (reactants) - bond enthalpy (products)

<p>bond enthalpy (reactants) - bond enthalpy (products)</p>
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endothermic reaction

enthalpy of reaction increases, with products ending with more energy than reactants started with

<p>enthalpy of reaction increases, with products ending with more energy than reactants started with </p>
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exothermic reaction

enthalpy of reaction decreases, with products ending with less energy than reactants started with

<p>enthalpy of reaction decreases, with products ending with less energy than reactants started with </p>
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enthalpy level digram

a diagram showing reactants, intermediates and products allowing you to see different routes and activation energy

<p>a diagram showing reactants, intermediates and products allowing you to see different routes and activation energy </p>
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calorimetry

used to determine energy given out or absorbed by a reaction by measuring temperature change of water

<p>used to determine energy given out or absorbed by a reaction by measuring temperature change of water </p>
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standard enthalpy change of neutralisation

enthalpy change when an acid and and alkali react to form 1 mole of water

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calorimetry of a flammable liquid

burn a amount of liquid and heat water, record the temperature change and the mass of water

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calorimetry of a solution

add a known volume of acid alkali to a insulated container record the start and end temperature and mass

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calculate enthalpy change kJ mol-1

q = mc∆T

q - enthalpy change

m - mass of water or solution

c - specific heat capacity of water

∆T - change in temp of water or solution

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cause of error in calorimetry

heat loss- shield

incomplete combustion

evaporation

flame distance

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catalysts

increases rate of reaction by providing an alternative pathway with an lower activation energy, without been used by

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haber process

uses an iron catalyst

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cracking

splitting of a long chain hydrocarbon in to smaller hydrocarbons using using a catalyst to reduce the temp needed to 450˚c

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heterogeneous catalyst

catalysts that are in a different physical state as reactants

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heterogeneous catalysts process

reactants adsorb to catalyst surface

bond are weakened so break (forms radicals)

new bonds made and desorb

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adsorption

process of a reactant bonding just enough to catalyst surface that bonds can be easily broken and released

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catalysts poisons

causes them not to work due to surface been covered eg iron by CO or lead on platinum catalytic converters

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alkane

saturated hydrocarbon with general formula CnH2n+2

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alkenes

unsaturated hydrocarbon with double bonds, general formula of CnH2n

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cycloalkanes

saturated hydrocarbon that forms ring, general formula CnH2n

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cyclic alkene

a unsaturated hydrocarbon ring with 2 less H than alkenes, stable due to delocalised structure eg benzene and cyclopentene

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aromatic compounds or arenes

names for compounds with benzene rings

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alcohols

compounds containing -OH hydroxyl group

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electron repulsion

shape is created by electrons trying to be as far aspart as possible

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tetrahedral

shape of alkenes with a bond angle of 109.5

<p>shape of alkenes with a bond angle of 109.5</p>
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trigonal planar

shape around a double bond with a bond angle of 120˚

<p>shape around a double bond with a bond angle of 120˚ </p>
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sigma

type of bond between a single covalent bond between atoms, due to the 2 orbitals overlapping in a straight line

<p>type of bond between a single covalent bond between atoms, due to the 2 orbitals overlapping in a straight line </p>
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<p>sigma and pi bond </p>

sigma and pi bond

type of bond between a double covalent bond, 1 central bond and 1 caused by the overlap of 2 p orbitals sideways, this second one is weaker than the first

<p>type of bond between a double covalent bond, 1 central bond and 1 caused by the overlap of 2 p orbitals sideways, this second one is weaker than the first </p>
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general formula

formula that can describe any member of a family of compounds eg CnH2n+1OH

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molecular formula

formula with the actual number of atoms in a molecule eg C2H10O

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shortened structural formula

shows the atoms carbon by carbon with attached atoms and functional groups eg CH3CH2OH

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structural formula

formula showing how the atoms are arranged with their bonds

<p>formula showing how the atoms are arranged with their bonds </p>
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skeletal formula

shows the bonds of the carbon chain only with any functional groups

<p>shows the bonds of the carbon chain only with any functional groups </p>
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different carbon skeleton

isomers with the carbon chain arranged differently, similar chemical properties but different physical properties

<p>isomers with the carbon chain arranged differently, similar chemical properties but different physical properties </p>
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functional group location

the carbon chain is the same but the functional group is attached to a different carbon, different physical properties and may have different chemical properties

<p>the carbon chain is the same but the functional group is attached to a different carbon, different physical properties and may have different chemical properties </p>
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different functional groups

same atoms arranged into different functional groups very different physical and chemical properties

<p>same atoms arranged into different functional groups very different physical and chemical properties </p>
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double bonds

bonds which atoms cannot freely rotate around causing E/Z isomerism

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stereoisomers

molecules with the same shortened structural formula but different arrangement

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E/Z isomerism

occurs due to lack of rotation around double bonds and different atoms/groups bonded the the carbons, involves H

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opposite sides

E or trans isomer

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same side

Z or cis is

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cis/trans isomerism

isomerism if no H on both sides

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addition polymer

formed when the double bonds in alkens break and bond to each other

<p>formed when the double bonds in alkens break and bond to each other</p>
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hydrogen added

added to change an alkene to an alkane in the presence of a nickel catalyst at 150 ˚c and high pressure or platinum and room temp and pressure

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bromine water

used to test for alkanes as it bonds to the double bond causing a colour change orange to colourless

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electrophilic addition

double bonds open up and atoms are added

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electrophiles

electron pair acceptors eg positively charged ions or polar molecules (double bond)

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electrophilic addition mechanism

  1. double bond repels electrons in Br2 polarising it ∂+Br-Br∂-

  2. electrons are transferred to one Br from the bond, electrons from the double bond are transferred to the other Br and it bonds

    1. a positively charged carbocation intermediate is formed which Br- bonds to
<ol>
<li><p>double bond repels electrons in Br2 polarising it  ∂+Br-Br∂-</p></li>
<li><p>electrons are transferred to one Br from the bond, electrons from the double bond are transferred to the other Br and it bonds </p>
<ol>
<li>a positively charged carbocation intermediate is formed which Br- bonds to </li></ol></li>
</ol>
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hydrating alkanes in presence of acid catalyst

produces an alcohol by electrophilic addition

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alcohol making process

  1. cold conc sulphuric acid reacts with an alkene in electrophilic addition reaction to make an intermediate

    1. add cold water and warm to hydrolyse in to product by removing the SO2 regenerating H2SO4
<ol>
<li><p>cold conc sulphuric acid reacts with an alkene in electrophilic addition reaction to make an intermediate </p>
<ol>
<li>add cold water and warm to hydrolyse in to product by removing the SO2  regenerating H2SO4</li></ol></li>
</ol>
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steam hydration

used to make ethanol by hydrating in steam at 300˚c and 60 atm using solid phosphoric acid catalyst, reversible and low yield 5% but recycles to yield 95%

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complete combustion

exothermic reaction of alkane in oxygen produces CO2 and water

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green house effect

earth radiates infrared radiation and greenhouse gases absorb some of this in the atmosphere keeping earth warm

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incomplete combustion

results in formation of carbon monoxide

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carbon monoxide

mainly produced in car engines and poisonous

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nitrogen oxides

contribute to smog, formed in high pressure and temp of car engines, reacts with sunlight to form ground level ozone which is an irritant

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sulfur dioxide

leads to acid rain, produce when fuel contains it, once in atmosphere it dissolves in moisture forming an acid, which destroys vegetation , corrodes buildings and kills fish in lakes, removed from fuels using calcium oxide

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particulates

tiny particles of liquid or solids suspended in air, which can settle in lungs and cause issues, removed with wet scrubbers and filters

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fossil fuels

non renewable resources like coal, oil and natural ga

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decrease pollution

  • change laws
  • emissions test, compulsory catalytic converter
  • tax fuel
  • car share, public transport, bikes
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renewable fuels

wind, solar and wave power, expensive and need to be extensive

biofuels- produce CO2 and take up farm land

hydrogen- burnt or fuel cell, energy transporter, difficult to transport(liquified)

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energy security

make sure there is enough clean and affordable energy