Salters OCR B Chemistry DF

• Functional group isomerism

  Same molecular formula but different functional groups
• positional isomers

  Same molecular formula but different position of the functional group on the carbon skeleton-different chemical and physical properties
• Chain isomers

  Compounds with the same molecular formula but different structures of the carbon skeleton-similar chemical properties but different physical properties
• What is a structural isomer?

  Structural isomers have the same molecular formula but a different structural formula
• structural formula

  an expanded molecular formula showing the arrangement of atoms within the molecule
• Skeletal formula

  The bonds of the carbon skeleton only, with any functional groups
• Shortened structural formula

  e.g Butan-1-ol is CH3CH2CH2CH2OH
• pi bond

  -a bond that is formed when parallel orbitals overlap to share electrons. -a double bind contains both a sigma and a pi -pi bonds are weaker than sigma so have a lower bond enthalpy
• sigma bond

  - stronger than a pi bond- in single and double bonds
• Alkene shape

  C=C is planar, C-H is 120 degrees
• What shape do alkanes form?

  Tetrahedral109.5degrees
• Halogenoalkanes

  Fluoro/ chloro/ bromo/ iodo
• Arenes

  Another name for aromatic hydrocarbons; they contain an aromatic ring, often benzene.End in -benzene e.g. ethyl benzen
• Alcohols


  CnH2n+1OH-ol
• What is a homologous series?

  Series of compounds with the same general formula
• Naming molecules

  Longest carbon chain :1. Meth2. Eth 3. Prop 4. But 5. Pent 6. Hex7. Hept 8. Oct 9. Non 10. DecBranches:2. Di3. Tri 4. Tetra
• Aliphatic compounds


  Straight, branched or non-aromatic chains Think: al I phatic The i is like a line
• Benzene formula

  C6H6
• Aromatic compounds


  Contain a benzene ringThink: ar O matic, the O is like a ring
• Arenes

  -a group of organic molecules with benzene ring structure
• alkenes

  -unsaturated hydrocarbons-double bond-> high electron density -> reactive-general formula CnH2n-cyclo alkenes have formula CnH2n-2
• alkanes

  -saturated hydrocarbons-no double bonds-general formula CnH2n+2-cyclo alkanes have formula CnH2n
• how can catalysts be poisoned?

  substances adsorb to the surface of the catalyst and block it/ coat it and stop it from working
• Heterogeneous catalyst steps

  1. substances ADSORB to surface of solid catalyst2. bonds weaken and BREAK 3.bonds FORM to make new substances4.new products DIFFUSE away
• why use a catalyst?

  -lower temp required -> cheaper -> less CO2-speeds up reaction-less waste-reduces pollution
• what is cracking?

  breaking longer chain alkanes into shorter hydrocarbons
• what is a heterogeneous catalyst?

  -catalyst in different state to the reactants-a catalyst speeds up a reaction and remains chemically unchanged at the end
• Common exam Question:why is the enthalpy change you have calculated not the same as the real amount?

  -energy lost to surroundings in experiment- incomplete combustion
• how do you find the enthalpy change of something?

  -use a caloromiter-energy from fuel transferred to water-lid prevents heat loss-wind shield to prevent draught moving flame
• energy lost equation


  q=mc∆Twhereq=energy lost/ gained in Joules (J)m=mass of water or solutionc= specific heat capacity T= temperature change in Kelvin (remember: temp change is the same in degrees C as it is in kelvin)
• Hess's Law

  total enthalpy change of reaction is independent of the route takenas long as the initial and final conditions remain the same
• enthalpy change of combustion

  1 mole completely burned

  
• enthalpy change of formation

  1 mole of compound formed

  
• enthalpy change of neutralisation

  acid + alkali -> 1 mole of water

  
• how to find average bond enthalpy

  -find energy needed to break each bond-divide by the number of bonds
• bond enthalpy

  the amount of energy required to break 1 mole of a bond type of a molecule in the gaseous state
• Exothermic reaction

  -releases energy-enthalpy change is NEGATIVE-bond making

  
• Endothermic reaction

  -absorbs energy-enthalpy change is POSITIVE- bond breakingthink: ENDothermic -> it's the END of those bonds because they've broken

  
• Define the term bond enthalpy.

  energy needed to break 1 mole of bondsin the substance in the gaseous state
• Why do bond enthalpies have positive values?

  to break a bond energy has to be put in/breaking bonds is endothermic