Cards (29)

    • Way to remember in calculations if its (products - reactants) or (reactants - products) for enthalpy change of
      formation,standard entropy,combustionandbond enthalpyFPAR(products-reactants) ΔfHSPAR(products-reactants) ΔS
      CRAP(reactants-products) ΔcHBRAP(reactants-products) Δ bond enthalpy
    • Conversion between cm^3 dm^3 m^3
      CDM remember this (Ngolo Kante)

      cm^3 → dm^3 → m^3

      going forwards multiply by 1000
      going backwards divide by 1000
    • Converting between mg and g and understanding how much a tonne is

      mg → g
      going forwards divide by 1000 from mg to get into g

      1 tonne= 1000kg = 1,000,000g
    • Explaining shapes/bond angle- EXAM TECHNIQUE
      -Electron pairs repel eachother as far away as possible-This molecule(s) has/have xbonding pairsand ylone pairs-Therefore the shape is...-Lone pairs repel more than bonding pairs-Therefore the bond angle is ….-If there’s a double bond involved, refer to areas of electron density instead of electron pairs. If there’s a double bond involved, talk about x single bonds, y double bonds and z lone pairs.
    • Explaining why a molecule is (
      non) polar- EXAM TECHNIQUE- if the bonds arepolarthe molecule isasymmetrical – so the dipoles don’t cancel out- if the bonds arenon-polarthe molecule issymmetrical – so the dipoles cancel out
    • How do London forces arise- EXAM TECHNIQUE
      -Electronsmove-They can get into anuneven distribution-This creates aninstantaneous dipolein an atom/molecule-Thisinduces dipoles in neighbouring atoms/molecules.
    • Explaining the trend in first ionisation energies- EXAM TECHNIQUE
      -Moving from ….. to …..-Thenuclear charge increases/decreases(however?)-Thedistancebetween thenucleus and the outermost electron(s) increase/decreases-Shieldingremains the same/increases/decreases-Nuclear attractionfor the outermost electronincreases/decreases-Theenergyneeded toremove an electronincreases/decreases.
    • Explaining dip from Beryllium to Boron (or Mg to Al) - EXAM TECHNIQUE

      outerelectron is in ap subshell, which is higher energy than thes subshellof Be/Mgthereforeless energyis required toremovetheelectron
    • Explaining the dip from
      NitrogentoOxygen(orPtoS)- EXAM TECHNIQUEouter electron inN/Pis in ap orbital on its own (p3 )whereasO/S has a p4 configurationwithtwo electrons in one orbital.Spin pair repulsionreduces the energyneeded toremoveanelectron.
    • Explaining the electrical conductivity of aqueous ionic compounds
      Aqueous salts conduct because they havemobileions.
      Ensure to saymobile(free mobile charged carriers)
    • Why is it unlikely that a reaction could take place in one step- 2 REASONS
      -stoichiometryin therate equation does not matchthestoichiometryin theoverall equation
      -collisionsareunlikelywith more than 2 or more ions/species/particles
    • Kc change with concentration/temperature- EXAM TECHNIQUE

      1. Kc does(n’t) change – itonly changes with temp
      2.Increase/decreaseof[X] increases/decreasesthenumerator/denominatorof the Kc expression
      3. (Refer to exo/endothermic reaction if relevant)
      4. So moreX/Yis made todecrease/increasethenumerator/denominatortorestore/increase /decreasetheequilibrium Kc.
    • Kc change with pressure- EXAM TECHNIQUE
      1. Kcdoesn’tchange – itonly changes with temp
      2. Theconcentrationsof (all reactants and products)increase/decrease
      3. However, thenumerator/denominatorincreases/decreases more/less
      4.So moreX/Yis made todecrease/increasethenumerator/denominatortorestoretheequilibrium Kc.
    • Factors to consider when explaining
      reactivity down/up groups2 and 7-Distance between nucleus and electron(s) to be lost/gained-Increased/decreasedshielding-Increased/decreasednuclear attraction-Easier/hardertoremove/gainan electron
    • Explaining indicator colour changes HA <=> H+ + A--EXAM TECHNIQUE
      Acid:[H+] increasesH+ + A- -> HAequilibrium shifts to the lefttherefore becomes (red)
      Alkali:[H+] decreases/ [OH-] increasesH+ + OH- -> H2OHA -> H+ + A-equilibrium shifts to righttherefore becomes (blue)
    • How does a buffer solution work- EXAM TECHNIQUE
      Acid:[H+] increasesH+ reacts with A- to form HAequilibrium shifts to the left removing most of the H+ ions
      Alkali:[OH-] increasesOH- reacts with H+ to form H2O[H+] decreases and HA dissociates to form more H+equilibrium shifts to right to restore the concentration of H+ ions
    • What effect will concentration changes have on a half-cell's electrode potential value- EXAM TECHNIQUE
      1) [X]increases/decreases2) equilibrium shifts to theright/left3) thereforereducing/oxidising[X]4) andabsorbing/releasingmore electrons5) and making E morepositive/negative6) if talking about cell potential, talk about thedifferencewhether its smaller or larger
    • What makes a fuel cell different from an ordinary cell? (COMMON QUESTION)
      A fuel cell usesenergyfrom the reaction of afuel with oxygentogenerate a voltage
    • Haemoglobin ligand substitution- EXAM TECHNIQUE
      -In the lungs, theiron (II) ionof haemoglobin forms acoordinate bondwithO2-O2is thenreleasedin thetissues(which is then replaced immediately by H2O/CO2)-CObinds tosame site as O2, replacing the O2-CObinds more strongly than O2, so theligand substitution is irreversible: the haemoglobin is useless-Tissuesbecomestarvedofoxygen
    • Reducing percentage uncertainty- 2 REASONS
      -usegreater quantitiese.g. a larger mass or larger volume of water-use equipment with greater precision
    • When you calculate Delta S (entropy) what must you remember to do

      Divide by 1000to get it from J to kJ
    • ORGANIC AFTER THIS CARD
      ORGANIC AFTER THIS CARD
    • Purifying a solid- EXAM TECHNIQUE
      -Filterreaction mixture underreduced pressure-(recrystallisation)Dissolveimpure product inminimum volume of hot solvent-Leave tocooland allowcrystalsto form-Filtercrystals underreduced pressureagain-Rinsethem withice-cold distilled water-Leave them todryon a dish-Decant-Record the melting point if you want to identify the product
    • Purifying a liquid- EXAM TECHNIQUE
      -Allow tocool-Decantintoseparating funneland run off aqueous layer-AddNa2CO3until bubbling stops toremove excess acidand run off aqueous layer again-Run into beaker-Addanhydrous MgSO4to dry-Redistiland collect atboiling point
    • Benzene's relative resistance to bromination compared to alkenes- EXAM TECHNIQUE

      1.Thepi-electronsaredelocalisedinbenzene, butlocalisedinalkenes2.Thepi-electronsare therefore more spread out benzene (lower pi-electron density)3.Therefore,bromineispolarised lessbybenzene…4.…andattracted less. (less susceptible to an electrophilic attack)
    • Why phenol does bromination more readily than benzene- EXAM TECHNIQUE
      1.Thelone pairfrom the-OH group in phenolisdelocalisedinto thebenzene ring. (spelling)2.So theelectron density increases…3.…and theelectrophileis more stronglyattracted.(more susceptible to an electrophilic attack)
    • Mass spec fragments: you must always...
      input the+chargenext to the fragment
      e.g. CH3CH2+, CH3CO+ etc.
    • Explaining stereoisomerism (or lack of it) in alkenes- EXAM TECHNIQUE
      -There isrestricted rotationaround theC=C group-EachC atomin that group is/n’t bonded totwo different atoms/groups
    • Markownikoff's rule: explain why one product is more abundant than the other- EXAM TECHNIQUE
      themajorproduct is formed from asecondary/tertiarycarbocation intermediate.
      Theminorproduct is formed from aprimary/secondary carbocation intermediate, which isless stable.