AQA alevel chemistry

• What is a half equation?

  An equation that shows oxidation or reduction
• How to find a half equation from a redox reaction?

  Identify Oxidation & ReductionWrite the half-reactions for oxidation and reduction.Balance Atoms (Except O, H)Balance O with H2OBalance H with H+Balance Charge with e-Combine and equalise electrons in each half equation
• what occurs at the anode

  oxidation
• what occurs at the cathode

  reduction
• in electropotential cells which is the negative electrode


  the anode,

  because oxidation occurs there

  and e- are produced there
• what is the purpose of the salt bridge?

  -completes the circuits

  -allows the flow ions from one electrode to the other (current)

  -prevents the build up of charge
• what does || mean

  salt bridge
• what does | mean

  phase boundary
• when is a comma used in the cell convention diagrams?


  when species are in the same phase
• when is there a phase change in electrochemical cells?

  when there is a change of PHYSICAL state (s, l, g, aq)
• what factors in an electrochemical cell effect it's voltage?

  -concentration of both substances

  -temperature

  -pressure
• what does not effect the cells voltage?

  -surface area of the electrodes
• what are standard conditions for an electro chemical cell?

  -298k

  -1moldm^-3

  -100kpa
• what would an ideal volt metre have?

  very very high resistance,

  so no current flows through it
• what effect does increasing the concentration of the oxidised substance do?

  -equilibrium favours the side of products being produced (le chatilier)-so oxidation happens at a faster rate-so more e- flow to the other side,producing a larger voltage
• what effect does increasing the concentration of the reduced substance do?

  -equillibrium now favours the side of the reactants-reduction happens at a faster rate, so less e- are being produced-so there is less flow of e- and there is asmaller voltage produced
• describe the structure of a standard hydrogen electrode

  -hcl acid electrolyte

  -unreactive and conducting plat electrode

  -hydrogen gas within platinum electrode

  -a copper wire that connects electrode to the other
• what is the emf of a hydrogen electrode

  0
• what does a negative electropotential mean

  substance more likely to oxidise
• what does a positive emf for a substances electropotential

  substance more likely to reduce
• what is the formula for calculating emf

  e potenital of reduced - e potential of oxidised
• when is does an emf show that an electrochemical cell is not feasible

  when the emf calculated in negative
• what are the uses for rechargeable lithium cells

  -tech

  -computers

  -phones

  -laptops
• give the equations for the reactions at the anode and cathode of the lithium cell respectfully

  Li -> Li+ + e-

  Li + CoO2 + e- -> Li+(CoO2)-
• give the overall equation for the lithium cell

  Li+ + CoO2 -> Li+(CoO2)-
• what are the advantages of using lithium rechargable batteries?

  -lightweight

  -rechargeable (less disposal waste)

  -sustainable if electricity used to recharge them is
• disadvantages of lithium batteries


  -incorrect disposal is bad for environment

  -lithium mining is bad for env

  -not sustainable if electricity reused to recharge them isnt
• what are the uses of alkaline hydrogen fuel cells

  -cars

  -electricity generators for spacecraft
• advantages of alkaline hydrogen fuel cells

  -only waste product is water

  -do not need recharging

  -very efficient
• disadvantages of alkaline hydrogen fuel cells

  -made from crude oil

  -storing and transporting hydrogen is dangerous

  -storing and transporting hydrogen is expensive
• what are the half equations for the alkaline hydrogen fuel cells?

  Anode: 2H2​ →4H+ + 4e−. | oxidisedCathode:O2​+4H++4e−→2H2​O \ reduced
• overall equation for alkaline hydrogen fuel cell reaction

  Overall: 2H2 ​+O2​→2H2​O