CHM5

 

Process has enthalpy change= standard enthalpy of formation of CaF2

 


Ca(s) + F2(g) –> CaF2(s)

Explain why the enthalpy of lattice dissociation for calcium fluoride is greater than that

for calcium chloride.

  • Because fluoride (ion) smaller than chloride
  • Electrostatic attraction stronger/ionic bonding stronger/attraction between ions stronger/more energy to separate ions

Use your knowledge of the equation ΔE = hν to suggest what happens to the e‘s

in fluorite when ultra-violet light is absorbed and when visible light is given out.

  • u.v. absorbed: electrons/they move to higher energy (levels)/ electrons excited

;

  • visible light given out: electrons/they fall back down/move to lower energy levels

Explain why Fe3+ ions are as effective as Fe2+ ions in catalysing this reaction.
Equations 1 and 2 can occur in any order.;
COMPLEX ION;

  • Has ligand(s)
  • linked by co-ordinate bonds

FUNCTION OF HAEMOGLOBIN IN THE BLOOD.

Transport of oxygen/O2
With reference to haemoglobin, explain why carbon monoxide is toxic.

  • Because it bonds to the iron/haemoglobin

;

  • Displaces oxygen

Give one reason why methanol, synthesised from carbon dioxide and hydrogen, may

not be a carbon-neutral fuel.

CO2 /CO/CH4 may be produced during H2 manufacture/building the

plant/transport/operating the plant

Describe a standard hydrogen electrode.

  • Hydrogen /H2 gas/bubbles
  • 1.0 mol dm;3 HCl / H+
  • At 298K and 100kPa
  • Pt (electrode)

Suggest one reason why poisoning reduces the effectiveness of a heterogeneous

catalyst.

Poison attaches to surface

Suggest how poisoning of a catalyst, used in an industrial process, can be

minimised.

  • Purify reactants
  • Remove impurities

Give one reason, other than cost, why the platinum electrodes are made by coating a

porous ceramic material with platinum rather than by using platinum rods.

Increases the surface area (so reaction faster)

Suggest why the e.m.f. of a hydrogen; oxygen fuel cell, operating in acidic conditions,

is exactly the same as that of an alkaline fuel cell.

Overall reaction is the same

main advantage of a fuel cell over a

re-chargeable cell such as the nickel; cadmium cell when used to provide power for an

electric motor that propels a vehicle.

  • Lack of pollution
  • Hydrogen and oxygen supplied continuously
  • Can be operated without stopping to recharge

Electron affinity of chlorine is an exothermic change.
Net attraction between the chlorine nucleus and the extra electron
perfect ionic model.

  • Ions can be regarded as point charges (or perfect spheres)
  • Allow no polarisation
  • Only bonding is ionic
  • No covalent character

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