Handouts Flashcards
When do you get high spin?
Always for tetrahedral as Pairing Energy always higher than CFS. Octahedral 1st series
Spontaneity of reaction, what does E show
E = +ve the reaction as written is spontaneous
E = -ve the REVERSE reaction is spontaneous
delta G = -nFE
What do electrodes show?
-ve = reducing agent, +ve = oxidising agent… magnitude shows strength
Latimer diagram
Highly oxidised on the left e.g. +7 –> +1
Standard potential for overall reaction
E RHD - E LHS
Can conclude that species is unstable if pot. on right of species is more +ve than left
Anything that alters delta G will change the redox potentials- 4 things
Conc. Temp. Other reagents which are not inert. pH
pH is most important so construct Latimer diagrams for two extremes of pH=0 and pH=14 (1M acid, 1M base)
In a Frost Diagram the most stable species…
lie lowest
plot a Frost Diagram
vE vs Oxidation no.
slope = standard potential, more +ve means more liable to undergo reduction, less +ve more liable to undergo oxidation
What do Frost Diagrams show?
Species high on rhs are oxidising agents towards species on lhs and vis versa
if line connecting two species is +ve the higher lying is oxid agent
if line has -ve slope higher species is reducing agent
species likely to undergo Disproportionation
species lying above line connecting neighbours- TDY unstab. towards disproportionation
How can you stabilise High oxidation state TMs
Complex by other species which are even stronger oxid. agents- O2-, F-
Conditions for Standard Solid State Reaction
Direct reaction of a mixture of solid starting materials
most widely used method for synthesis of organic solids
High temperatures- over 900C
Long reaction times- several hours/ days with intermediate grinding
need correct ratios otherwise will have impurities
controlled atmosphere- o2, air, n2 or vacuum
why need high temp and long times?
Formation of product nuclei is difficult- large distance between reactants and products- large amount of structural reorganisation
2- growth product layer may be even more difficult
3 possibilities for RDS in SS reaction
- Transport of matter (IONS) to reaction surface
- reaction at the surface/ interface
- Transfer of matter away from reaction interface
Ad. of SS
Disad.
+ easy, effective
- high temp + long therefore, lots of energy
- inhomogeneity of mixture- impurities (regrind + reheat)
- volatile products (high temp can lead to loss of reactant)
- some phases only stable at low temperatures
