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Entropy Changes

High Entropy: Can be rearranged in many ways and leave the same structure. Very chaotic/disordered.

Low Entropy: Can be rearranged in very few ways and leave the same structure. Very ordered/regular.

HIGH  Gas --> Liquid --> Solid  LOW

Entropy change of reaction = 

total entropy of products - total entropy of reactants.

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Positive and Neagtive Entropy changes

If a change makes a system more random, DeltaS is positive.

If a change makes a system more ordered, DeltaS is negative.

H2 (g) + 1/2O2 (g) --> H2O (l)          Sign: -ve

The reactants have gaseous molecules and the product is a liquid. Gas has a higher entropy than liquid, so the product side is more ordered, therefore Delta S is negative.

2C (s) + O2 (g) --> CO2 (g)                Sign: +ve

The reactants have more moles of solid than gas. Because the product is a gas, it has less order than the reactants, therefore Delta S is positive.

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Enthalpy Change of Solution/Hydration

Enthalpy Change of Solution: The enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions.

Can be an endothermic or an exothermic process (Delta H is positive or negative).

Enthalpy Change of Hydration: The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water, forming one mole of aqueous ions under standard conditions.

Hydration is an exothermic process (Delta H is negative).

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Addition of NaOH (OH-) to complex Ions.

Cu2+ (aq) + 2OH- (aq) --> Cu(OH)2 (s)

Blue solution --> Blue/Green precipitate

Co2+ (aq) + 2OH- (aq) --> Co(OH)2 (s) 

Dark red/pink solution --> Dark blue precipitate (Beige in presence of air)

Fe2+ (aq) + 2OH- (aq) --> Fe(OH)2 (s)

Pale Green solution --> Dark green precipitate 

Fe3+(aq) + 3OH- (aq) --> Fe(OH)3 (s) 

Dark Orange solution --> Rusty Brown precipitate



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Ligand Substitution colour changes.

Copper (II) Sulphate + Ammonia:

 Blue solution--> Light Blue Precipitate --> Dark Blue Solution

Copper (II) Sulphate + HCL:

 Blue solution -->  Yellow Solution

Cobalt (II) Chloride + HCL: 

 Dark red/pink solution --> Dark Blue/ Purple solution

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