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CHEM5

Chapter 12.1 Enthalpy change

When we measure heat change at a constant pressure we call it enthalpy change.

Standard enthalpy of formation is the enthalpy change when one mole of a compound is
formed from its constituent elements under standard conditions and all reactants and
products in their standard…

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CH4(g) CH3(g) + H(g)

12.2 BornHaber cycles

The BornHaber cycle is a thermochemical cycle that includes all the enthalpy changes
involved in the formation of an ionic compound.





















Trends in lattice enthalpies:

With smaller radius positive ions and negative ions the lattice enthalpy of formation is more
negative and therefore…

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Reactants Products

The arrows go the wrong way because you are given Bond enthalpy which is the change in
breaking a bond and so in effect forming the elements. All you do is total up the sum of each
arrow, swap one round and add them together. (when you swap…

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Na, Mg and Cl are the only ones that react with cold water

13.2 the oxides of elements in Period 3


The metal oxides are giant ionic lattices. The bonding in aluminium oxide has some covalent
character, this is because Al forms a very small ion that can get close…

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13.3 Oxides of the elements of period 3 and their reaction with acids and bases

Oxide Reaction with H2SO4 Reaction with HCl Reaction with hot conc. NaOH
Na2O Na2O + H2SO4 = Na2SO4
. + H2O
MgO MgO + 2HCl = MgCl2 + H2O
Al2O3 Al2O3 + 6HCl = 2AlCl3…

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When we have the voltage of two half cells you know that the electrons from the more
negative voltage will go to the more positive voltage. This means the more negative one is
going to be producing electrons and getting oxidised.
If a cell ends up having a negative emf…

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Coloured



15.2 Complex formation and the shape of complex ions

All transition metal ions can form coordinate bonds by accepting electron pairs from other
ions or molecules. The number of dative/coordinate bonds a complex has is called the
coordination number.

The electron pair donor to a transition metal is called:…

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15.4 Variable oxidation states of transition elements

Potassium manganate(VII) as an oxidising agent:

MnO4 + 5e + 8H+ Mn2+ + 4H2O

Potassium dichromate(VI) can be used in titration to find out the concentration of Fe2+ ions:

6Fe2+ + Cr2O72 + 14H+ 6Fe3+ + Cr3+ + 7H2O
(the colour change cannot…

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2V2O4 + O2 2V2O5

This is an example of the use of variable oxidation states as a two step catalyst
The overall equation is 2SO2 + O2 2SO3
Homogenous catalysts:

When the catalyst is in the same phase an intermediate species is formed (such as chlorine in
the decomposition of…

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Water ligands can be replaced by neutral ligands, negatively charged ligands, bi or
multidentate ligands (this is called chelation) and replacement can be complete or partial.

Chelation is the formation of complexes with multidentate ligands. An EDTA molecule can
displace all 6 H2O ligands from [M(H2O)6]2+.
16.3 A summary of…

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