Chemistry Unit 5 all notes

These are the notes I made, not everything is in great detail as I made them for myself and didn't focus on the bits I didn't really need to. hope they help

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  • Created on: 21-06-12 16:11
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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 states.
H2(g) + ½ O2(g) H2O(l)
Standard enthalpy of atomisation is the enthalpy change when one mole of gaseous atoms is
formed from its element in its standard state under standard conditions.
Mg(s) Mg(g)
First ionisation energy is the enthalpy change when one mole electrons is removed from one
mole of gaseous atoms.
Na(g) Na+(g) + e
First electron affinity is the enthalpy change when one mole of electrons is added to one
mole of gaseous atoms.
O(g) + e O(g)
Lattice formation enthalpy is the enthalpy change when one mole of solid ionic compound is
formed from its gaseous ions.
Na2+(g) + Cl2(g) NaCl(s)
Enthalpy of lattice dissociation is the enthalpy change when one mole of solid ionic
compound is broken into its constituent gaseous ions.
Enthalpy of hydration is the enthalpy change when water molecules surround one mole of
gaseous ions.
Na(g) Na(aq)
Enthalpy of solution is the enthalpy change when one mole of solute dissolves completely in
sufficient solvent to form a solution which the ions are far enough apart to not interact.
NaCl(s) Na2+(aq) + Cl2(aq)
Mean bond enthalpy is the enthalpy change when one mole of gaseous molecules each
break one covalent bond to form two free radicals, averaged over a range of compounds.

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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 the arrow make sure you
swap if its negative number to a positive or visa versa)
12.…read more

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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 to O and distort its
electron cloud.
Silicon oxide is macromolecular
P and S oxides are simple covalent molecules.…read more

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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
.…read more

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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 it is not feasibl.
14.…read more

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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.…read more

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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 be seen though so an indicator of diphenylaminesulfonate is used
which turns from colourless to purple)
Typical transition metal species:
[M(H2O)6]2+ acid solution
[M(H2O)4(OH)2] neutral
[M(H2O)2(OH)4]2 alkaline
2CrO4 is yellow
Cr2O72 is orange
15.…read more

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V2O4 + 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 ozone)
In an energy profile diagram it would show as
two lower bumps rather than one large one
due to the 2 step process, the first step being
making the reactive intermediate.…read more

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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 acidbase and substitution reactions of some metal ions
The orange highlighted compounds
are ones that do not follow the
pattern of either the M2+ or M3+
metal ions.…read more

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