Energy, OCR- Unit 5, module 2

Energy, OCR- Unit 5, module 2

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  • Created on: 13-05-12 18:53
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Sameer Biology
Jahabarali
Unit 5 Modul
e 2 Ener
gy
Lattice Enthalpy
Lattice enthalpy ( ) is the enthalpy change when one mole of an ionic compound is formed from its
gaseous ion under standard conditions. It is an exothermic reaction (hence the enthalpy change is negative),
which measures the strength of the ionic bond (the larger
(negative) the Lattice enthalpy, the stronger the bond).
Lattice enthalpy cannot be measure directly.
Born-Haber cycle is a method of calculating enthalpy change that cannot be measured directly, such a
lattice enthalpy using other measurable enthalpy changes, such as:
Signs Enthalpy Changes Definition
Standard enthalpy Enthalpy change when one mole of compound is formed
change of formation by its constituent elements (natural form)
Standard enthalpy Enthalpy change when one mole of gaseous atoms is
change of atomisation formed from its elements in its standard state
first ionisation energy One mole of gaseous 1+ ion forms from its gaseous atoms
second ionisation One mole of gaseous 2+ ions forms from its gaseous 1+ ions
energy
first electron affinity One mole of gaseous 1- ion forms from its gaseous atoms
second electron One mole of gaseous 2- ions forms from its gaseous 1- ions
affinity

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Sameer Biology
Jahabarali
Unit 5 Modul
e 2 Ener
gy
Born Haber cycle is constructed by drawing:
Zero energy level- with all elements in their standard states (datum line)
Lowest energy level- with the ionic solid
Atomisation energy levels- with the element being atomised in gaseous form
Ionisation energy level- with the element being ionised increased by one charge
Electron affinity level- with the element accepting the electron decreased by one charge
All levels are join by arrows indicating:
o Exothermic enthalpy change arrow going…read more

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Sameer Biology
Jahabarali
Unit 5 Modul
e 2 Ener
gy
The tendency of a process to take place depends:
Temperature ( T)
Entropy change in the system ( S),
Enthalpy change( H)
Gibbs free energy change( G) is the balance between entropy and enthalpy changes which determines the
feasibility of a reaction, the relationship being the more negative G, the more feasible the reaction. For
the reaction to take place only thing is required is the activation energy.…read more

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Sameer Biology
Jahabarali
Unit 5 Modul
e 2 Ener
gy
metals or non-metals in contact with their ions in aqueous solution
Ions of the same element in different oxidation states
The standard cell potential is the emf between the two half cells making up the
cell under standard condition.…read more

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Sameer Biology
Jahabarali
Unit 5 Modul
e 2 Ener
gy
Hydrogen absorption within solid materials, through dissociation of H atoms which are
incorporated within a solid lattice as `hydrides'
Limitations of hydrogen fuel cells:
Large-scale storage and transportation, is cost and energy effective
Feasibility of storing pressurised liquid
Current absorbers and absorber of hydrogen have limited life time
Current fuels cells have limited life time
Toxic chemicals in production of fuel cells
`Hydrogen economy' limitations:
Hydrogen fuel cells has to be accepted by the public…read more

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