thermodynamics (alevel only)

  • Created by: lridgeway
  • Created on: 21-10-18 17:05
What is the alternative route used to calculate enthalpy of solution?
lattice enthalpy of formation(or dissociation) then hydration enthalpies of ions
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Will enthalpy of solution be exothermic or endothermic?
can be either it depends on the reaction
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what would you use to calculate lattice enthalpy of formation or dissociation?
born-harber cycle
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If you are calculating lattice enthalpy of formation which order do you move round the cycle?
-enthalpy of formation + atomisation of metal + ionisation of metal + atomisation of non metal + electron affinity of non metal
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What is the perfect ionic model (PIM)?
a way of thinking about ions in order to make useful prediction about properties
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What does the PIM say a perfect ion is?
perfectly spherical and has an even distribution of charge
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What does the PIM always do with enthalpy?
under estimate them (lower value than reality)
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What actually happens to ions which the PIM fails to account for and if the reason for the under estimation of enthalpies?
In reality ions are not perfect spheres, they become polarised, this means ionic compounds often have a little bit of covalent character which makes the bonds stronger and therefore enthalpies stronger.
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What is entropy?
disorder
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What state has most entropy?
gases have most entropy then liquids and least entropy is solids
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How does entropy vary with temperature?
it increases with temperature as more kinetic energy so more movement which means more disorder is created?
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Where are there big entropy jumps?
between state changes, liquid to gas change is greater than solid to liquid change as larger amount of disorder created
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What happens to entropy at 0K?
entropy is 0
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What is the symbol for entropy and what are the units?
S and Jmol-1K-1
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How do you calculate entropy change?
entropy of products - entropy of reactants
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What is Gibbs free energy (G) equation?
^G = ^H - T^S
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What happens when ^G is < 0?
the reaction is feasible
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What is meant by the term feasible?
the reaction can happen not that it will happen
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What happens at state changes?
^G = 0
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What must a reaction be to always be feasible?
exothermic (^H -ve) and positive entropy change (^S +ve)
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What must a reaction be to never be feasible?
endothermic (^H +ve) and negative entropy change (^S -ve)
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What must a reaction be to be feasible at high temperatures?
endothermic (^H +ve) and positive entropy change (^S +ve)
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What must a reaction be to be feasible at low temperatures?
exothermic (^H -ve) and negative entropy change (^S -ve)
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Other cards in this set

Card 2

Front

Will enthalpy of solution be exothermic or endothermic?

Back

can be either it depends on the reaction

Card 3

Front

what would you use to calculate lattice enthalpy of formation or dissociation?

Back

Preview of the front of card 3

Card 4

Front

If you are calculating lattice enthalpy of formation which order do you move round the cycle?

Back

Preview of the front of card 4

Card 5

Front

What is the perfect ionic model (PIM)?

Back

Preview of the front of card 5
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