2/Lattice enthalpy and free energy Flashcards
What effects ionic interactions?
Charge, Ionic Size, Lattice structure
What is lattice enthlpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard condiditions.
Features of lattice enthalpy?
- Exothermic - as bonds are forming
- large number = strong bond
- cant measure directly
DIfference between a born haber cycle and hess cycle?
born haber shows the energy on the side
Born haber will show it step at a time in a complete circle, hess can have two routes back up.
How to use a cycle to find lattyice enthalphy? (using formation)
- Lattice enthally (gas ions -> lattice)
- enthalpy of formation (elemenets ->lattice)
- enthalpy of atomisation (elements -> gaseous elements)
- Electron affinity and ionisation energy(gaseos elements -> gaseous ions)
Enthalphy of formation?
enthalphy change that takes place when one mole of a compound is formed from its consituent elements in their sandard states under standard conditions
enthalphy change of atomisation?
the enthalphy change that takes place when one mole of gaseous atomes forms from the element in its standard state.
first ionisation energy?
the enthalphy change that takes place when one electron is removed from every atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
first electron affinity
the enthalphy change that takes place when one electron is added to every atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.
how do theoretical lattice enthalpy and experimental one different?
- theoretical from carege size and sturcture
- theoretical always less exothermic
- this is due to theorectical assumic all atoms go ionic when they dont
- More polar= less difference.
what is the enthalpy change of solution
the enthalphy change when one mole of a compound is compleltly disolved in water under standard condiitons.
enthalpy change of hydration?
the enthalpy change when one mole of isolated gaseous ions is disolved in water forming one mole of aqeuous ions under standard conditions.
How to use a cycle to find lattyice enthalphy? (using solution)
- enthalpy of solution (compound -> aqeous ions)
- enthalphy of hydration (gaseous ions to aqeous ions)
- Lattice enthalphy (gaseous ions -> compound)
as ionic size increases ….
- attractio is less
- less negative (exothermic) lattice enthalpy (and hydration enthalpy)
what effects enthalpy of hydration?
- ionic size
- charge
define entropy
the quantitative measure of the degree of disorder in a system.
entropy units
J K-1 mol-1
high entropy=
high disorder, things like gasses
ΔSreaction=
ΣSProducts - ΣSReactants
standard entropy change of reaction is
the entropy change that accompanies a reactiin in the molar quantities expressed in a chemical equation under standard conditions, with reactants and products in standard state.
What is ΔG or free energy?
is the balance between thropy , enthalpy and temperature for a process.
A process can take place spontaneously when ΔG<0
ΔG=
ΔH-TΔS
what is a spontanoeus process?
its overall energy increases and its more stable
(has the potential to happen)
what is needed for a spontanous process?
ΔG=ΔH-TΔS<0
how do endothermic reactons take place
- ΔS must be positive
- temp must be high enough so that TΔS>ΔH
What is an ellingham diagram?
Shows how ΔG varies with temp for reactions
what is reaction coupling?
combining a very -ve ΔG reaction with a +ve ΔG reaction inorder to make overall ΔG -ve and the +ve reaction can then happen.
what are standard conditions?
- 1atm (100kPa)
- 25oC (298K)
- 1 mol dm-3
