Energetics II Flashcards
what’s the standard lattice energy
2
energy change when one mole of an ionic SOLID is FORMED from its GASEOUS ions under standard conditions .
GAS–> SOLID
whats two factors affect lattice energy ?
explain ?
6
1)attratction /energy
- ionic charge :higher charge = stronger electrostatic attraction between ions meaning there will be more energy released when lattice forms
-size: smaller ions = higher charge density = ions can sit closer together = stronger electrostatic forces .
the smaller the ionic radius the more exothermic the reaction= more energy released when lattice forms.
what happens when you FORM a bond ?
energy released = exothermic
what happens when you BREAK a bond ?
energy taken in =endothermic
What can Born Harber Cycles calculate ?
lattice Energies
How can you calculate the lattice energies ?
- 2 methods
- experimental way (harber cycle )
- theoretical way ( given )
How can you tell “ how ionic ,” an ionic lattice is ?
- the difference in the lattice energies( theo and expermental )
- if the difference is small then it’s purley ionic .
- if the difference is large then it has covalent character
What the charge density ?
- charge / volume
what is the atomisation enthalpy ? (2)
- energy required to produce one mole of free gaseous atoms of that atom .
What’s the bond dissociation enthalpy ?2
-enthalpy change when covalent bond is broken homolytically
whats the first ionisation energy ? 3
- energy required to remove one electron from each atom -from a mole of free gaseous atoms of that element
- under standard states and conditions
What’s the first electron affinity ?2
- energy change when an electron is added
- to each of a mole of free gaseous atoms of that element .
whats the atomisation enthalpy of Na? 2
state symbols
Na(s)–> Na (g)
first ionisation enthalpy of Na ?2
state symbols
Na (g)–> Na+(g) + e-
what the first electron affinity for Cl ?2
state symbols
- Cl(g) + e- –>Cl-(g)
the lattice enthalpy can have two meanings ?
2
1) lattice enthalpy of formation
2) lattice enthalpy of dissociation
why is the Lattice enthalpy of formation always negative ?
3
- negative = EXOTHERMIC
- this means that bonds are being formed
- which releases energy
why is the lattice enthalpy of dissociation positive ?
3
-it is ENDOTHERMIC
- this means that bonds a being broken
- Breaking something requires an input of energy
hence why it absorbs energy .
why is atomisation energy always endothermic?
2
- requires energy INPUT to go from solid to gas
- bonds need to be broken
- positive value (+)
Why are ionisation ethalpies always positive ?
2
- ENDOTHERMIC
- removing an electron requires an INPUT of energy
Why are second ionisation enthalpies more endothermic than the first ionisation energies ?
4
- the energy input required is higher
- this is because the remaining electrons have less repulsion towards one another
- meaning they are more attracted to one another , harder to remove
- HENCE more ENDOTHERMIC ( more input required )
why are first electron affinities exothermic ?1
- adding an electron releases energy ( hence exothermic )
why is second electron affinity endothermic ?5
NOT FINSHED
- so when you add one electrons (1st electrons affinity) : the charge becomes negative .
- So when you add the second electron , the incoming electron is repelled by over all negative charge .
- its endothermic becauseeeeeee…..
how can we tell if a reaction is spontaneous ?
- it is exothermic
whats the hydration enthalpy ?
2
energy released when a gaseous ion dissolves in water .
M^x+-(g)->M^x+ (aq)
whats the enthalpy of solution ?2
- what happens if it’s exothermic .?
- enthalpy change when one mole of ionic compound dissolve in excess water
- the more exothermic the enthalpy of solution is , the more likely the compound is to dissolve .
what’s the hydration enthalpy dependant on ?
2 factors ?
1) size of ion = small charge = High hydration enthalpy
2) charge on ion =Greater charge = stronger attraction to water molecules = High hydration enthalpy .
when an exothermic reaction occurs ? what happens to potential energy ?
- potential energy is lowered so that substances become more stable .
whats entropy ?1
- the measure of disorder in a system ?
Why does a high degree of disorder make something more stable ?
- gases have high entropy : but they are also more spread out ; hence energy is more spread out .
= more stable .
state the states in increasing levels of entropy
solid = lowest entropy
liquid
gas = most entropy
