Lattice Enthalpy Flashcards
Why is lattice enthalpy always endothermic?
Because the process is bond breaking.
What does the strength of an ionic lattice depend on?
Depends on the strength of the force of attraction between ions.
How does Ionic charge effect lattice enthalpy?
The greater the charge on one/both ions the stronger the attractive forces which require more energy to break. Bond breaking is an endothermic process. This means 1+/- ions form compounds with lower lattice enthalpies than 2+/- ions.
How does ionic radii effect lattice enthalpy?
The larger the ionic radius, the lower the lattice enthalpy. This is because the packing of the ions is less efficient and there is less interaction between them. Therefore, a group 2 ion will have a lower lattice enthalpy than a group 7 ion.
Arrows up
Endothermic
Arrows down
Exothermic
Enthalpy of formation
exothermic
Enthalpy of atomisation of metal
endothermic
Ionisation energy of metal
endothermic
Enthalpy of atomisation of non-metal
endothermic
Electron affinity of non-metal
1st exothermic, 2nd endothermic
lattice energy of ionic compound
endothermic
Atomisation of metal down group.
Strength of metallic bonds decreases down group as atomic radius increases therefore atomisation becomes less endothermic (less attraction to break bonds).
Bond enthalpy down group 7
Strength of covalent bonds decreases down group as atomic radius increases. Bond enthalpy gets less endothermic.
First ionisation energy down group 1
decreases down group as atomic radius and shielding increases , outer electron less attracted to nucleus and less energy required to remove therefore, less endothermic.
first ionisation energy across period 2
increases across a period. Atomic radius decreases ad shielding remains constant. Outer electron more attracted to the nucleus and more energy required to remove outer electron, more endothermic.
First electron affinity down group 7
Atomic radius and shielding increases, outer shell is further from attraction of nucleus. Incoming electron is less attracted to nucleus, becomes less exothermic.
first electron affinity across period 2
Atomic radius decreases, shielding remains constant, and outer shell is closer to attraction of nucleus. Incoming electron is more attracted and becomes more exothermic up to group 7.
Enthalpy change of solution occurs in 2 steps.
Crystal lattice is separated into ions (endothermic/bonds broken.)
Cations and anions are surrounded by a shell of water and is hydrated (exothermic/ bonds formed.)
Enthalpy of hydration
Always exothermic, new bonds are formed.
Value of enthalpy of hydration depends on;
charge on ion; larger the charge, the larger enthalpy of hydration.
ionic radius; larger the ionic radius, smaller the enthalpy of hydration.
Solubility of gp2 sulfates
Become less soluble. SO42- ion is large and lattice enthalpy approximately constant. Solubility depends on hydration enthalpy of cation which becomes less exothermic down group as cations get larger. Enthalpy of solution becomes less.
Why is MgSO4 more soluble than BaSO4?
SO42- ion is large and approximately constant for a ll group 2 sulfates. Solubility depends on hydration enthalpy of cations. Ba2+ is larger so enthalpy of hydration is less exothermic. this means enthalpy of solution will be less exothermic.
^Hsol
^Hlatt +^Hhyd (cation) + ^Hhyd(anion)
solubility of gp2 hydroxides
Become more soluble. Cations get larger, lattice enthalpy and hydration enthalpy of cation become less exothermic. Lattice enthalpy decreases in magnitude, more than hydration enthalpy. Enthalpy of solution becomes mire exothermic and solubility increases.
2nd law of thermodynamics
States spontaneous changes result in an increase in disorder/ entropy.
2nd law of thermodynamics determines;
Whether a physical or chemical change will occur at a certain temp.
if redox reactions will occur
equilibrium position
