5.2.2 Enthalpy and Entrophy Flashcards
Lattice enthalpy
a measure of strength of ionic bonding in a giant ionic lattice
- enthalyp change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions
is lattic enthalpy an exothermic or endothermic change and what is the value for the enthalpy change
exothermic
always negative
what does a Born-Harber cycle show
indirect determination of lattice enthalpy
- an energy cycle
dissolving ionic compounds
water molecules break up giant ionic lattice structure and overcome the strong electrostatic attractions between oppositely charged ions
Standard enthalpy change of solution
enthalpy change that takes place when one mole of a solute dissolves in a solvent
is enthalpy change of solution exo or endothermic
can be either
dissolving process steps when a solid ionic compund dissolves in water
ionic lattice breaks up
water molecules are attracted to and surroud the ions
the 2 types of energy changes involved in dissolving a solid ionic compound
ionic lattice is broken up forming seperate gaseous ions
enthalpy change of hydration when gaseous ions interact with the polar water molecules to form hydrated aquueous ions
general properties of ionic compounds
high melting and boiling point
soluble in polar molecules
conduct electricity when molten or in aqueous solution
what factors effect lattic enthalpy
ionic size and ionic charge
what is the effect of increasing ionic radius
attraction between ions decreses
lattice energy is less negative
melting point decreases
what is the effect of increasing ionic charge
attraction between ions increases
lattic energy becomes more negative
melting point increases
factors affecting hydration enthalpies
ionic size
ionic charge
how does increasing ioinc radius affect hydration energy
attraction between ions and water molecules decreases
hydration energy is less negative
how does increasing ionic charge affect hydration energy
attraction with water molecules increases
hydration energy becomes more negative
Entropy
used to explain things that occur naturally-
gas spereading in a room
heat from fire spreading
ice melting in a hot room
the greater the entropy=
the greater the dispersal of energy and the greater the disorder
units for entropy
J K-1 mol-1
what states have the smallest to largest entropy
solid
liquid
gas
when is the entropy change positive
if a system changes to become more random, energy can be spread out more
when is the entropy change negative
if system changes to become less random, energy becomes more concentrated
what reactions cause an increase in entropy and why
reactions that produce gas as it increases the disorder of the particles and energy is more spread out
Standard entropy definition
is entropy of one mole of a substance under standard conditions
are standard entropies always positive or negative
positive
entropy change of a reaction equation
ΣS°(products) - ΣS°(reactants)
Feasability
used to describe whether a reaction is able to happen and is energetically feasible
Free energy change
overall energy change during a chemical reaction
free energy change symbol
ΔG
Gibbs’ equation
ΔG = ΔH - TΔS
What is the condition for feasability
ΔG<0
limitations of predictions made for feasibility
many reaction have negative ΔG but dont seem to take place
this is due to a very large activation energy resulting in a slow rate so must be left for a very long time
