Thermodynamic Flashcards
what is enthalpy change
heat change at constant pressure
what reaction is the first ionisation energy
endothermic
first electron affinity
energy change when 1 mole of gaseous atoms gain an electron to form 1 mole of gaseous 1- ions
N (g) + e- -> N-(g)
what reaction is the first electron affinity
exothermic
second electron affinity
energy change when 1 mole of gaseous 1- ions gain an electron to form 1 mole of gaseous 2- ions
V- (g) + e- -> V2- (g)
what reaction is the second electron affinity
endothermic
enthalpy of atomisation
enthalpy change when 1 mole of gaseous atoms are formed from an element in its standard state
Na(s) -> Na(g)
1/2 F2(g) -> F (g)
what reaction is the enthalpy of atomisation
endothermic
lattice enthalpy
enthalpy change when 1 mole of an ionic compound is formed from its constituent gaseous ions
Na+(g) + CL-(g) -> NaCl (s)
Zn2+(g) + 2Br-(g) -> ZnBr2
what reaction is the lattice enthalpy
exothermic
lattice dissociation enthalpy
enthalpy change when 1 mole of an ionic compound is broken into its constituent gaseous ions
NaCl(s) -> Na+(g) + Cl-(g)
what reaction is the lattice disassociation enthalpy
endothermic
bond dissociation enthalpy
enthalpy change when 1 mole of covalent bonds is broken in the gaseous state
Cl2 (g) -> 2Cl (g)
what reaction is the bond dissociation enthalpy
endothermic
what does the perfect ionic model assume:
- bonding is 100% ionic
- ions exist as perfectly spherical point charges
what does the value for lattice enthalpy on the born-haber cycle not match
the perfect ionic model
perfect ionic model
Al2O3
Al3+ is a highly charged small ion that is able to distort the electron density of the O2- ion toward itself
Al2O3 has a degree of covalent character
how to cause a greater covalent character
- a highly charged small cation
- a large negatively charged anion
what does the difference between born haber cycle and the perfect ionic model mean
if they differ significantly, there is a larger degree of covalent character
to increase electrostatic attraction:
- higher the charge of +ve and -ve
- the smaller the ionic radii
enthalpy of solution
enthalpy change when 1 mole of an ionic compound is dissolved in water
what reaction is the enthalpy of solution
can be endothermic or exothermic
enthalpy of hydration
enthalpy change when 1 mole of gaseous ions are dissolved in water
what reaction is the enthalpy of hydration
exothermic
what is entropy (s)
measure of disorder within a system or substance
JK-1mol-1
what is the entropy at 0 kelvins
entropy is also 0
order of entropy
solid - lowest
liquid
gas - highest
what features does a high entropy have
- large Mr/ molecules
- higher temperature
- liquid -> gas causes an increase
how to work out the change in entropy
change in entropy of products - change in entropy of reactants
what is Gibbs energy
gives us a way of linking enthalpy and entropy changes during a reaction. tells us about the feasibility of a reaction
gibbs energy formula
change in Gibbs = change in enthalpy - kelvin x entropy change
G = H - TS
convert entropy into kJmol-1
how can a reaction to be feasible
change in gibbs must be equal to or less than 0
formula to see when a reaction is feasible
T = change in enthalpy / change in entropy
change in entropy - +ve
change in enthalpy - -ve
-ve = feasible
change in entropy -ve
change in enthalpy +ve
+ve = not feasible
change in entropy -ve
change in enthalpy -ve
only feasible at low temperatures
change in entropy +ve
change in enthalpy +ve
only feasible at high temperatures
why does water melt
melts at 0 degrees/ 273k . this is because the value of delta G for the change is 0
what is a spontaneous reaction
has sufficiently low activation energy to take place immediately
+ve entropy value
what is a feasible reaction
has a high activation energy, so must be supplied for the reaction to start
when does covalent character occur
covalent character occurs in ions when two joined ions have different sizes/charged meaning the distribution of the charge in not even
how to work out lattice enthalpy
LE = hyd - sol
