thermodynamics Flashcards
Define The Standard Enthalpy of Formation, ∆Hɵf
The enthalpy change when one mole of a compound is formed
from its elements
under standard conditions, all reactants and products in their standard states.
e.g. Na(s) + ½Cl2(g) à NaCl(s)
Define First Ionisation Enthalpy, 1st∆Hɵi
The standard enthalpy change when one mole of electrons
is removed from one mole of gaseous atoms
to give one mole of gaseous ions each with a single positive charge.
e.g. Ca(g) à Ca+(g) + e
The Standard Enthalpy of Atomisation, ∆Hɵat
The enthalpy change when one mole of gaseous atoms are formed
from an element in its standard state.
e.g. ½ Br2(l) à Br(g)
Mean Bond Enthalpy ΔHBEΘ
The enthalpy change when one mole of gaseous molecules
each break a covalent bond to form two free radicals
averaged over a range of compounds.
e.g. Br2(l) à 2Br(g)
Define First Electron Affinity, 1st∆Hɵea
The standard enthalpy change when one mole of gaseous atoms
is converted into a mole of gaseous ions
each with a single negative charge under standard conditions.
e.g. O(g) + e- à O-(g)
Define Lattice Formation Enthalpy ΔHLFΘ
The standard enthalpy change when one mole of solid ionic compound
is formed from its gaseous ions.
e.g. Mg2+(g) + 2Br-(g) à MgBr2(s)
Define Lattice Dissociation Enthalpy ΔHLDΘ
The standard enthalpy change when one mole of solid ionic compound
dissociates into its gaseous ions.
e.g. MgBr2(s) à Mg2+(g) + 2Br-(g)
Define Standard Enthalpy of Hydration ΔHhydΘ
The standard enthalpy change when one mole of gaseous ions
is converted into one mole of aqueous ions.
e.g. Cl-(g) + aq à Cl-(aq)
Define Standard Enthalpy of Solution ΔHsolΘ
The standard enthalpy change when one mole of solute dissolves
to form its aqueous ions
e.g. NaCl(s) + aq à Na+(aq) + Cl-(aq)
What does CRAM stand for
Charge on the ions
Radius/size of the ions
Attraction between the ions
More exothermic/endothermic
Definition of an ionic bond:
The strong electrostatic attraction between oppositely charged ions.
The strength of an ionic bond will increase dependent on:
• The size of the ions - Smaller ions have a stronger attraction
• The charge of the ions – Higher charged ions have a stronger attraction
Stronger ionic lattices have a more exothermic lattice formation enthalpy
Stronger ionic lattices have a more endothermic lattice dissociation enthalpy
Comparing the data from different techniques for measuring ionic bond strength
Model Theoretical Experimental
Model Name. Perfect Ionic Model Born Haber Cycle
The assumption Perfect spheres/point charges Perfect spheres/point charges
Polarisable ions
Nature of the bonding Purely Ionic Ionic plus some covalent character
What is the Gibbs equation
∆G = ∆H - T∆S
∆G = Gibbs Free Energy measured in kJmol-1
∆H = Enthalpy Change measured in kJmol-1
T = Temperature measured in Kelvin
∆S = Entropy Change measured in kJK-1mol-1
Define entropy
Entropy (S) is a measure of the amount of disorder in a system.
Units: JK-1mol-1
