3.1.8 - thermodynamics
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Enthalpy change of formation (∆fHƟ)
the enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states, under standard conditions. * E.g. 2C(s) + 3H2(g) + ½O2(g) → C2H5OH(l)
Enthalpy change of combustion (∆cHƟ)
the enthalpy change when 1 mole of a substance is completely burned in O2 under standard conditions with all reactants + products in their standard states. * E.g. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
Bond dissociation enthalpy (∆BDEHƟ):
the enthalpy change when 1 mole of bonds of the same type are broken under standard conditions in the gaseous state. * E.g. Cl2(g) → 2Cl(g)
Enthalpy change of atomisation (∆atHƟ)
the enthalpy change for the formation of 1 mole of gaseous atoms from the element/compound in its standard state. * E.g. NaCl(s) → Na(g) + Cl(g
First ionisation enthalpy (∆ie1HƟ)
enthalpy change when 1 mole of electrons is removed from 1 mole of gaseous atoms to form one mole of gaseous ions with a +1 charge. * E.g. Na(g) → Na+(g) + e
Second ionisation enthalpy (∆ie2HƟ)
enthalpy change when 1 mole of electrons is removed from 1 mole of gaseous ions with a charge of +1 to form one mole of gaseous ions with a charge of +2. * E.g. Na+(g) → Na2+(g) + e
First electron affinity (∆EA1HƟ)
enthalpy change when 1 mole of gaseous atoms form 1 mole of gaseous ions w/ a charge of -1. * E.g. O(g) + e- → O-(g)
values of first electron affinity are negative bc
process is exothermic
. Second electron affinity (∆EA2HƟ)
enthalpy change when 1 mole of gaseous ions with a charge of -1 form 1 mole of gaseous ions with a charge of -2. * E.g. O-(g) + e- → O2-(g)
whats significant ab second electron affinity value and why is this the case
Values of second electron affinities are +ve as the process is endothermic. - This is due to the repulsion from the negative ion toward the negative electron being added.
Enthalpy of lattice dissociation (∆LHƟ)
the enthalpy change when 1 mole of an solid ionic compound is dissociated into its constituent gaseous ions under standard conditions * E.g. NaCl(s) → Na+(g) + Cl-(g)
Enthalpy of lattice formation (∆LHƟ)
the enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions. * E.g. Na+(g) + Cl-(g) → NaCl(s)
Enthalpy of hydration (∆hydHƟ):
the enthalpy change when 1 mole of gaseous ions is converted into 1 mole of aqueous ions. * E.g. Na+(g) → Na+(aq)
Enthalpy of solution (∆solHƟ)
the enthalpy change when 1 mole of an ionic substance dissolves in enough solvent to form an infinitely dilute solution.
What can we link enthalpy of atomisation with
Bond dissociation enthalpy
What 2 things must be present to link enthalpy of atomisation with bond dissociation enthalpy
Gaseous in its standard state and or covalently bonded in its standard state
So enthalpy of atomisation of O =?
enthalpy of atomisation of O = 1/2 x bond dissociation enthalpy of O=O
Equation for the bond dissociation enthalpy of a Cl-Cl bond is
Cl2(g) —> 2Cl(g)
Equation for enthalpy of atomisation of chlorine is
1/2Cl2 (g) —> Cl(g)
Equation for first electron affinity of nitrogen
N(g) + e- —> N-(g)
Equation for second electron affinity of Nitrogen
N-(g) + e- —> N2-(g)
Enthalpy change of solution =
Enthalpy change of solution = lattice diss enthalpy + sum of enthalpy of hydrations
Lattice diss is the reverse…
Of lattice formation