Thermodynamics Flashcards
Hess’s law
The Enthalpy change for a chemical reaction is the same, no matter what route is taken from reactants to products
The standard Enthalpy of formation
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) + 1/2Cl(g) ——> Nacl(s)
C(s) + O2(g) ——> CO2(g)
The standard enthalpy of combustion
The enthalpy change when one mole of a compound is completely burned in oxygen under standard conditions, all reactants and products in their standard states.
E.g.
C2H6(g) + 7/2O2(g) ——> 2CO2(g) + 3H20(l)
The standards enthalpy of atomisation
The enthalpy change when one gaseous atom is formed from an element in its standard state.
E.g.
Mg(s) ——> Mg(g)
1/2Br2(l) ——> Br(g)
Mean bond enthalpy
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.
CH4(g) ——> CH3(g) + H(g)
How is atomisation and bond enthalpy related?
Bond enthalpy is double atomisation
First ionisation enthalpy
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.
Na(g) ——> Na(g)* + e-
Ca(g) ——> Ca(g)* + e-
Second ionisation energy
The standard enthalpy change when one mole of electrons is removed from one mole of gaseous 1+ ions to give one mole of gaseous ions each with a 2+ charge
E.g
Ca*(g) ——> Ca^2+(g) + e-
First electron affinity
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.
Cl(g) + e- ——> Cl-(g)
Second electron affinity
The standard enthalpy change when one mole of electrons is added to a mole of gaseous ions each with a single negative charge, to form a mole of ions each with a two negative charge.
E.g.
S-(g) + e- ——> S^2-(g)
Lattice formation enthalpy
The standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions
E.g.
Na+(g) + Cl-(g) ——> NaCl(s)
Lattice dissociation enthalpy
The standard enthalpy change when one mole of solid ionic compound dissociates into its gaseous ions.
E.g.
NaCl(s) ——> Na+(g) + Cl-(g)
Standard enthalpy of hydration
The standard enthalpy change when one mole of gaseous ions is converted into one mole of aqueous ions.
E.g.
Na+(g) ——> Na+(aq)
Cl-(g) ——> Cl-(aq)
Standard enthalpy of solution
The standard enthalpy change when one mole of solute dissolves in enough solvent to form a solution in which the ions are far enough apart not to interact with each other.
E.g.
NaCl(s) ——> Na+(Aq) + Cl-(aq)
What are the two key factors that determine how exothermic a lattice enthalpy will be
1) Size of ions (radius)
2) charge of the ions
