Thermodynamics (ADD SOLUBILITY) Flashcards
Enthalpy of formation
The enthalpy change when 1 mole of the compound is formed from its elements under standard conditions, all reactants and products being in their standard states.
Na(s) + 1/2Cl2(g) → NaCl(s)
Is enthalpy of formation endothermic or exothermic
Exothermic for most substances
Enthalpy of atomisation
The enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state
Na(s) → Na(g)
1/2O2 → O(g)
Is enthalpy of atomisation exothermic or endothermic
Endothermic
First ionisation energy/enthalpy
The enthalpy change needed to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous ions with a charge of +1.
Mg(g) → Mg+(g) + e-
Bond dissociation enthalpy
The standard molar enthalpy change when one mole of a covalent bond is broken into two gaseous atoms
Cl2(g) → 2Cl(g)
CH4(g) → CH3(g) + H(g)
Is ionisation energy endothermic or exothermic
Endothermic
Is bond dissociation enthalpy endothermic or exothermic
Endothermic
What happens to the bond dissociation enthalpy for diatomic molecules
It is the same as x2 of the enthalpy of atomisation of the element
First electron affinity
The enthalpy change that occurs when 1 mole of gaseous atoms gain 1 mole of electrons to form 1 mole of gaseous ions with a -1 charge.
O(g) + e- → O-(g)
Is first electron affinity exothermic or endothermic
Exothermic for atoms that normally form negative ions / non-metals
Why is first electron affinity exothermic for many non-metals
The ion is more stable than the atom and there is an attraction between the nucleus and the electron.
Second electron affinity
The enthalpy change when one mole of gaseous 1- ions gains one electron per ion to produce gaseous 2- ions.
O-(g) + e- → O2-(g)
Is the second electron affinity exothermic or endothermic
Endothermic
Why is the second electron affinity endothermic
It takes energy to overcome the repulsive force between the negative ion and the electron
Enthalpy of lattice formation
The enthalpy change when 1 mole of an ionic compound is formed from its constituents in gaseous form.
Na+(g) + Cl-(g) → NaCl(s)
Is enthalpy of lattice formation exothermic or endothermic
Exothermic
Enthalpy of lattice dissociation
The enthalpy change when one mole of an ionic compounds dissociates into its constituent ions in gaseous form.
Is enthalpy of lattice dissociation exothermic or endothermic
Endothermic
Enthalpy of hydration
The enthalpy change when one mole of gaseous ions become aqueous ions.
X+(g) + aq → X+ (aq)
Mean bond enthalpy
The energy required to break a covalent bond in a molecule averaged over a range of compounds.
Why is the first ionisation energy of barium less negative/ less endothermic than that of calcium
The atomic radius of barium is bigger than calcium
There is more shielding of the outer electrons in barium
The nuclear attraction decreases, so less energy is needed to remove the outer electron in barium.
Describe the steps to draw a born haber cycle
- Write the lattice enthalpy equation.
- If there is a number in front of any ions, multiply any step involving that ion by the number
- Enthalpy of formation
- Enthalpy of atomisation of positive ion
- Ionisation energies
- Enthalpy of atomisation of negative ion
- Electron affinities
- Lattice enthalpy
How to calculate enthalpy of formation from born haber cycle
Enthalpy of formation = everything else added up