Thermodynamics Flashcards
Lattice Formation Enthalpy
The enthalpy change when one mole of an ionic lattice is formed from its gaseous ions.
Na⁺(g) + Cl⁻(g) → NaCl(s)
Enthalpy of Formation
The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states.
Na(s) + 1/2 Cl₂(g) → NaCl(s)
Enthalpy of Atomisation
The enthalpy change when one mole of gaseous atoms is produced from an element in its standard state.
Na(s) → Na(g)
First ionisation energy
The enthalpy change when each one mole of gaseous atoms loses an electron and forms a 1+ ion.
Mg(g) → Mg⁺(g) + e⁻
First electron affinity
The enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions.
O(g) + e⁻ → O⁻(g)
Bond dissociation Enthalpy
The bond dissociation Enthalpy is the standard molar Enthalpy change when one mole of a covalent bond is broken into two gaseous atoms.
I₂(g) → 2I(g)
Second electron affinity
Second electron affinity is always endothermic as it takes energy to overcome the repulsive force between the negative ion and the electron
Enthalpy of hydration
Enthalpy change when one mole of gaseous ions become aqueous ions
X⁺(g)→X⁺(aq)
Always exothermic
Enthalpy of solution
The Enthalpy of solution is the standard Enthalpy change when one mole of an ionic solid dissolves in a large enough amount of water to ensure that the dissolved ions are well separated and do not interact with one another
NaCl(s) → Na⁺(aq) + Cl⁻(aq)
What factors effect the strength of lattice formation Enthalpy?
The sizes of the ions
The larger the ions the less negative the Enthalpies of lattice formation
The charges of the ions
The larger the charge the greater the attractions between the ions
What is the perfect ionic model?
Ions are 100% ionic and spherical and the attractions are purely electrostatic
How to determine when a compound shows covalent character?
The difference between the theoretical and Born Haber lattice enthalpies. The larger the difference the more covalent character.
What is a spontaneous process?
A process which will proceed on its own without any external influence.
What is entropy?
Entropy is a description of the number of ways atoms can share quanta of energy. If number of ways of arranging the energy is high then the system is disordered and the entropy is high.
How to calculate ∆S?
∆S = ∑S products -∑S reactants
What is Gibbs free energy equation?
∆G = ∆H -T∆S
What value for ∆G means the reaction is feasible?
0 or negative
What to remember when using Gibbs free energy equation?
Divide ∆S by 1000
How to calculate Enthalpy of Solution?
∆H dissociation + ∑∆H hydration
Or
-∆H formation + ∑∆H hydration
Are hydration enthalpies Exothermic or Endothermic?
They are exothermic
What is interesting about the Enthalpy of solution?
It is usually very close to 0 and is not very exo or endothermic.
Usually if it is exothermic the substance is likely to be soluble and vice versa for endothermic.
Explain why there is a difference between the hydration in the hydration enthalpies of the magnesium and sodium ions.
Magnesium ions have a higher charge and a smaller ions and magnesium will attract water more strongly.
Why would the gradient the Gibbs Free Energy line change?
The substance could have change the state so the value of entropy changes
Suggest why the hydration of the chloride ion is an exothermic process
Water is polar
Chloride ion attracts the water molecules
Explain why the theoretical enthalpy of lattice dissociation is different from the experimental value ?
Experimental lattice and the value includes covalent interaction. Theoretical lattice and will be value assumes only ionic interaction.
