Chapter 17 - Thermodynamics Flashcards
What is lattice dissociation enthalpy ΔL Hd?
Enthalpy change when one mole of an ionic crystal lattice is broken down into its constituent ions in their gaseous states
What is lattice formation enthalpy ΔL Hf?
Enthalpy change when one mole of an ionic crystal lattice is formed from its constituent ions in their gaseous states
What is an example equation for lattice dissocation enthalpy?
NaCl (s) –> Na+ (g) + Cl- (g)
What is an example equation for lattice formation enthalpy?
Na+ (g) + Cl- (g) –> NaCl (s)
What is enthalpy of formation?
Enthalpy change on forming one mole of a substance from its elements in their standard states under standard conditions, 298K, 100 kPa
What is an example equation for enthalpy of formation?
Na (s) + 0.5 Cl2 (g) –> NaCl (s)
What is first ionisation energy Δi H1?
Enthalpy change when one mole of gaseous atoms loses one mole of electrons to form one mole of gaseous monopositive ions
What is an example equation for first ionisation energy?
Na (g) –> Na+ (g) + e-
What is second ionisation energy Δi H2?
Enthalpy change when one mole of gaseous monopositive ions loses one mole of electrons to form one mole of gaseous dipositive ions
What is an example equation for second ionisation energy?
Na+ (g) –> Na 2+ (g) + e-
What is enthalpy of atomisation Δat H?
Enthalpy change when one mole of gaseous atoms are made from its element in standard states under standard conditions
What are some example equations for enthalpy of atomisation?
Na (s) –> Na (g)
0.5 Cl2 (g) –> Cl (g)
What is bond enthalpy/ bond dissociation energy?
Energy required to break one mole of a specified covalent bond, all substances in their gaseous states
What is an example equation for bond enthalpy?
Cl2 (g) –> 2Cl (g)
What is electron affinity Δea H/ EA?
Enthalpy change when mole of electrons is added to one mole of gaseous atoms to make one mole of gaseous mononegative ions
What is an example equation for electron affinity?
Cl (g) + e- –> Cl- (g)
What is a Born-Haber cycle?
A cycle that applies Hess’s Law used to calculate lattice enthalpy of an ionic compound
What is enthalpy of solution ΔsolH?
Enthalpy change when one mole of an ionic substance dissolves in water under standard conditions to give a solution of infinite dilution
What is enthalpy of hydration ΔhydH?
Enthalpy change when one mole of gaseous ions dissolve in sufficient water to give a solution of infinite dilution
What is an example equation for enthalpy of solution?
NaCl (s) –> Na+ (aq) + Cl- (aq)
What is an example equation for enthalpy of hydration?
Na+ (g) –> Na+ (aq)
Cl- (g) –> Cl- (aq)
Why are there discrepancies between experimental and theoretical lattice enthalpies?
Theoretical lattice enthalpies assume that bonding in lattice is purely ionic meaning ions are perfectly spherical and have no covalent character
In reality, lots of ionic bonds have some covalent character, meaning the bonds are stronger so |ΔH|is greater.
What is entropy and what are its units?
A measure of disorder of a system. Everything has some disorder so S is always greater than 0.
Units are J/Kmol
What is change in entropy?
ΔS is the change in entropy for a reaction and can be negative.
How does the entropy of different states compare?
Solid have lowest entropy and gases have highest entropy as disorder increases
How does ΔS vap compare to ΔS fus?
ΔS vap is a lot greater as gases are a lot more disordered compare to liquids than liquids are to solids
How is ΔS for a reaction calculated?
ΔS = ΣS products - ΣS reactants
What is Gibbs Free Energy?
A measure of the feasibility of a chemical reaction
What is the equation for Gibbs Free Energy?
ΔG = ΔH - TΔS
ΔG: gibbs free energy / kJ/mol
ΔH: enthalpy change / kJ/mol
T: temp/ K
ΔS: entropy change/ J/Kmol
What is important to remember when using ΔS for Gibbs Free Energy equation?
ΔS is given in J/Kmol but needs to be converted to kJ/Kmol
When is a reaction feasible?
When ΔG is less than or equal to 0, becomes feasible at the temperature where ΔG= 0
