Physical Chemistry 2 Flashcards
1
Q
Thermodynamics- Enthalpy Change of Formation
A
- enthalpy change when one mole substance formed from constituent elements under standard conditions, standard states
- Na(s) + 1/2Br2(l) -> NaBr(s)
2
Q
Thermodynamics- Born-Haber Cycles
A
- Method:
Enthalpy of formation AB -
Atomisation of A +
Atomisation of B +
Ionisation energy A +
Electron affinity B -
Lattice formation enthalpy AB -
3
Q
Thermodynamics- Enthalpy of Solution
A
- Enthalpy change of solution=Enthalpy change when one mole of substance completely dissolved in water
- Made of two steps:
Lattice dissociation enthalpy (endo)
Hydration enthalpy (exo) - Hydration enthalpy=enthalpy change when one mole gaseous ions completely dissolved in water
- Factors affecting size of hydration enthalpy:
Smaller ion=stronger attraction
More highly charged an ion=stronger attraction
4
Q
Thermodynamics- Perfect Ionic Model
A
- Theoretical value:
Fully ionic (no covalent character)
All ions are point charges - Experimental value:
Born-Haber cycles- standard enthalpy changes
Hess cycles - Shared electrons add covalent character
- Theoretical and experimental similar (no covalent character):
High difference in electronegativity
Relatively small anion(negative) - Theoretical and experimental different (add covalent character):
Small difference in electronegativity
Large anions(negative)
5
Q
Thermodynamics- Entropy Change
A
- Entropy=a numerical measure of disorder in a chemical system
- Factors affecting entropy:
High temp=high entropy
Arrangement in space
Highly ordered (solid)=low entropy
Highly disordered (gas)=high entropy - Entropy(ΔS)=products - reactants
- Gibb’s free energy:
ΔG=ΔH-TΔS - When ΔG=0, this is the point at which the reaction is feasible (reaction takes place of its own accord)
6
Q
Equilibrium Constant Kp- Homogenous Systems
A
- Partial pressure=the pressure the gas would exert if it occupied a container on its own
- Total pressure=sum of partial pressures of all the gases in a mixture
- Partial pressure of A=mole fraction of A x total pressure
- Mole fraction of gas A=number of moles of gas A in mixture / total number of moles of gas in mixture
- Kp=products / reactants
- Effect of changing temp and pressure on gaseous equilibrium:
Increase temperature=decrease Kp=decrease yield
Increase pressure=increase Kp=increase yield
7
Q
Thermodynamics- Enthalpy Change of Combustion
A
- enthalpy change when one mole of substance completely burned in oxygen under standard conditions, standard states
8
Q
Thermodynamics- Enthalpy Change of Atomisation
A
- enthalpy change when one mole of gaseous atoms is formed from an element under standard conditions in standard states
- 1/2 O2(g) -> O(g)
9
Q
Thermodynamics- First Ionisation Energy
A
- standard enthalpy change when one mole gaseous atoms converted into one mole of positive gaseous ions
- Mg(g) -> Mg+(g) + e-
10
Q
Thermodynamics- First Electron Affinity
A
- standard enthalpy change when one mole gaseous atoms converted into one mole of negative gaseous ions
- O2(g) + e- -> O2-(g)
11
Q
Thermodynamics- Lattice Enthalpy of Formation
A
- standard enthalpy change when one mole solid ionic compound formed from constituent elements
- Na+(g) + Br-(g) -> NaBr(s)
12
Q
Thermodynamics- Lattice Enthalpy of Dissociation
A
- standard enthalpy change one mole solid ionic compound dissociates into gaseous ions
13
Q
Thermodynamics- Enthalpy of Hydration
A
- standard enthalpy change one mole gaseous ions converted into aqueous ions
14
Q
Thermodynamics- Enthalpy of Solution
A
- standard enthalpy change when one mole solute dissolves completely in sufficient solvent to form solution where ions won’t interact with each other
15
Q
Thermodynamics- Mean Bond Enthalpy
A
- enthalpy change when one mole gaseous molecules breaks covalent bond to form two free-radicals, averaged over range of compounds
