Thermodynamics Flashcards
(30 cards)
Enthalpy change of formation
Energy change when 1 mole of a compound is formed from its elements under standard condition, all reactants and products being in their standard states
Enthalpy of atomisation
Enthalpy change when 1 mole of gaseous atom is formed from the element in its standard state
Bond Enthalpy
Standard molar Enthalpy change when 1 mole of a covalent bond is broken into 2 gaseous atoms
First enthalpy Enthalpy
Enthalpy change required to remove 1 electron from 1 mol of a gaseous atom to form 1 mole of a gaseous ion with a 1+ charge
Second ionisation enthalpy
Enthalpy change to remove 1 electron from one mol of gaseous 1+ ion to form one mole of gaseous 2+ ion
First electron affinity
Enthalpy change when 1 mole of gaseous atom gains an electron to form 1 mole of gaseous ion with a 1- charge
Second electron affinity
Enthalpy change when one mole of gaseous 1- ion gains an electron to form one mole of gaseous 2- ion
Enthalpy of lattice formation
Enthalpy change when 1 mole of ionic crystal lattice is formed from its constituent ions in gaseous form
Enthalpy of lattice dissociation
Enthalpy change when 1 mole of ionic crystal lattice is separated into its constituent ions in gaseous form
Enthalpy of hydration
Enthalpy change when one mole of gaseous ions becomes aqueous ions
Enthalpy of solution
Enthalpy change when one mole of ionic solid dissolves in enough water to ensure ions dissolved are separated and don’t interact
How do you find lattice formation
Enthalpy of formation - sum of everything else
How do you find lattice dissociation?
Enthalpy of formation + lattice dissociation = sum of everything else
2 factors affecting lattice formation
1) Size of ions
- Larger ions –> less negative enthalpies of lattice formation –> charges get further away so have weaker attractive forces between them
2) Charge of ion
- Bigger charge –> greater attraction between ions –> stronger lattice enthalpy (more negative value)
Describe the perfect ionic model
Assumes ions are 100% ionic and spherical and attractions are purely electrostatic
4 factors that cause covalent characteristics in ionic substances
1) Positive ion is small
2) Positive ion has multiple charges
3) Negative ion is large
4) Negative ion has multiple negative charges
What causes the difference between theoretical ad born hater lattice nthalpies?
More covalent character –> larger different between the two values
When does the negative ion become polarised?
When it becomes more distorted and more covalent
What is entropy?
The number of ways atoms can share energy
What does high entropy mean?
There is disorder
What causes a significant increase in entropy?
1) Change in state –> from solid / liquid to gas
2) Significant increase in number of molecule between products and reactants
How do you calculate entropy quantitatively?
ΔS = products - reactants
What is the only thing with zero entropy?
Perfect crystals at absolute zero (0 Kelvin)
How do you work out Gibbs’s free energy?
ΔG = ΔH - TΔS
ΔG = gibbs free energy (kJ mol^-1)
ΔH = enthalpy change (kJ mole ^-1)
T = temperature (K)
ΔS = entropy (kJ mol ^-1)
