Physical Chapter 6: Thermodynamics Flashcards
What is the symbol for enthalpy change?
ΔH
What is enthalpy change defined as?
The heat energy transferred in a reaction at a constant pressure
What is enthalpy change of formation?
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions
What is enthalpy change of atomisation?
The enthalpy change when 1 mole of an element or compound in standard state is converted to gaseous atoms.
What is lattice dissociation enthalpy?
The enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken
What is first ionisation energy?
The enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms
What is second ionisation energy?
The enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions.
What is first electron affinity?
The enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms
What is second electron affinity?
The enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of gaseous 1- ions.
What is enthalpy change of hydration?
The enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions
What is enthalpy change of solution?
Enthalpy change when 1 mole of solute is dissolved in enough solvent that no further enthalpy change occurs on further dilution.
What is lattice enthalpy a measure of?
Bond Strength
How do we calculate lattice enthalpies?
Born-Haber Cycles
What do you have to do to values for enthalpy if you are forming 2 moles in a born-haber cycle?
Double the value
Why are theoretical lattice enthalpies often different from experimental values?
They asume a purely ionic model, where all ions are spherical. This doesn’t account for covalent character, where ions aren’t all spherical.
What happens when you dissolve a substance in water?
The bonds between the ions break - endothermic
Bonds between ions and water are made - exothermic
Enthalpy of solution is the overall effect of these 2 changes
What enthalpies do you use to calculate enthalpy of solution?
Lattice dissociation and enthalpy of hydration
What is Entropy?
A measure of how disordered something is.
More directly, a measure of how many possible ways the particles can be arranged.
Which state has highest entropy?
Gas
What is the effect of an increased number of particles on entropy?
Entropy increases
What is the effect of higher entropy in stability?
More stable
How do you calculate entropy change for a reaction?
Entropy of products - entropy of reactants
How do you measure the feasability of a reaction?
Gibbs Free Energy must be negative or 0.
What is Gibbs Free energy?
ΔG = ΔH -TΔS
(temperature in kelvin)
How do you find the temperature when a reaction is just feasible?
T = ΔH/ΔS
(rearrangement of ΔG formula)
