Thermodynamics Flashcards
Define Hess’ Law
The enthalpy change for a reaction is independent to the route taken
Define lattice enthalpy of formation
Enthalpy change when one mole of solid ionic lattice is formed from its constituent gaseous ions
Define enthalpy of hydration
Enthalpy change when one mole of gaseous ions becomes hydrated in water to infinite dilution
Define enthalpy of solution
Enthalpy change when one mole of solute dissolves completely in a solvent to infinite dilution
Define mean bond dissociation enthalpy
Enthalpy change when one mole of covalent bonds is broken with all the species in a gaseous state
Explain what bonds are most ionic
Between large positive and small negative ions
What does it mean if a reaction is feasible?
The reaction will take place by itself (spontaneous)
What must a reaction have in order to be feasible / spontaneous?
Gibbs free energy (/\G) must be negative
What is entropy + give its units?
The disorder of a system
Higher entropy = more disordered
Units = J K-1 mol-1
Compare entropy values for solids, liquids and gases
Solids < Liquids < Gases
How do you calculate entropy change?
Entropy change = entropy (products) - entropy (reactants)
/\S = sum of S (products) - sum of S (reactants)
How do you calculate Gibbs free energy?
/\G = /\H - T/\S
G = Gibbs
H = enthalpy
S = entropy
T = temperature
What does the value for Gibbs free energy (G) in a reaction show?
If G < 0, reaction is feasible
If G > 0, reaction is NOT feasible
If G = 0, shows temp at which reaction becomes feasible
If the reaction is endothermic and temperature increases, what is the value of G?
Temperature dependant
If the reaction is endothermic and temperature decreases, what is the value of G?
G is positive
