Euqilibrium Flashcards
Enthalpy as a driving force
Reactions proceed towards lower energy states. Lower enthalpy is favourable
Entropy
Tendency towards randomness/disorder
How the energy is SPREAD OUT within a system
Systems move towards maximum enthalpy
Second Law of Thermodynamics
All systems move towards maximum entropy
Entropy affected by:
- state
solid<liquid<aqueous<gas - number of particles
if same state, more particles = greater entropy
Third Law of Thermodynamics
A pure crystal at 0 K (absolute zero) has zero entropy
Particles are not moving , so there is no disorder
Entropy of all systems is measured relative to this
Driving forces summary
- Tendency to minimum enthalpy (-H)
- Tendency to maximum entropy (+S)
Enthalpy decreases (-H)
Entropy increases (+S)
Both driving forces favour the products
Reaction is spontaneous and proceeds far right
Irreversible
Enthalpy increases (+H)
Entropy decreases (-S)
Both driving forces favour the reactants
Reactions is non-spontaneous and DOES NOT proceed
Impossible as written
Enthalpy increases (+H)
Entropy increases (+S)
Driving forces act in opposite directions (H - reactants, S - products)
Reversible and proceeds towards equilibrium
Temp. dependent (spontaneous at high temp.)
Enthalpy decreases (-H)
Entropy decreases (-S)
Driving forces act in opposite directions (H - products, S - reactants)
Reversible and proceeds towards equilibrium
Temp. dependent (spontaneous at low temp.)
Gibb’s Free Energy Change (ΔG)
ΔH - TΔS
Affect of temperature
Affects entropy, NOT enthalpy
ΔG is negative
- releases a large amount of free energy
- proceeds towards product
- spontaneous
ΔG is positive
- absorbs a large amount of free energy
- will not proceed to products, favours reactants
- non-spontaneous
ΔG is zero
- forward and reverse equally favoured
- no net free energy charge
- system is in equilibrium
What happens as a reaction proceeds?
- High concentration of reactants, no products
- Collisions b/w reactant, forward reaction rate is high
- Reactants get used up, fewer reactant molecules, rate slows
- Collisions now: RR, RP, PP
- Products can convert back into reactants, at first, reverse rate is slow
- More product = faster rate of reverse reaction
- Reactions never stop happening
Equilibrium
The forward and reverse reaction rates are the same, so the concentrations of both are constant
Dynamic equilibrium
Reactions never stop happening (continuously), but the rate of the forward reaction is equal to the rate of the reverse, so the system does not appear changing (constant MACROSCOPIC properties)
For a system to be able to reach equilibrium:
- Reversible
- Closed system (w/ respect to reaction)
- Macroscopic (observable) properties are constant when equilibrium reached
- Equilibrium can be reached in either direction (R to P, or P to R = same equilibrium conditions)
Steady state
Open systems that have constant properties
EX. burning candle
Homogenenous equilibrium
Closed system with all R and P in same phase
Heterogeneous equilibrium
Closed system with R and P in different phase
