6. Equilibrium Flashcards
What is equilibrium?
rate for forward rxn = rate for backwards rxn
How to find equil constant?
Keq = ([C]^c * [D]^d)/([A]^a * [B]^b)
EXPONENTS ARE FROM COEFF
Know trends of Keq
Keq < 1 or large neg exponent –> favors reactants, Keq = 1 –> equil, Keq > 1 or large pos exponent –> favors products
Know trends of Q/delta G in terms of spontaneity
Q < Keq, deltaG < 0 –> spontaneous in forward direction; Q > Keq, deltaG > 0 –> non-spontaneous in forward direction; Q = Keq, deltaG = 0 –> equil
What does it mean to be a spontaneous rxn?
It reacts without having an outside force upon it. Doesn’t necessarily mean it happens fast (ex: do you see a match ignite itself? Nah, you need lots of thermal energy). They also don’t have to go to completion, some may just reach equil
What are the eqns for deltaG vs deltaG0?
deltaG = deltaG0 + RTlnQ vs deltaG0 = -RTlnK
Diff b/w Q and K
K = constant at equil, Q = constant at any point during rxn
Keq aka Kc vs Kp
Equil constant for aq slns vs gases
Law of mass action and properties
For a generic reversible rxn, if the system is at equil at a CONSTANT TEMP—> Keq = ([C]^c[D]^d)/([A]^a[B]^b)
Keq = depends on temp
The larger the Keq —> equil is more to the right
Pure solids and pure liq don’t matter in expression
If equil constant of rxn in one direction is Keq, then equil constant of reverse rxn is 1/Keq
When is x negligible?
When it’s at least 2 or more orders in magnitude less than init conc
Kinetic product vs thermodynamic product
Lower Ea needed —> forms faster, get it at low temps, ends with higher deltaG compared to thermodynamic product —> less stable product; IRREVERSIBLE vs high Ea needed —> forms slower, get it at high temps, ends with lower deltaG than kinetic product —> more stable product; REVERSIBLE
Inc temp indefinitely can alter Keq. What would happen?
At extremely high temps, reactants and products can decompose
How do catalysts affect k?
They inc rate constants for both forward and reverse rxn
REMEMBER CATALYST ONLY INC KINETICS AND DO NOTHING W/ THERMODYNAMICS
How to change equil constants?
Change temp and/or identity of slns
