Chem 1A Unit 3

Very product-favored

“spontaneous”, “exergonic”, “irreversible” only stops if you run out of something, aka the “limiting reactant”, +ΔS_tot, -ΔG°, +E°

Very reactant-favored

“non-spontaneous”, “endergonic”, -ΔS_tot, +ΔG°, -E°

everything in between

“reversible”, ΔS_tot, ΔG°, E°, ≈ 0, X(aq) ↔ Y(aq)

Reversible reactions

reactants ↔ products

Chemical equilibrium

A state all reversible reactions eventually reach, where the amounts of reactants and products are no longer changing. Happens with different starting conditions (all reactants, a mixture, all products)

Equilibrium constants

K_c = [C]^c [D]^d/[A]^a [B]^b , aA + bB ↔ cC + dD, units of molarity (M = mol/L), use for (g) or (aq), c means concentration. also expressed as K_p = P_C^c P_D^d /P_A^a P_B^b , units of partial pressure, use for (g) only, p means pressure. DO NOT INCLUDE (s) or (l). K itself is often treated as unitless

Interpreting K

reactant-favored K < 1, product-favored K > 1. value of K depends on T

Reaction rates

forward rate: k_f [X], [X] depends on how many reactants you have, k rate constant depends on how “easy” the forward reaction is. backward rate: k_b [Y], depends on how many products you have and on how “easy” the backward reaction is. forward and backward reaction rates are equal at equilibrium.