Ch 15 Principles of Reactivity: Equilibria

Requirements for equilibrium

• Reaction must be reversible

• Not all RXNs will go to completion and only form products, those that don’t are reversible equilibrium reactions

Characteristics of an equilibrium system

• Beginning of a reaction = Form a lot of products (Rate law)

• Later - Reverse reaction begins

• Dynamic Equilibrium (←→) two opposing processes occur exactly at the same rate

• Reactants → Products = Products → Reactants

Formula for equilibrium constant

K_c =[C]^c[D]^d/[A]^a[B]^b Product of products over product of reactants

K_c is independent of ___

Concentration

K_c is dependent of _____

Temperature, and what the reaction is + coefficients of those reactions

(T or F) Pure liquids, solids, and solvents get dropped in K expression

True; because their concentrations do not change during the reaction.

Q

ratio of Products/Reactants at ANY given point of time; not necessary equilibrium

K_c

is the equilibrium constant for EQUIBLIBRIUM CONDITIONS ONLY

K_c of reverse reaction is the _____ of K_c

reciprocal

K_c of a coefficient factor change is ____ of K_c

K_c raised to the exponent on K

Le Chatlier’s Principle

When a system is stressed (changing [], temp, pressure, or volume), the system will respond by attaining new equilibrium conditions that reduce that stress

Add reactant

Shifts towards products

Remove reactants

Shifts towards reactant

Add product

Shifts towards reactants

Remove product

Shift towards products

Change in amounts of solids, pure liquids, or solvents

NO EFFECT on equilibrium as long as concentrations are LARGER than other reactants/products

when pressure is increased

shifts in the direction producing the least amount of moles of gas

when pressure is decreased

system shifts to direction producing most amount of moles of gas

When both sides produce the same amount of moles of gas

No change in equilibrium

(T or F) adding a catalyst changes the equilibrium

False; no effect on equilibrium

Increase temp

Equilibrium shifts to the side that decreases heat

Decrease temp

Equilibrium shifts to the side that increases heat