15.2: Le Châtelier’s Principle

can predict how certain changes in a reaction will affect the position of equilibrium

when a chemical system at equil. is disturbed by a change in the system, the system will react in a direction opposing the change until a new equil. is reached

he described a 3 stage process Initial equilibriumShifting non-equilibriumNew equilibrium

Catalysts can be used to decrease the time to reach the new equil. position

• does not affect the final position of that equilibrium

system will shift away from the added component or towards a removed component

a change in conc. of a pure solid or liquid does not cause an equil. shift

Ex: N2 + 3H2 2NH3

if more N2 is added, then equilibrium position shifts to the right

if some NH3 is removed, then equilibrium position shifts to the right

adding or removing gaseous reactant or product is same as changing conc.

adding inert or uninvolved gas increase the total pressure doesn’t effect the equilibrium position

changing the volumedecrease V

decrease in # gas moleculesshifts towards the side of the

reaction with less gas molecules increase V

increase in # of gas moleculesshifts towards the side of the

reaction with more gas molecules

all other changes alter the concentration at equilibrium position but don’t actually change value of K

value of K does change with temperature

if energy is added, the reaction will shift in direction that consumes energy

treat energy as a: reactant: for endothermic reactionsproduct: for exothermic reactions

add COto left

add Cno shift

remove Cno shift

add As4O6

no shift

remove As4O6

no shift remove As4

to right decrease volume

to left add Ne gas

no shift

decrease volumeto right

increase volumeto left

add P4

no shift

remove Cl2to left

add Kr gasno shift

add PCl3no shift

endo or exo?endothermic

increase tempto right

increase volumeno shift

decrease tempto left

Textbook p695 #1-3, LSM 15.2J LSM summary 15.2C,D,F