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Section 7.3 Qualitative Changes in Equilibrium Systems Le Châtelier’s Principle. What is Le Châtelier’s Principle (LCP) ?. When a chemical system at equilibrium is disturbed by a change in a property, the system adjusts in a way that opposes the change.
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Section 7.3 Qualitative Changes in Equilibrium SystemsLe Châtelier’s Principle
What is Le Châtelier’s Principle (LCP)? When a chemical system at equilibrium is disturbed by a change in a property, the system adjusts in a way that opposes the change.
LCP provides a method of predicting the response of a chemical system to a change of conditions i.e. the equilibrium shift. • Practical Use: can produce more of the desired product and making processes more efficient/economical
LCP and Concentration Changes • If there is an increase in concentration of an entity then the reaction will shift to consume what was added (i.e. shifts to opposite side of the arrow). • If there is a decrease in concentration of an entity then the reaction will shift to replace what was taken away (i.e. shifts to the same side of the arrow).
LCP and Temperature Changes • Equate temperature (energy) as either a reactant or product (treat like a conc. change) • Endothermic (+H): reactants + energy ⇌ products • Exothermic (-H): reactants ⇌ products + energy • Energy can be added or removed by changing the temperature (heating/cooling).
LCP and Gas Volume Changes • Boyles’ Law: the conc of a gas in a container is directly related to the pressure of the gas • pressure = volume so it will shift to the side with fewer molecules to decrease pressure (b/c there would be fewer molecules) • pressure = volume, so it will shift to the side that produces more gas molecules (b/c this would increase the number of molecules and thus pressure).
Changes that do not affect the position of equil systems • Adding catalysts • Adding inert gases (i.e. the Noble Gases)
Drawing Conc. Vs. Time graphs • Reactants will go down & Products will go up • At a certain time the lines will straighten out =equil. • If equil. is shifted then draw a dashed vertical line and make appropriate changes and re-establish equil.
Predict the effect of the following changes on the reaction: 2 SO3(g) + 197.78 kJ 2 SO2(g) + O2(g) • Increasing the temperature of the reaction. • Shifts to the right to use up the extra heat. • Increasing the pressure on the reaction. • Shifts to the left b/c there are fewer gas molecules • Adding more O2 when the reaction is at equilibrium. • Shifts to the left to use up O2 • Removing O2 from the system when the reaction is at equilibrium. • Shifts to the right to make more O2
Seatwork • Check out the summary chart on Pg. 456 • Pg. 457 #1,2 & Pg. 459 #2-6,8,12