CHM 13 Ppt. 2
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What is Le Chatelier's Principle
if a stress is applied to a system at equilibrium, the system adjusts in such a way as to relieve the stress
What can be changed to relieve stress?
- the concentration of reactants or products can be changed
- the pressure and volume can be changed
- the temperature can be changed
The concentration stress is added..
the concentration stress of an added reactant or product is relieved by reaction in the direction that consumes the added substance
the concentraiton stress is removed
the concentration stress of a removed reactant or product is relieved by reaction in the direction that replenishes the removed substance
Volume and Pressure Changes
- only reactions containing gases are affected by changes in volume and pressure
- Increaising pressure= decreasing volume
What does PV=nRT tell us?
that increasing pressure or decreasing volume INCREASES concentration
In general, when an equilibrium is distubred by a chagne in volume which results in a corresponding change in pressure, what does Le Chatelier's principle predict?
- an increase in pressure by reducing the volume will bring about net reaction in the direction that decreases the number of moles of gas
- a decrease in pressure by expanding the volume will bring about net reaction in the direction that increases the number of moles of gas
If Qc > K, what?
the product is too high and the reaction progresses in the reverse direction
If Qc< kc, what?
more reactans wil be consumed and the net reaction will be from left to right
changes in temperature can change the equilibrium constant
Endothermic and exothermic in terms of temperature changes
- endo= favored when temperature increases
- exo= favored when temperature decreases
In general, when an equilibrium is disturbed by a change in temperature, what does Le Chatelier's principle predict?
- the equilibrium constant for an exothermic reaction (negative delta H) decreses as teh temperature increses
- the equilibrium constant for an endothermic reaction (positive delta H) increses as the temperature increases
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