Chemical Equilibrium Chapter 15 Chemical Equilibrium opposing reactions
Chemical Equilibrium Chapter 15
Chemical Equilibrium opposing reactions proceeding at equal rates at the same time
![Equilibrium & Rate A B Rate = k[A] B A Rate = k[B] At](http://slidetodoc.com/presentation_image/403ea4ac07c76c0e234726d6e617b835/image-3.jpg "Equilibrium & Rate A B Rate = k[A] B A Rate = k[B] At")
Equilibrium & Rate A B Rate = k[A] B A Rate = k[B] At equilibrium, kf[A] = kr[B]
Equilibrium Constant a. A + b. B ↔ c. C + d. D Law of Mass Action – relationship between [reactant] and [product] @ equilibrium in any reaction Equilibrium constant expression kc (aka keq) – equilibrium constant kc indicates M concentrations are used depends on stoichiometry, not on mechanism!
kc in term of Pressure used for gaseous substances Remember, P = MRT; PA = [A]RT kp is pressure @ equilibrium In general, kp = kc(RT)Dn Dn =(mol gas product) – (mol gas reactants)
Value of kc magnitude of kc indicates the position of equilibrium k > 1; eq lies to the right ( [products]) k < 1; eq lies to the left ( [reactants]) Direction of Equilibrium & k is irrelevant; the kc value for a forward rxn is the reciprocal of the kc value for the reverse rxn
Heterogeneous Equilibria substances in equilibrium are in different phases If a pure solid or pure liquid is involved in equilibrium, its concentration is not involved in the keq expression; [pure solid or liquid] is constant the substances do need to be present in the rxn to establish equilibrium
![Calculating Eq Constants 1. Make a table for known values of [initial] and [eq]](http://slidetodoc.com/presentation_image/403ea4ac07c76c0e234726d6e617b835/image-8.jpg "Calculating Eq Constants 1. Make a table for known values of [initial] and [eq]")
Calculating Eq Constants 1. Make a table for known values of [initial] and [eq] of all rxn species 2. calculate the change in [ ] for all species where both [initial] and [eq] is known 3. use stoichiometry of rxn to determine D[ ] for all other rxn species 4. calculate [equilibrium] from [initial]; use values to determine keq
Application of keq 1. predict direction a rxn will proceed to reach equilibrium 2. calculate [reactant] & [product] @ eq
Reaction Quotient (Q) equal to keq only when system is at equilibrium Q > keq; not @ eq, eq’n moves R L Q < keq; not @ eq, eq’n moves L R for [ ]’s @ any point in time
Le. Chatelier’s Principle a system @ eq will shift in response to the application of stress in the direction that reduces stress Stressors: 1. D[ ] 2. DP 3. DT Changing [ ]: 1. Adding a substance – shift consumes added material to reestablish eq 2. removing a substance – shift produces material to reestablish eq (see pckt p 6)
Changing Volume & Pressure only affects gases Boyle’s Law: PV = k P ; shift towards side of eq’n that has fewer moles of gas P ; shift toward side of eq’n that has more moles of gas When a nonreacting gas is added, PT , but partial pressures of reacting gases remain proportionally constant, therefore no shift
Changing Temperature increase in temp results in a shift to the endothermic direction decrease in temp results in a shift to the exothermic direction Heat may be quantified within the reaction equation (stoichiometrically proportionate) Endo: temp = k Exo: temp = k
Effect of Catalysts on Eq catalyst increases rate of forward and reverse reaction equally equilibirum is attained more quickly with the addition of a catalyst, but the position of equilibrium will not be affected (no shift)
- Slides: 14
