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Chemical Equilibrium

Chemical Equilibrium. Reversible Reactions and Equilibrium. Completion Reactions. Reactions that consume ALL of the reactants (perhaps leaving only trace amounts of one reactant of the other) are known as _______________________. Why may some of one reactant remain?

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Chemical Equilibrium

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  1. Chemical Equilibrium Reversible Reactions and Equilibrium

  2. Completion Reactions • Reactions that consume ALL of the reactants (perhaps leaving only trace amounts of one reactant of the other) are known as _______________________. • Why may some of one reactant remain? • The products, in this case, are final… they do not recombine to form the reactants

  3. Reversible Reactions • Reactions in which the products rearrange or reorient themselves to reform the original reactants are known as REVERSIBLE REACTIONS. • In this process, the reactants are resupplied by the constant breakdown of the products. • These reactions are going back and forth, back and forth, back and . . . . . • This is what is occurring in the ionization process

  4. Chemical Equilibrium • Eventually, this constant exchange will even out, creating a constant, ongoing shift back and forth, back and forth . . . • Reactions in which the forward and reverse reaction rates are equal are at CHEMICAL ________________. • At first, the reactants are colliding _______________, however quickly begin to turn into ______________ and thus slows the collisions, and in turn the forward reaction rate.

  5. As the forward reaction goes further, we start to run low on reactants. • Their concentrations go down as the concentration of product goes up. • Collision rates thus also decrease. • However, from the other direction…. What is happening??

  6. Dynamic vs. Static Equilibrium • Static equilibrium would be like dropping a ball in a bowl and allowing it to come to rest. Eventually, nothing happens anymore… no movement. • Chemical equilibrium is not static… it is DYNAMIC. Meaning there is no net change in the system. • Two opposite changes are occurring at the same time like hockey players coming off the ice as others go on. There is no net change but constant motion.

  7. Notations of equilibrium rxns • In some cases, one way may be favored, meaning there is a higher concentration on the reactant side or the product side. Equal length arrows: Reactants Products Favor the reactants: Reactants Products Favor the Products: Reactants Products

  8. What Determines the “Shift” • Everything is constantly changing in an attempt to come to equilibrium • According to LeChâtelier’s Principle, If a stress is applied to a system in dynamic (shifting) equilibrium, the system will change to relieve the stress. • Meaning, if you add more hamburgers and buns... Then we need to make more ________.

  9. LeChâtelier and Concentration • Considering the following reaction: H2CO3(aq) CO2(aq) + H2O(l) • Adding more H2CO3(aq)will make this reaction “heavy on the reactants” side, making it necessary to USE UP this addition. • While using this new addition up, the reaction is said to favor the creation of products and thus “favors the forward reaction”

  10. LeChâtelier and Concentration H2CO3(aq) CO2(aq) + H2O(l) • If more carbon dioxide were to be added what would happen? • How about adding more water?

  11. LeChâtelier and Temperature • Increasing the temperature causes the equilibrium to shift in the direction that absorbs heat. • An exothermic reaction – heat is a ___________ (released) • An endothermic reaction – heat is a _________ (absorbed)

  12. LeChâtelier and Temperature • Consider the following reaction: 2SO2(g) + O2(g) 2SO3(g) + heat (exo) • If heat were added (treat it as a ___________) • According to LeChâtelier, the _______________ reaction will be favored. • How about for an endothermic reaction?

  13. LeChâtelier and Pressure • Consider the following reaction: N2(g) + 3H2(g) 2NH3(g) • Which side has more gas?? • If I increase the pressure of this system, the shift will favor the forward reaction (the production of fewer gases). What if I reduced the pressure??

  14. Practice with LeChâtelier • Consider the following reaction: PCl5(g) + heat PCl3(g) + Cl2(g) • What direction will be favored if I were to: • Add more Cl2 to the system • Increase the pressure of the system • Remove heat from the system • Remove some of the PCl3 as it forms

  15. Practice Problems • How is the equilibrium position of this reaction affected by the following changes? C(s) + H2O(g) + heat CO(g) + H2(g) • Lowering the temperature • Increase in pressure • Removing H2 • Adding H2

  16. Practice Problems • What effect does each change have on the equilibrium position of this reaction? N2(g) + 3H2(g) 2NH3(g) + 92kJ • Addition of heat • Increase in pressure • Addition of a catalyst • Removal of heat

  17. Homework: Vocab Sheets will be due on Thursday Page 572 #38, 39, 40, 41 44, 45, 46, 47

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