EquilibriumEquilibrium

Reversible ReactionsReversible Reactions

Many reactions are reversible.Many reactions are reversible.

Once product is formed, it can go back Once product is formed, it can go back and reform reactants.and reform reactants.

http://www.youtube.com/watch?v=br8lKynV1Hc&safe=active (2:45 min)

EquilibriumEquilibriumA state of balance exists between the forward A state of balance exists between the forward

and reverse reactions.and reverse reactions.

Rate of forward rxn = Rate of reverse rxnRate of forward rxn = Rate of reverse rxn

EquilibriumEquilibrium

Concentration of reactants and products Concentration of reactants and products become constantbecome constant at equilibrium. at equilibrium.

This This does not meandoes not mean the amount or quantities are the amount or quantities are equal to each other.equal to each other.

Concentrations constant, not equalConcentrations constant, not equal

Con Con, Requal!!! Con Con, Requal!!!

EquilbriumEquilbrium

Must have a Must have a closed systemclosed system..

This is so no reactants or products This is so no reactants or products (especially gases) can escape.(especially gases) can escape. If they did you could not reach equilibriumIf they did you could not reach equilibriumThe reaction will instead “go to completion” in The reaction will instead “go to completion” in

one directionone directionhttp://www.youtube.com/watch?v=LMIbJ-B92Ho&safe=active (1:25 min)

EquilibriumEquilibrium

Dynamic ProcessDynamic Process: the reactions : the reactions (forward/reverse) have not stopped.(forward/reverse) have not stopped.

You can no longer see changes in materials You can no longer see changes in materials because the forward/reverse rxns happening because the forward/reverse rxns happening at same rate.at same rate.

http://www.youtube.com/watch?v=JsoawKguU6A&safe=active (1:47 min) goodhttp://www.youtube.com/watch?v=JsoawKguU6A&safe=active (1:47 min) good

Parking Lot Equilibrium Interactive:Parking Lot Equilibrium Interactive:http://highered.mcgraw-hill.com/sites/http://highered.mcgraw-hill.com/sites/

0023654666/student_view0/chapter14/0023654666/student_view0/chapter14/animations_center.html#animations_center.html#

Types of EquilibriumTypes of EquilibriumPhase EquilibriumPhase Equilibrium: :

Gas/liquid:Gas/liquid:

Rate of vaporization = rate of condensationRate of vaporization = rate of condensation

Ex: HEx: H22O O (l) (l) ↔ H↔ H22O O (g)(g)

Results in constant amount of vapor at a specificResults in constant amount of vapor at a specific

temperature we measure as “equilibrium vapor pressure”temperature we measure as “equilibrium vapor pressure”

Phase EquilibriumPhase Equilibrium: :

Solid/liquid:Solid/liquid:Rate of melting (fusion) = rate of solidificationRate of melting (fusion) = rate of solidification

Ex: HEx: H22O (s) ↔ HO (s) ↔ H22O (l)O (l)

Types of EquilibriumTypes of Equilibrium

Solution EquilibriumSolution Equilibrium::Rate of dissolving = rate of crystallizationRate of dissolving = rate of crystallization

Ex: NaCl (s) ↔ NaCl (aq)Ex: NaCl (s) ↔ NaCl (aq)

Occurs in Occurs in saturated solutionssaturated solutionsSolution holds maximum solute it can at that temp.Solution holds maximum solute it can at that temp.

Even if you add more solute the conc. will not changeEven if you add more solute the conc. will not change

Types of EquilibriumTypes of Equilibrium

Chemical EquilibriumChemical Equilibrium::Happens during chemical reactionsHappens during chemical reactions

Forward/reverse reactions occur at same rate.Forward/reverse reactions occur at same rate.Concentrations become constantConcentrations become constantNo longer see observable changesNo longer see observable changes

Ex: Ex: NN22(g) + 3H(g) + 3H22(g) ↔ 2NH(g) ↔ 2NH33(g)(g)

http://www.kentchemistry.com/links/Kinetics/Equilibrium.htmhttp://www.kentchemistry.com/links/Kinetics/Equilibrium.htm

Going to Completion

Reactions will not reach equilbrium if:

You remove product preventing reverse reaction

If system left open and gas leavesIf an insoluble product forms (ppt)If water is formed

Helpful VideosHelpful Videos

Equilibrium Overview Equilibrium Overview (Good Review) (18min)(Good Review) (18min) https://www.youtube.com/watch?v=yFqYrBxbURYhttps://www.youtube.com/watch?v=yFqYrBxbURY

Practice Questions

Which balanced equation represents a

phase equilibrium?

(1) H2(g) + I2(g) ↔ 2HI(g)

(2) 2NO2(g)  ↔ N2O4(g)

(3) Cl2(g)  ↔ Cl2(l)

(4) 3O2(g) ↔   2O3(g)

Which statement about a system at equilibrium is true?

(1) The forward reaction rate is less than the reverse reaction rate.

(2) The forward reaction rate is greater than the reverse reaction rate.

(3) The forward reaction rate is equal to the reverse reaction rate.

(4) The forward reaction rate stops and the reverse reaction rate continues.

A chemical reaction is at equilibrium.

Compared to the rate of the forward

reaction, the rate of the reverse reaction is

(1) faster and more reactant is produced

(2) faster and more product is produced

(3) the same and the reaction has stopped

(4) the same and the reaction continues in both directions

Which quantities must be equal for a chemicalreaction at equilibrium?

(1) the activation energies of the forward and reverse reactions

(2) the rates of the forward and reverse reactions

(3) the concentrations of the reactants and products

(4) the potential energies of the reactants and products

Given the equation representing a phase change at equilibrium: H2O(s)  ↔ H2O(l)

Which statement describes this equilibrium?

(1) The H2O (s) melts faster than the H2O(l)  freezes.

(2) The H2O (l) freezes faster than the H2O (s) melts.

(3) The mass of H2O(s) must equal the mass of H2O(l).

(4) The mass of H2O (l) and the mass of H2O (s) each remain constant.