Chemical
Sponsored Links
This presentation is the property of its rightful owner.
1 / 43

Chemical Equilibrium PowerPoint PPT Presentation


  • 66 Views
  • Uploaded on
  • Presentation posted in: General

Chemical Equilibrium. A Balancing Act. Equilibrium. two opposing processes occurring at the same rate. a system at equilibrium is in balance. During a game, players enter and leave. Always the same number of players on field. H 2 O(l) H 2 O(g). Photochromic sunglasses.

Download Presentation

Chemical Equilibrium

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Chemical

Equilibrium

A Balancing Act


Equilibrium

two opposing processes occurring at the same rate

a system at equilibrium is in balance


During a game, players enter and leave.

Always the same number of players on field.


H2O(l) H2O(g)


Photochromic

sunglasses

AgCl + light Ag + Cl

(transparent) (dark)


Reversible reaction

a chemical reaction that can occur in both the forward and the reverse directions

N2(g) + 3H2(g) 2NH3(g)


Chemical equilibrium

a state in which the forward and reverse reactions balance each other because they take place at equal rates

dynamic state; no net change


Law of chemical equilibrium

At a given temperature, a chemical system might reach a state in which a particular ratio of reactant and product concentrations has a constant value.


Equilibrium constant expression

ratio of molar concentrations of products to reactants; each raised to a power equal to coefficient in balanced equation


aA + bB cC + dD


Equilibrium constant(Keq)

numerical value of the ratio of product to reactant concentrations

constant only at a specific temperature


Value of equilibrium constant (Keq) shows

the extent to which reactants are converted into products.


Keq > 1: Products are favored at equilibrium

Keq < 1: Reactants are favored at equilibrium


Homogeneous equilibrium

all reactants and products in same phase


Write an equilibrium constant expression for:

N2(g) + 3H2(g) 2NH3(g)

[NH3]2

Keq =

___________

[N2] [H2]3


Heterogeneous equilibrium

reactants and products present in more than one physical state

H2O(l) H2O(g)


Heterogeneous equilibrium

Since concentrations of pure liquids and solids remain constant, these substances are omitted from the equilibrium constant expression.


Write an equilibrium constant expression for:

H2O(l) H2O(g)

Keq =

[H2O(g)]


Equilibrium constant expression Keq = . . .

Products over reactants raised to power of coefficient; leave out pure solids and liquids.


Equilibrium position

Equilibrium concentrations can vary from trial to trial.


H2(g) +I2(g) 2HI(g)


Each set of equilibrium concentrations represent an equilibrium position.

A system has only one value for Keq at a specific temperature, however there are unlimited number of equilibrium positions.


A system at equilibrium must:

  • take place in closed

  • system

  • temperature remain

  • constant

  • all reactants and

  • products are present

  • (both reactions can occur)


Write the equilibrium constant expression for

N2(g) + O2(g) 2NO(g)


Calculate the value of Keq if [N2] = 0.20 mol/L,

[O2] = 0.15 mol/L, and

[NO] = 0.0035 mol/L.

Keq = 4.1 x 10-4

What does the value of Keq tell you about the equilibrium?


What happens when a system is at equilibrium and you upset the balance?


Le Chatelier’s Principle

If a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress.


Le Chatelier’s Principle

Used to predict how a equilibrium system will react to changes in concentration, pressure (volume) and temperature.


Changes in Concentration

Add reactant

1. Forward rxn speeds up.

2. Over time, forward

rxn slows down and

reverse rxn speeds up.


3. At equilibrium,

forward and reverse

rxns occur at same

rate, new equilibrium

position established.

  • Equilibrium has

  • shifted right, value

  • of Keq unchanged.


Changes in Concentration

Remove reactant

1. Reverse rxn speeds up.

2. Over time, reverse

rxn slows down and

forward rxn speeds up.


3. At equilibrium,

forward and reverse

rxns occur at same

rate, new equilibrium

position established.

  • Equilibrium has

  • shifted left; value of

  • Keq unchanged.


Changes in Pressure (Volume)

  • For a gas, decreasing

  • volume of container

  • increases pressure;

  • particles have less

  • space, collide more

  • frequently.


2. System will respond

by trying to relieve

stress (decrease

pressure.)

3. Shifts to the side with

fewer moles of gas.


4. Forward rxn speeds up.

5. Over time, forward

rxn slows down and

reverse rxn speeds up.


6. At equilibrium,

forward and reverse

rxns occur at same

rate, new equilibrium

position established.

7. Equilibrium has

shifted right, value

of Keq unchanged.


Changes in Pressure (Volume)

Note:

If volume is decreased concentrations of all gaseous substances increases.

Side with fewer moles of gas increases more.


Changes in Temperature

Review:

If DH is negative

rxn is exothermic

heat written as product

If DH is positive

rxn is endothermic

heat written as reactant


Changes in Temperature

N2O4(g) 2NO2(g)

DH = 55.3 kJ

55.3 kJ + N2O4(g) 2NO2(g)

light dark


55.3 kJ + N2O4(g) 2NO2(g)


Le Chatelier’s Principle

Used to predict how a equilibrium system will react to changes in concentration, pressure (volume) and temperature.

Chemists can change conditions to make rxn more productive.


  • Login