Chemical equilibrium
This presentation is the property of its rightful owner.
Sponsored Links
1 / 26

Chemical Equilibrium PowerPoint PPT Presentation


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

Chemical Equilibrium. Many chemical reactions are reversible and the reaction will proceed until chemical equilibrium is reached. Characteristics of Chemical Equilibrium. The rate of the forward reaction occurs at the same rate as the reverse reaction.

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

Chemical Equilibrium


Chemical equilibrium

  • Many chemical reactions are reversible and the reaction will proceed until chemical equilibrium is reached.


Characteristics of chemical equilibrium

Characteristics of Chemical Equilibrium

  • The rate of the forward reaction occurs at the same rate as the reverse reaction.

  • Concentrations of reactants and products remain constant at equilibrium.

  • Attainment of equilibrium is not immediate and often requires an extended period of time.


Equilibrium constant

Equilibrium Constant

  • Because the concentration of reactants and products are constant (not equal), we can calculate this ratio. Consider:

    aA + bB  cC + dD

    where the lowercase letters represent the coefficients of the balanced equation.


Chemical equilibrium

Equilibrium constant, Keq, is found by:

products

Keq = [C]c[D]d

[A]a[B]b

  • Square brackets, [ ], indicate molar concentrations.

  • Each concentration is raised to the power of its balancing coefficient.

reactants


Chemical equilibrium

  • Product concentrations are in the numerator while reactant concentrations are in the denominator.

  • The expression for Keq is also known as the law of chemical equilibrium.


Values of k eq

Values of Keq

  • The value of the equilibrium constant tells us something about the position of the equilibrium.

  • If Keq is very large, the reaction favors the formation of products (most of the reactants will be converted to products).

  • If Keq is very small, the reaction favors reactants (very little reactants are converted to products).


Chemical equilibrium

  • If Keq is between 0.01 and 100, neither reactants nor products are strongly favored.


Chemical equilibrium

Once a reaction has reached chemical equilibrium, it will remain at equilibrium as long as it is undisturbed.


Le ch telier s principle

Henri LeChatelier

Le Châtelier’s Principle

Shifts in Equilibrium


Le ch telier s principle1

Le Châtelier’s Principle

“If a change is imposed, the system will adjust to counteract the effect of the change and then establish a new equilibrium.”


3 types of stress

3 Types of Stress

  • 1) CHANGE IN CONCENTRATION OF REACTANTS OR PRODUCTS ( no change to Kc)

  • 2) CHANGE IN TEMPERATURE (Kc will change)

  • 3) CHANGE IN PRESSURE (GASES ONLY)

    (no change to Kc)


Chemical equilibrium

1) Changes in Concentration


Chemical equilibrium

Consider the reaction at equilibrium:

N2(g) + O2(g) 2NO(g)

  • If we add more O2, the equilibrium will shift to the right, meaning O2 will react with N2 to produce more NO.

  • The result is that the concentration of O2 decreases, counteracting the effect of the change.


In other words

In other words,

  • a reaction will shift away from a substance added and toward a substance removed from an equilibrium mixture.

  • What would happen to: 3H2 + N2 2NH3

  • if we added H2?

    Shift to the right

    b) if we added NH3?

    shift to the left

    c) if we removed N2?

    shift to the left


Chemical equilibrium

Adding or removing substances causes a shift in the equilibrium, but it does not change the value of Keq.


Chemical equilibrium

2) Changes in Temperature


Chemical equilibrium

When the temperature is raised, the reaction shifts in the direction away from the energy term.

Example 1: Temperature increased for this reaction will shift in the direction of the products:

2SO3(g) + 197kJ 2SO2(g) + O2(g)

Kc is increased

Example 2: Temperature increased for this reaction will shift in the direction of the reactants:

C2H4(g) + 3O2(g)  2CO2(g) + H2O(g) + 1250.9kJ

Kc is decreased


Chemical equilibrium

  • When the temperature is lowered, the reaction shifts in the direction toward the energy term.

    Example 1: Temperature decreased for this reaction will shift in the direction of the reactants:

    2SO3(g) + 197kJ 2SO2(g) + O2(g)

    Kc is decreased

    Example 2: Temperature decreased for this reaction will shift in the direction of the products:

    C2H4(g) + 3O2(g)  2CO2(g) + H2O(g) + 1250.9kJ

    Kc is increased


Chemical equilibrium

  • The value of Kcdoes change when the temperature is changed.


Chemical equilibrium

Given the reaction:

PCl5 PCl3 + Cl2+ energy

  • If the temperature is increased, what effect will that have on:

  • the position of the equilibrium?

    shifts to the left

  • the value of Kc

    decreases


Chemical equilibrium

3) Changes in Pressure


Chemical equilibrium

  • An increase in pressure on a gaseous system always favors a shift towards the side with the lowest total number of gaseous particles and vice versa.

  • Example: Pressure increased for this reaction will shift in the direction of the reactants:

    2SO3(g)  2SO2(g) + O2(g)

    (2 molecules)(3 molecules)


To increase pressure

To increase pressure:

Decrease volume of container (at a constant temp)

To decrease pressure:

Increase volume of container (at a constant temp)


No effect

No Effect:

  • If the total number of molecules in reactants and products is equal, pressure changes will not affect the system.

  • If a non-reacting (inert) gas is added to the reaction container


Summary

SUMMARY:

  • Changes in concentration: a reaction shifts away from a substance added and toward a substance removed

  • Changes in temperature: when temperature is raised, the reaction shifts away from the energy term and vice versa

  • Changes in pressure: when pressure is increased on a gaseous system, the reaction shifts towards the side with the lowest total number of gaseous particles and vice versa.


  • Login