Chemical equilibrium
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Chemical Equilibrium. What is Chemical Equilibrium?. Reversible Reaction - a chemical reaction in which the products can react to re-form the reactants. Chemical Equilibrium

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Chemical Equilibrium

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Chemical equilibrium

Chemical Equilibrium


What is chemical equilibrium

What is Chemical Equilibrium?

  • Reversible Reaction

    -a chemical reaction in which the products can react to re-form the reactants.

    Chemical Equilibrium

  • the forward reaction equals the rate of its reverse reaction and the concentrations of its products and reactants remain unchanged

    How is it Written?

  • use double arrows

    2HgO(s)  2Hg(l) + O2(g)


The equilibrium expression

The Equilibrium Expression

  • Equilibrium Constant

    -ratio of the concentrations of the products to the concentrations of the reactants

  • there is no unit and it is dependent on temperature

    Equilibrium Expression

    K= [C]x [D]y

    [A]n [B]m

    n,m,x,y are the coefficients and are raised to the power equal to the coefficient of the substance

    The [ ] represent the concentrations of the substances


Equilibrium constant example

Equilibrium Constant Example

  • An equilibrium mixture of N2, O2, and NO gases at 1500 K is determined to consist of 6.4 x 10-3 M of N2, 1.7 x 10 –3 M of O2, and 1.1 x 10-5 M of NO. What is the equilibrium constant for the system at this temperature?

  • N2(g) + O2(g)  2 NO(g)


Shifting equilibrium

Shifting Equilibrium

  • What is Le Chatelier’s Principle?

  • If a system at equilibrium is subjected to a stress, the equilibrium is shifted in the direction that tends to relieve the stress.


What stresses or changes affect equilibrium

What stresses or changes affect equilibrium?

  • Changes in Concentration

    a. Increase(add) a reactant or product will shift away from the added reactant or product

    b. Decrease ( remove) a reactant or product will shift toward the removed reactant or product


Change in concentration cont

Change in concentration cont.

  • A + B  C + D

  • Which way will it shift if we:

  • Add B

  • Shift right

  • Add C

  • Shift left

  • Remove A

  • Shift left

  • Remove D

  • Shift right


Equilibrium stresses cont

Equilibrium stresses cont.

  • Changes in pressure

  • only affects equilibrium systems in which gases are involved

    a. If the pressure is increased,it will shift towards the side with the smaller number of molecules

    b. If the pressure is decreased, it will shift towards the side with the larger number of molecules.


Change in pressure cont

Change in pressure cont.

N2(g) + 3H22NH3

What would happen if we increased the pressure?

Shift right

What would happen if we decreased the pressure?

Shift left


Equilibrium stresses cont1

Equilibrium stresses cont.

  • Changes in Temperature

    a. Increase ( add) temperature will cause a shift away from the added temperature

    b. Decrease (removal) temperature will cause a shift toward the removed temperature


Changes in temperature cont

Changes in temperature cont.

556 kJ + CaCO3(s)  CaO(s) + CO2(g)

What would happen if we increased the temperature?

Shift right

What would happen if we decreased the temperature?

Shift left


States of matter in equilibrium problems

States of matter in Equilibrium problems

  • Have you noticed that all the examples that I have used have only included the gas or aqueous state? Why?

  • The concentrations of pure substances in solids and liquids phases are not changed by adding or removing quantities of the substance

  • They are not included in the equilibrium expression.


Solubility product constant

Solubility Product Constant

  • Is the product of the molar concentrations of its ions each raised to the power of its coefficients

  • Example:

    BaSO4(s)  Ba2+(aq) + SO42-(aq)

    Ksp= [Ba2+] [SO42-]


Example of k sp

Example of Ksp

Consider the dissociation of the salt CaF2.

CaF2(s)  Ca2+(aq) + 2F-(aq)

At a temperature of 298 K, the concentration of Ca2+ ions is 2.2 x10-4 M, and Ksp for the salt is 1.46 x 10-10. What is the concentration of F- in the solution?


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