Chapter 14 - Chemical Equilibrium

14.1 - The Concept of Equilibrium and the Equilibrium Constant

• When the rates of forward and reverse reactions are similar and the concentrations of the reactants and products stay constant, chemical equilibrium is reached.

  • Because the changes that occur are physical processes, physical equilibrium between two phases of the same substance is called physical equilibrium.

• The number of skiers carried up the ski lifts is equal to the number descending the pistes at this busy resort.

  • Chemical equilibrium is a dynamic process.
  • It is also possible to compare it to the movement of skiers at an occupied ski resort.

• Chemical balance includes various substances, such as reactants and products.

• The balance between two phases is called physical balance because physical processes are the changes that occur.

  

• For a particular temperature reaction K [C]c [D]d [A]a [B]b(14.2) with a constant balance of K.

• Two Norwegian chemists, Cato Guldberg in the first place and Peter Waage in the second place, formulated equation (14.2), in 1864.

• It is the mathematical expression of their law of mass action whereby a certain ratio of reactant and product levels is constant for a reversible reaction at balance and a constant temperature, K (the equilibrium constant).

14.2 - Writing Equilibrium Constant Expressions

• All interacting species are in the same phase, which is referred to as homogeneous equilibrium.
• As you could expect, the reversible effect involving reactants and products at different stages results from a heterogeneous balance.
• However, the "concentration" of a solid is an intense property, like its density, and is not dependent on how much it contains.
• If the total amount of two or more reactions is a reaction, the product for the equilibrium constant of the individual reactions gives the equilibrium constants.

14.3 - The Relationship Between Chemical Kinetics and Chemical Equilibrium

• We can see that the equilibrium constant of a reaction can be defined as a ratio of the rate constants of the forward and reverse processes in terms of chemical kinetics.
  • The equilibrium constant is a constant, and its value changes with temperature, as explained in this analysis.
• kc is constant regardless of the reacting species' balancing concentrations, since it is always identical to kf/KR
  • The double-meter quotient is itself constant at a given temperature. Since temperature-dependent rate constants,
  • the equilibrium constant must therefore also change with temperature.

14.4 - What Does the Equilibrium Constant Tell Us

• We obtain the reaction quotient (Qc) instead of the equilibrium constant for processes that have not achieved equilibrium
  • The generation of HI is discussed above, by replacing the initial concentrations into the equilibrium constant expression.
• The ratio of initial product to reactant concentrations is too low.
  • Reactants need to be converted into products to achieve balance.
  • The system is left-to-right
• The initial levels are concentrations of balance.
  • The system is in balance.
• There is too high a ratio of initial product concentrations to reactants.
• Products have to be converted into reactants to achieve balance.
  • The system proceeds from right to left to achieve a balance.
• If we know the balance constant for a specific reaction, we can calculate from initial concentrations the concentrations in the balance mixture.
  • Usually, there are only initial reactant levels

14.5 - Factors That Affect Chemical Equilibrium

• If external stress is applied to a system at equilibrium, the system adapts in such a way that the stress is partially offset when the system reaches a new equilibrium point, according to Le Châtelier's principle.
  • The term "stress" refers to a shift in concentration, pressure, volume, or temperature that throws the system out of balance.
• Thiocyanate [Fe(SCN)3] of iron(III) is readily dissolved in water to solve redness.
  • The red is because of FeSCN2+ hydrated ion. FeSCN2(aq) Fe3(aq) SCN provides the balance between undissociated FeSCN2+ and Fe3+ ions and SCN− ions (aq)
  • Colorless red pale yellow
• This experiment shows that all reactants and products are balanced in the reaction system.
• Second, increasing product concentration (Fe3+ or SCN−) shifts the balance to the left, and lowering the product Fe3+ concentration shifts the balance to the right.
  • These findings are predicted in the principle of Le Châtelier.
  • Remember that the principle of Le Châtelier resumes the compatibility of balancing systems observed
  • It should be wrong to say that there is a certain change of balance "because of" the principle of Le Châtelier.
• At a certain temperature, the heat effect is zero because the net reaction does not occur.
  • Then when we treat the heat as a chemical reagent, the heat "adds" to the system, and the heat is "removed" from the system by decreasing.
  • Like any change of parameter, the system shifts to reduce the change effect.