equilibrium

Examples of equilibrium in the following topics:

• Homogeneous versus Heterogeneous Solution Equilibria

  • The equilibrium constants for homogeneous and heterogeneous solutions need to be calculated differently.
  • The equilibrium constant K for a given reaction is defined as the ratio of the products of a reaction to the reactants, measured at equilibrium.
  • The reaction quotient measured at equilibrium is the equilibrium constant K.
  • A heterogeneous equilibrium is a system in which reactants and products are found in two or more phases.
  • The equilibrium constant K is simply [Br2], with the concentration of the pure liquid Br2 excluded.

• Equilibrium Constant Expression

  • The equilibrium constant is an expression that gives the ratio of reactants and products at equilibrium.
  • This constant is known as the equilibrium constant.
  • Their activity is 1, so they do not need to be written in the equilibrium constant.
  • The progress of an equilibrium reaction can be visualized.
  • The equilibrium constant,denoted by K, is the ratio of products to reactants at equilibrium.

• Reaction Quotients

  • If Q < Keq, the reaction will move to the right (in the forward direction) in order to reach equilibrium.
  • If Q > Keq, the reaction will move to the left (in the reverse direction) in order to reach equilibrium.
  • Eventually, the concentrations become constant; at this point, the reaction is at equilibrium.
  • The equilibrium constant, Keq, can be expressed as follows:
  • However, most reactions will generally reach equilibrium in a finite period of time.

• Equilibrium

  • The concentrations of A and B will change over time, until they reach equilibrium.
  • This is the point at which the system has reached chemical equilibrium.
  • While there are various factors that can increase or decrease the amount of time it takes for a given system to reach equilibrium, the equilibrium position itself is unaffected by these factors.
  • We also explain how the concentrations remain constant at equilibrium.
  • Chemical equilibrium is akin to two cities connected a bridge.

• Heterogeneous and Multiple Equilibria

  • Therefore, the equilibrium expression for this reaction will be written as:
  • Both steps must be included in the equilibrium constant equation.
  • K1 and K2 are examples the equilibrium constants for each step.
  • Notice that the equilibrium expression for the overall reaction, Keq, is equal to the product of the equilibrium expressions for the two reaction steps.
  • Calculate the equilibrium constant of a multiple-step reaction, given the equilibrium constant for each step

• Expressing the Equilibrium Constant of a Gas in Terms of Pressure

  • Up to this point, we have been discussing equilibrium constants in terms of concentration.
  • Our equilibrium constant in terms of partial pressures, designated KP, is given as:
  • Note that this expression is extremely similar to KC, the equilibrium expression written in terms of concentrations.
  • Inside this tank, propane is compressed into a liquid, which is in equilibrium with its gaseous headspace.
  • Write the equilibrium expression, KP, in terms of the partial pressures of a gas-phase reaction

• Calculating Equilibrium Concentrations

  • Equilibrium constants can be used to calculate the concentrations of reactants and products that will be present at equilibrium.
  • ICE stands for "initial, change, equilibrium."
  • Only one of these values involves equilibrium concentrations that are actually possible.
  • Knowing the initial concentration values and equilibrium constant we were able to calculate the equilibrium concentrations for N2, O2 and NO.
  • Calculate the concentrations of reaction components at equilibrium given the starting concentrations and the equilibrium constant

• Predicting the Direction of a Reaction

  • Equilibrium constants can be used to predict whether a reaction will favor the products or the reactants.
  • K is the equilibrium ratio of products to reactants.
  • The equilibrium constant is only used when a reaction has reached equilibrium.
  • This value is greater than the equilibrium value: there is now too much of the products for equilibrium to exist.
  • Evaluate whether a chemical reaction has reached equilibrium from the reaction coefficient (Q) and the equilibrium constant (K), and use the latter to predict whether the reaction will favor the reactants or products

• Calculating the pH of a Buffer Solution

  • The pH of a buffer solution can be calculated from the equilibrium constant and the initial concentration of the acid.
  • The strength of a weak acid is usually represented as an equilibrium constant.
  • The acid-dissociation equilibrium constant (Ka), which measures the propensity of an acid to dissociate, for the reaction is:
  • ICE (Initial, Change, Equilibrium) tables are very helpful tools for understanding equilibrium and for calculating the pH of a buffer solution.
  • Describes the final concentration of the reactants and products at equilibrium.

• The Effect of a Catalyst

  • Catalysts speed up the rate of a reaction, but do not have an affect on the equilibrium position.
  • Reactions can be sped up by the addition of a catalyst, including reversible reactions involving a final equilibrium state.
  • Recall that for a reversible reaction, the equilibrium state is one in which the forward and reverse reaction rates are equal.
  • In the presence of a catalyst, both the forward and reverse reaction rates will speed up equally, thereby allowing the system to reach equilibrium faster.
  • To reiterate, catalysts do not affect the equilibrium state of a reaction.