chemical equilibrium

Examples of chemical equilibrium in the following topics:

• Equilibrium

  • Chemical equilibrium is the state in which the forward reaction rate and the reverse reaction rate are equal.
  • However, we will now consider forward/reverse reaction pairs that exist in chemical equilibrium with one another.
  • In a chemical reaction, chemical equilibrium is the state in which the forward reaction rate and the reverse reaction rate are equal.
  • This is the point at which the system has reached chemical equilibrium.
  • Chemical equilibrium is akin to two cities connected a bridge.

• Changes in Volume and Pressure

  • The effects of changes in volume and pressure on a reversible reaction in chemical equilibrium can be predicted by Le Chatelier's Principle.
  • The effects of changes in volume and pressure on chemical equilibrium can be predicted using Le Chatelier's Principle.
  • Le Chatelier's Principle states that disturbances to a system in equilibrium can be predicted: opposing shifts in the system will occur to restore equilibrium.
  • Le Chatelier's Principle can be used to predict the response of a reversible chemical reaction to a change in the system.
  • Evaluate the effect of pressure on the equilibrium of a chemical reaction

• Chemical Kinetics and Chemical Equilibrium

  • Chemical kinetics is the study of how quickly a chemical reaction occurs and what factors affect its rate.
  • Obviously, there are factors that affect the rates of chemical reactions.
  • The study of these factors and rates is known as chemical kinetics.
  • As described in previous sections, the reaction reaches equilibrium when its rate is constant, as seen in .
  • A plot of time versus concentration for two species in chemical equilibrium.

• Changes in Temperature

  • Changes in temperature shift the equilibrium state of chemical reactions; these changes can be predicted using Le Chatelier's Principle.
  • Changes in temperature can affect the equilibrium state of a reversible chemical reaction.
  • The effect of changes to the equilibrium state can be predicted using Le Chatelier's Principle.
  • Le Chatelier's Principle states that when changes are made to a reversible chemical reaction in equilibrium, the system will compensate for that change with a predictable, opposing shift.
  • Evaluate the effect of temperature on the equilibrium state of a chemical reaction

• Equilibrium Constant Expression

  • The equilibrium constant is an expression that gives the ratio of reactants and products at equilibrium.
  • The law of chemical equilibrium states that, at any given temperature a chemical system reaches a state in which a particular ratio of reactant and product activities has a constant value.
  • This constant is known as the equilibrium constant.
  • By convention, the equilibrium concentrations of the substances appearing on the right hand side of the chemical equation (the products) are always placed in the numerator of the equilibrium constant expression; the concentrations of the substances appearing on the left hand side of the chemical equation (the reactants) are placed in the denominator.
  • The equilibrium constant,denoted by K, is the ratio of products to reactants 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.
  • To reiterate, catalysts do not affect the equilibrium state of a reaction.
  • To state this in chemical terms, catalysts affect the kinetics, but not the thermodynamics, of a reaction.
  • Try running the reaction with and without a catalyst to see the effect catalysts have on chemical reactions. 1.

• Changes in Concentration

  • If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change.
  • A new equilibrium is established.
  • Because products and reactants in a chemical equation do not always have the same number of moles, as demonstrated in , disturbances in the concentration of atoms can affect the equilibrium.
  • The chemical system will attempt to partially counteract the change imposed on the original state of equilibrium.
  • Evaluate how a change in concentration will affect a chemical equillibrium

• Equilibrium Constant and Cell Potential

  • The equilibrium constant K can be calculated using the Nernst equation.
  • We say that the sugar molecules have a "chemical potential," which is higher in the high-concentration areas, and the molecules move to lower their chemical potential.
  • These two examples show that an electrical potential and a chemical potential can both give the same result: a redistribution of the chemical species.
  • Empirically, an equilibrium situation would arise where the chemical concentration gradient could be balanced by an electrical gradient that opposes the movement of charge.
  • The cell potential is zero at equilibrium (E=0), and Q (the reaction quotient) can now be designated as the equilibrium constant K.

• 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.
  • The chemical species involved can be molecules, ions, or a mixture of both.
  • The equilibrium constant K is simply [Br2], with the concentration of the pure liquid Br2 excluded.

• Reaction Quotients

  • The reaction quotient is a measure of the relative amounts of reactants and products during a chemical reaction at a given point in time.
  • The reaction quotient, Q, is a measure of the relative amounts of reactants and products during a chemical reaction at a given point in time.
  • 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.