the equilibrium position

Examples of the equilibrium position in the following topics:

• The Effect of a Catalyst

  • Catalysts speed up the rate of a reaction, but do not have an affect on the equilibrium position.
  • 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.
  • However, it is very important to keep in mind that the addition of a catalyst has no effect whatsoever on the final equilibrium position of the reaction.
  • To reiterate, catalysts do not affect the equilibrium state of a reaction.

• Equilibrium

  • Chemical equilibrium is the state in which the forward reaction rate and the reverse reaction rate are equal.
  • The result of this equilibrium is that the concentrations of the reactants and the products do not change.
  • 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.
  • For instance, if a catalyst is added to the system, the reaction will proceed more quickly, and equilibrium will be reached faster, but the concentrations of both A and B will be the same at equilibrium for both the catalyzed and the uncatalyzed reaction.

• Le Chatelier's Principle

  • What would happen to the equilibrium position of the reaction if an inert gas, such as krypton or argon, were added to the reaction vessel?
  • The effect of temperature on equilibrium has to do with the heat of reaction.
  • Recall that for an endothermic reaction, heat is absorbed in the reaction, and the value of $\Delta H$ is positive.
  • Therefore, increasing the temperature will shift the equilibrium to the left, while decreasing the temperature will shift the equilibrium to the right.
  • Our heat of reaction is positive, so this reaction is endothermic.

• Stability, Balance, and Center of Mass

  • An object in static equilibrium remains in the same state forever, but not all forms of equilibrium are the same.
  • If it starts accelerating away from its current position, it would hardly be in equilibrium.
  • Being in equilibrium means that we expect no changes to the linear momentum or the angular momentum.
  • When the first derivative is zero, we can take the second derivative to find whether the equilibrium is stable or unstable.
  • A ball on top of a hill can initially be balanced, but if it moves slightly left or right, it gets pushed further and further away from the initial equilibrium position.

• The Zeroth Law of Thermodynamics

  • The Zeroth Law of Thermodynamics states that systems in thermal equilibrium are at the same temperature.
  • Systems are in thermal equilibrium if they do not transfer heat, even though they are in a position to do so, based on other factors.
  • For example, food that's been in the refrigerator overnight is in thermal equilibrium with the air in the refrigerator: heat no longer flows from one source (the food) to the other source (the air) or back.
  • Temperature is the quantity that is always the same for all systems in thermal equilibrium with one another.
  • The double arrow represents thermal equilibrium between systems.

• Equilibrium Constant and Cell Potential

  • The equilibrium constant K can be calculated using the Nernst equation.
  • Thus, zinc metal will lose electrons to copper ions and develop a positive electrical charge.
  • The cell equilibrium constant, K, can be derived from the Nernst equation:
  • The cell potential is zero at equilibrium (E=0), and Q (the reaction quotient) can now be designated as the equilibrium constant K.
  • Calculate the equilibrium constant, K, for a galvanic cell using the Nernst equation

• Calculating Equilibrium Concentrations

  • Equilibrium constants can be used to calculate the concentrations of reactants and products that will be present at equilibrium.
  • Similarly, we designate +2x as the change in concentration for NO, but it's positive because it's being produced.
  • Knowing the initial concentration values and equilibrium constant we were able to calculate the equilibrium concentrations for N2, O2 and NO.
  • The equilibrium concentration is the sum of the initial concentration and the change, which is derived from the reaction stoichiometry.
  • Calculate the concentrations of reaction components at equilibrium given the starting concentrations and the equilibrium constant

• 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.
  • Reactions with positive enthalpies—those that absorb heat from their surroundings—are known as endothermic.
  • Evaluate the effect of temperature on the equilibrium state of a chemical reaction

• Conductors and Fields in Static Equilibrium

  • In the presence of charge or an electric field, the charges in a conductor will redistribute until they reach static equilibrium.
  • Once the charges are redistributed, the conductor is in a state of electrostatic equilibrium.
  • It should be noted that the distribution of charges depends on the shape of the conductor and that static equilibrium may not necessarily involve an even distribution of charges, which tend to aggregate in higher concentrations around sharp points.
  • Negative charges in the conductor will align themselves towards the positive end of the electric field, leaving positive charges at the negative end of the field.
  • Describe behavior of charges in a conductor in the presence of charge or an electric field and under static equilibrium

• Homogeneous versus Heterogeneous Solution Equilibria

  • The equilibrium constants for homogeneous and heterogeneous solutions need to be calculated differently.
  • The equilibrium constants for reactions that contain substances that are all in the same phase, and reactions that contain substances in different phases, 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 equilibrium constant K is simply [Br2], with the concentration of the pure liquid Br2 excluded.