EQUILIBRIUM_S13 - CHEMICAL EQUILIBRIUM In this chapter we...

This preview shows page 1 - 4 out of 14 pages.

CHEMICAL EQUILIBRIUM In this chapter we will try to answer the following questions: How does the free energy of a chemical reaction vary with the composition of the reaction mixture? To what extent does a reaction proceed before it reaches equilibrium? How can we describe the concentrations of reactants and products at equilibrium? What are the factors that affect chemical equilibrium? How can exploit those factors to enhance the occurrence of certain reactions? THE REVERSIBILITY OF REACTIONS A system reaches equilibrium when there is no further tendency for its composition to change. Such equilibrium is dynamic! Meaning that both the forward and the reverse reactions are occurring simultaneously at the same rate and therefore, one can observe no net change in composition. A + B C + D Changes in concentration for the reaction H 2 O and CO as equilibrium is reached Zumdahl, S. S. Chemical Principles , 6 th ed.; Boston: Houghton Mifflin Company, 2010. Changes with time in reaction rates of forward and reverse reactions for H 2 O + CO as equilibrium is reached 1
Image of page 1

Subscribe to view the full document.

Zumdahl, S. S. Chemical Principles , 6 th ed.; Boston: Houghton Mifflin Company, 2010. EQUILIBRIUM AND THE LAW OF MASS ACTION The law of mass action states: at equilibrium, the composition of a reaction mixture can be expressed in terms of the equilibrium constant. The equilibrium constant, K, is equal to the activities of the products raised to the power of their coefficients in the balanced chemical equation divided by the activities of the reactants raised to the power of their coefficients. - For pure solids or liquids the activity = 1 (no units). - For components of an ideal solution, the activity of each component is the ratio of its molar concentration to a standard concentration of 1M (therefore, units cancel). - For a mixture of gases, the activity of each component is the ratio of its partial pressure to a standard pressure of 1 atm (therefore, units cancel). - For reactions mixtures that involve ions in solution, we write the equilibrium constant for the net ionic equation using activities of ions. Heterogeneous equilibria involve species in more than one phase. While homogeneous equilibria involve all species in the same phase. For mixtures of gases, K can be referred to as K p . (Partial pressures are always in atmosphere for the calculation of Kp) Examples: Write the expression for the equilibrium constant for each of the following reactions: 1- Nitrogen reacts with hydrogen to give ammonia. 2
Image of page 2
2- Silver nitrate reacts with sodium chloride in water to produce silver chloride as a precipitate. 3- 2NH 3 (g) + 3CuO(s) N 2 (g) + 3H 2 O(l) + 3Cu(s) 4- MgCO 3 (s) MgO(s) + CO 2 (g) THE THERMODYNAMIC ORIGIN OF EQUILIBRIUM CONSTANTS Every chemical process proceeds spontaneously toward equilibrium.
Image of page 3

Subscribe to view the full document.

Image of page 4
  • Spring '13
  • fakhreddine
  • Equilibrium, Chemical reaction, Kc

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern