Equilibrium Concentrations
Equilibrium concentrations refer to the relative amounts of reactants and products in a chemical reaction when the rates of the forward and reverse reactions are equal. At equilibrium, the concentrations of the reactants and products remain constant over time. These concentrations are determined by the equilibrium constant, which is a measure of the extent to which a reaction proceeds.
6 Key excerpts on "Equilibrium Concentrations"
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
...7.2, when the reactants of a reversible reaction are first combined, the forward reaction occurs rapidly increasing the concentrations of the products and decreasing the concentrations of the reactants. As the reaction proceeds and the concentration of products increases, the forward reaction slows and the reverse reaction begins to occur. After some time, an equilibrium is reached where the concentrations of reactants and products do not change with time and the forward and reverse reaction rates are equal. This is known as a dynamic equilibrium because, although forward and reverse reactions still occur, the rate of the forward reaction equals the rate of the reverse reaction. So, the ratio of concentrations of the products to the concentrations of the reactants remains constant, although the reaction is constantly proceeding in both directions. Fig. 7.2 A reversible chemical reaction reaches dynamic equilibrium when the rate of the forward and reverse reactions are equal (left) and the concentrations of reactants and products do not change with time (right). 7.2 The Equilibrium Constant Since the concentrations of reactants and products of a reversible reaction at equilibrium are constant, an expression can be written for an equilibrium constant (K eq) that describes the concentrations of the products and reactants at equilibrium. For the generic reversible reaction (3) at equilibrium, the equilibrium constant expression is; K eq = C c D d A a B b (4) As with the acid ionization constants described in Section 5.2, the equilibrium constant for a reversible reaction is expressed as the ratio of the Equilibrium Concentrations of the products in the numerator to the Equilibrium Concentrations of the reactants in the denominator. The superscript letters are the stoichiometric coefficients of the reactants and products in the balanced chemical equation...
eBook - ePub- Adrian Dingle, Derrick C. Wood(Authors)
- 2014(Publication Date)
- Research & Education Association(Publisher)
...PART VII EQUILIBRIUM Chapter 23 Dynamic Equilibrium I. Equilibrium A. Dynamic Equilibrium: Physical, Biological, Environmental, and Chemical 1. Many chemical reactions are reversible. 2. Many biological and environmental examples of equilibrium exist, such as oxygen binding to, and being released from, hemoglobin, and the carbon cycle. 3. Physical examples include the evaporation and condensation of H 2 O. 4. Chemical examples include the exchange of H + ions in acid base reactions, and the exchange of electrons in REDOX reactions. 5. Double arrows indicate reversibility of the reaction (). B. Equilibrium Conditions 1. At equilibrium, both reactants and products are present. 2. The forward reaction is favored when the concentration of reactants is high, and, hence, the rate of conversion of reactants to products is high. 3. The backward reaction is favored when the concentration of products is high, and, hence, the rate of conversion of products to reactants is high. 4. Dynamic equilibrium is reached when the forward and backward reactions continue at the same rate, and the concentrations of the reactants and products are constant. Constant concentration of reactants and products does not necessarily mean identical concentrations of reactants and products. In fact, they are very rarely the same numerical value. All concentrations being constant (not changing) is not the same thing as concentrations being equal (all having the same value)...
eBook - ePubChemistry
Concepts and Problems, A Self-Teaching Guide
- Richard Post, Chad Snyder, Clifford C. Houk(Authors)
- 2020(Publication Date)
- Jossey-Bass(Publisher)
...12 Chemical Equilibrium You have just learned several properties of solutions (mixtures of solids, liquids, and gases). We have discussed reactions that go to completion (reactants totally consumed, leaving only new products) in Chapter 5 and electrolytes that dissociate completely in water in Chapter 11. Both of these concepts imply a one-way reaction, continuous movement toward the product side. However, in Chapter 10 we discussed a dynamic equilibrium where the rate of evaporation equals the rate of condensation, that is, the reactions are “reversible.” Many chemical reactions are reversible. The products formed react to give back the original reactants, even as the reactants are forming more products. After some time, both the forward and reverse reactions will be going on at the same rate. When this occurs, the reaction is said to have reached equilibrium. There is no further change in the amount of any reactant or product, though both reactions still go on (forever). Since there are many such reactions that appear to go only partway to completion, their study is of major importance to the chemist. We will discuss several types of equilibrium in this chapter, along with their associated problems and concepts...
- Kevin Reel, Derrick C. Wood, Scott A. Best(Authors)
- 2014(Publication Date)
- Research & Education Association(Publisher)
...Chapter 12 Equilibrium Equilibrium Constants • Equilibrium constants are ratios. See the following reaction: The ratio of the product concentrations raised to their stoichiometric coefficients, divided by the reactant concentrations raised to their stoichiometric coefficients, is the equilibrium constant, K. This is also called the law of mass action. • Pure liquids or solids do not show up in the equilibrium expression because they do not change in concentration; only solutions measured as molar concentrations or pressures (as in the case of gases). • The equilibrium constant for a multi-step process is equal to the product of the equilibrium constants for each step. Example: For a set of three reactions that add to equal a total reaction: • The equilibrium constant for a reverse reaction is the inverse of the equilibrium constant for a forward reaction. • There are different equilibrium constants for different types of reactions. See Table 12.1. Table 12.1. Types of Equilibrium Constants TEST TIP The magnitude of the value of K indicates the strength of a particular species: Larger K a values mean greater acid strength, larger K b is a stronger base, and larger K sp values mean that more solid is able to dissolve in a given amount of solvent. Le Chatelier’s Principle • Le Chatelier’s principle states that when a system at equilibrium is disturbed by a change in pressure, temperature, or the amount (concentration) of product or reactant, the reaction will shift to minimize the change and establish a new equilibrium. • Change in concentration: Adding products to a reaction at equilibrium will shift the reaction to produce reactants; adding reactants will shift the reaction to produce products. In contrast, removing reactants will cause the reaction to shift to replace the reactants, while removing product will cause the reaction to shift to replace the products...
eBook - ePub- Kevin R. Reel(Author)
- 2013(Publication Date)
- Research & Education Association(Publisher)
...CHAPTER 6 Equilibrium CHAPTER 6 EQUILIBRIUM LE CHATELIER’S PRINCIPLE • Le Chatelier’s principle states that when a system at equilibrium is disturbed by a change in pressure, temperature, or the amount (concentration) of product or reactant, the reaction will shift to minimize the change and establish a new equilibrium. • Change in concentration: Adding products to a reaction the equilibrium will shift the reaction to produce reactants; adding reactants to a reaction at equilibrium will shift the reaction to produce products. See the section on the reaction quotient, Q, below. • Change in temperature: An increase in temperature causes the equilibrium to shift to use up the added heat. For example, when heat is added to an exothermic reaction, it will shift to the left to use up the heat. An endothermic reaction will shift to the right to use up heat when heat is added. • Change in pressure: An increase in pressure causes the equilibrium to shift in the direction that produces the fewest number of gas moles. For example, in the reaction that dissolves a gas into a liquid, increasing the pressure on the system will cause the equilibrium to shift to produce more dissolved gas. • Addition of a catalyst or an inert gas will not cause the equilibrium to shift; the amounts of reactants and products would remain unchanged. EQUILIBRIUM CONSTANTS • Equilibrium constants are ratios. For the reaction, aA + bB ↔ cC + dD, The ratio of the product concentrations, raised to their stoichiometric coefficients, to the reactant concentrations, raised to their stoichiometric coefficients, is the equilibrium constant, K eq...
eBook - ePub- Paul F. Cook, W. W. Cleland(Authors)
- 2007(Publication Date)
- Garland Science(Publisher)
...Theory will first be presented for cases where reactant concentration is much greater than that of the enzyme, followed by a consideration of single-turnover experiments, and equilibrium perturbation and relaxation. Reactant Concentration in Excess of Enzyme Concentration Time courses can be treated as pseudo-first-order if A ≫ E t, and we will consider several common cases. The steady-state approximation no longer applies because the concentrations of enzyme species are not negligibly small. In some cases, the time courses reflect the approach to steady state. Irreversible First-order Reactions The treatment of irreversible first-order processes has been presented in Chapter 2. In brief, the first-order conversion of A to B, where A ≫ E t is given in equation 7-1 : A → k 1 B (7-1) The rate equation, −d A /d t = k 1 A, is shown in integrated form in equation 7-2 when the initial concentration of A is A 0 : A t = A 0 e − k 1 t (7-2) This simple case will be observed when dealing with an equilibrium that is far toward B. This could be a chemical step or some other step along the reaction pathway. Reversible First-order Reactions Allowing for reversibility in the first-order process increases the complexity of the overall process. Consider the following approach to equilibrium starting with A. A ⇌ k 2 k 1 B (7-3) In this case the differential equation in terms of A is given by equation 7-4 : − d A d t = k 1 A − k 2 B (7-4) At any time A 0 = A + B (7-5) where A 0 is the initial concentration of A. Substitution of equation 7-5 into equation 7-4 gives − d A d t = k 1 A − k 2 [ A 0 − A ] (7-6) Integration, with B = 0 and A = A 0 when t = 0, then gives A A = [ A 0 k 1 + k 2 ] [ k 1 e − (k 1 + k 2) t + k 2 ] (7-7) where A is the concentration of A at any time t...
