Chemical Equilibrium PDF

Chemical Equilibrium 1stBiology Students Dr. Osama Farouk Type of Chemical Reactions in Aqueous Solutions Ionic equilibrium Type of Chemical Reactions in Aqueous Solutions 1) Acid-Base Reactions 2) Oxidation-Reduction Reactions 3) Precipitation Reactions I. Acid-Base Reactions...

Chemical Equilibrium 1stBiology Students Dr. Osama Farouk Type of Chemical Reactions in Aqueous Solutions Ionic equilibrium Type of Chemical Reactions in Aqueous Solutions 1) Acid-Base Reactions 2) Oxidation-Reduction Reactions 3) Precipitation Reactions I. Acid-Base Reactions acid + base → salt + water HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)  Acids & Bases Definition of acids and bases Arrhenius concept Brønsted-Lowry concept Lewis's concept  Arrhenius concept An acid is a compound that releases H+ ions in water A base is a compound that releases OH- in water. HCl (aq) H+ (aq) + Cl- (aq) NaOH (aq) Na+ (aq) + OH- (aq) Limitations: Some bases do not contain OH-  2- Brønsted-Lowry Concept An acid is any molecule or ion that can donate a proton H+. A base is any molecule, or ion can accept a proton. proton-transfer reaction 3- Lewis Concept An acid as an electron pair acceptor (electron- deficient) A base as an electron pair donor (electron-rich). Strength of Acids and Bases A strong acid or base ionizes completely in water Strong Acids Strong bases HCl LiOH HBr NaOH HI KOH HNO3 Ca(OH) 2 H2SO4 Sr(OH) 2 HClO4 Ba(OH) 2 Equilibrium Constant Law A reversible reaction is a reaction in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously Cc +Dd⇆Aa+Bb at equilibrium neither the forward nor the reverse reaction has stopped An irreversible reaction is a reaction that proceeds in one direction only; the products do not react together to reform the reactants. A reaction where all reagents and products are in the same phase is considered homogenous reactions. H2 (g)+I2 (g)⇋2HI (g) Heterogeneous reactions are reactions where reagents and products contain at least two different phases CaCO3​(s)⇋CaO(s)+CO2​(g)  Weak Acids and Bases A weak acid or base ionizes only to a limited extent in water Examples: CH3COOH, NH3 Acid or Base Ionization Constant It is a measure of the strength of acid or base. The ionization constant has the same equilibrium expression. CH3COOH + H2O CH3COO- + H3O+ [CH 3COO − ] [ H 3O + ] Ka = [CH 3COOH ] NH3 + H2O NH4+ + HO- + [ NH 4 ] [ HO − ] Kb = [ NH 3 ] Self-ionization of water Water acts either as an acid or a base H 2O(l) + H 2O(l) → H 3O+(aq) + OH −(aq) K w = [H 3O + ][OH − ] Or K w = [ H + ][OH − ] Kw = water dissociation constant an acidic solution, [H+] > [OH-] a neutral solution, [H+] = [OH-] a basic solution, [H+] < [OH-]  2 SO2 (g) + O2 (g) 2 SO3 (g) equilibrium constant [ SO3 ]2 Kc = 2 [ SO2] [O 2] Le Chatelier's principle A change in one of the variables that describe a system at equilibrium produces a shift in the position of the equilibrium that counteracts the effect of this change. (1) changing the concentration of one of the components of the reaction (2) changing the pressure on the system (3) changing the temperature at which the reaction is run. Predict the effect of the following changes on the reaction in which SO3 decomposes to form SO2 and O2. 2 SO3(g) 2 SO2 (g) + O2 (g) Ho = 197.78 kJ (a) Increasing the temperature of the reaction. (b) Increasing the pressure on the reaction. (c) Adding more O2 when the reaction is at equilibrium. (d) Removing O2 from the system when the reaction is at equilibrium. Answer (a) Because this is an endothermic reaction, which absorbs heat from its surroundings, an increase in the temperature of the reaction leads to an increase in the equilibrium constant and therefore a shift in the position of the equilibrium toward the products. (b) There is a net increase in the number of molecules in the system as the reactants are converted into products, which leads to an increase in the pressure of the system. The system can minimize the effect of an increase in pressure by shifting the position of the equilibrium toward the reactants, thereby converting some of the SO2 and O2 into SO3. (c) Adding more O2 to the system will shift the position of the equilibrium toward the reactants. (d) Removing O2 from the system has the opposite effect; it shifts the equilibrium toward the products of the reaction.