Chemical Equilibrium Notes PDF

Ch. 7- Chemical Equilibrium CHEMICAL SYSTEMS Equilibrium Systems Main Idea: Some chemical reactions do not go to completion, but to a chemical equilibrium, which is a dynamic equilibrium in which the forward and reverse reaction occurs at equal rates. Chemical e...

Ch. 7- Chemical Equilibrium CHEMICAL SYSTEMS Equilibrium Systems Main Idea: Some chemical reactions do not go to completion, but to a chemical equilibrium, which is a dynamic equilibrium in which the forward and reverse reaction occurs at equal rates. Chemical equilibrium: the state of a reaction in which all reactants and products have reached constant concentrations in a closed system. Equilibrium deals with the question…WILL A REACTION GO TO COMPLETION? EQUILIBRIUM There are many reactions that do not go to completion. The products reform the reactants. This is indicated by a double arrow: This indicates the reaction is proceeding in both directions simultaneously. Since the reaction continues this is called a dynamic equilibrium. Dynamic Equilibrium: A balance between forward and reverse processes occurring at the same rate. forward N2O4 🡪 2NO2 reverse REVERSIBLE REACTIONS: A reaction that can achieve equilibrium in forward and reverse direction. Closed systems are always in a state of dynamic equilibrium. Features of Equilibrium State 1) Equilibrium is dynamic (always moving) 2) Equilibrium is achieved in a closed system 3) The concentration of reactants and products remain constant at equilibrium 4) At equilibrium there is no change in macroscopic properties (observable properties) 5) Equilibrium can be reached from either direction Under the conditions of a closed vessel, a chemical reaction can progress and the concentrations of reactants & products changes. At a certain point in time, the concentration of reactants and products remain stable. This is the point in which chemical equilibrium has been reached. Solubility Equilibrium Kinetic motion theory states that things are always moving and thus collisions are always occurring. When solubility equilibrium is reached the rate of dissolving and crystal formation are equal. Phase Equilibrium: Liquid and Gas o Some molecules have the necessary energy to evaporate. o These molecules will collide and lose energy causing them to condense o The vaporization and condensation reaction rates will be equal when equilibrium is reached. Changes in temperature will change at what point equilibrium is reached Equilibrium cannot be reached in open containers as the gas will leave the system. Solid and Liquid i.e. ice melts quickly in water at first but eventually levels out Stoichiometry & Chemical Equilibria Main Idea: The concentrations of reactants and products at equilibrium can be determined from the starting concentration of reactant(s) or from the initial and final concentrations of reactant(s). Calculating Concentration at Equilibrium In reversible reactions equilibrium is reached before all the reactants become products. You can predict the changes in concentration of reactants and products as a system approaches equilibrium from the coefficients of a balanced chemical equation (stoichiometry). i.e. 2NH3(g) 🡪 N2(g) + 3H2(g) The decrease in ammonia concentration is 2 times the increase of nitrogen concentration. ICE TABLES an ICE table is a convenient way to organize the information. ▪ I initial concentration (mol/L) before the reaction ▪ C change between the starting concentration and when equilibrium is reached ▪ E concentration at equilibrium Example: When ammonia gas is heated, it decomposes into nitrogen gas and hydrogen gas according to the following equation 2NH3(g) 🡪 N2(g) + 3H2(g) If the reaction begins with 2.0 mol/L of ammonia gas and no nitrogen or hydrogen gas, calculate the concentration of N2 and H2 gas at equilibrium if the equilibrium concentration of NH3(g) is 1.0 mol/L 2 NH3 🡨 N2 + 3 H2 Initial Concentration Change in Conc Equilibrium Conc