chapter 16 chemical equilibrium. before we look at chemical equilibrium, lets look at the past...

Download Chapter 16 Chemical Equilibrium. Before we look at chemical equilibrium, lets look at the past A.Many reactions in chemistry go to 100% completion 1.Example:

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Here is where equilibrium comes in B.Some reactions dont go to completion because they are reversible - the products collide and react to produce the original reactants A B Does NOT make 100% of the products, because products regenerate reactants

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Chapter 16 Chemical Equilibrium Before we look at chemical equilibrium, lets look at the past A.Many reactions in chemistry go to 100% completion 1.Example: burning methane. CH 4 + O 2 CO 2 + H 2 O 100% of the products are made Here is where equilibrium comes in B.Some reactions dont go to completion because they are reversible - the products collide and react to produce the original reactants A B Does NOT make 100% of the products, because products regenerate reactants I.Chemical Equilibrium: 1. The RATE At equilibrium, both the forward and reverse reactions are occurring at the same rate, equal. 2. Concentration At equilibrium the amount of each reactant and constant product remains constant. II.How to express chemical equilibrium Keq: Equilibrium Constant a.aA+bB cC+dD b. keq= [products] coefficient [reactants] coefficient [ ]=Concentration, Molarity c.keq= [C] c [D] d [A] a [B] b III.Homogeneous and Heterogeneous Equilibria Homogeneous: All states of matter the same Heterogeneous: Different states of matter in the chemical reaction Only use the gases (g) when writing the Keq equation!!! Problems on overhead. IV.Calculating Keq On Overhead What Does the Value of Keq Mean? If Keq >> 1, the reaction is product-favored; product predominates at equilibrium. If Keq (Q) Since K >Q, the reaction will proceed in the forward direction in order to increase the concentrations of both SO2 and Cl2 and decrease that of SO2Cl2 until Q = K. Q = 1.Proposed by a Chemistry Professor, Henry Chatelier 2.Came up with this (LeChateliers) principle in If a change in condition occurs in a system, the system will change to offset the change. What will happen to a system that is already at equilibrium if I change conditions?? Possible changes (stressors) Temperature Pressure Concentration 1.Change in Concentration 2NO 2(g) a.More NO 2 is added: b.More N 2 O 4 is added: c.N 2 O 4 is taking away: d.NO 2 is taken away: Shift Right Shift Left N 2 O 4(g) Example: N2O4N2O4 2. Change in Pressure: When pressure is applied the shift goes from more moles of gas to less moles of gas. 2NO 2(g) N 2 O 4(g) NO 2 a.What will happen if the pressure is increased?? Shift to the Right Applies only to gases N2O4N2O4 N2O4N2O4 N2O4N2O4 N2O4N2O4 P Pressure AnimationAnimation LeChatelier Principle ----->TutorialTrue Question #2 In the reaction,N 2(g) + 2O 2(g) 2NO 2(g), when a pressure increases, what happens to [N 2(g) ] and [NO 2(g) ]? [A] [N 2(g) ] increases and [NO 2(g) ] increases. [B] [N 2(g) ] decreases and [NO 2(g) ] decreases. [C] [N 2(g) ] increases and [NO 2(g) ] decreases. [D] [N 2(g) ] decreases [NO 2(g) ] increases. ANSWER-->ANSWER--> Choice D, equilibrium shifts to the rightChoice D, equilibrium shifts to the right Question #3 N 2 O 4(g) 2NO 2(g) From the reaction above, describe the change in concentration as the pressure decreases. [A] [N 2 O 4(g) ] increases and [NO 2(g) ] increases. [B] [N 2 O 4(g) ] decreases and [NO 2(g) ] decreases. [C] [N 2 O 4(g) ] decreases and [NO 2(g) ] increases. [D] [N 2 O4 (g) ] increases and [NO 2(g) ] decreases. ANSWER-->ANSWER--> Choice C, equilibrium shifts to the rightChoice C, equilibrium shifts to the right Question #4 If the concentration of a substance in the system at equilibrium changes the system will relieve the stress by adjusting it to reach a new equilibrium. True False ANSWER-->ANSWER--> True True Question #5 In the reaction 2CO (g) + O 2(g) 2CO 2(g),when [CO 2(g) ] increases, [O 2(g) ] [A] increases. [B] decreases. [C] remains the same. [D] is unpredictable. ANSWER-->ANSWER--> Choice B, equilibrium shift to the rightChoice B, equilibrium shift to the right ANSWER-->ANSWER--> Choice A, equilibrium shift to the leftChoice A, equilibrium shift to the left Question #7 If the temperature increases the reaction releasing heat (exothermic) is favored. True False ANSWER-->ANSWER--> FalseFalse Question #8 N 2(g) + O 2(g) 2NO (g), change in heat = KJ determine whether this reaction is endothermic or exothermic, and predict what will happen to [N2(g)] if the temperature increases. [A] endothermic; [N 2(g) ] will increase. [B] endothermic;[N 2(g) ] will decrease. [C] exothermic;[N 2(g) ] will increase. [D] exothermic;[N 2(g) ] will decrease. ANSWER-->ANSWER--> Choice B, equilibrium shift to the rightChoice B, equilibrium shift to the right Question #9 Given the reaction at equilibrium : 2C (s) + H 2(g) + energy C 2 H 2(g) What change will result in an increase in the amount of C 2 H 2(g) ? [A] decreasing the pressure [B] increasing the concentration of H 2 [C] decreasing the concentration of C [D] decreasing the temperature ANSWER-->ANSWER--> Choice B, increasing Carbon has no affect because it is a solid.Choice B, increasing Carbon has no affect because it is a solid. b.What will happen if the pressure is decreased? 2NO 2(g) N 2 O 4(g) Pressure will shift to the left. Bottom line: The shift will always be toward the deficiency and away from the excess. P 3.Change in: Temperature 1.Heat + NH 4 Cl (s) NH 3(g) + HCl (g) 2.H 2 O 2(l) H 2 O (l) + O 2(g) + 190KJ 3.Heat + H 2 O (s) H 2 O (l) 4.H 2(g) + Cl 2(g) 2 HCl (g) + Heat IF HEAT IS INCREASED IF HEAT IS DECREASED Equilibrium video Chatelier.htm Warm up 3/__/13