CHEM 113 1st EditionExam # 2 Study Guide Lectures: 10 - 18Lecture 10 (September 17)CHP.17: EQUILIBRIUM: THE EXTENT OF CHEMICAL REACTIONS17.1: The equilibrium state and the equilibrium constant- At equilibrium, reactant and product concentrations are constant because a change in onedirection is balanced by a change in the others as the forward and reverse rates becomeequal.o At equilibrium rate (forward)= rate (reverse)- The equilibrium constant (K), a number equal to a particular ratio of equilibrium concentrations of product(s) and reactant(s) at a particular temperature.o The magnitude of K is an indication of how far a reaction proceeds toward product at a given temperature. Small K means the reaction favors the reactants Large K means the reaction favors the products Intermediate K means the reaction is at equilibrium17.2 The reaction quotient and the equilibrium constant- At a give temperature, a chemical system reaches a state in which a particular ratio of reactant and product concentrations has a constant value. That particular ratio of concentrations is called the reaction quotient.- The reaction quotient (Q), gives the ratio of product concentrations to reactant concentrations at any point in a reactions.o If a system is at equilibrium then Q=Ko The value of Q tells us how close a reaction is to equilibrium and in which direction it must proceed to reach equilibrium. Lecture 11 (September 19)- Writing the reaction quotient in various formso The reaction quotient must be derived from the balanced equationo Q is a ratio of product concentration terms multiplied together and divided by reactant concentration terms multiplied together, with each term raised to the power of its balancing coefficient. See equation 17.4 on page 681o If all the coefficients of the balanced equation are multiplied by some factor, that factor becomes the exponent for relating the reaction quotients and the equilibrium constants. See equation 17.7 on page 684o Q and K are unit lesso Form of Q for a Forward and a Reverse reaction The form of the reaction quotient depends on the direction in which thebalanced equation is written. A reaction quotient (or equilibrium constant) for a forward reaction is the reciprocal of the reaction quotient (or equilibrium constant) for the reverse reaction Lecture 12 (September 22)- Form of Q for a reaction involving pure liquids or solidso A heterogeneous equilibrium involves reactants and/or products in different phases. Solids and liquids have constant concentrations and are eliminated from the reaction quotient. The expressions for Q and K only include species whose concentrations change as the reaction approaches equilibrium17.3: Expressing equilibria with pressure terms: Relation between Kc and Kp-We often express the reaction quotient in terms of partial pressures instead of concentrations.-Using the Ideal Gas Law, equation 17.8 on page 687 can be derived to equate the equilibrium constant based on pressures. o Kp often has a different value then Kc, but if you know one the change in amount(mol) of gas from the balanced equation allows you to calculate the other.17.4: Comparing Q and K to determine reaction direction- The value of Q indicates the direction in which a reaction must proceed in order to reach equilibriumo If Q< K the reactants must increase and the products decreaseo If Q> K the reactants must decrease and the products increaseo If Q=K, the system is at equilibrium and no further net change takes place.Lecture 13 (September 24) & Lecture 15 (September 26)17.5: How to solve equilibrium problems- There are two types of equilibrium problemso 1). When we know the equilibrium quantities and solve for K Here you simply substitute those values into the K of concentration expression and calculate.o 2). When we know some of the quantities. Then we use a reaction table to calculate quantities and find K of concentration by doing the following.- 1). Balance the equation- 2). Write the expression for K and Q- 3). Set up a Reaction Table by entering the followingo Initial quantities of reactants and products o Changes in the previous quantities during the reactiono Equilibrium quantities These amounts are calculated by adding the changeto the initial amount- 4). For most problems, values we put into the Reaction Table will be in terms of x. So then we use other information given in the problem to solve for x. Lecture 14 (September 29)17.6: Reaction conditions and equilibrium: Le Chateliers principle- Le Chatelier’s Principleo When a chemical system at equilibrium is disturbed, it retains equilibrium by undergoing a net reaction that reduces the effect of the disturbance A shift to the left is a net reaction from product to reactant A shift to the right is a net reaction from reactant to product- The Effect of a Change in Concentrationo If the concentration of A increases, the system reacts to consume some of it If a reactant is added, the equilibrium position shifts to the right If a product is added, the equilibrium position shifts to the lefto If the concentration of B decreases, the system reacts to consume some of it If a reactant is removed, the equilibrium shifts to the left If a product is removed, the equilibrium shifts to the righto Only substances that appear in the expression for Q can have an effect Meaning that if it is a heterogeneous equilibrium, pure solids and liquids do not have an effect.o A change in concentration has no effect on the value of K- The Effect of a Change in Pressure (volume)o Changes in pressure effect equilibrium systems containing gaseous components If pressure is increased, the reaction shifts so that the total number of gasmolecules decreases If pressure is decreased, the reaction shifts so that the total number of gas molecules increases Adding an inert gas has no effect on the equilibrium position, as long as the volume does not changeo Changes in pressure due to a change in volume has no effect on the value of K- The Effect of a Change in Temperatureo To determine the effect of a change in temperature on equilibrium, heat is considered a component of the system and whether the system is exothermic or endothermic o An increase in temperature adds heat, which favors the endothermic reactiono A decrease in temperature removes heat, which favors the exothermic reactiono Temperature and K The only factor that