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AP CHEMISTRY CHAPTER 15: CHEMICAL KINETICS (Pgs. 628-660) EQ: _______________________________________________________________________________________________ Questions: SECTION 1-The Concept of Equilibrium-2 • Chemical Equilibrium occurs when: The Concept of Equilibrium -3 As a system approaches equilibrium: At equilibrium, the forward and reverse reactions are proceeding _____________ ___________________________ Once equilibrium is achieved, the _______________ of each reactant and product remains ________________. Writing the Equation for an Equilibrium Reaction-4 In a system at equilibrium, both the ________________ and _________________ reactions are being carried out, so we write the equation with _________________________. Comparing Rates-5 For the forward reaction: The rate law is: For the reverse reaction: Ex. The rate law is: • Meaning of Equilibrium-6 At equilibrium: SECTION 2-The Haber Process-7 Consider the Haber Process, which is the industrial preparation of ammonia: N2(g) + 3 H2(g) ⇌ 2 NH3(g) Ex: The equilibrium constant depends on stoich: Rewriting this, it becomes the expression for the equilibrium constant, Keq. Ex: Ex: The Equilibrium Constant-8 Under the generalized reaction: The equilibrium expression for this reaction would be: Since pressure is _________________ to _____________________ for gases in a closed system, it can be written: Questions: • More with Gases and Equilibrium-9 We can compare the equilibrium constant based on _________________ to the one based on ______________________. For gases: • • Rearranging, P = (n/V)RT; (n/V) is [ ]. The result is: • Where: Equilibrium Can Be Reached from Either Direction-10 • • • As you can see, the ratio of ________________ to ___________ remains constant at this temperature no matter what the initial concentrations of NO2 and N2O4 are. SECTION 3: Magnitude of K-11 If K>>1, the reaction favors _____________; products predominate at equilibrium. If K<<1, the reaction favors _______________; reactants predominate at equilibrium. The Direction of the Chemical Equation and K-12 The equilibrium constant of a reaction in the reverse reaction is the ______________of the equilibrium constant of the _____________________ reaction: EX: Stoichiometry and Equilibrium Constants-13 To find the new equilibrium constant of a reaction when the equation has been multiplied by a number, simply ____________________________________________________________________. Here, the stoichiometry is doubled; the constant is the squared! EX: Questions: Consecutive Equilibria-14 • • SECTION 4: Homogenous vs. Heterogeneous-15 • Homogeneous equilibria: ________________________________ ________________________________ ________________________________ ________________________________ • Heterogeneous equilibria: ________________________________ ________________________________ ________________________________ When two consecutive equilibria occur, the equations can be __________ to give a single equilibrium. The equilibrium constant of the new reaction is the ____________ of the two constants: K3= • EX: Decomposition of CaCO3-A Heterogeneous Equilibrium-16 • The equation for this reaction: The value used for the concentration of a pure substance is always ____ SECTION 5: Deducing Equilibrium Concentrations17 1) 2) • This results in: 3) 4) 5) • An Example-18-22 A closed system initially containing 1.000 × 10–3 M H2 and 2.000×10–3 M I2 at 448 °C is allowed to reach equilibrium. Analysis of the equilibrium mixture shows that the concentration of HI is 1.87 × 10–3 M. Calculate Kc at 448 °C for the reaction taking place, which is H2(g) + I2(g) ⇌ 2 HI(g) Initially [H2], M [I2], M [HI], M 1.000 × 10–3 2.000 × 10–3 0 Change At equilibrium 1.87 × 10–3 Questions: And, Therfore, the Equilibrium Constant is-23 • • • • SECTION 6: Is a Mixture in Equilibrium? Which Way does the Reaction Go?-24 • To answer these questions, we calculate the ____________________________, Q. • Q looks like the equilibrium constant, K, but the values used to calculate it are the __________________________, not necessarily those for __________________. • To calculate Q, one substitutes the ___________________________ of reactants and products into the equilibrium expression. Comparing Q and K-25 Nature wants ___________ If Q < K, nature will make the reaction proceed to _________________. If Q = K, the reaction is ___________________________. If Q > K, nature will make the reaction proceed to ______________________ Calculating Equilibrium Concentrations-26 If you know the _______________________________, you can find equilibrium concentrations from initial concentrations and changes (based on _____________________). 2) You will set up a table similar to the ones used to find the equilibrium concentration, but the “change in concentration” row will simple be a factor of “x” based on the stoichiometry. 1) An Example-27-29 A 1.000 L flask is filled with 1.000 mol of H2(g) and 2.000 mol of I2(g) at 448 °C. Given a Kc of 50.5 at 448 °C, what are the equilibrium concentrations of H2, I2, and HI? H2(g) + I2(g) ⇌ 2 HI(g) initial concentration (M) 1.000 2.000 0 change in concentration (M) –x –x +2x equilibrium concentration (M) 1.000 – x 2.000 – x 2x Questions: • Set up the equilibrium constant expression, filling in equilibrium concentrations from the table. • Solving for x is done using the quadratic formula, resulting in x= • Since x must be subtracted from 1.000 M, 2.323 makes no physical sense. (It results in a negative concentration!) The value must be 0.935. So: • SECTION 7: LeChatelier’s Principle-30 • Change in Reactant or Product Concentration-32 If the system is in equilibrium • adding a reaction component will result in: • • How Conditions Change Equilibrium-31 We will use LeChâtelier’s Principle qualitatively to: Change in Volume or Pressure-33 When gases are involved in an equilibrium, a change in pressure or volume will affect equilibrium: removing a reaction component will result in: Change in Temperature-34 An Endothermic Equilibrium-35 Is the reaction endothermic or exothermic as Example Equation: written? That matters! • Endothermic: • Exothermic: Questions: An Exothermic Equilibrium-36 The ________________________ for producing ammonia from the elements is exothermic. • One would think that cooling down the reactants would result in more product. • However, the activation energy for this reaction is _______________! • This is the _______ instance where a system in equilibrium can be affected by a _________________! • Catalysts-37 • Catalysts: • Equilibrium is achieved ____________, but the equilibrium composition remains unaltered. Activation energy is _______________, allowing equilibrium • SUMMARY __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ _________________________________________________________________________________________________