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Unit 9B: Equilibrium, Enthalpy, and Entropy

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Unit 9B: Equilibrium, Enthalpy, and Entropy Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Unit 9b: Equilibrium, Enthalpy, and Entropy 1. Student Name: _______________________________________ Class Period: ________ Website upload 2015 Page 1 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Page intentionally blank Website upload 2015 Page 2 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Unit 9b Vocabulary: 1. Activated Complex: The species that are formed and decomposed during the mechanism, and is also called the intermediate. 2. Activation Energy: The energy that must be added to allow the reactants to complete the reaction and form the activated complex. 3. Catalyst: A chemical that is added to a reaction to eliminate steps in the mechanism and increase the reaction rate and decrease the activation energy without itself being consumed by the reaction. 4. Effective Collision: A collision between reactant particles that results in a chemical reaction taking place. 5. Enthalpy: The total amount of potential energy stored in a substance. 6. Endothermic: A reaction that absorbs and stores energy from the surrounding environment. 7. Entropy: A system’s state of disorder. Entropy increases as temperature increases. Entropy increases as a substance goes from solid to liquid to gas. 8. Equilibrium: A system where the rate of forward change is equal to the rate of reverse change. At equilibrium there is no net change. 9. Exothermic: A reaction that releases stored energy into the surrounding environment. 10. Favored: A change in a thermodynamic property that contributes towards the reaction being spontaneous. 11. Free Energy: The total amount of energy available in a system to do work. Free Energy is a combination of both enthalpy and entropy. 12. Heat of Reaction: The net gain or loss of potential energy during a chemical reaction. 13. Inhibitor: A chemical that is added to a reaction to add steps to the mechanism to decrease the reaction rate and increase the activation energy without itself being consumed by the reaction. 14. Kinetics: The study of reaction mechanisms and reaction rates. 15. Nonspontaneous: A reaction that requires a constant input of energy to occur, or the reaction will reverse or stop. 16. Reaction Rate: The amount of reactant consumed in a given unit of time. Website upload 2015 Page 3 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch 17. Spontaneous: A reaction that continues independently once started. 18. Thermodynamics: The study of heat flow during physical and chemical changes. 19. Unfavored: A change in a thermodynamic property that contributes towards the reaction being nonspontaneous. Website upload 2015 Page 4 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Notes page: Website upload 2015 Page 5 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Unit 9b Homework Assignments: Assignment: Date: Due: Website upload 2015 Page 6 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Topic: Equilibrium Objective: What is the role equilibrium has in chemistry? Equilibrium: Equilibrium is a continuous state of the rate of balance between two opposing changes. In a state of equilibrium the rate of the forward change is equal to the rate of the reverse change. Most chemical reactions are reversible: A + B C + D + energy = forward reaction When the rate of the C + D + energy A + B = reverse reaction forward reaction equals A + B (±energy) C + D Double arrows () the rate of the reverse indicate that BOTH reaction, a state of reactions are occurring equilibrium is reached. at the same time. If you ride up a moving escalator, you are moving at the rate that the escalator is moving upwards. However, if you turn around and start to walk DOWN the up escalator, and you match the escalator’s rate (up) but in the opposite direction (down), to someone watching you it looks as if you are not moving. However, you are still expending energy trying to go to the bottom, and the escalator is expending energy trying to carry you uphill. If anything was to upset the process (power failure to the escalator; you trip and fall, etc.), the equilibrium would be upset and you would either make it to the bottom or ride to the top. Website upload 2015 Page 7 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Equilibrium examples: Haber Process for ammonia gas: Forward reaction: N2(g) + 3 H2(g) 2 NH3(g) + 92 kJ (exo) Reverse reaction: 2 NH3(g) + 92 kJ N2(g) + 3 H2(g) (endo) Equilibrium: N2(g) + 3 H2(g) 2 NH3(g) + 92 kJ Website upload 2015 Page 8 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Topic: Equilibrium Properties Objective: What properties of equilibrium will systems have? Properties of Systems at Equilibrium: 1. Equilibrium is a dynamic state; think of equilibrium as a continuous pathway, never achieving a ‘set’ endpoint. Particles of reactants are reacting and forming products at the same rate that products are decomposing back into the reactants they came from. Remember that the system is in continuous motion, though it may look like the reaction is stagnant. 2. Equilibrium can only be maintained in a closed system. A closed system neither gains nor loses anything. This includes energy (loss or gain), adding reactants, or the removal of products. 3. As long as the system is closed, a system at equilibrium will remain that way forever. Changing ANY condition of equilibrium will alter the balance of the entire equilibrium (see pgs. 33-40). 4. Equilibrium occurs at different concentrations of product and reactant. Depending on the nature of the species involved, assuming we start with the forward reaction, the rate of the reverse reaction will increase as the product is formed during the forward reaction. When the forward AND reverse reaction rates are equal, equilibrium is achieved. This may occur at different concentrations of product and reactant. Website upload 2015 Page 9 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Equilibrium Diagram: Equilibrium may be reached ANYWHERE along a line that starts at 0% and ends at 100%. At any point along the line the percentage of the reaction going forward (reactants) ADDED to the percentage of the reaction going backward (products) equals 100%. (% forward reaction) + (% reverse reaction) = 100% Website upload 2015 Page 10 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Topic: Three Types of Equilibrium Objective: What forms of equilibrium are possible in chemistry? 1. Chemical Equilibrium: i. If the rate of the forward reaction is equal to the rate of the reverse reaction the reaction has achieved chemical equilibrium. You have seen the Haber Process for the production of ammonia: N2(g) + 3 H2(g) 2 NH3(g) + 92 kJ This reaction produces ammonia (and heat), but some of the ammonia, NH3(g), produced will decompose during the reaction back into reactants, N2(g) and 3 H2(g). ii. When the rate of synthesis (forward reaction) equals the rate of decomposition (reverse reaction), and no other changes occur, this system will be at equilibrium. iii. As stated before, changing ANY component of the system will change the equilibrium of the entire system. Website upload 2015 Page 11 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch 2. Solution Equilibrium: i. If a solution becomes saturated, the rate of dissolving equals the rate of precipitation, and the reaction has achieved solution equilibrium. +1 -1 NaCl(s) Na (aq) + Cl (aq) ii. When sodium chloride is first placed into pure water, the solid ionic crystals dissolve. As the concentration of the dissolved ions +1 -1 increases, some of those dissolved Na (aq) and Cl (aq) ions will temporarily rejoin to form a soluble precipitate which almost immediately dissolves again. Eventually all the ions will be held apart by the polar water molecules, and no more solid may enter the solution until some ions come out of solution as precipitate. At this point the rate of dissolving equals the rate of precipitation, and you have a SATURATED solution. Additional added solid would not dissolve, or only as a temporary supersaturated solution. Solution Equilibriums Unsaturated - solute almost all Close to Saturation - solute Saturated-dissolving rate is undissolved; reaction almost all almost all dissolved; reaction equal to precipitate formation forward mostly forward, some reverse rate; no net change Website upload 2015 Page 12 of 45 Unit 9b: Equilibrium Systems Unit 9: Kinetics, Thermodynamics, & Equilibrium-lecture Regents Chemistry ’14-‘15 Mr. Murdoch 3. Physical Equilibrium: i. If the rate of a forward phase change is equal to the rate of a reverse phase change, then the system is in Physical (or Phase) Equilibrium. ii. Physical equilibrium occurs AT the phase change temperature. Remember that during a phase change, all energy input is going towards increasing the potential energy of the substance, as there is no increase in average kinetic energy (temperature) at the phase change temperature. For water, the boiling (vaporization point) at 1 atm is 373 K. This means if water is maintained in a sealed container at 1 atm and 373 K, for each water molecule that changes from liquid to gaseous, another water molecule will change from gaseous to liquid.
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