CHM 145 Lecture Notes - Lecture 21: Boiling Point, Chemical Equation, Jmol

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24 Mar 2017

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G = g o + rt ln q: under standard conditions , all concentration values are 1, q=1, rt ln q = 0, and g = g o. Equilibrium and thermodynamics: at equilibrium, g=0 and q=k: Thus, g o = rt ln k or k = e go /rt. Note: this equation can only be applied at t=298 k! G o = rt ln k: if k is large (>> 1), g o becomes a large negative value ( spontaneous = large k) Spontaneous = product-favored reaction: if k is small (<< 1), go becomes a large positive value ( nonspontaneous = small k) Nonspontaneous = reactant-favored reaction: if k 1, go 0 & you are near equilibrium equilibrium lies between reactants & products, and significant amounts of each are present. The point where free energy is at a minimum defines the composition of a system at equilibrium under standard conditions!

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ree Energy and Chemical Equilibrium Why? The free energy change for a chemical reaction depends on the temperature concentrations of the reactants and the products. You, like chemists in and the research and manufacturing, can use the free energy change to identify suitable temperatures for reactions, to determine the direction a reaction will go to reu equilibrium, and to obtain values for equilibrium constants and equibrium ch concentrations. Learning Objectives Understand the relationship between the free energy change and the reaction quotient expression. Identify the effect of temperature on the free energy change and on equilibrium constants Success Criteria the free energy change for a reaction at various temperatures and various concentrations of reactants and products. Identify the direction a reaction will proceed spontaneously. Calculate one or more of ÎGo ,aHo, aso, and K given the others. Resources Olmsted and Williams Prerequisites Chemistry 3/e, Wiley, 2002) pp. 615 - 625, 721-729. emical equilibrium, spontaneous processes and free energy change, standard free energy change, reaction quotient, equilibrium constant Information ard The free energy change in a chemical reaction, DG, is related to the stand free energy change, AGe, and the concentrations of reactants and products by the following equation. AG, AGT+RT In(Q) 4Gy and Î = free energy change and standard free energy change at temperature T Q reaction quotient R ideal gas constant T temperature in K When reactants and products are in their standard states, their concentrations are 1 in the free energy when concentrations are 1 M is just the standard free energy change M, then Q is 1, In(Q1-1n(1) = 0, and ÎG = ÎGo. The change An increase in the entropy of the universe or a decrease in the free energy of the system is the driving force behind a spontaneous change. Concentrations in a chemical reaction change spontaneously to lower the free energy. Equilibrium is reached in a chemical because the free energy The freee reaction when the free energy can no longer decrease of the reactants equals the free energy of the products. for the reaction, aG, then is 0, Using Q = K at ã1/2005 all rights reserved 57

Hi, So I collected the data and just need answers for these questions. not sure where to start and don't understand them. Please, answer all or don't answer. Thanks in advance and I appreicate it. I'll rate it if you do answer all, and I appreciate your help!Conclusions:

1. Create a data table that displays the voltage of each trial (Ecell) and the temperature of each trial. Then, calculate and display as a calculated column ?G for the cell at each of the temperatures, using ?G = -n F E.

2. Calculate a ?G0 value for each temperature, given that ?G = ?G0 + RT ? ln Q, and include a calculated column for this in your data table.

3. Calculate and include a column for an E0 value for 25 0C, given your E0 value and the relationship ?G0 = -nFE0 . Using the standard reduction potential table, calculate an accepted E0 value at 250C. Then, calculate your percentage of error. Offer explanation for why these values are different!

4. Determine the equilibrium constant K for this reaction from your value of ?G0 at 250C, given that ?G0 = - RT ? ln K. Include a calculated column in your data table for K. Assume 250C for the standard free energy in order to determine the equilibrium constant.

5. What is the relationship between temperature and cell potential, E?

6. What is the relationship between cell potential, E, and ?G? Explain why this makes sense!

7. Define the Faraday constant, F.

8. Are most oxidation/reduction reactions exothermic, endothermic, or both, do you think? Explain why you think this?

9. Should your reaction be exothermic or endothermic? Explain in terms of your calculated energy and/or voltage values!

10. From your value of ?G0 at 250C, and an accepted value of ?S0 , calculate the ?H0 for this reaction at standard temperature conditions. Is this consistent with your answer to number 9? Explain!

CHM 145 Lecture Notes - Lecture 21: Boiling Point, Chemical Equation, Jmol

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