CHEM 112 Lecture Notes - Lecture 33: Electrochemistry

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2 May 2016

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Chem112 lecture 33 effects on free energy and electrochemistry. When rg is negative, k > 1 and it product favored. As the value of rg becomes more negative, the k increases. Free energy is how much energy is available in the system to do work on its surroundings. From the equation g = h t s. When entropy is favored (+ s) and enthalpy is disfavored (+ h) When entropy is disfavored (- s) and enthalpy is favored (- h) Oxidation-reduction reactions are also known as redox reactions. When one species gets oxidized and one species gets reduced by the transfer of electrons. Real life electrochemistry and redox reactions: batteries are based on electrochemistry, glucose sensors are based on electrochemistry, aluminum metal is produced from its ore (al2o3) using electrochemistry. You can use oilrig or leo the lion says ger. Oilrig = oxidation is loss, reduction is gain.

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I need help on this chemistry work. Thanks.

DATA ANALYSIS

Using the example, calculate the Gibbs free energy for the process of dissolving ammonium nitrate and the process of dissolving sodium hydroxide (equation: ÎG = ÎH â TÎS).

Use the standard temperature 298 K.

Use the experimental data to calculate enthalpy of dissolving (ÎH).

Use the following data to calculate the entropy change (ÎS):

	S (J/K mol)
NH₄NO₃(s)	151
NH₄⁺(aq)	113.4
NO₃^-(aq)	146.4
NaOH(s)	64.46
Na⁺(aq)	59.0
OH^-(aq)	- 10.7

After completing the calculations answer the following questions separately for each experiment:

Is the dissolving exothermic or endothermic?

Does the entropy decreases or increases during dissolving?

Is the Gibbs free energy positive or negative? Is the process of dissolving spontaneous?

Using data in the appendix in your textbook, calculate Gibbs free energy for the reaction of dissolving

lithium phosphate, Li₃PO₄, in water at 25 Â°C. Do the calculations in two ways:

1) Use standard enthalpy of formation (ÎH) and entropy (S) from the appendix in your textbook, and use the same formula as you did in the lab experiments: ÎG = ÎH â TÎS. Remember that both ÎH and ÎS has to include three lithium ions.

2) Use standard free energies of formation from Appendix 6 (ÎG) and equation

ÎG = âÎG _products â âÎG _reactants

Are the results similar in both calculations?

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

CHEM 112 Lecture Notes - Lecture 33: Electrochemistry

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