CHM 2046 Lecture Notes - Lecture 19: Evaporation, Internal Fixation

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coraleagle969

23 Feb 2017

School

University of Florida

Department

Chemistry

Course

CHM 2046

Professor

Korolev Maria

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Document Summary

The entropy of the surroundings increases because the reaction has a negative change in enthalpy. Chemical reactions produce spontaneously (are favored) if the free energy change is negative. When a chemical has a positive g it can be coupled with an energetically favorable reaction so overall is negative. As long as the overall reaction is thermodynamically favorable event he. As long as the overall reaction is thermodynamically favorable event he unfavorable reaction will proceed. Reactions have to be related to one another. Work produced is less than the heat produced because some of the heat can not be converted to work. Maximum useful work is equal to delta g. Free energy is the maximum amount of work we can get out of a reaction. It is minimum amount of work you have. Difference between is the amount of heat that can not be converted to work.

Related Questions

Model 1 â Spontaneous Processes Process Description Change in Enthalpy (âH) Change in Entropy (âS) Spontaneous? A Two pure â Homogeneous substances mixture ~ 0 Increasing Yes B Solute on Solute on one side of â both sides of membrane membrane ~ 0 Increasing Yes C Polypeptide â Individual chain amino acids Exothermic (negative) Increasing (positive) Yes D C3 H8 + 5O2 â 3CO2 + 4H2 O Exothermic Increasing Yes E 6CO2 + 6H2 O â C6 H12O6 + 6O2 Endothermic Decreasing No F Glucose â Starch Endothermic Decreasing No G Water â Ice Exothermic Decreasing Below 0 Â°C, yes Above 0 Â°C, no H Cold water (25 Â°C) â Hot water (60 Â°C) Endothermic Increasing Below 60 Â°C, no Above 60 Â°C, yes

Some of the processes in Model 1 are spontaneousâthat is, they will occur without any additional work being done on the system. For example, a solute will diffuse across a membrane until the concentrations of both sides are equal. However, glucose will not spontaneously form from carbon dioxide and water in the atmosphere. The Second Law of Thermodynamics states that a process will be spontaneous when it results in an increase of total entropy in the universe. In other words, either the system or the surroundings must have an increase in entropy, or both. (Please note that the term âspontaneousâ does not imply that the change will happen quickly. Rusting is spontaneous under the right conditions, but it can still occur very slowly.)

13. Predict the change in entropy of the surroundings for an endothermic reaction.

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

Q1. Which of the following processes are spontaneous and which are non spontaneous.
a) The combustion of natural gas
b) Extraction of Aluminum metal from its ore
c) A ball rolling down a hill
d) A bike going up a hill

Q2. Predict the entropy change (positive or negative) for the following processes/reactions
a) a lake freezing
b) weeding a garden
c) N2(g) + 2 H2(g) ? N2H4 (g)
d) Mg(s) + 2H2O(l) ? Mg(OH)2 (s) + H2(g)

Q3. The element Cesium (Cs) freezes at 28.4 C and its molar enthalpy of fusion ΔH_fusion = 2.09 kJ/mol.
a) When molten Cs solidifies to Cs (s) at its normal melting point, is the entropy change ΔS positive or negative?
b) Calculate the entropy change S when 15.0 g of Cs(l) solidifies at 28.4 C.

Q4. Using the values for standard molar entropies ΔS_f° from the appendix in your textbook, calculate ΔS° for the following reactions.
a) Be(OH)₂ (s) ? BeO (s) + H2O (g)
b) Mg(OH)2 (s) + 2 HCl (g) ? MgCl2 (s) + 2H2O (l)
c) 2CH4(g) ? C2H6 (g) + H2(g)

Q5. Using the data in the appendix of your textbook, calculate the Gibbs free energy change ΔG° for the following reactions. In each case, indicate whether the reaction is spontaneous or not
a) H2 (g) + Cl2(g) ? 2HCl (g)
b) 2 POCl3 (g) ? 2 PCl3 (g) + O2 (g)

Q6. Consider the reaction 2 NO2 (g)---N2O4 (g)
a) Using the data in the appendix in your text, calculate the standard Gibbs free energy change (ΔG°) for the reaction at 298K.
b) For the above reaction, calculate the value of Keq at 298K
c) For the same reaction, calculate G at 298 K when the partial pressures for NO₂ and N2O4 are 0.40 atm and 0.36 atm, respectively.

Q7. Consider the reaction I2 (g) + Cl2 (g)----2 ICl (g) Kp = 81.9 at 298 K
a) Calculate the standard free energy change (ΔG°)
b) What will be the Free energy change when the above reaction is at equilibrium
c) Calculate G for the reaction at 298 K when PICl = 2.55 atm, PI2=0.325 atm and PCl2 = 0.221 atm

Q8. Consider the decomposition of Lead carbonate PbCO3 (s) ? PbO(s) + CO2 (g)
a) Calculate the Gibbs free energy change (ΔG°) for the reaction at298 K.
b) Calculate G for the reaction at 400 K.
c) Write down the equilibrium expression and calculate the value of Keq at 298 K
d) Calculate the partial pressure of CO2 at 298 K. (Hint: Look at the equilibrium expression and the value of Keq at 298 K)

Q9. For the reaction: 2Al(s) + 3/2 O2(g) ? Al2O3(s), ΔH^o_rxn = -1617 kJ/mol and ΔH^o_rxn = -1577 kJ/mol. Use this data to calculate ΔS^o_rxn reaction at 298 K.

Q10. Calculate the ΔG^o for the following reaction using the data from your text:
2SO2(g) + O2(g) ? 2SO3(g)

Q11. Using the thermodynamic data available from the Appendix(?Goâs), calculate ΔG^o rxn and calculate the equilibrium constant(K) for the reaction at 25 oC:
CaCO3(s) ? CaO(s) + CO2(g)

Q12. What is the minimum temperature required for the spontaneous conversion of CCl4(l) to CCl4(g) when ΔH°(vap) is 57.3 kJ/mol andΔS°(vap) is 164 J/(mol K)? reaction: CCl4(l) ? CCl4(g)

Q13. Given the following
Fe2O3(s) + 3CO(g) . ? 2Fe(s) + 3CO2(g) ΔG° = 29.4 kJ
3Fe2O3(s) + CO(g) . ? 2Fe3O4(s) + CO2(g) ΔG° = 61.6 kJ
Calculate ΔG° for Fe(s) + Fe2O3(s) + CO2(g) ? Fe3O4(s) +CO(g)

Q14. Calculate ΔG° rxn for 2CO(g) + O2(g) ? 2CO2(g) and then calculate ΔG for the reaction at 298K; if the pressure of CO =20. atm,P O2 = 10. atm and P CO2= 0.50 atm. Will increasing the pressure of the reactants make the reaction more or less spontaneous? Explain using your calculations and Le Chatelierâs principle.

Q15. Write the reaction for photosynthesis (production ofC6H12O6(s) and oxygen from carbon dioxide and water as a gas).Calculate ?H, ? S, and ?G for the reaction at standard state. Is the reaction spontaneous?

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CHM 2046 Lecture Notes - Lecture 19: Evaporation, Internal Fixation

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