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#Chem 162-2008 homework 12th week

#Chem 162-2008 homework 12th week - Chem 162-2008 Hill...

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Chem 162-2008 Hill & Petrucci Homework Chapter 18 E o cell and the Spontaneity of Redox Reactions Use data from Table 18.1 and Appendix C, as necessary. 43. Predict whether a spontaneous reaction will occur in the forward direction in each of the following. Assume that all reactants and products are in their standard states. (a) Sn 4+ (aq) + 2I - (aq) → Sn 2+ (aq) + I 2 (s) Sn 4+ + 2e - → Sn 2+ 0.154V 2I - → I 2 + 2e - -0.535V Sn 4+ (aq) + 2I - (aq) → Sn 2+ (aq) + I 2 (s) -0.381; therefore non-spontaneous (b) 2MnO 2 (s) + 3ClO - (aq) + 2OH - (aq) → 2MnO 4 - (aq) + 3Cl - (aq) + H 2 O(l) 2(MnO 2 (s) + 2H 2 O → MnO 4 - (aq) + 4H + + 3e - ) -1.70 3(ClO - (aq) + H 2 O + 2e - → Cl - (aq) + 2OH - ) +0.890 2MnO 2 (s) + 4H 2 O + 3ClO - (aq) + 3H 2 O → 2MnO 4 - (aq) + 8H + + 3Cl - (aq) + 6OH - -0.81, non-spontaneous 2MnO 2 (s) + 4H 2 O + 3ClO - (aq) + 3H 2 O → 2MnO 4 - (aq) + 2H + + 3Cl - (aq) + 6H 2 O 2MnO 2 (s) + H 2 O + 3ClO - (aq) → 2MnO 4 - (aq) + 2H + + 3Cl - (aq) 2MnO 2 (s) + H 2 O + 3ClO - (aq) + 2OH - → 2MnO 4 - (aq) + 2H + + 2OH - + 3Cl - (aq) 2MnO 2 (s) + 3ClO - (aq) + 2OH - → 2MnO 4 - (aq) + H 2 O + 3Cl - (aq) The above is incorrect because it shows the MnO2 half-cell reaction as taking place in an acidic solution; yet, the total reaction takes place in basic solution. So this is inconsistent. Therefore, find an MnO2 reaction, if possible, that takes place in a basic solution. (b) 2MnO 2 (s) + 3ClO - (aq) + 2OH - (aq) → 2MnO 4 - (aq) + 3Cl - (aq) + H 2 O(l) 2(MnO 2 (s) + 4OH - → MnO 4 - (aq) + 2H 2 O + 3e - ) -0.60 3(ClO - (aq) + H 2 O + 2e - → Cl - (aq) + 2OH - ) +0.890 +0.29, spontaneous 45. Predict whether each of the following processes will proceed in the forward direction to any appreciable extent. (a) the reduction of Sn 4+ (aq) to Sn 2+ (aq) by Cu(s) Sn 4+ (aq) + 2e - → Sn 2+ (aq) +0.154 Cu → Cu2+ + 2e- -0.34 -0.19 not spontaneous, to any extent. (b) the oxidation of I 2 (s) to IO 3 - (aq) by O 3 (g) in acidic solution I 2 + 6H 2 O → 2IO 3 - + 12H + + 10e - -1.20 O 3 + 2H + + 2e - → O 2 + H 2 O +2.075 +0.88; therefore, spontaneous (c) the oxidation of Cr(OH) 3 (s) to CrO 4 2- (aq) by H 2 O 2 in basic solution Cr(OH) 3 (s) → CrO 4 2- Voltages are not available in Table 18.1 or Appendix c for this half-cell reaction. 47. Silver does not react with HCl(aq), but it does react with HNO 3 (aq). (a) Explain the difference in the behavior of silver toward these two acids. (b) Write a plausible net ionic equation for the reaction of silver with HNO 3 (aq). 1
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Ag → Ag + + 1e - -0.800V 2Cl - → Cl 2 + 2e - -1.358V Silver can only be oxidized. Cl - can only be oxidized. Hence, there is no redox reaction for this combination. However, while Ag can be oxidized, NO 3 - can be reduced. Hence, there is a redox reaction between these two substances. Ag → Ag + + 1e - -0.800V NO 3 - + 4H + + 3e - → NO + 2H 2 O +0.956 +0.156V E o cell , ∆G o , K eq 51. Determine the values of E o cell and ∆ G o for the following reactions. (a) O 2 (g) + 4I - (aq) + 4H + (aq) → 2H 2 O(l) + 2I 2 (s) O 2 + 4H + + 4e - → 2H 2 O +1.229 2(2I - → I 2 + 2e - ) -0.535 +0.694 = E o G = -nFE cell G o = -nFE o cell G o = -4 x 96500 x 0.694 = -2.68 x 10 5 J (b) Cr 2 O 7 2- (aq) + 3 Cu(s) + 14 H + (aq) → 2Cr 3+ (aq) + 3 Cu 2+ (aq) + 7H 2 O(l) Cr 2 O 7 2- (aq) + 14 H + (aq) + 6e- → 2Cr 3+ (aq) + 7H 2 O(l) +1.33 3(Cu(s) → 3 Cu 2+ (aq) + 2e - ) -0.340 +0.99 = E o G = -nFE cell G o = -nFE o cell G o = -6 x 96500 x 0.99 = -5.73 x 10 5 J 53. Write the equilibrium constant expression for each of the following reactions, and determine the numerical value of K eq at 25 o C.
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