EXTRA HOMEWORK 3A - Saddleback College · PDF fileEXTRA HOMEWORK 3A 1. ... The standard...

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Transcript of EXTRA HOMEWORK 3A - Saddleback College · PDF fileEXTRA HOMEWORK 3A 1. ... The standard...

  • EXTRA HOMEWORK 3A

    1. Calculate the standard enthalpy change, H, for the reaction:

    2H2O2 (l) 2H2O (l) + O2 (g)

    (a) using the standard enthalpy of formations from Handout 5

    (b) using bond energies from the Chem 1A Handout 8

    2. In each of the following pairs, tell which has the higher entropy.

    (a) One mole of ice or one mole of liquid water

    (b) One mole of liquid propane or one mole of gaseous propane

    (c) One mole of tin or one mole of lead

    (d) One mole of solid magnesium nitrate or one mole of aqueous magnesium nitrate

    3. Will the entropy change of each of the following processes be positive or negative, and will the

    disorder in each process increase or decrease?

    (a) One mole of solid aluminum melting to one mole of molten aluminum.

    (b) One mole of iodine vapor deposing to one mole of solid iodine

    (c) One mole of dissolved sodium acetate crystallizing out of an aqueous solution

    (d) One mole of dissolved carbon dioxide bubbling out of a soda

    4. Predict the sign of the entropy change in each of the following reactions. (a) BaCO3 (s) BaO (s) + CO2 (g)

    (b) Mg (s) + Cl2 (g) MgCl2 (s)

    (c) CH4 (g) + 2O2 (g) 2CO2 (g) + 2H2O (l)

    (d) Ni3(PO4)2 (s) 3Ni2+

    (aq) + 2PO43-

    (aq)

    (e) 2H+

    (aq) + SO32-

    (aq) H2O (l) + SO2 (g)

    (f) Br2 (l) + Cl2 (g) 2BrCl (l)

    5. Using the data from Handout 5, what is the standard enthalpy of formation of N2O (g)? What does this

    mean?

    6. Using the data from Handout 5, what is the standard absolute entropy of N2O (g)? What does this mean?

    7. Using data from the appendix, calculate the standard change in entropy, S, for the following

    reactions.

    (a) 2S (s, monoclinic) + 3O2 (g) 2SO3 (g)

    (b) C3H8 (g) + 5O2 (g) 3CO2 (g) + 4H2O (g)

    (continued on next page)

  • *8. 4 molecules are placed in a two-bulbed container. Calculate the positional probability of finding all 4

    molecules in the left bulb.

    *9. 8 molecules are placed in a two-bulbed container. Calculate the positional probability of finding all 8

    molecules in the left bulb.

    EXTRA HOMEWORK 3B

    1. Predict whether each of the following processes will be spontaneous, nonspontaneous, or it cannot be

    determined.

    (a) H = + and S = +

    (b) H = + and S =

    (c) H = and S = +

    (d) H = and S =

    2. Using the data from Handout 5, what is the standard free energy of formation of N2O (g)? What does

    this mean?

    3. For the reaction at 298 K

    Fe2O3 (s) + 3H2 (g) 2Fe (s) + 3H2O (g)

    use data from Handout 5 to answer the following.

    (a) Calculate H

    (b) Calculate S

    (c) Calculate G

    (d) Calculate G from G = H - T S

    (e) Is the reaction spontaneous under standard conditions at 298 K?

    (f) Do the enthalpy change and the entropy change work for or against spontaneity?

    (g) At a temperature higher than 298 K, would the forward reaction be more or less spontaneous?

    4. For the reaction at 298 K

    3AuCl (s) 2Au (s) + AuCl3 (s)

    use the data below to answer the following.

    298

    Hf (kJ/mol) 298

    Gf (kJ/mol) 298

    S (J/molK)

    AuCl (s) -97 -105 91

    AuCl3 (s) -118 -127 157

    (a) Calculate H, G, and S for the reaction at 298 K.

    (b) Calculate the absolute entropy of elemental gold at 298 K.

    (c) What is H, S, and G for the reaction at 398 K?

    (continued on next page)

  • 5. For the phase change:

    C6H6 (l) C6H6 (g)

    H = 33.9 kJ and S = 96.4 J/K.

    (a) Calculate the standard free energy change, G, for the reaction at 293 K, and tell if the forward

    or reverse reaction is spontaneous at this temperature

    (b) Calculate the standard free energy change, G, for the reaction at 353 K, and tell if the forward

    or reverse reaction is spontaneous at this temperature

    (c) Calculate the boiling point of liquid benzene

    *6. For the phase change:

    I2 (s) I2 (g)

    H = 62.24 kJ/mol and S = 143.6 J/molK.

    (a) Calculate the standard free energy change, G, for the reaction at 100.C, and tell if the forward

    or reverse reaction is spontaneous at this temperature.

    (b) Calculate the standard free energy change, G, for the reaction at 200.C, and tell if the forward

    or reverse reaction is spontaneous at this temperature.

    (c) Calculate the sublimation point of solid iodine.

    *7. The combustion reaction for butyric acid is:

    C3H7CO2H (l) + 5O2 (g) 4H2O (l) + 4CO2 (g)

    The standard enthalpy change of combustion for butyric acid at 298 K is -2,184 kJ/mol, and the

    standard entropy change of combustion for butyric acid at 298 K is -117 J/molK .

    Hf (kJ/mol) S (J/molK)

    C (s) 0 +6

    CO2 (g) -394 +214 H2 (g) 0 +131

    H2O (l) -286 +70. O2 (g) 0 +205

    C3H7CO2H (l) ? +226

    (a) Calculate the standard enthalpy change of formation, Hf, for butyric acid at 298 K.

    (b) Write the correctly balanced equation for the formation of butyric acid from its elements.

    (c) Calculate the standard entropy change of formation, Sf, for butyric acid at 298 K.

    (d) Calculate the standard free energy change of formation, Gf, for butyric acid at 298 K.

  • EXTRA HOMEWORK 3C

    1. For the reaction:

    2NO2 (g) N2O4 (g)

    use data from Handout 5 to answer the following.

    (a) Calculate G at 298 K

    (b) If the pressures of the gases are pNO2 = 0.29 atm and pN2O4 = 1.6 atm, calculate G at 298 K, and

    predict the direction the reaction will shift to reach equilibrium.

    (c) If the pressures of the gases are pNO2 = 0.21 atm and pN2O4 = 0.50 atm, calculate G at 298 K, and

    predict the direction the reaction will shift to reach equilibrium.

    (d) If the pressures of the gases are pNO2 = 1.0 atm and pN2O4 = 1.0 atm, calculate G at 298 K, and

    predict the direction the reaction will shift to reach equilibrium.

    2. For the reaction

    3H2 (g) + N2 (g) 2NH3 (g)

    use data from Handout 5 to answer the following.

    (a) Calculate G at 298 K

    (b) Is the forward reaction spontaneous under standard conditions?

    (c) Predict whether the equilibrium constant be > 1 or < 1 at 298 K.

    (d) Calculate Keq at 298 K

    (e) Does the Keq favor reactants or products?

    (f) What effect would an increase in pressure have on the spontaneity of the reaction?

    3. For the combustion of liquid methanol:

    C2H5OH (l) + 3O2 (g) 2CO2 (g) + 3H2O (l) (a) Calculate G at 298 K

    (b) Is the reaction spontaneous under standard conditions? (c) Predict whether the equilibrium constant be > 1 or < 1 at 298 K

    (d) Calculate Keq at 298 K

    (e) Does the Keq favor reactants or products?

    (f) What effect would an increase in temperature have on the spontaneity of the reaction?

    (g) What effect would an increase in pressure have on the spontaneity of the reaction?

    (continued on next page)

  • 4. Nitrous acid ionizes according to the following equation:

    HNO2 (aq) H+

    (aq) + NO2- (aq)

    At 298 K the Gf for nitrous acid is -51.6 kJ/mol, and the Gf for the nitrite ion is -32.2 kJ/mol.

    (a) Calculate the standard free energy change of the reaction at 298 K.

    (b) Is the reaction spontaneous under standard conditions?

    (c) Predict whether the Ka of nitrous acid will be > 1 or < 1 at 298 K.

    (d) From the standard free energy change of the reaction, calculate the Ka of acetic acid at 298 K.

    (e) How does your calculated Ka compare with the value found on Handout 3?

    (f) If the concentrations of each species in solution are [HNO2] = 0.100M, [H+] = 1.00 x 10

    -3 M, and

    [NO2-] = 1.00 x 10

    -3 M, calculate G at 298 K.

    (g) Is the reaction spontaneous under the conditions in (f)?

    5. Benzoic acid (C6H5CO2H) is a weak organic acid with Ka = 6.5 x 10-5

    at 298 K.

    (a) Write the equilibrium constant expression for the ionization of benzoic acid in water.

    (b) What is molarity of the benzoate ion, C6H5CO2- ion in a 1.00 M solution of benzoic acid in water?

    (c) What is the pH of the solution?

    (d) Predict whether G for the reaction in (a) will be > 0 or < 0 at 298 K.

    (e) What is the standard free energy change of the ionization of benzoic acid in water?

    6. The solubility of tin (II) fluoride in water is 0.049 g/L at 20.C and 0.093 g/L at 80.C.

    (a) Calculate the Ksp for tin (II) fluoride at each temperature.

    (b) Determine the heat of solution and the entropy change of solution of tin (II) fluoride by using a

    vant Hoff plot.

    (continued on next page)

  • *7. Hydrazine is a weak base that dissociates in water according to:

    N2H4 (aq) + H2O (l) N2H5+

    (aq) + OH- (aq)

    The Kb for hydrazine at 298 K is 2.4 x 10-6

    . and aqueous hydrazine has a standard free energy of

    formation of 128 kJ/mol. Calculate the standard free energy of formation of the hydrazinium ion.

    *8. The tables below contain information for determining thermodynamic properties of the following