Assignment: Electrochemistry

    1. Why do we balance the charge in redox reactions, but not in other chemical equations?
    2. Balance each reaction below, and write a cell schematic representing the reaction as it would occur in a galvanic cell.
      1. Al(s) + Zr4+(aq) ⟶ Al3+(aq) + Zr(s)
      2. Ag+(aq) + NO(g) ⟶ Ag(s) + NO3–(aq)  (acidic solution)
      3. CO32−(aq) + Mg(s) ⟶ C(s) + Mg(OH)2(s)  (basic solution)
      4. BrO3–(aq) + MnO2(s) ⟶ Br−(aq) + MnO4−(aq)  (basic solution)
    3. Explain why a salt bridge is needed in galvanic cell reactions.
    4. If a metal electrode loses mass in a galvanic cell reaction, was it the cathode or the anode? Explain your reasoning.
    5. Write the balanced cell reaction for the cell schematic below, calculate the standard cell potential, and note whether the reaction is spontaneous under standard state conditions.

    Cu(s)│Cu2+(aq)║Ag1+(aq)│Ag(s)

    1. Determine the cell reaction and standard cell potential at 25 °C for a cell made from a cathode half-cell consisting of a silver electrode in 1 M silver nitrate solution and an anode half-cell consisting of a zinc electrode in 1 M zinc nitrate. Is the reaction spontaneous at standard conditions?

 

Calculate the Gibbs free energy change (G) for the following chemical reaction (The reaction occurs at 72 °F, the change in heat (H) = 18,070 cal, and the change in entropy (S) = 90 cal/K.):

ATP → ADP + Pi

Calculate the Gibbs free energy change (G) for the following chemical reaction (The reaction occurs at 72 °F, the change in heat (H) = 4104 cal, and the change in entropy (S) = 2.4 cal/K.):

glutamate + NH3→ glutamine + H2O

  1. Will either of these reactions occur spontaneously?
  2. How does the Gibbs free energy in each of the two reactions change if the temperature were raised to normal body temperature (98.6 °F)?
  3. Does putting the reaction at normal body temperature change the spontaneity of either of the reactions? Explain.
  4. In an electrolysis reaction, water is being decomposed into oxygen gas and hydrogen gas.

 

Litmus can be used as an indicator in the water. In the following reaction, the litmus turns red in test tube #1 and blue in test tube #2.

Test tube 1: 2 H2O(l) → O2(g) + 4H+(aq) + 4e-

Test tube 2: 4 H2O(l) + 4e- → 2H2(g) + 4OH–(aq)

    1. Find the oxidation numbers for the species in each of the two test tubes, then identify which species is being oxidized and which is being reduced?
    2. Which test tube contains the anode?
    3. Explain why the litmus turns blue in test tube #2