Thermodynamics and electrochemistry flashcards

Thermodynamics and electrochemistry connect energy changes to chemical reactions and electrical work. Students must understand Gibbs free energy (delta G), enthalpy (delta H), and entropy (delta S) and how they determine spontaneity. The relationship delta G = delta H - T delta S is central. A negative delta G means a reaction is spontaneous. In electrochemistry, students study galvanic and electrolytic cells, standard cell potential (E degrees), and the Nernst equation, which adjusts E for non-standard conditions. The key link between the two topics is delta G = -nFE, connecting cell potential to free energy. Students must also relate E degrees to the equilibrium constant K using delta G = -RT ln K. Understanding oxidation and reduction half-reactions, electrode labeling, and how concentration affects cell voltage are all essential skills.

1. Card 1

   What does a negative delta G indicate about a reaction?

   A negative delta G means the reaction is spontaneous, releasing free energy and proceeding without continuous energy input under given conditions.

2. Card 2

   State the Gibbs free energy equation relating H, T, and S.

   delta G = delta H - T delta S, where T is temperature in Kelvin, delta H is enthalpy change, and delta S is entropy change.

3. Card 3

   What is a galvanic (voltaic) cell?

   A galvanic cell converts chemical energy into electrical energy using a spontaneous redox reaction, producing a positive cell potential.

4. Card 4

   Define standard cell potential (E degrees cell).

   E degrees cell = E degrees cathode minus E degrees anode; it measures the voltage of a cell under standard conditions (1 M, 1 atm, 25 degrees C).

5. Card 5

   How are delta G and cell potential E related?

   delta G = -nFE, where n is moles of electrons transferred and F is the Faraday constant (96,485 C/mol). Spontaneous cells have positive E and negative delta G.

6. Card 6

   What is the Nernst equation used for?

   The Nernst equation (E = E degrees - (RT/nF) ln Q) calculates cell potential at non-standard conditions by accounting for the reaction quotient Q.

7. Card 7

   How does delta G relate to the equilibrium constant K?

   delta G degrees = -RT ln K; when K is large, delta G degrees is very negative, meaning the reaction strongly favors products at equilibrium.

8. Card 8

   What happens to cell potential when a reaction reaches equilibrium?

   At equilibrium, Q equals K, delta G equals zero, and the cell potential E equals zero, meaning no net electrical work can be done.

9. Card 9

   What is an electrolytic cell and how does it differ from a galvanic cell?

   An electrolytic cell uses electrical energy to drive a non-spontaneous redox reaction, the opposite of a galvanic cell which generates electricity spontaneously.

10. Card 10

    Which electrode is the anode in a galvanic cell?

    The anode is where oxidation occurs. In a galvanic cell it is the negative electrode, and in an electrolytic cell it is the positive electrode.

11. Card 11

    When is a reaction spontaneous at all temperatures?

    When delta H is negative and delta S is positive, delta G is always negative, making the reaction spontaneous at every temperature.

12. Card 12

    What is the role of the salt bridge in a galvanic cell?

    The salt bridge maintains electrical neutrality by allowing ions to flow between half-cells, completing the circuit without mixing the electrode solutions.

• Students often confuse the sign conventions for the anode and cathode between galvanic and electrolytic cells, forgetting that the anode is negative in galvanic cells but positive in electrolytic cells.
• Many students incorrectly apply delta G = delta H - T delta S using delta S in joules without converting to kilojoules to match the units of delta H, leading to wrong answers.
• A common error is assuming a positive E degrees cell always means the reaction is spontaneous under all conditions, ignoring that non-standard concentrations can make E negative via the Nernst equation.

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