AP Chemistry Unit 9 - Applications of Thermodynamics

University:
Kentucky State University
Course:
CHE 101 | General Chemistry I
Academic year:

2022
Views:

377

Pages:

4
Author:

Charlee Buchanan

Unit 9 - Applications of Thermodynamics Entropy S: A driving force for a spontaneous process is an increase in the entropy of the universe. Entropy represents the disorder of a reaction. ● Ssolid < Sliquid < Sgas ● Gas has the largest S because it has the most disorder between the gas molecules. On the other hand, solid has the smallest S because it has the least disorder between molecules in the solid. Second Law of Thermodynamics: In any spontaneous process, there is always an increase in the entropy of the universe. Total energy of the universe is constant, but entropy is increasing. Suniverse = Ssystem + Ssurrounding Third Law of Thermodynamics: Entropy of a perfect crystal at 0 K is 0. Standard Entropy Values (Sº) represents the increase in entropy that occurs when a substance is heated from 0 K to 298 K at 1 atm pressure. Sºreaction = 𝛴𝑆ºproducts - 𝛴𝑆ºreactants Gibbs Free Energy G: Total energy (entropy and enthalpy) that is available to do work. It determines the spontaneity of a reaction. ● G=H-TS Standard Free Energy Change (Gº): The change in free energy that will occur if the reactants in that standard state are converted to the products in their standard states. Gºreaction = 𝛴𝐺ºproducts - 𝛴𝐺ºreactants Here’s a chart with relationship between enthalpy, entropy, and free energy: There’s also a relationship between Gibbs free energy and K. Gº K Gº = 0 K=1 Gº < 0 K>1 Gº > 0 K<1 Galvanic/Voltaic Cell Because Cu is the positive cathode, electrons are attracted and will flow toward Cu. These electrons come from the oxidation of Zn, which results in Zn2+ in solution. These electrons combine with Cu2+ in solution to form Cu(reduction), increasing the mass of the Cu cathode. The salt bridge keeps the charge in the cell neutral(K+ ion from KCl replaces Cu2+ in solution, and Cl- balances Zn2+ in solution) Standard cell notation/line notation template(see image for example without concentrations) anode|anode solution(concentration)||cathode solution(concentration)|cathode Helpful mnemonic devices ● AN OX - oxidation happens at the anode ● RED CAT - reduction happens at the cathode ● FAT CAT - the cathode’s mass increases(cats gain weight) ● Electrons flow alphabetically(Anode to Cathode) ● CATs and PAW-SITIVE - the cathode is positive Use a table of standard reduction potentials(given on AP exam) to determine what is the cathode and anode. The largest E° is the cathode(reduced). Cell voltage - E° of cathode - E° of anode ΔG°=-nFE°, n=moles of electrons in balanced equation, F=96485 Coulombs/mole electron, 𝑅𝑇 Nernst Equation: Ecell = Eºcell - 𝑛𝐹 𝑙𝑛𝑄 There’s also a relationship between the Gibbs Free Energy, Equilibrium and the Galvanic cell: Gº K Eºcell Gº = 0 K=1 0 Equally Favored Gº < 0 K>1 + Products Favored Gº > 0 K<1 - Reactants Favored