Chapter 17 Exam 2 Review: Spontaneous Processes, Entropy, and Gibbs Free Energy
Prepare for Exam 2 by reviewing key topics including spontaneous processes, entropy, and Gibbs free energy in Chapter 17. Understand concepts, predict changes, and calculate values essential for thermodynamics. Get ready for the exam with detailed insights provided in this review.
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Announcements I Exam 2: Thursday (10/27) Will Cover Titrations, Solubility, Complex Ions (from Ch. 16) + Chapter 17 (Thermodynamics) Same Format as Exam 1 Besides being able to do calculations (a big part of lectures), should know how to set up problems (e.g. calculation approach for titrations) Help Session today 3:30 to 4:30 (replacing 2nd30 min. of office hours) Sequoia 452 Finishing Topic Review today
Announcements II Lab/Quiz 7 Quiz 7 next Monday and Tuesday (Experiment 8 + Electrochem basics) Today s Lecture Review of Exam 2 Topics Chapter 17 Electrochemistry (Ch. 18 Exam 3 material) Review (Chapter 4.9 Oxidation States, Redox Reactions) Balancing Redox Reactions Voltaic (or Galvanic) Cells
Exam 2 Review Chapter 17 Spontaneous Processes Understand main concepts regarding spontaneous processes Chapter 17 Entropy Understand basic concept of entropy Be able to predict sign of entropy change for various processes (change in state, change in temperature, change in number of moles) Know what state has an entropy of zero Know the second law of thermodynamics (change in entropy for the universe)
Exam 2 Review Chapter 17 Entropy cont. Be able to predict the change in entropy for the surroundings based on the change in entropy for the system Be able to calculate the change in entropy for the surroundings based on the enthalpy change of the system and the temperature Be able to calculate the standard change in entropy for a reaction using standard entropies of reactants and products
Exam 2 Review Chapter 17 Gibbs Free Energy Be able to calculate the Gibbs free energy change from H, T and S values Know how G relates to whether a process is spontaneous Be able to predict the temperature regime where a process is spontaneous from H and S information Be able to calculate G for standard conditions from either H , T and S or from Gf values Know how Grxndepends on reaction conditions (I will give equation: Grxn= Grxn + RTlnQ)
Exam 2 Review Chapter 17 Gibbs Free Energy cont. Be able to calculate K from Grxn (or visa versa) Know how temperature changes affect equilibrium shifts
Chapter 18 Electrochemistry Not on Exam 2 Electrochemical Reactions Redox Reactions: A redox reaction is the coupling of an oxidation with a reduction These need to be coupled so that there is not net gain or loss of electrons Definitions: Reduction: a reduction of the oxidation state (gain of electrons) Oxidation: an increase in the oxidation state (loss of electrons)
Chapter 18 Electrochemistry Electrochemical Reactions Oxidation States: How do we determine these? Examples: H2O, NH3, CaF2, H2CO, MnO4-, SO42- Note: examples with unusual oxidation states (Mn+7) are generally less stable (good as electrochemical reactants) Electrochemical Reactions Balancing Redox Reactions: 6 step method: 1) Assign oxidation states 2) Separate overall reaction into oxidation and reduction reactions
Chapter 18 Electrochemistry Electrochemical Reactions Balancing Redox Reactions: 6 step method cont. 3. Balance each half reaction with respect to mass in order a) mass all elements other than H, O, b) O by adding H2O, c) by adding H+, d) Add OH-to both side if in alkaline sol n 4. Balance each half reaction for charge by adding electrons 5. Use common multiplier to get equal numbers of electrons for each half-reaction 6. Add each half reaction together to get net reaction without electrons as reactants or products
Chapter 18 Electrochemistry Electrochemical Reactions Balancing Redox Reactions Cont. Examples (unbalanced): AgNO3(aq) + Zn(s) HClO(aq) + Fe2+(aq) MnO4-(aq) + C2O42-(aq) Ag(s) + Zn(NO3)2(aq) Cl2(g) + Fe3+(aq) Mn2+(aq) + CO2(g)
Chapter 18 Electrochemistry Electrochemical Reactions Different Forms Beaker Reactions Products form along with heat (assuming H < 0) Little control of reaction Products co-mingled (from reduction and oxidation) Example: nail rusts (oxidation of Fe, reduction of O2) Voltaic (Galvanic) Cells Oxidation and reduction reactions may be divided into different parts (half-cells sometimes physically separated through two reaction cells) Two electrodes are also needed Reaction can be harnessed through voltage/power production Examples: batteries, pH measuring electrodes
Chapter 18 Electrochemistry Electrochemical Reactions Different Forms Electrolytic Cell In this type of cell, external electrical energy is used to force unfavorable reactions (e.g. 2H2O(l) occur Also requires two electrodes but some differences from electrodes of voltaic cells Examples: Production of Cl2gas from NaCl(aq), production of H2gas from water (above), instruments that measure degree of oxidation/reduction at specific voltages (analogous to spectrometers) 2H2(g) + O2(g)) to
Chapter 18 Electrochemistry GALVANIC CELL Voltaic Cells - Description of how example cell works Reaction on anode = oxidation Anode = Zn electrode (as the E for Zn2+is less than for that for Ag+) So, reaction on cathode must be reduction and involve Ag Oxidation produces e-, so anode has ( ) charge (galvanic cells only); current runs from cathode to anode Salt bridge allows replenishment of ions as cations migrate to cathode and anions toward anodes voltmeter Ag+ + e- Ag(s) Zn(s) Ag(s) + AgNO3(aq) ZnSO4(aq) Zn(s) Zn2+ + 2e- Salt Bridge
