Chem 1B Dr. White 1

Exam 3 Study Guide This study guide provides the topics covered for exam 3. A BAD way to study for the exam is just to look at this study guide, check things off and think you are ready for the exam. A GOOD way to study for the exam is to look at this study guide and find the appropriate sections in your notes and/or the textbook to go over the material in detail. Also, you MUST work problems for each section in order to succeed on the exam! Be able to do the problems without looking at the solutions. It’s a good idea to rework the class examples without looking at the solutions.

Be sure to review notes and your text. Be able to work all pertinent problems from homework assignments,

worksheets, lecture problems, and example problems in the textbook Below are some guidelines of what will be emphasized but you should be

prepared for anything from the chapters or lectures, unless otherwise specified in lecture.

You must bring your own non-programmable, scientific calculator. Sharing of calculators during the exam will not be allowed. You will also need a pen/pencil, but will not need any other materials.

Keys to studying chemistry

Use frequent but short study periods, rather than long hours just before an exam

Practice! Chemistry uses lots of terms and can seem like a foreign language. Practice problems in writing, do old homework or other exercises in the text to check your answers.

Read each problem carefully to determine what is being asked, make a plan for solving the problem, check the answer to see if it is reasonable!

Chapter 17

Spontaneity o Understand what constitutes a spontaneous process and a nonspontaneous

process Entropy, S

o Know the definition o Understand why a +ΔS is favored o Be able to predict the absolute entropy based on Temperature, Phase, number

of moles of products and reactants and/or Molecular Complexity o Be able to predict sign of ΔS for a given reaction or process o Understand the term standard entropy (S°). Understand why no substances

have a value of 0 for the S° (unlike standard enthalpy values) o Be able to calculate ΔS˚ given S˚ for reactants and products

ΔS˚rxn = Σ m S˚ products – Σ n S˚ reactants (you must know this equation and the related equations for ΔH° and ΔG°)

The Second Law of Thermodynamics

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o Know the second law and how it is different from the first law o Understand that the ΔSsurr depends on ΔHsys and T (ΔSsurr = -ΔHsys/T) o Understand how the ΔHsys affect ΔSsurr o Be able to explain what happens to the entropy of the surroundings with an

increase in T. Why is it inversely proportional to T? Free Energy (ΔG)

o Determine Spontaneity of Reaction using Gibb’s Free Energy, ΔG o Be able to calculate ΔG: ΔG = ΔH - TΔS, o Be able to predict sign ofΔG given ΔH and ΔS

Be able to determine which cases are spontaneous at high Temps, which are spontaneous at low temps

o Be able to predict sign of ΔH given ΔG and ΔS, or sign of ΔS given ΔG and ΔH, be able to calculate any one given other two.

o Be able to calculate temperature T at which reaction crosses over from –ΔG to +ΔG (crossover temperature)

Know how to calculate the temperature of a phase change o Know how ΔG relates to work o Understand the relationship between equilibrium and free energy

Be able to predict if a reaction is spontaneous in the forward or reverse direction (goes forward or backward) using ΔG

Understand that ΔG relates to Q and both change throughout the reaction

Know how to calculate ΔG using the following equations:

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ΔG = ΔG˚ + RT ln Q

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ΔG = RT ln QK

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ΔG = RT ln Q - RT ln K Standard Free Energy (ΔG°)

o Determine whether products or reactants are favored in a reaction using Standard Gibb’s Free Energy, ΔG°

o Know how to calculate ΔG° using the following relationships: ΔG˚ = ΔH˚ - TΔS˚, ΔG˚rxn = Σ m ΔG ˚ products – Σ n ΔG ˚ reactants (know this equation) ΔG° = -RT lnK

Using a Free Energy Diagram: o Be able to determine the sign of ΔG° o Be able to label the equilibrium point o Be able to show where the reaction is spontaneous in the forward and reverse

direction Understand the relationship between T and K

o Be able to use the equation in the form of y=mx +b or the 2-point form of the equation

o Be able to use a graph to determine ΔH° and ΔS° Chapter 18 Electrochemistry (Chapter 4.9-4.10 Reviews the basics of redox reactions)

Understand the following for redox reactions: o the difference between a redox reaction and nonredox reactions (exchange of

electrons)

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o what is oxidation, what is reduction o what is the reducing agent, what is the oxidizing agent o how to assign oxidation numbers o how to balance them in an acid and/or in base

Be able to diagram a Galvanic Cell. Make sure you can label the following: o Anode & cathode, electrodes and compartments, polarity of each (signs) o Salt bridge o Ions in solution o Direction of electron flow o Direction of anion and cation flow

Galvanic Cells o Know what an inactive electrode is and when it would be used in a galvanic cell o Be able to write half-cell reactions for a galvanic cell o Be able to calculate standard cell potential E˚cell given half-cell potentials o Be able to write the Shorthand (line) notation for a cell o Be able to decide which should be anode and which cathode

Given info on signs of electrodes Given Table of Reduction Potentials

o Be able to rank the relative strengths of oxidizing and reduction agents o Be able to write a spontaneous redox reaction given Table of Reduction

Potentials or similar info (based on the standard reduction potential, which is going to be reduced and which will be oxidized?)

The connection between E˚cell, ΔG˚ and K o Know how to use the equations that connect E˚cell, ΔG˚ and K  o What constitutes a product favored reaction? o Know what conditions correspond to a product-favored reaction, a reactant-

favored reaction, a spontaneous reaction, a nonspontaneous reaction o Know when a battery dies (Using the Nernst equation, you can see that the

battery will eventually “die” – when does it die?) o Use the Nernst equation to calculate the cell potential for a cell at nonstandard

conditions o Understand Concentration Cells

Be able to predict the flow of electrons Be able to do calculations involving concentration cells

Batteries o Understand that Batteries are galvanic cells

Corrosion of Iron o Know the steps involved in rusting (you don’t have to memorize all the

reactions, but you should know that iron is oxidized to Fe2+ and oxygen is reduced)

o Know the cathode and anode for the rusting process o Understand the effect of metal-metal contact on rusting.

Be able to determine which metals protect iron from rusting and explain why

Electrolysis o Know the difference between galvanic cells and electrolytic cells o Be able to label diagrams for electrolytic cells o Know the Applications of electrolytic cells

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Be able to do stoichiometric calculations involving electroplating Be able to predict what will be oxidized and reduced in an electrolytic cell

involving a molten salt or a mixture of molten salts o

Given  Equations  and  Constants:  

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ΔG = ΔG˚ + RT ln Q

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ΔG = RT ln QK

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ΔG = RT ln Q - RT ln K

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ln K =−ΔHrxn

o

RT + ΔSrxn

o

R

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ln K2K1

=−ΔHrxn

o

R1T2

−1T1

⎛

⎝ ⎜

⎞

⎠ ⎟

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Ecell = E˚cell − RTnF

lnQ

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E˚cell= RTnF

lnK

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at 25˚C, Ecell = E˚cell− 0.0257n

lnQ

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at 25˚C, E˚cell= 0.0257n

lnK

Constants  &  Conversion  Factors   Any thermodynamic data (i.e. ΔG°f, ΔH°f, and S° values) you may need A table of standard reduction potentials