The exam will be held Thursday March 20, in CB 285, from 10:30 am until 12:30 pm. Bring a calculator. Partial credit for multi-step problems will be given ONLY if you show your work. Equations (e.g. Clausius-Clapeyron, DG = DH -TDS, etc.), constants (e.g. Henry’s Constants, R, etc.), tables of thermodynamic data, and a “bare bones” periodic table will be given to you.
- Office hrs will
be drop-in 9am-5pm Monday 3/17, 2-5pm Tuesday 3/18, and 9am-1pm Wednesday 3/19.
The exam covers the material in Chapters 7-10, 13 and 17. This list is not guaranteed to be comprehensive, but it is a very good idea to review the following topics in preparation for the exam.
Your answers must ALWAYS have the
appropriate units!
Concepts to study:
Phase
Transitions
- interpretation of phase diagrams
what do phase boundaries represent?
what are the triple point, and critical point?
Predict what phases are present for a given set of Temp. and Press.
- variation of vapor pressure with temperature
Clausius-Clapeyron equation and its application to calculate Pvap at new temp. (remember to use a value for P that corresponds to the value
it would have in units of bar (unless the units cancel)
Calculation of DHvap and DSvap from plot of ln(P) vs. 1/T
- what is the boiling point for any liquid?
- why is the slope negative for the phase boundary between liquid water and ice, but positive for most other materials?
Solubility
- What is meant by “like dissolves like”?
polarity as a predictor of solubility
-solubility of gases: Henry’s law
Colligative Properties
- definition of molality; use of molality to predict freezing point depression/boiling point elevation
what is the “van’t Hoff i factor”?; how is it used?
- calculating vapor pressure of a solution of non-volatile solutes using Raoult’s law.
rationalize deviations from ideal Raoult’s
law behavior
- osmotic pressure; definition
calculate molality and molar mass of solute in solution
Vapor pressure and composition of vapor
vs. solution of two volatile liquids
- relation of mol fraction in vapor vs. mol fraction in liquid
- predict composition of vapor from composition of liquid
How is the equilibrium state defined?
What are the reaction quotient “Q” and the equilibrium constant “K”; how are they similar; how are they different?
How is Q (or K) determined by inspection of a chemical equation?
Know how to evaluate equilibrium concentrations of reactants and products from K or DGº.
DG = DGº + RTlnQ
DGº =
- RTlnK
Know how to evaluate K from:
Equilibrium activities of reactants and products
DGºr
DGºformation data (ONLY FOR REACTIONS AT 25 ºC!!!)
DHºr and DSºr data (for reactions at temperatures other than 25 ºC [using DGºr = DHºr –TDSºr])
Know how to evaluate DG to determine whether the forward or reverse reaction is favored.
e.g., is Q > K, Q < K, or Q = K?
Le Châtelier Principle
How does a change in Q, pressure (by compression or expansion) or temperature affect a reaction at equilibrium?
Know how to evaluate the equilibrium concentrations of reactants and products after perturbation of a system that was at equilibrium.
definitions: Bronsted-Lowry and Lewis definitions of acids and bases; “conjugate” acid/base pairs
equations and their applications:
Kw = aH3O+ a-OH ≈ [H+][-OH] = 10-14
pH = -log(aH3O+) ≈ -log[H+] pOH = -log(a-OH) ≈
-log[-OH]
pH + pOH = 14
calculate pH from [H+] and vice versa
for:
HA + H2O ⇄ H3O+
+ A-
Ka = ((aH3O+)(aA-))/((aHA)(aH2O)) ≈
([H3O+][A-])/[HA]
for: A- + H20 ⇄ HA + -OH
Kb = ((a-OH)(aHA))/((aA-)(aH2O)) ≈ ([-OH][HA])/[A-]
Recall that A- + H20 ⇄ HA + -OH is another useful expression for Kb
pKa + pKb = 14
a strong acid has a weak conjugate base (and a low pKa)
a weak acid has a stronger conjugate base (and a higher pKa)
as acid strength increases, pKa decreases; as base strength increases, pKa increases
Calculation of pH for a strong acid or strong base solution (assume complete dissociation)
Calculation of pH for a weak acid or weak base solution
Use of Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA])
Why is it reasonable to assume that a molecule is ~100% deprotonated when pH > (pKa + 3)?
Why is it reasonable to assume that a molecule is ~100% protonated when pH < (pKa - 3)?
Titrations
Rationalize the shape of the pH profile for strong acid/strong base or weak acid/strong base titrations
- steepness near equivalence point
- shallowness near pKa of weak acids (buffering region)
- why is pH = 7 @ equivalence point of strong acid/strong base titration?
- why is pH > 7 @ equivalence point of weak acid/strong base titration?
(see lab #2)
Calculate pH before, near, and after equivalence point (see class notes)
- near equivalence point include contribution for autoprotolysis (only for strong acids!)
For A → B rate = -d[A]/dt = -k[A]
Calculate initial rates given a rate law and initial concentrations
Calculate order of rate from:
rate law
units on rate constant
experimental data
Using integrated rate laws
ln([A]t/[A]0) = -kt or [A]t = [A]0 e-kt t½
= (0.693)/k
-1/[A]t + 1/[A]0 = -kt or 1/[A]t = 1/[A]0 + kt t½ = 1/([A]0 k)
Arrhenius equation (effect of temperature on rate)
ln k = ln A - Ea/RT or k = A e-Ea/RT
Calculate Ea (i.e., DG‡ ) using the Arrhenius equation given k, A, T
Calculate k using the Arrhenius equation given DG‡, A, T
Calculate k at
T = T2 given k at T = T1, DG‡,
T1
‡ = highest energy state on a reaction coordinate diagram; = state in which bond breaking/formation occurs
You should be able to draw a reaction coordinate diagram
Show: reactant, ‡, product states, DG‡ (Eact) for forward and reverse reactions, and DGºrxn
You should be able to derive the relationship between rate constants and K (equilibrium constant) for an elementary reaction using
DGºrxn = (DG‡for – DG‡rev) and the
Arrhenius equation
How does a catalyst accelerate the approach to equilibrium?
Calculate the rate acceleration or DG‡, given one or the other
Using kinetic data to select the most likely reaction mechanism from a set of possible mechanisms
Define rate laws for elementary steps
Use elementary steps and observed rate law to identify the RDS (rate-determining step)
Use the “steady-state approximation” to derive the rate law for an RDS that is not the first step in a mechanism
What is meant by “pseudo first order” kinetics? Under what conditions would you expect to see pseudo first order kinetics? (review these concepts in lab #4 and in text)
Will not be covered on the exam.
Preparation
Strategy:
- Rework the
midterm exams!!!
- Work as
many problems
as you can. Here are some specific
suggestions for review problems from your text:
Chapter 13: 9,
17-23odd, 27, 29, 35, 41, 45-51odd, 57, 59, 63, 65, 71, 77, 83, 85, 89, 91, 95,
101, 103
Chapter 7: 1, 5, 7,
17, 19, 23, 33, 39, 45, 49, 51, 55, 63, 79, 85, 91, 93
Chapter 8: 1, 7, 9,
13, 19, 21, 27, 37, 39, 43-51odd, 57, 59, 69, 71, 83, 85, 97, 101, 107, 113,
115
Chapter 9: 1, 17, 19,
23, 25, 41, 47, 53, 59, 63, 69, 71, 75, 81, 87, 93, 101, 107, 113, 119
Chapter 10: 1, 15, 21, 25,
29, 31, 45, 53, 57, 61, 69a, 69b, 73, 125
- Review the online homework assignments and make sure you can solve all the questions. HW assignments #1 and #2 are in review mode already and #4 is a review assignment that will not be graded- it is there to help you prepare for the final. Recall that HW assignment #3 is due Wednesday March 19 by 11pm.