## Search found 29 matches

Sun Mar 17, 2019 1:53 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: When is delta U = 0?
Replies: 4
Views: 405

### When is delta U = 0?

Under what conditions is delta U = 0?
Sat Mar 16, 2019 9:37 pm
Forum: First Order Reactions
Topic: Integrated Rate Law graphs
Replies: 1
Views: 292

### Integrated Rate Law graphs

What is the purpose behind integrating rate laws? What do the integrated rate law equations do?
Sat Mar 16, 2019 2:00 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Mechanisms without unknown rate-determining step
Replies: 2
Views: 130

### Reaction Mechanisms without unknown rate-determining step

If the problem gives a reaction mechanism, but doesn't state which is slow / fast, how can we determine the determining step rate law or overall rate reaction rate law?
Sat Mar 16, 2019 11:45 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Nernst Equation
Replies: 2
Views: 133

### Nernst Equation

In the constants and equations sheet, I noticed that there are 2 equations for Nernst's Equation:

E = Enot - (RT/nF) x lnQ .

E = Enot - (0.05916/n) logQ

What is the difference between the two?
Sat Mar 16, 2019 11:02 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Concentration cells Ecell
Replies: 1
Views: 82

### Concentration cells Ecell

Would the Ecell naught of a concentration cell be 0? Because the E naughts of the cathode and anode would just be the opposite of each other and thus cancel out?
Sat Mar 16, 2019 10:45 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Concentration Cells
Replies: 1
Views: 97

### Concentration Cells

When given 2 different concentrations, how do we know which concentration belongs to the oxidation / reduction reactions? In other words, how do we determine which concentration belongs to the anode and the cathode? The problem I am looking at states that the electrons are flowing from the left elec...
Fri Mar 15, 2019 10:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka Kb = Kw
Replies: 5
Views: 446

### Ka Kb = Kw

I know this isn't exactly equilibrium, but I wasn't sure where to ask it. For the final, in what context are we going to need to know and apply the Ka x Kb = Kw?
Thu Mar 14, 2019 6:52 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation question
Replies: 2
Views: 144

### Arrhenius Equation question

When finding the activation energy with the arrhenius equation in a temperature change, we use ln(k1/k2) = Ea/R (1/T2 - 1/T1).

Will k2 and k1 both always be given? If only one is given, how do we find the other?
Thu Mar 14, 2019 12:33 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Effect of concentration on cell potential
Replies: 2
Views: 124

### Effect of concentration on cell potential

How do changes in concentrations of reactants and products affect the cell potential?
Wed Mar 13, 2019 11:51 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: What is the difference between electrochemical series and reduction potentials?
Replies: 1
Views: 141

### What is the difference between electrochemical series and reduction potentials?

What is the difference between electrochemical series and reduction potentials?
Wed Mar 13, 2019 10:27 pm
Forum: General Rate Laws
Topic: Deriving integrated rate laws
Replies: 1
Views: 85

### Deriving integrated rate laws

Are we going to be required to know how to derive the integrated rate laws? Doesn't that require a background in calculus?
Wed Mar 13, 2019 10:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When to put Pt(s) in a cell diagram?
Replies: 3
Views: 177

### When to put Pt(s) in a cell diagram?

When are we required to write Pt(s) on the outsides of the cell diagram? What exactly is Pt(s)?
Thu Feb 28, 2019 12:13 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.27, 6th Edition
Replies: 1
Views: 85

### 14.27, 6th Edition

Why do we have to do use delta G = -nFE? Why can't we just add the E values of the 2 half reactions that make up the U4+ +4e- -> U(s)
Wed Feb 27, 2019 11:43 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6h Edition; 14.23
Replies: 2
Views: 119

### 6h Edition; 14.23

In part a, the half reaction within the main reaction is 6Hg -> 3Hg2 2+ + 6e-

In the reduction potential E values, Hg2 2+ + 2e- -> 2Hg E = +.79.

Why are we to use the +.79 instead of flipping the sign to -.79 since the oxidation version of this reaction is done in the actual reaction?
Tue Feb 12, 2019 10:00 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cv vs. Cp
Replies: 1
Views: 99

### Cv vs. Cp

So Cv = (3/2)R is used when volume is constant

and Cp = (5/2)R is used when pressure is constant.

In the practice midterm worksheets, when volume is being changed, the answer key says to use Cv. Why is this so?
Tue Feb 12, 2019 12:48 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 2nd law of Thermodynamics
Replies: 1
Views: 120

### 2nd law of Thermodynamics

How does the 2nd law of thermodynamics relate to the equation of delta S = q(rev) / T ?

The 2nd law states that spontaneous processes lead to an increase in entropy. However, if q is negative, isn't the change in entropy negative? How does this make sense?
Tue Feb 12, 2019 12:21 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Calculating change in entropy from 1st and 2nd laws of Thermodynamics
Replies: 1
Views: 113

### Calculating change in entropy from 1st and 2nd laws of Thermodynamics

In the Learning Outcomes for thermodynamics, it lists that we should know how to calculate change in energy and entropy from the 1st and 2nd laws of thermodynamics. How do we calculate entropy with the first and second laws?
Tue Feb 12, 2019 12:19 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Equations
Replies: 2
Views: 146

### Re: Entropy Equations

I believe boltzmann equation will be used when dealing with microstates. The other equation is used when calculating change in entropy within a volume change in the system: delta S = n R ln(v2 / v1)
Tue Feb 12, 2019 12:01 am
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Explaining Boltzmann's Equation
Replies: 6
Views: 672

### Explaining Boltzmann's Equation

What is the explanation behind Boltzmann's Equation? What exactly does it solve for?
Mon Feb 11, 2019 1:26 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Applying to biological and organic examples
Replies: 2
Views: 140

### Applying to biological and organic examples

How will we be required to relate thermochemistry / thermodynamics to organic and biological examples?
Mon Feb 11, 2019 1:16 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Difference between delta U and delta H?
Replies: 3
Views: 183

### Difference between delta U and delta H?

What is the difference between delta U and delta H?

Delta U is the change in internal energy of a system... and delta H is the change in heat energy. What is the difference between the two in respect to a system?
Mon Feb 11, 2019 1:10 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Explaining Hess's Law with enthalpy = a state function?
Replies: 3
Views: 156

### Explaining Hess's Law with enthalpy = a state function?

I saw this on the learning outcomes for thermochem; how does enthalpy being a state function justify Hess's Law?
Mon Feb 11, 2019 1:05 am
Forum: Calculating Work of Expansion
Topic: Proving the work equation
Replies: 2
Views: 136

### Proving the work equation

Will we be required to know / explain the integral justification for w = P delta V?
Thu Feb 07, 2019 4:57 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Difference between 2 delta S equations?
Replies: 1
Views: 95

### Difference between 2 delta S equations?

In the textbook, the equation for delta S with given temperature change is Delta S = C x ln(T2/T1)

However, in the answer book, the equation Delta S = n x C x ln(T2/T1) is used.

Why is n neglected? Thank you for your time.
Wed Jan 30, 2019 9:19 pm
Forum: Phase Changes & Related Calculations
Topic: Phase change equations
Replies: 1
Views: 108

### Phase change equations

Why is it that when calculating for the enthalpy of a phase change, it is (moles)(standard enthalpy of phase change) but when calculating a change in temperature, it becomes (grams)(specific heat)? For example, how much heat is needed to convert 80.0 g of ice at 0.0 C into liquid water at 20.0 C: th...
Tue Jan 29, 2019 1:49 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Cp vs. Csp
Replies: 2
Views: 123

### Re: Cp vs. Csp

Christopher Tran 1J wrote:Cp refers to the heat required to raise the temperature of one mole gas by 1 degree C at constant pressure, and Csp refers to the heat required to raise the temperature of one gram gas by 1 degree C at constant pressure.

How will we know when to use Cp or Csp? Will it be give in the question?
Tue Jan 29, 2019 1:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: What is the difference between delta H and q?
Replies: 3
Views: 618

### What is the difference between delta H and q?

delta H is the change in heat; the measure of heat; isn't q also a measure of heat? what is the difference between delta H and q?
Thu Jan 17, 2019 3:41 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14b weekly homework
Replies: 2
Views: 140

### Chem 14b weekly homework

Are we required the write the questions from the textbook down? Or is only showing work OK?
Thu Jan 17, 2019 3:39 pm
Forum: Student Social/Study Group
Topic: ICE Table
Replies: 5
Views: 203

### Re: ICE Table

if X is smaller than 10^-3, adding it into a number will have nearly no effect. However, X^2 is significantly larger than just X. Therefore if X is smaller than 10^-3, it is negligible.