## Search found 33 matches

Sat Mar 17, 2018 7:00 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Winter 2013 Midterm Q7
Replies: 1
Views: 207

### Winter 2013 Midterm Q7

Calculate K and delta G at 298 K for the following redox reaction. Hint: Identify the two half-reactions and show a balanced equation to receive full credit. Use: MnO4- + 8H+ + 5e- -> Mn2+ + 4H2O E= -1.49 V Br2 + 2e- -> 2Br- E= +1.07 V How come when calculating for K, we assume that the redox equati...
Sat Mar 17, 2018 12:39 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Rate Laws and Catalysts
Replies: 1
Views: 125

### Rate Laws and Catalysts

Do we incorporate catalysts when writing the rate law?
Sat Mar 17, 2018 11:15 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Step Vs. Steady State Approximation
Replies: 3
Views: 246

### Re: Slow Step Vs. Steady State Approximation

rate-determining step is used when you know which elementary reaction is the slow step. steady state approximation is used when you don't know the rate-determining step or when there's multiple rate-determining steps
Fri Mar 16, 2018 10:35 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test 2 Q7
Replies: 3
Views: 315

### Test 2 Q7

Calculate the standard potential for the following reaction using the reduction potentials on the last page of the test: Fe3+ + 3e- ->Fe

I found two related half-reactions: Fe3+ + e- -> Fe2+ and Fe2+ + 2e- -> Fe
but I dont know what to do next. How do I solve this problem?
Thu Mar 15, 2018 12:37 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Section 15.12
Replies: 1
Views: 159

### Section 15.12

What material do we need to understand from Section 15.12 (Collision Theory) in the textbook? do we have to know the formulas?
Thu Mar 15, 2018 10:47 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow vs Fast Reactions
Replies: 2
Views: 185

### Slow vs Fast Reactions

Will we be given whether the reaction is a slow or fast reaction? If so, how do we find that out?
Wed Mar 14, 2018 3:07 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Net rate of formation of products
Replies: 2
Views: 179

### Net rate of formation of products

For the net rate of formation of products, is it rate of formation - rate of consumption or rate of consumption - rate of formation (or does this even matter at all?)
Wed Mar 07, 2018 4:21 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Stopped Flow Technique
Replies: 2
Views: 281

### Stopped Flow Technique

What is the role of the stopping syringe in the stopped flow technique? How is this technique supposed to measure the change of concentrations over time?
Sun Mar 04, 2018 11:04 pm
Forum: Balancing Redox Reactions
Topic: Test 2, Q5
Replies: 4
Views: 235

### Re: Test 2, Q5

For increasing oxidizing power, do we organize the elements from low to high standard reduction potentials then?
Sun Mar 04, 2018 10:34 pm
Forum: Balancing Redox Reactions
Topic: Balancing number of electrons
Replies: 10
Views: 462

### Re: Balancing number of electrons

It doesn't matter how you multiply as long as everything cancels out. However, it's most convenient to multiply by the least common factor
Sun Mar 04, 2018 10:10 pm
Forum: First Order Reactions
Topic: Derivations
Replies: 6
Views: 342

### Re: Derivations

My TA also mentioned that it's fair game for derivations to appear on the final exam. However, if I were you, I'd focus on other concepts first and when there's time left, look over the derivations. Remembering the derivations will also help you understand the equations better
Sun Feb 25, 2018 10:07 pm
Forum: Balancing Redox Reactions
Topic: Finding half reactions
Replies: 4
Views: 258

### Re: Finding half reactions

List of half reactions should be provided on the test with their standard potentials
Sun Feb 25, 2018 10:00 pm
Forum: Balancing Redox Reactions
Topic: Recognizing a redox reaction in acidic or basic solution
Replies: 5
Views: 254

### Recognizing a redox reaction in acidic or basic solution

Will we be explicitly told that the redox reaction is specifically in a acidic/basic solution? Or will we have to recognize this on our own based on the given ions?
Sun Feb 25, 2018 9:56 pm
Forum: Calculating Work of Expansion
Topic: Midterm Q4A
Replies: 3
Views: 197

### Midterm Q4A

A piston containing 0.10 mol of nitrogen gas at 298 K has an initial volume of 2.24 L and
undergoes an expansion against 0.5 atm external pressure until its volume doubles.
Calculate the work involved in Joules.

How come for this problem we don't use the equation -nRT ln V2/V1?
Fri Feb 16, 2018 2:05 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: S=klnW
Replies: 7
Views: 1383

### Re: S=klnW

you'd also use this equation if some information is given about W (like any info about number of ways a molecule can exist)
Fri Feb 16, 2018 2:01 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Delta U as 0
Replies: 3
Views: 251

### Re: Delta U as 0

how come delta u is zero for an isothermal expansion?
Fri Feb 16, 2018 1:55 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Is enthalpy a state function?
Replies: 12
Views: 956

### Re: Is enthalpy a state function?

Yup, enthalpy is a state function, which explains why we are able to use Hess's law to calculate the reaction enthalpy.
Fri Feb 09, 2018 10:39 pm
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: Box 9.6
Replies: 1
Views: 121

### Box 9.6

Calculate the entropy of vaporization of acetone at 296 K with an external pressure of 1 bar. The molar heat capacity of liquid acetone is 127 J/K-mol, its boiling point is 329.4 K, and its enthalpy of vaporization is 29.1 kJ/mol. Step 1: change in entropy= C ln(T2/T1)= 127 * ln (329.4/296)= +13.5 J...
Mon Feb 05, 2018 11:53 pm
Forum: Phase Changes & Related Calculations
Topic: Differential Thermal Analysis
Replies: 2
Views: 155

### Differential Thermal Analysis

Do we have to read and understand Box 8.1 in the textbook for the midterm? It talks about the differential thermal analysis.
Mon Feb 05, 2018 6:48 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Conceptual Help on Cv vs Cp
Replies: 1
Views: 150

### Conceptual Help on Cv vs Cp

I understand mathetmatically how we find the equations for Cv and Cp, but I'm having a bit of trouble with this conceptually. How come Cv is change in internal energy/change in temperature? Why can't it be the change in enthalpy/change in temperature (and vice versa for Cp)?
Sun Feb 04, 2018 10:37 pm
Forum: Calculating Work of Expansion
Topic: Solving Reversible vs irreversible [ENDORSED]
Replies: 2
Views: 188

### Solving Reversible vs irreversible[ENDORSED]

Will the problems explicitly say whether or not the system is reversible/irreversible? Or will we have to identify them? Especially for the midterm?
Sun Feb 04, 2018 10:25 pm
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: Entropy and Disorder
Replies: 1
Views: 117

### Entropy and Disorder

How come Dr. Lavelle doesn't like associating entropy with disorder?
Sun Feb 04, 2018 10:22 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Equipartition Theorem
Replies: 3
Views: 241

### Equipartition Theorem

How come we don't consider the contribution of vibrational energy when calculating the molar internal energy (Um)?
Sun Jan 28, 2018 3:26 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: isothermal system
Replies: 4
Views: 230

### Re: isothermal system

But when an ideal gas expands isothermally, volume increases and pressure decreases. Since volume increased, the system did work on the surroundings...so wouldn't work be non-zero, making the change in internal energy non-zero as well?
Sun Jan 28, 2018 1:52 am
Forum: Calculating Work of Expansion
Topic: The integral equation
Replies: 8
Views: 337

### Re: The integral equation

The integral is used for deriving the equation for finding work in a reversible gas expansion. The integral is used to find the area of the curve in a volume vs. pressure graph (you can find that on p 266 of the textbook). The graph is curve because in a reversible gas expansion, the external pressu...
Sun Jan 28, 2018 1:44 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Reversible vs Irreversible
Replies: 2
Views: 164

### Reversible vs Irreversible

Is it possible to show an infinitesimal change of the gas expansion experimentally (like has anyone found a video of an experiment that shows a reversible gas expansion)? Or is the concept of reversibility theoretical?
Sat Jan 27, 2018 7:38 pm
Forum: Calculating Work of Expansion
Topic: U for Reversible & Irreversible Expansion
Replies: 2
Views: 146

### U for Reversible & Irreversible Expansion

According to the textbook, the "change in internal energy is the same regardless of the path taken between the same initial and final states"

So does that mean the change in internal energy would be the same regardless if the gas expanded reversibly or irreversibly? If so, why?
Sat Jan 20, 2018 9:10 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capcity for Water
Replies: 8
Views: 332

### Re: Heat Capcity for Water

We'll be given those values for the test, right?
Sat Jan 20, 2018 8:54 pm
Forum: Calculating Work of Expansion
Topic: Equation from Friday Lecture
Replies: 2
Views: 166

### Equation from Friday Lecture

Can someone explain why this equation is true? I'm having some difficulty understanding it.

change in U= qP + w= qP= change in H
Thu Jan 18, 2018 12:31 am
Forum: Calculating Work of Expansion
Topic: Homework 8.11
Replies: 8
Views: 484

### Homework 8.11

8.11 A piston confi nes 0.200 mol Ne(g) in 1.20 L at 25 'C. Two experiments are performed. (a) The gas is allowed to expand through an additional 1.20 L against a constant pressure of 1.00 atm. (b) The gas is allowed to expand reversibly and isothermally to the same fi nal volume. Which process does...
Sat Jan 13, 2018 2:01 pm
Forum: Phase Changes & Related Calculations
Topic: Standard Reaction Enthalpy
Replies: 8
Views: 367

### Re: Standard Reaction Enthalpy

As long as the substance is in its most stable form, I'm pretty sure you can use compounds (combination of elements)for the standard enthalpy formation
Sat Jan 13, 2018 1:07 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Closed System
Replies: 7
Views: 353

### Re: Closed System

I think a calorimeter is a closed system...but can anyone think of an example that works as an isolated system?
Sat Jan 13, 2018 12:47 am
Forum: Phase Changes & Related Calculations
Topic: Using Bond Enthalpies for Resonance Structures
Replies: 2
Views: 142

### Using Bond Enthalpies for Resonance Structures

Just out of curiosity, is it possible to find the enthalpy change of a reaction using bond enthalpies for reactants/products that have resonance structures?