## Search found 29 matches

Sat Mar 17, 2018 2:11 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.103
Replies: 3
Views: 268

### Re: 8.103

(3/2)*R deals with an ideal gas at a constant volume
Sat Mar 17, 2018 2:10 am
Forum: Phase Changes & Related Calculations
Topic: Endothermic/exothermic
Replies: 4
Views: 393

### Re: Endothermic/exothermic

Exothermic processes give off heat while endothermic processes absorb heat. It is important to identify which you consider to be the system and which are the surroundings.
Sat Mar 17, 2018 2:07 am
Forum: Balancing Redox Reactions
Topic: Ranking elements
Replies: 8
Views: 404

### Re: Ranking elements

By looking at standard reduction potentials, you can determine the reducing or oxidizing power. The more positive the potential, the greater the electron pulling power of the reduction half-reaction which means it is more likely to be reduced.
Sat Mar 17, 2018 2:05 am
Forum: First Order Reactions
Topic: k
Replies: 16
Views: 662

### Re: k

Usually the problem will specify a unit of time and we would want to use that same unit of time for K. Otherwise, using units of time as seconds is usually a safe bet.
Sat Mar 17, 2018 2:03 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Identifying a catalyst in a reaction
Replies: 4
Views: 244

### Re: Identifying a catalyst in a reaction

Intermediates will always be consumed while catalysts are not consumed.
Sat Mar 17, 2018 2:02 am
Forum: Balancing Redox Reactions
Topic: Half-Reactions Sheet
Replies: 5
Views: 242

### Re: Half-Reactions Sheet

We will likely be given the half reactions and the potentials along with them similar to our test.
Sat Mar 17, 2018 2:01 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibb's Energy and Work
Replies: 4
Views: 357

### Re: Gibb's Energy and Work

Gibbs free energy does not apply only to nonexpansion work
Sat Mar 17, 2018 2:00 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.1
Replies: 5
Views: 299

### Re: 9.1

Heat is leaving the body so you regard the body as the "system" and therefore q is negative
Sat Mar 17, 2018 1:59 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Why is entropy extensive?
Replies: 5
Views: 591

### Re: Why is entropy extensive?

Extensive is dependent while intensive is independent
Sat Mar 17, 2018 1:58 am
Forum: Balancing Redox Reactions
Topic: determining cathode from anode
Replies: 11
Views: 523

### Re: determining cathode from anode

Calculate cathode - anode substituting both numbers and the combination that gives the most positive output is the correct one
Fri Mar 16, 2018 7:19 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Finding n
Replies: 15
Views: 810

### Re: Finding n

n is the number of electrons
Fri Mar 16, 2018 7:18 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Standard Gibbs
Replies: 3
Views: 369

### Re: Standard Gibbs

The sign indicates standard state which means it is taking place under standard conditions (aka 25 degrees Celsius and 1 atm)
Fri Mar 16, 2018 7:17 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: S=klnW
Replies: 7
Views: 1170

### Re: S=klnW

Residual enthalpy can be calculated when a reaction is taking place at a very low temperature almost close to 0
Fri Mar 16, 2018 7:16 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isothermal system
Replies: 5
Views: 454

### Re: Isothermal system

The term free expansion implies work is = 0 and in that case q would also be zero as the deltaU value needs to remain 0
Fri Mar 16, 2018 7:15 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Midterm #6A
Replies: 2
Views: 311

### Re: Midterm #6A

A was the more precise answer but if you put B, you were given points back.
Fri Mar 16, 2018 7:14 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: State functions?
Replies: 9
Views: 464

### Re: State functions?

It is important to know the difference between state functions and those that aren't state functions. Entropy and enthalpy are state functions while heat and work are not.
Wed Mar 14, 2018 1:26 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Test 1 #3
Replies: 4
Views: 317

### Re: Test 1 #3

since the problem says "same temperature" we can infer it is isothermal which means deltaU is zero. Expansion work is occurring as the balloon grows
Tue Mar 13, 2018 11:23 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: change in internal energy
Replies: 3
Views: 256

### Re: change in internal energy

Separating the steps allows us to perform two different calculations which would give us the final correct answer. It is impossible to calculate them simultaneously as there is not an equation we have learned to allow us to deal with both forms of energy change at the same time.
Tue Mar 13, 2018 11:21 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: The First Law
Replies: 6
Views: 421

### Re: The First Law

The only way to change the internal energy of a closed system is to transfer energy into it as heat or work
Tue Mar 13, 2018 11:15 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: enthalpy of sublimation
Replies: 5
Views: 360

### Re: enthalpy of sublimation

Hsub can also be deltaH(fusion) + deltaH(vaporization)
Tue Mar 13, 2018 11:14 pm
Forum: First Order Reactions
Topic: Help on 15.3
Replies: 7
Views: 418

### Re: Help on 15.3

if you convert all given mmol values to mol values and then run the calculation, you should get the correct answer as given in the solutions manual
Tue Mar 13, 2018 11:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow and Fast Steps
Replies: 2
Views: 176

### Re: Slow and Fast Steps

We may be given K values or will be told which is step is the fast or slow one. Always remember the slow step is the rate-determining step.
Tue Mar 13, 2018 11:10 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Reversible or irreversible?
Replies: 2
Views: 319

### Re: Reversible or irreversible?

We know the reaction is isothermal because it takes place in a thermally insulated vessel. At a constant temperature, these reactions are usually reversible
Tue Mar 13, 2018 11:08 pm
Forum: General Rate Laws
Topic: Unique Reaction Rates [ENDORSED]
Replies: 32
Views: 61640

### Re: Unique Reaction Rates[ENDORSED]

The unique reaction rate depends on the coefficients of the reaction
Fri Feb 23, 2018 10:58 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Nernst Equation
Replies: 6
Views: 355

### Re: Nernst Equation

Be sure to remember with nr that the unit "mol" isn't incorporated
Fri Feb 16, 2018 11:05 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Units of S and H
Replies: 4
Views: 423

### Re: Units of S and H

Hi Megan!
Although sometimes understanding the units can be quite difficult, in class, Dr. Lavelle mentioned either unit would be correct.
Just be sure to make the units for your Gibbs Free Energy of formation to be in "per mole".
Good luck!
Mon Feb 12, 2018 4:39 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy and Spontaneity
Replies: 2
Views: 205

### Re: Gibbs Free Energy and Spontaneity

Yes with a positive deltaG, the reaction is not spontaneous in the forward direction but will be spontaneous if reversed.
With a negative deltaG, the reaction IS spontaneous in the forward direction but not so if reversed.
Mon Feb 12, 2018 4:36 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Calculations on Internal Energy
Replies: 4
Views: 255

### Re: Calculations on Internal Energy

Calculations about internal energy and work were omitted from the first test because Dr. Lavelle felt we had not covered it as well as we needed to at the time.
He expects us to be able to do calculations for both internal energy and work on the midterm!
Mon Feb 12, 2018 4:33 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Useful Summary of Thermodynamic Definitions
Replies: 23
Views: 13766

### Re: Useful Summary of Thermodynamic Definitions

To clarify, intensive properties are ratios. For example, density would be an intensive property because it is mass/volume. Where mass and volume are both extensive properties.