Search found 74 matches
- Sat Mar 17, 2018 4:12 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: wmax
- Replies: 4
- Views: 793
Re: wmax
I think it is just delta G, but that being said, wmax=deltaG when pressure and temperature are constant.
- Sat Mar 17, 2018 4:06 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Reversible reactions
- Replies: 1
- Views: 413
Re: Reversible reactions
If you are referring to reversible expansion, in our case, almost always will reversible reactions be isothermal. Usually tests and problems state them together.
- Sat Mar 17, 2018 4:04 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Writing Cell Diagrams
- Replies: 2
- Views: 380
Re: Writing Cell Diagrams
On the anode side, write the element that is getting reduced first, then its reduced state. On the cathode side, write the element getting oxidized, and then its oxidized state.
- Thu Mar 15, 2018 7:37 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard Enthalpy of combustion
- Replies: 2
- Views: 521
Re: Standard Enthalpy of combustion
I believe that would be correct!
- Thu Mar 15, 2018 7:35 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat curve
- Replies: 2
- Views: 530
Re: Heat curve
Conceptually, if a metal has a lower specific heat, it should take less time to get to the same temperature as a metal with a higher one, giving it a steeper slope.
- Thu Mar 15, 2018 7:30 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: 9.101 (b)
- Replies: 2
- Views: 430
Re: 9.101 (b)
a. The entropy of the inside is increasing due to the fact that heat is getting pumped into the system. The entropy of the outside is decreasing as it is losing heat. The inside change is greater due to higher change in temperature (the outside does not change in temperature by much).
- Wed Mar 07, 2018 9:19 am
- Forum: First Order Reactions
- Topic: Pseudo First Order Reactions
- Replies: 2
- Views: 424
Re: Pseudo First Order Reactions
I would think they would give you details about using a pseudo first order.
- Mon Mar 05, 2018 2:36 pm
- Forum: General Rate Laws
- Topic: 3rd order, 4th order, etc.
- Replies: 5
- Views: 1830
Re: 3rd order, 4th order, etc.
Seeing as it hasn't been covered too in depth in lecture, I would not think we need to know the half lives.
- Mon Mar 05, 2018 2:34 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Catalyst in a Equilibria
- Replies: 2
- Views: 338
Catalyst in a Equilibria
If you apply a catalyst to a system that has both a forward and a reverse reaction, does the catalyst have an effect on the activation energy for both sides?
- Mon Mar 05, 2018 2:29 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Which Step is Slower?
- Replies: 8
- Views: 891
Re: Which Step is Slower?
Many times, a problem will give you mechanisms, and in turn tell you explicitly which step is the slow mechanism.
- Mon Mar 05, 2018 2:28 pm
- Forum: General Rate Laws
- Topic: Order?
- Replies: 3
- Views: 427
Re: Order?
To elaborate, essentially if you take two experiments and only change one initial concentration of reactant, you can observe how the rate of the rxn is affected, thus determining the order in respect to the reactant you altered.
- Sun Feb 25, 2018 9:05 pm
- Forum: General Rate Laws
- Topic: Rate Constants
- Replies: 4
- Views: 632
Re: Rate Constants
You could also relate this to our delta g equation last chapter as the higher the temperature is with a positive delta s, the more favorable a reaction is.
- Sun Feb 25, 2018 9:03 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Initial Rates
- Replies: 3
- Views: 439
Re: Initial Rates
I am pretty sure I heard lavelle reference that we would learn that at a later date.
- Sun Feb 25, 2018 9:02 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 14.13 part d
- Replies: 2
- Views: 336
Re: 14.13 part d
Au becomes a reactant because you flip the anode half reaction.
- Sun Feb 18, 2018 9:02 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Open System
- Replies: 5
- Views: 934
Re: Open System
A good way to remember is that an open system is 'open to the surrounding' meaning the system is able to lose some of its particles, or gain some from the surroundings.
- Wed Feb 14, 2018 3:25 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Choosing Cp or Cv [ENDORSED]
- Replies: 3
- Views: 526
Re: Choosing Cp or Cv [ENDORSED]
I think usually it can be implied because one of two is usually changing, thus you would use the other.
- Tue Feb 13, 2018 10:06 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Super basic question about systems
- Replies: 1
- Views: 203
Re: Super basic question about systems
It is a closed system because no matter can leave/enter the system, however, energy can, thus, it is a closed system.
- Tue Feb 13, 2018 9:37 pm
- Forum: Calculating Work of Expansion
- Topic: Expansion against a vacuum [ENDORSED]
- Replies: 1
- Views: 295
Expansion against a vacuum [ENDORSED]
When you expand against a vacuum, can there be energy still transferred in the form of heat?
- Tue Feb 13, 2018 4:57 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Boiling point at room temperature
- Replies: 5
- Views: 610
Boiling point at room temperature
When you are finding the boiling point of water at room temperature, why do you have to cool the water back down to room temperature?
- Mon Feb 12, 2018 10:30 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Test 1 Question 1c
- Replies: 3
- Views: 378
Re: Test 1 Question 1c
No, the bond enthaply method is less accurate because it is an average energy released between the bond between two atoms across a multitude of molecules.
- Sun Feb 11, 2018 9:07 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: q vs delta H
- Replies: 2
- Views: 403
Re: q vs delta H
deltaH is equal to q at constant pressure.
- Sun Feb 11, 2018 9:06 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Practice Midterm from Sunday's Review Sess - #3C
- Replies: 3
- Views: 427
Re: Practice Midterm from Sunday's Review Sess - #3C
You can still calculate it by taking values and equations you know already. Because deltaS is a state function, you can take multiple steps to get there rather than just one. Just because water is not boiling at room temp, you can still find it the entropy of vaporization.
- Sun Feb 11, 2018 9:02 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Irreversible vs Reversible
- Replies: 3
- Views: 452
Re: Irreversible vs Reversible
If the pressure is constant, you known the process is irreversible.
- Fri Feb 09, 2018 6:06 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: delta U [ENDORSED]
- Replies: 10
- Views: 2982
Re: delta U [ENDORSED]
Not necessarily. There can be work done.
- Sun Feb 04, 2018 11:44 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: 9.31
- Replies: 2
- Views: 363
Re: 9.31
I would assume that we will be given that information as he has given us other similar information on prior tests.
- Sun Feb 04, 2018 11:41 pm
- Forum: Van't Hoff Equation
- Topic: Equation
- Replies: 4
- Views: 626
Re: Equation
I believe he said it is more commonly used in the form that he stated, and that it is more applicable.
- Sun Feb 04, 2018 11:40 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Constant K and reaction quotient
- Replies: 3
- Views: 469
Re: Constant K and reaction quotient
So if Q=K, then a system is at equilibrium. If Q>K, then the system will favor the reverse because that means there is too much product (higher the value the more it favors the products. If Q<K, then the system will favor the forward reaction.
- Sun Feb 04, 2018 11:38 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Delta S vs Delta U [ENDORSED]
- Replies: 5
- Views: 2882
Re: Delta S vs Delta U [ENDORSED]
Delta U represents the internal energy of a system, whether that is in the form of heat or work while Delta S represent the variability of different states that a molecule can be in (relating to degeneracy). Furthermore, Delta U uses strictly Jules as units while Delta S uses J/degree K.
- Sun Feb 04, 2018 11:36 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Equations
- Replies: 3
- Views: 461
Re: Equations
Delta G represent free energy which is essentially saying the energy that is able to perform work. Thus the max amount of work a system can do corresponds to the free energy of the system.
- Sun Feb 04, 2018 11:34 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Sig Figs
- Replies: 6
- Views: 706
Re: Sig Figs
One thing I would say is to wait to round with sig figs until your final answer!
- Sun Feb 04, 2018 11:33 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: test question 5
- Replies: 5
- Views: 672
Re: test question 5
Because neither energy nor matter can be added to system, nor can it leave the container. Just because a system is isolated does not mean that it cannot have heat or energy already in the system, but rather that it cannot be lost/gained.
- Sun Feb 04, 2018 11:30 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm
- Replies: 5
- Views: 716
Re: Midterm
In 14a, Dr. Lavelle made an announcement before the midterm stating which exact topics would be covered on the midterm.
- Sun Feb 04, 2018 11:29 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: 9.37 d
- Replies: 1
- Views: 163
Re: 9.37 d
I believe it is because KCl is a very ordered crystal, giving it a lower entropy than KClO4 and KClO3 has less variability in where the Cl can be than KClO4, thus also resulting in lower entropy.
- Sun Feb 04, 2018 11:25 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Friday Lecture Concept
- Replies: 2
- Views: 276
Re: Friday Lecture Concept
I was under the impression that we really only care about systems at equilibrium because biological systems are at equilibrium. I believe that he just made the reference that if Gn=Gp then the equilibrium is not at equilibrium.
- Sun Feb 04, 2018 11:22 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Test 1 Question
- Replies: 4
- Views: 593
Re: Test 1 Question
An isolated system just means that energy can not be released/gained in the system. That does not mean that there can't be energy already in the system, and in this case, that energy is in the form of heat.
- Tue Jan 30, 2018 10:12 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: 9.27 A
- Replies: 5
- Views: 654
Re: 9.27 A
The more particles the molecule has, the higher the molar entropy. Because HBr is a bigger molecule (thus more particles) it will have the higher molar entropy.
- Tue Jan 30, 2018 10:10 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 9.11
- Replies: 4
- Views: 596
Re: 9.11
I believe it is because the starting equation is deltaS=nRTln(V2/V1) with volumes instead of pressure. If we apply Boyle's law that Pressure and Volume are inversely proportional (V1P1=V2P2) then we would be able to inverse the volumes to be pressures, thus deltaS=nRTln(P1/P2). To my knowledge, that...
- Mon Jan 29, 2018 11:16 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: 9.27a
- Replies: 4
- Views: 452
Re: 9.27a
More particles usually results in a higher entropy, which would explain why HBr (being the bigger molecule) has the higher entropy.
- Mon Jan 29, 2018 11:14 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: 9.23 Determining what has higher entropy state
- Replies: 4
- Views: 640
Re: 9.23 Determining what has higher entropy state
Because there are only F atoms around the B, there is no variability in how the molecule is structured. However, with COF2, the Oxygen atom can be in one of three places, which causes a higher molar entropy.
- Mon Jan 29, 2018 11:11 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropies of Condensation
- Replies: 2
- Views: 300
Re: Entropies of Condensation
I am fairly certain that the signs are just flipped.
- Mon Jan 29, 2018 11:06 pm
- Forum: General Science Questions
- Topic: Significant Figures
- Replies: 2
- Views: 674
Re: Significant Figures
I think a helpful tip to avoid this confusion is to always convert to Kelvin when working with entropy!
- Fri Jan 26, 2018 2:39 pm
- Forum: Calculating Work of Expansion
- Topic: Irreversible expansion
- Replies: 4
- Views: 405
Re: Irreversible expansion
A gas prefers to be at a lower pressure, and thus a higher volume. If it is able to do work to get to a lower pressure, it will stay there, making the process irreversible.
- Fri Jan 26, 2018 2:36 pm
- Forum: Phase Changes & Related Calculations
- Topic: When to use Kelvin or Celsius
- Replies: 10
- Views: 6774
Re: When to use Kelvin or Celsius
For the most part, in thermochem we use a change in temperature, which means either kelvin or celsius will work considering they use the same scale. That being said, the ideal gas law uses kelvin.
- Sun Jan 21, 2018 8:21 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.31
- Replies: 3
- Views: 460
Re: 8.31
part b
- Sun Jan 21, 2018 8:19 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.31
- Replies: 3
- Views: 460
8.31
I am struggling a bit on problem 8.31. Could someone explain how to approach this question?
- Sun Jan 21, 2018 8:17 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Intensive vs. Extensive Properties
- Replies: 4
- Views: 597
Re: Intensive vs. Extensive Properties
Put more simply, the specific heat of water will be the same in a 1g sample and a 1000g sample. Essentially, the property does not differ due to the amount of sample present.
- Sun Jan 21, 2018 8:17 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Intensive vs. Extensive Properties
- Replies: 4
- Views: 597
Re: Intensive vs. Extensive Properties
Put more simply, the specific heat of water will be the same in a 1g sample and a 1000g sample. Essentially, the property does not differ due to the amount of sample present.
- Sun Jan 21, 2018 7:56 pm
- Forum: Calculating Work of Expansion
- Topic: What do these variables mean?
- Replies: 4
- Views: 457
Re: What do these variables mean?
Those are correct!
- Sat Jan 13, 2018 7:49 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Intensive vs Extensive [ENDORSED]
- Replies: 4
- Views: 375
Re: Intensive vs Extensive [ENDORSED]
Also to add, extensive properties are just things that we can alter about the substance not just the amount.
- Fri Jan 12, 2018 2:47 pm
- Forum: Phase Changes & Related Calculations
- Topic: Heating Curve
- Replies: 6
- Views: 523
Re: Heating Curve
The length of the sloped lines will just represent the time it takes(horizontal) or the amount of temperature change after a phase change(vertical)
- Fri Jan 12, 2018 2:44 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Can homework be written in pencil?
- Replies: 6
- Views: 599
Re: Can homework be written in pencil?
I would suggest doing homework in pen to practice for tests and finals, that do require pen, however, I do not think points would be taken off if you used pencil.
- Sat Dec 09, 2017 5:35 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Remembering VSEPR
- Replies: 3
- Views: 625
Re: Remembering VSEPR
Try to study the shapes in groups of the amount of bonding regions, that way when you substitute a lone pair for a bond, you will know the still know the shape.
- Tue Dec 05, 2017 6:50 am
- Forum: Lewis Acids & Bases
- Topic: Classifying Oxides as Amphoteric
- Replies: 3
- Views: 525
Re: Classifying Oxides as Amphoteric
An easy way to tell is if the molecule has both an acidic functional group and an acidic functional group. For example, most amino acids will have both. Another easy way to tell is if when a conjugate base to an acid still has a hydrogen in the molecule. HCO3^- can both accept a proton and give on a...
- Tue Dec 05, 2017 6:43 am
- Forum: Conjugate Acids & Bases
- Topic: HW 12.3 c
- Replies: 2
- Views: 451
Re: HW 12.3 c
I believe that is because H2PO4^2- is a more stable ion than H3PO4 is. Thus, the atom would be more likely to donate, so it would gain more stability.
- Tue Nov 28, 2017 12:59 pm
- Forum: Hybridization
- Topic: Hybridization and lone pairs
- Replies: 3
- Views: 517
Re: Hybridization and lone pairs
Yes you can consider lone pairs as a region of electron density! For example, H2O has two lone pairs but still has a hybridization of sp3.
- Tue Nov 28, 2017 12:56 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 4.19 b
- Replies: 3
- Views: 466
Re: 4.19 b
I believe that is just a mistake in the book because the hybridization of the molecule is sp, implying that the molecule is linear.
Re: Naming
I believe we are going to need to know the most common ligates from memory.
- Wed Nov 22, 2017 11:04 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K and Kc
- Replies: 7
- Views: 1034
Re: K and Kc
They are essentially the same thing. If you are given just K, you can usually infer whether to use concentration or partial pressure by what you are given in the problem.
- Wed Nov 22, 2017 11:02 am
- Forum: Naming
- Topic: di, bis, tri, tris, etc
- Replies: 4
- Views: 580
Re: di, bis, tri, tris, etc
Just to emphasize, polydentate refers to molecules that connect to the central atoms at multiple points.
- Wed Nov 15, 2017 2:32 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Specifying molecular geometry
- Replies: 3
- Views: 459
Re: Specifying molecular geometry
I would venture to say you will never have to verify the derivation of the molecular structure, but rather just what it is.
- Wed Nov 15, 2017 2:29 pm
- Forum: Electronegativity
- Topic: Isoelectronic [ENDORSED]
- Replies: 11
- Views: 1470
Re: Isoelectronic [ENDORSED]
However, these elements will have varying atomic radii.
- Wed Nov 15, 2017 2:25 pm
- Forum: Lewis Structures
- Topic: Unrelated midterm question
- Replies: 2
- Views: 416
Re: Unrelated midterm question
I believe there is a link on Lavelle's website about the midterm and possible partial credit.
- Wed Nov 15, 2017 2:09 pm
- Forum: Sigma & Pi Bonds
- Topic: Sigma and pi
- Replies: 12
- Views: 1550
Re: Sigma and pi
Yes and this is due to the molecule having a non-hybrid p orbital.
- Wed Nov 15, 2017 2:07 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Electron geometry vs molecular geometry
- Replies: 2
- Views: 264
Re: Electron geometry vs molecular geometry
I would be prepared to identify both, as both have been covered.
- Wed Nov 15, 2017 2:06 pm
- Forum: Hybridization
- Topic: Hybridization beyond d orb
- Replies: 1
- Views: 180
Re: Hybridization beyond d orb
The f orbitals are extremely complex, with some shapes looking like a double sided pacifier.
- Wed Nov 15, 2017 2:05 pm
- Forum: Octet Exceptions
- Topic: Why do octets expand?
- Replies: 4
- Views: 571
Re: Why do octets expand?
They are able to expand their valence shells by adding electrons to the d orbital!
- Mon Nov 06, 2017 12:30 am
- Forum: Lewis Structures
- Topic: Lewis Structures
- Replies: 10
- Views: 1063
Re: Lewis Structures
I think if there are possible resonance structures, the potential question will instruct you to include how many or at least inform you there are multiple structures.
- Sun Nov 05, 2017 12:45 pm
- Forum: Lewis Structures
- Topic: Lewis Structures for Molecules with Expanded Octet
- Replies: 1
- Views: 296
Re: Lewis Structures for Molecules with Expanded Octet
Personally, I think it would be smart to model your Lewis structure to match the VSEPR shape just to incorporate both in your answer, but I don't think it would be incorrect to just put the lone pair on top, with four surrounding bonds for SF4.
- Fri Oct 20, 2017 11:01 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: s-,p-, d-, and f- orbitals
- Replies: 7
- Views: 1328
Re: s-,p-, d-, and f- orbitals
In essence and put simply, all the four different orbitals have different shapes relating to their axes. S has very simplistic orbitals, while f has very complex ones.
- Fri Oct 20, 2017 10:58 am
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg Uncertainty
- Replies: 1
- Views: 284
Re: Heisenberg Uncertainty
When using the uncertainty equation, you in fact use the uncertainty given rather than the certainty. So in this case, you would use the 0.1
- Fri Oct 13, 2017 5:54 pm
- Forum: *Black Body Radiation
- Topic: Blackbody
- Replies: 2
- Views: 555
Re: Blackbody
From what I understand, a blackbody is an object that absorbs all frequencies of visible light, and does not reflect any of them. An example would be glass. It is useful because we are able to study light with them.
- Fri Oct 13, 2017 5:34 pm
- Forum: Photoelectric Effect
- Topic: Difference Between Work Function and the Energy Required to Remove an Electron from one Atom [ENDORSED]
- Replies: 4
- Views: 1016
Re: Difference Between Work Function and the Energy Required to Remove an Electron from one Atom [ENDORSED]
The question asked for the energy for a single atom, not for a mole of sodium, while the work function was given in KJ/mol. In order to find the energy for a singular atom, divide the work function by Avogadro's number (6.022* 10^23)
- Wed Oct 04, 2017 10:08 am
- Forum: Significant Figures
- Topic: Sig Figs in 0.0380 [ENDORSED]
- Replies: 5
- Views: 975
Re: Sig Figs in 0.0380 [ENDORSED]
Zeroes are only considered significant figures when they are "sandwiched" between two non-zero numbers or a non-zero number and decimal point ( ex. 505, 9.09, 50.); or if it is at the end of decimal showing precision (34.0).
- Wed Oct 04, 2017 9:50 am
- Forum: General Science Questions
- Topic: Sig Figs
- Replies: 9
- Views: 1707
Sig Figs
When doing a problem that does not have any number values in the question but uses molar masses that extend to 4 sig figs, should you use the standard 3 sig figs in your answer or 4 sig figs coming from the molar masses?