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Fri Mar 16, 2018 1:00 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Which is which k?
Replies: 4
Views: 313

Re: Which is which k?

It shouldn't matter. As long as you make sure to make the T' and k' line up correctly in the formula. -Ln(k'/k)=Ln(k/k')
Fri Mar 16, 2018 12:58 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 6
Views: 327

Re: 15.63

Assuming the other posts about this are correct, the solutions manual has an error. It should be LnK=.59, so the .59 is not actually subtracted.
Fri Mar 16, 2018 12:53 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63 How to know what A is
Replies: 7
Views: 554

Re: 15.63 How to know what A is

if you think about it, If A=1, then Ln(A) should be 0. I'm not sure if this is correct, but its the way I think of it.
Fri Mar 09, 2018 4:13 pm
Forum: General Rate Laws
Topic: Reaction Rates
Replies: 4
Views: 419

Re: Reaction Rates

Yes, the way I think of it is: a rate is something changing. The opposite of change is not a negative change.
Fri Mar 09, 2018 4:11 pm
Forum: General Rate Laws
Topic: Units
Replies: 11
Views: 923

Re: Units

When working with rate laws, it is not necessary to convert to Si units immediately but is done to simplify/ make the answer more relevant. If you choose not to, just make sure to properly perform dimensional analysis to give your answer the proper units.
Fri Mar 09, 2018 4:04 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Effect of Activation Energy on a Reaction [ENDORSED]
Replies: 2
Views: 192

Re: Effect of Activation Energy on a Reaction[ENDORSED]

As temperature increases, the movement of molecules generally increases along with it. This allows the molecules to collide more frequently by increasing the coefficient of the collision frequently. With more collisions, molecules become more likely to collide at the correct angle with enough energy...
Sat Mar 03, 2018 2:29 pm
Forum: General Rate Laws
Topic: Test 3
Replies: 3
Views: 298

Re: Test 3

43 is a good number to stop at. In lecture, Lavelle mentioned that mechanics onward would not be on the exam.
Sat Mar 03, 2018 2:27 pm
Forum: First Order Reactions
Topic: Psuedo 1st order rate law [ENDORSED]
Replies: 2
Views: 231

Re: Psuedo 1st order rate law[ENDORSED]

The post above me explains it well. The pseudo rate law assumes two of the variables are in excess allowing us to reduce the number of variables in our equation, simplifying the calculation.
Sat Mar 03, 2018 2:23 pm
Forum: Zero Order Reactions
Topic: Zero Order Reactions and Rate of Reaction
Replies: 5
Views: 406

Re: Zero Order Reactions and Rate of Reaction

Yes, the answers above describe it well. The way I think if it, zero order reactions aren't affected by the reaction and as a result don't change. Therefore, graphing it would be a straight line with a slope of 0.
Fri Feb 23, 2018 11:54 pm
Forum: Balancing Redox Reactions
Topic: Half Reaction Order
Replies: 9
Views: 2262

Re: Half Reaction Order

It depends on what you are going to do with the half reactions. If you are doing it simply to determine the number of electrons being exchanged or identifying the anode and cathode while finding the standard potential, then the direction of your reactions shouldn't matter.
Fri Feb 23, 2018 11:51 pm
Forum: Balancing Redox Reactions
Topic: Acidic and Basic Solution
Replies: 3
Views: 289

Re: Acidic and Basic Solution

Its usually in acidic conditions, as many modern batteries are in acidic solutions. If it were in basic conditions it would state so.
Fri Feb 23, 2018 11:49 pm
Forum: Balancing Redox Reactions
Topic: Gibbs free energy of half reactions
Replies: 4
Views: 401

Re: Gibbs free energy of half reactions

Yes we can. Gibbs free energy is a state function because it is defined by other state functions. Therefore it can be added together to find the free energy of the reaction.
Fri Feb 16, 2018 6:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Equilibrium
Replies: 4
Views: 255

Re: Equilibrium

From my understanding, it stops because as it reaches equilibrium the chemical/electrical gradient becomes smaller until it disappears and begins to grow when it passes equilibrium.
Fri Feb 16, 2018 6:08 pm
Forum: Balancing Redox Reactions
Topic: electrons
Replies: 3
Views: 206

Re: electrons

Yes, because the electrons need to be on both sides so they can be canceled out. If one side does not have electrons, I would double check or consider if the half reaction I identified was incorrect.
Fri Feb 16, 2018 6:02 pm
Forum: Balancing Redox Reactions
Topic: Balancing redox rxns [ENDORSED]
Replies: 7
Views: 507

Re: Balancing redox rxns[ENDORSED]

I don't know if this is of any help, but I start by identifying the two half-reactions and identifying the difference in electrons, then I balance it as if I were using hess's law.
Fri Feb 09, 2018 10:50 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Kelvin
Replies: 4
Views: 347

Re: Kelvin

For the homework problems, it is safe to assume that you always have to convert to Kelvin. However, if you are finding the change in temperature, you can choose to stay in C rather than K because 273 will be added to both addends.
Fri Feb 09, 2018 10:46 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.1
Replies: 4
Views: 363

Re: 9.1

The solutions manual uses the entropy generation formula which has a negative answer because the system will be releasing entropy. But the question asks for the rate of entropy your body generates. So we are answering the question, at what rate is the entropy in our surrounding changing, which would...
Fri Feb 09, 2018 10:29 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15
Replies: 4
Views: 362

Re: 9.15

Delta H fus is negative because the phase change is going from a liquid to a solid. Since a solid has less possible positions for its atoms, there is less entropy. So the system is losing entropy when it freezes.
Fri Feb 02, 2018 1:54 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Lunchbox?
Replies: 3
Views: 327

Re: Lunchbox?

A lunch box would be an attempt at an isolated system, though in practice it is not. If it were on a test, I believe they will make it clear that they mean a very insulated lunch box or not.
Fri Feb 02, 2018 1:50 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: sign of q
Replies: 7
Views: 619

Re: sign of q

I also have trouble with the sign of q. I found that it helps me to try to think whether the q applies to the system or surrounding and determine what is losing and what is gaining.
Fri Feb 02, 2018 1:49 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.13
Replies: 5
Views: 341

Re: 9.13

I agree that this question was poorly worded. However, aside from its flaw of failing to mention the number of moles, it is a relatively straight-forward, good question. It forces us to recall the properties of an ideal gas and standard conditions.
Fri Jan 26, 2018 5:33 pm
Forum: Calculating Work of Expansion
Topic: Work Equation
Replies: 3
Views: 269

Re: Work Equation

w=integralPdV and w=-PdV mean the same thing. This is because the integral is simply the sum of all pressures as the limit between them approaches zero. So when pressure is constant, we no longer need the integral and can use the formula w=-PdV.
Fri Jan 26, 2018 5:27 pm
Forum: Calculating Work of Expansion
Topic: 8.17 Work done by a system
Replies: 6
Views: 411

Re: 8.17 Work done by a system

Work is negative because when we work with systems that have zero internal energy, the q and w cancel out. Because in the formula U=q+w they are both on the same side, we can manipulate q=-w when U=0.
Fri Jan 26, 2018 5:25 pm
Forum: Calculating Work of Expansion
Topic: 8.93
Replies: 3
Views: 200

Re: 8.93

The reaction takes place at room temperature, and water at room temperature is liquid.
Sat Jan 20, 2018 4:33 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Change Question
Replies: 3
Views: 265

Re: Phase Change Question

Hvap = kJ/moles is what the book gives as the value of enthalpy of vaporization. For the question, we are given a value in kJ and in moles. Just put those value into the formula to get the answer.
Sat Jan 20, 2018 4:22 pm
Forum: Phase Changes & Related Calculations
Topic: Calculating the Enthalpy of Vaporization
Replies: 2
Views: 238

Re: Calculating the Enthalpy of Vaporization

To solve this problem I find that it is easiest to use the definition of the enthalpy of vaporization which is as follows: Hvap=kJ/moles. Since we are given kJ and the moles, it becomes a plug and chug question.
Sat Jan 20, 2018 4:15 pm
Forum: Phase Changes & Related Calculations
Topic: 8.13
Replies: 3
Views: 230

Re: 8.13

In this question the q(of the cylinder) = -w(of the fuel). Which is why when calculating the work of the fuel, the value of q is negative.
Fri Jan 12, 2018 2:19 pm
Forum: Phase Changes & Related Calculations
Topic: Exothermic Rxn
Replies: 6
Views: 518

Re: Exothermic Rxn

The method explained in class is the most common and easiest way to determine if a reaction is exo- or endo- thermic because it uses the definition. If the reaction produces/releases heat to the surroundings it is exothermic, and if it absorbs heat it is endothermic.
Fri Jan 12, 2018 2:15 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.41
Replies: 2
Views: 104

Re: Question 8.41

The method that the solutions manual uses for phase changes uses the molar heat capacity because it is the one we use with Hfus. The specific heat is also used for the second half of the question because the information we were given is in grams, making specific heat easier to use.
Fri Jan 12, 2018 1:58 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Change Calculations
Replies: 2
Views: 221

Re: Phase Change Calculations

For the tests, we will be given all the constants. Just make sure you know how to use them. The textbook provides very helpful tables which provide all the constants you will need to do the hw. To my knowledge, lavelle doesn't make us memorize anything.
Fri Dec 08, 2017 10:47 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Pka and Pkb values
Replies: 2
Views: 309

Re: Pka and Pkb values

If there is a question on the final regarding Pka and Pkb values, just make sure you know how to use/find those values. All the constants and equations are always given.
Fri Dec 08, 2017 10:40 am
Forum: Lewis Acids & Bases
Topic: Bronsted vs. Lewis
Replies: 6
Views: 464

Re: Bronsted vs. Lewis

Acids are both bronsted acids and lewis acids. The difference between the two are what defines them as acids. Using the lewis definition we look at the electron pairs, and the bronsted look at the protons. Essentially they are the same thing, just described differently.
Fri Dec 01, 2017 10:35 am
Forum: Properties & Structures of Inorganic & Organic Bases
Topic: Weak Bases
Replies: 4
Views: 898

Re: Weak Bases

Wayland Leung wrote:How do you determine just by looking at a molecule that it is a weak base?

I'm not quite sure, but I do know that there is chart towards the end of the course reader, right before the sample tests, listing common weak bases.
Fri Dec 01, 2017 10:21 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: which is more acidic
Replies: 3
Views: 631

Re: which is more acidic

the H3- is electron-donating relative to hydrogen and it donates electrons to the carboxyl group which makes it more negative. This causes the acid to be weaker, because the proton now has to be separated from a more negative conjugate base. likewise, CH3CH2- is more electron-donating than CH3-, an...
Sat Nov 25, 2017 5:17 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Homework question 17.33
Replies: 4
Views: 292

Re: Homework question 17.33

Timothy Kim 1F wrote:If the atoms have a formal charge of 0, it will not want to bind with anything, correct?

I may be mistaken, but I think that the potential to bind is not caused by the formal charge, but rather the presence of lone pairs on an atom.
Sat Nov 25, 2017 5:15 pm
Forum: Naming
Topic: Cyano vs Cyanido
Replies: 3
Views: 280

Re: Cyano vs Cyanido

As mentioned above, both are correct. If you choose not to use the naming from the textbook, go to the class website and you can find a list of the alternate accepted names.
Fri Nov 17, 2017 3:36 pm
Forum: Octet Exceptions
Replies: 2
Views: 260

No, they are not stable. It is very likely that another atom/molecule seeking to finish its valence shell with one electron will bond with the radical.
Fri Nov 17, 2017 3:33 pm
Forum: Dipole Moments
Topic: 4.25 part a
Replies: 2
Views: 249

Re: 4.25 part a

Alex is correct. Even if the molecule is symmetrical, it is still possible to be polar. The bond polarities, which can be determined by electronegativity, must be checked in order to determine this. A good example is HCN where despite being linear, is polar.
Sat Nov 11, 2017 9:29 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty Principle [ENDORSED]
Replies: 5
Views: 400

Re: Uncertainty Principle[ENDORSED]

An easy way to remember this is to think of delta v as the change in v like in math. So, we arent concerned with the value of v, but rather the difference between the two limits to its domain.
Sat Nov 11, 2017 9:20 am
Forum: Trends in The Periodic Table
Topic: 2.67 [ENDORSED]
Replies: 2
Views: 199

Re: 2.67[ENDORSED]

A quick way to know which element has a higher electron affinity is to look at the number of valence electrons it has. Chlorine has 7; whereas nitrogen has 5. Therefore, Chlorine is going to hold its outer electrons more strongly.
Fri Nov 03, 2017 10:19 am
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 10
Views: 687

Re: Lewis Structures

Depending on the wording of the question, it may be more appropriate to draw the most stable Lewis Structure rather than all of the resonance structures. However, if the question asks specifically for resonance structures the list as many as you can. Usually, there aren't too many.
Fri Nov 03, 2017 10:14 am
Forum: Lewis Structures
Topic: Expanded rules
Replies: 4
Views: 198

Re: Expanded rules

When finding the lewis structure of SO 4 2- , it can be drawn where each oxygen has a single bond with sulfur. However, the most stable diagram is one where sulfur has 12 valence electrons and 2 of the oxygen atoms have double bonds with sulfur while the other 2 have single bonds. Are there elements...
Fri Oct 27, 2017 8:14 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3.5 HW Problem
Replies: 1
Views: 215

Re: 3.5 HW Problem

Cu was one of the exceptions that was discussed in lecture. The electron configuration of Cu takes an electron from the s orbital and places it in the d orbital in order to fill it because of pairing energies. Because you are working with Cu+, you take away another electron from the s orbital.
Mon Oct 23, 2017 4:55 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2.45 Part D
Replies: 1
Views: 132

2.45 Part D

45 gives us the electron configuration [Rn] 7s2 6d2. Initially I thought that the answer was rutherfordium; however, the correct answer is Thorium. Why is this the case?
Thu Oct 19, 2017 11:21 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Module Question 18
Replies: 3
Views: 444

Re: Module Question 18

Would you plug in the mass of a hydrogen atom? So the atomic mass 1.01? I haven't seen the original problem, but the way the question is described by the OP makes it seem as if you are finding the uncertainty of finding an electron. In which case, you would use the mass of an electron ("9.1x10...
Thu Oct 19, 2017 11:09 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: ch1 question 43
Replies: 8
Views: 769

Re: ch1 question 43

I believe that the difference in symbol between Planck's constant and h=h/2pi is denoted by a serif near the peak of the h. So if you see the letter h, it might be safe to assume it refers to Planck's constant.
Fri Oct 13, 2017 10:45 am
Forum: DeBroglie Equation
Topic: question on how to determine if something has wavelike properties.
Replies: 6
Views: 1305

Re: question on how to determine if something has wavelike properties.

Does this mean that even large objects like cars and balls still demonstrate wavelike behavior even though we can't visibly detect it? I believe it does. However, in one of the peer learning workshops, I recall the UA telling me that the DeBroglie equation generally only works with things that are ...
Fri Oct 13, 2017 10:41 am
Forum: Properties of Electrons
Topic: Energy Levels
Replies: 6
Views: 548

Re: Energy Levels

What causes electrons to move up in energy levels? I understand that once they have enough energy they can "hop" up or down energy levels, but what causes this change in energy?
Thu Oct 05, 2017 10:58 am
Forum: Limiting Reactant Calculations
Topic: Help with M9
Replies: 5
Views: 574

Re: Help with M9

In ionic equations, how do you know when to split up molecules (as Kourtney did for both reactant molecules) vs keeping molecules together? (Such as keeping Cu(OH)2 together in the products but splitting up 2NaNO3 to 2Na+ + 2NO3-? When in an aqueous solution, solubility rules apply. 2NaNO3 is solub...
Thu Oct 05, 2017 10:44 am
Forum: Limiting Reactant Calculations
Topic: L #39
Replies: 4
Views: 350

Re: L #39

For part B of this question, how is the name of the oxide determined? To my understanding, the roman numeral refers to the subscript of the metal. Why is SnO2 called tin(IV) oxide?

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