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by Charles Ang 1E
Fri Mar 16, 2018 1:00 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Which is which k?
Replies: 4
Views: 129

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')
by Charles Ang 1E
Fri Mar 16, 2018 12:58 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 6
Views: 162

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.
by Charles Ang 1E
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: 232

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.
by Charles Ang 1E
Fri Mar 09, 2018 4:13 pm
Forum: General Rate Laws
Topic: Reaction Rates
Replies: 4
Views: 142

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.
by Charles Ang 1E
Fri Mar 09, 2018 4:11 pm
Forum: General Rate Laws
Topic: Units
Replies: 11
Views: 475

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.
by Charles Ang 1E
Fri Mar 09, 2018 4:04 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Effect of Activation Energy on a Reaction [ENDORSED]
Replies: 2
Views: 68

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...
by Charles Ang 1E
Sat Mar 03, 2018 2:29 pm
Forum: General Rate Laws
Topic: Test 3
Replies: 3
Views: 130

Re: Test 3

43 is a good number to stop at. In lecture, Lavelle mentioned that mechanics onward would not be on the exam.
by Charles Ang 1E
Sat Mar 03, 2018 2:27 pm
Forum: First Order Reactions
Topic: Psuedo 1st order rate law [ENDORSED]
Replies: 2
Views: 97

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.
by Charles Ang 1E
Sat Mar 03, 2018 2:23 pm
Forum: Zero Order Reactions
Topic: Zero Order Reactions and Rate of Reaction
Replies: 5
Views: 168

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.
by Charles Ang 1E
Fri Feb 23, 2018 11:54 pm
Forum: Balancing Redox Reactions
Topic: Half Reaction Order
Replies: 9
Views: 187

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.
by Charles Ang 1E
Fri Feb 23, 2018 11:51 pm
Forum: Balancing Redox Reactions
Topic: Acidic and Basic Solution
Replies: 3
Views: 120

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.
by Charles Ang 1E
Fri Feb 23, 2018 11:49 pm
Forum: Balancing Redox Reactions
Topic: Gibbs free energy of half reactions
Replies: 4
Views: 142

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.
by Charles Ang 1E
Fri Feb 16, 2018 6:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Equilibrium
Replies: 4
Views: 78

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.
by Charles Ang 1E
Fri Feb 16, 2018 6:08 pm
Forum: Balancing Redox Reactions
Topic: electrons
Replies: 3
Views: 85

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.
by Charles Ang 1E
Fri Feb 16, 2018 6:02 pm
Forum: Balancing Redox Reactions
Topic: Balancing redox rxns [ENDORSED]
Replies: 7
Views: 185

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.
by Charles Ang 1E
Fri Feb 09, 2018 10:50 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Kelvin
Replies: 4
Views: 142

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.
by Charles Ang 1E
Fri Feb 09, 2018 10:46 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.1
Replies: 4
Views: 150

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...
by Charles Ang 1E
Fri Feb 09, 2018 10:29 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15
Replies: 4
Views: 152

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.
by Charles Ang 1E
Fri Feb 02, 2018 1:54 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Lunchbox?
Replies: 3
Views: 145

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.
by Charles Ang 1E
Fri Feb 02, 2018 1:50 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: sign of q
Replies: 7
Views: 188

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.
by Charles Ang 1E
Fri Feb 02, 2018 1:49 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.13
Replies: 5
Views: 150

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.
by Charles Ang 1E
Fri Jan 26, 2018 5:33 pm
Forum: Calculating Work of Expansion
Topic: Work Equation
Replies: 3
Views: 114

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.
by Charles Ang 1E
Fri Jan 26, 2018 5:27 pm
Forum: Calculating Work of Expansion
Topic: 8.17 Work done by a system
Replies: 6
Views: 209

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.
by Charles Ang 1E
Fri Jan 26, 2018 5:25 pm
Forum: Calculating Work of Expansion
Topic: 8.93
Replies: 3
Views: 99

Re: 8.93

The reaction takes place at room temperature, and water at room temperature is liquid.
by Charles Ang 1E
Sat Jan 20, 2018 4:33 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Change Question
Replies: 3
Views: 102

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.
by Charles Ang 1E
Sat Jan 20, 2018 4:22 pm
Forum: Phase Changes & Related Calculations
Topic: Calculating the Enthalpy of Vaporization
Replies: 2
Views: 108

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.
by Charles Ang 1E
Sat Jan 20, 2018 4:15 pm
Forum: Phase Changes & Related Calculations
Topic: 8.13
Replies: 3
Views: 107

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.
by Charles Ang 1E
Fri Jan 12, 2018 2:19 pm
Forum: Phase Changes & Related Calculations
Topic: Exothermic Rxn
Replies: 6
Views: 242

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.
by Charles Ang 1E
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: 82

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.
by Charles Ang 1E
Fri Jan 12, 2018 1:58 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Change Calculations
Replies: 2
Views: 141

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.
by Charles Ang 1E
Fri Dec 08, 2017 10:47 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Pka and Pkb values
Replies: 2
Views: 154

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.
by Charles Ang 1E
Fri Dec 08, 2017 10:40 am
Forum: Lewis Acids & Bases
Topic: Bronsted vs. Lewis
Replies: 6
Views: 216

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.
by Charles Ang 1E
Fri Dec 01, 2017 10:35 am
Forum: Properties & Structures of Inorganic & Organic Bases
Topic: Weak Bases
Replies: 4
Views: 664

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.
by Charles Ang 1E
Fri Dec 01, 2017 10:21 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: which is more acidic
Replies: 3
Views: 453

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...
by Charles Ang 1E
Sat Nov 25, 2017 5:17 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Homework question 17.33
Replies: 4
Views: 197

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.
by Charles Ang 1E
Sat Nov 25, 2017 5:15 pm
Forum: Naming
Topic: Cyano vs Cyanido
Replies: 3
Views: 161

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.
by Charles Ang 1E
Fri Nov 17, 2017 3:36 pm
Forum: Octet Exceptions
Topic: Radicals
Replies: 2
Views: 147

Re: Radicals

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.
by Charles Ang 1E
Fri Nov 17, 2017 3:33 pm
Forum: Dipole Moments
Topic: 4.25 part a
Replies: 2
Views: 136

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.
by Charles Ang 1E
Sat Nov 11, 2017 9:29 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty Principle [ENDORSED]
Replies: 5
Views: 282

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.
by Charles Ang 1E
Sat Nov 11, 2017 9:20 am
Forum: Trends in The Periodic Table
Topic: 2.67 [ENDORSED]
Replies: 2
Views: 157

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.
by Charles Ang 1E
Fri Nov 03, 2017 10:19 am
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 10
Views: 337

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.
by Charles Ang 1E
Fri Nov 03, 2017 10:14 am
Forum: Lewis Structures
Topic: Expanded rules
Replies: 4
Views: 140

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...
by Charles Ang 1E
Fri Oct 27, 2017 8:14 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3.5 HW Problem
Replies: 1
Views: 126

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.
by Charles Ang 1E
Mon Oct 23, 2017 4:55 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2.45 Part D
Replies: 1
Views: 111

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?
by Charles Ang 1E
Thu Oct 19, 2017 11:21 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Module Question 18
Replies: 3
Views: 318

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...
by Charles Ang 1E
Thu Oct 19, 2017 11:09 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: ch1 question 43
Replies: 8
Views: 524

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.
by Charles Ang 1E
Fri Oct 13, 2017 10:45 am
Forum: DeBroglie Equation
Topic: question on how to determine if something has wavelike properties.
Replies: 6
Views: 777

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 ...
by Charles Ang 1E
Fri Oct 13, 2017 10:41 am
Forum: Properties of Electrons
Topic: Energy Levels
Replies: 6
Views: 282

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?
by Charles Ang 1E
Thu Oct 05, 2017 10:58 am
Forum: Limiting Reactant Calculations
Topic: Help with M9
Replies: 5
Views: 313

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...
by Charles Ang 1E
Thu Oct 05, 2017 10:44 am
Forum: Limiting Reactant Calculations
Topic: L #39
Replies: 4
Views: 198

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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