Search found 53 matches

by Justin Chang 2K
Tue Mar 13, 2018 11:02 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: UV catalyst
Replies: 3
Views: 167

Re: UV catalyst

This is the steps:
NO+1/2 O^2-->NO^2
NO^2--> NO + O (under UV light)
O + O^2 --> O^3

Overall: 3/2 O^2--> O^3

NO is the catalyst because it is first consumed, and then produced.
NO2 is the intermediate it is first produced, and then consumed.
by Justin Chang 2K
Tue Mar 13, 2018 11:00 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: UV catalyst
Replies: 3
Views: 167

Re: UV catalyst

NO is the catalyst. The reaction needs to occur under UV light.
by Justin Chang 2K
Tue Mar 13, 2018 10:58 pm
Forum: *Alkanes
Topic: Naming compounds
Replies: 3
Views: 2695

Re: Naming compounds

We are only expected to be able to recognize functional groups. I assume he will give us a compound (for example, CH3CH2CH2COOH) and ask us to identify functional groups (in this case, carboxylic acid). I don't think naming organic compounds will be on the final.
by Justin Chang 2K
Tue Mar 13, 2018 10:56 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: catalysts
Replies: 5
Views: 235

Re: catalysts

I am not completely sure, but I think catalysts can appear in the rate law. If there is more of the catalyst, then it makes sense that the rate would be faster since more catalysts are able to catalyze more reactions and thus the rate is faster.
by Justin Chang 2K
Wed Mar 07, 2018 5:54 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Method of initial rate vs more than one reactant
Replies: 2
Views: 144

Re: Method of initial rate vs more than one reactant

If you have, say, A+B-->C, the rate would be in the form of k[A]^n[B]^m. In order to determine n, you need to see how [A] changes over time. This can be done by making the concentration of [B] extremely high, so it can be regarded as a constant. If it is regarded as a constant, then that means the r...
by Justin Chang 2K
Wed Mar 07, 2018 5:40 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.51
Replies: 6
Views: 234

Re: 15.51

It is important to not think that the rate is based on the stoichiometric coefficients. Usually, the rate will NOT agree with the stoichiometric coefficients of the balanced equation. If they do, that's merely coincidence.
by Justin Chang 2K
Wed Mar 07, 2018 5:36 pm
Forum: General Rate Laws
Topic: Psuedo Rate Laws
Replies: 1
Views: 98

Re: Psuedo Rate Laws

I'm not sure, but I would understand how to do it incase it comes up on the final.
by Justin Chang 2K
Fri Mar 02, 2018 1:38 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units for the Different Order Reactions [ENDORSED]
Replies: 2
Views: 164

Re: Units for the Different Order Reactions [ENDORSED]

Yes, the units for the rate constants will change depending on what the order of the reaction is. I find it helpful to always include units in your calculations so you know what the units for the rate constant should be.
by Justin Chang 2K
Fri Mar 02, 2018 1:36 am
Forum: First Order Reactions
Topic: After Integration [ENDORSED]
Replies: 3
Views: 171

Re: After Integration [ENDORSED]

Yeah, zero and first order reactions both have a -kt, but second order reactions have +kt.
by Justin Chang 2K
Fri Mar 02, 2018 1:34 am
Forum: General Rate Laws
Topic: Deriving integrated rate laws
Replies: 4
Views: 189

Re: Deriving integrated rate laws

Yeah, since both differential and integrated rate laws are provided on the equations, I would just worry about memorizing which equation relates to zero order, first order, and second order.
by Justin Chang 2K
Wed Feb 21, 2018 10:33 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.17 Potassium Permanganate?
Replies: 3
Views: 152

Re: 14.17 Potassium Permanganate?

From what I understand, MnO4- reacts with something and produces MnO2. This shows that Mn goes from 7+ to 2+. I am not quite sure why it does this, but the example of MnO4- was in Dr. Lavelle's first lecture on electrochemistry and in examples 14.1 and 14.2 in the textbook, so you can look at those ...
by Justin Chang 2K
Wed Feb 21, 2018 10:30 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: 14.101
Replies: 4
Views: 439

Re: 14.101

E^o=0V because the standard potentials inside and outside the cell are the same. The reaction only involves potassium going in and out of the cell. Therefore, if you do E=E(cathode)-E(anode), you will get 0 because the same number minus the same number is 0. However, keep in mind that this is referr...
by Justin Chang 2K
Wed Feb 21, 2018 10:27 pm
Forum: Balancing Redox Reactions
Topic: Example 14.7 (c)
Replies: 1
Views: 103

Re: Example 14.7 (c)

I'm not completely sure, but I think that confirms that the reaction is done in acidic conditions (which for this reaction makes sense since there is H+ on one side of the reaction).
by Justin Chang 2K
Wed Feb 21, 2018 10:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.17 Potassium Permanganate?
Replies: 3
Views: 152

Re: 14.17 Potassium Permanganate?

In this reaction, the potassium and chloride ions do not participate in the reaction. Mn is being reduced from +7 to +2, and Fe is being oxidized from +2 to +3. Because K and Cl remain +1 and -1 charge throughout, respectively, they do not participate in the redox reaction and are just spectator ions.
by Justin Chang 2K
Mon Feb 12, 2018 6:26 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Joe’s Review Session
Replies: 1
Views: 108

Re: Joe’s Review Session

yes, here is the problem! Ethanol: what is the entropy of vaporization of 1 mol of ethanol at 285K? C(l)=111J/Kmol C(g)=78.3J/Kmol B.P=351.5K deltaHvap=43.5kJ/mol 1) deltaS=n*C(l)*ln(351.5/285)= 23.28J/K 2) deltaS=(43500J/mol) / 351.5= 123.755J/K 3) deltaS=n*C(g)*ln(285/351.5)= -16.42J/K deltaStotal...
by Justin Chang 2K
Mon Feb 12, 2018 6:10 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Gas Constant, R
Replies: 6
Views: 273

Re: Gas Constant, R

I agree, always make sure that you check your units of everything else before deciding what value of R to use.
by Justin Chang 2K
Fri Feb 09, 2018 1:44 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Exercise 11.19
Replies: 2
Views: 95

Re: Exercise 11.17

Are you talking about 11.17, or another problem? 11.17 is about the formation of ammonia, not a reaction about carbon dioxide.
by Justin Chang 2K
Fri Feb 09, 2018 1:39 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Entropy
Replies: 7
Views: 247

Re: Entropy

S^o (m) is the standard molar entropy (the values in the back of the textbook). I think S^o (f) is similar to the S^o (m). I don't quite know what S^o (r) is though.
by Justin Chang 2K
Fri Feb 09, 2018 1:36 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.77
Replies: 1
Views: 89

Re: 11.77

Here's the way I think about it: If you heat up the reaction, the equilibria will shift towards the side that does NOT have heat on it (I like to think that the reaction does not want to produce more heat, so it shifts towards the side with no heat). If you cool down the reaction, the equilibria wil...
by Justin Chang 2K
Thu Feb 01, 2018 7:19 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy change
Replies: 4
Views: 191

Re: Entropy change

Yes, deltaS(total)=deltaS(system)+deltaS(surroundings). We also talked about how deltaS(surroundings)= -Hsys/T. This is helpful because it tells us an exothermic reaction is usually spontaneous because of the increase in total entropy. The two negatives will cancel, and deltaS(surroundings) will be ...
by Justin Chang 2K
Thu Feb 01, 2018 7:06 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Energy calculation precision
Replies: 2
Views: 94

Re: Energy calculation precision

I don't think Dr. Lavelle has told us which one is most/least accurate of the three methods, so I wouldn't worry about it unless he says it in lecture sometime. You will just have to calculate deltaG based on the information that is given to you (if you have deltaH, deltaS, and a temperature, then u...
by Justin Chang 2K
Thu Feb 01, 2018 7:04 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reversible vs. Irreversible reactions
Replies: 2
Views: 126

Re: Reversible vs. Irreversible reactions

Yes. Also, because in reversible reactions, you increase/decrease the pressure by small increments, that explains why we must use w=-nRTln(V2/V1) since pressure will not be constant. However, because in irreversible reactions, the external pressure remains constant, we use w=-PdeltaV because the ext...
by Justin Chang 2K
Thu Jan 25, 2018 4:06 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Changing the energy of a system
Replies: 6
Views: 255

Re: Changing the energy of a system

Adding more of a system increases the internal energy. Also it is good to know you cannot add/remove something from a system in a closed and isolated system.
by Justin Chang 2K
Thu Jan 25, 2018 4:04 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: constant pressure
Replies: 5
Views: 206

Re: constant pressure

Yes. As long as you know the reaction is performed under constant pressure (if it's in an open beaker) then q=deltaH(rxn)
by Justin Chang 2K
Thu Jan 25, 2018 3:59 pm
Forum: Phase Changes & Related Calculations
Topic: enthalpy of fusion/vaporization
Replies: 3
Views: 139

Re: enthalpy of fusion/vaporization

Yes, you would make the sign negative.

The rule also applies to chemical equations in general. If you found that deltaH of A-->B is -50 kJ, then that means deltaH of B-->A is +50 kJ.
by Justin Chang 2K
Thu Jan 18, 2018 3:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Lewis structures for bond enthalpies
Replies: 3
Views: 122

Re: Lewis structures for bond enthalpies

For me at least, drawing the Lewis structures gives me a really good visual as to what bonds are broken and what bonds are being formed. So I would personally recommend reviewing the Lewis structures to help prepare you for the tests.
by Justin Chang 2K
Thu Jan 18, 2018 3:23 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Delta H and q Interchangeability
Replies: 5
Views: 249

Re: Delta H and q Interchangeability

Yeah, the definition of enthalpy is the heat absorbed or released at a constant pressure. q with a subscript p means the heat absorbed or released at a constant pressure, so the two are interchangeable. If there is no subscript p after the q, however, then the two are not interchangeable.
by Justin Chang 2K
Thu Jan 18, 2018 3:17 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Knowing which equation to use when finding q
Replies: 2
Views: 154

Re: Knowing which equation to use when finding q

I think because 8.53 says the reaction took place in a bomb calorimeter, so you would use q=C(cal)*deltaT, which relates the heat to the specific heat capacity of the calorimeter.
by Justin Chang 2K
Sat Jan 13, 2018 10:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Infinite Forms of Hess's Law
Replies: 5
Views: 138

Re: Infinite Forms of Hess's Law

Yeah, you can use Hess’s Law indefinitely to calculate enthalpies, since enthalpy is a state function you can just keep on adding and adding enthalpies. However, I guess for time’s sake, 2-4 equations is enough to test our knowledge of how enthalpy works and how chemical reactions work (for example,...
by Justin Chang 2K
Sat Jan 13, 2018 10:27 pm
Forum: Phase Changes & Related Calculations
Topic: Clarification
Replies: 3
Views: 205

Re: Clarification

Yeah, for heat transfer you need to know every single individual step that is involved in the reaction. However, for enthalpy you only need to know the initial and final amounts since it is a state function; it doesn’t matter the pathway that is taken in order to reach the final amount.
by Justin Chang 2K
Sat Jan 13, 2018 10:24 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: The 3 Methods for Calculating the Enthalpy of a Reaction
Replies: 4
Views: 187

Re: The 3 Methods for Calculating the Enthalpy of a Reaction

It honestly depends on what’s given to you in the problem. For example, if you’re given the bond enthalpies of the compounds, then you should definitely use the bonds broken- bonds formed way of calculating enthalpy.
by Justin Chang 2K
Thu Dec 07, 2017 4:53 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: alternate method
Replies: 1
Views: 130

Re: alternate method

I would still just use the ice table method. That way, incase the final answer you get is wrong, you at least get partial credit by setting up the ice table and showing that you understand the concept.
by Justin Chang 2K
Thu Dec 07, 2017 4:48 pm
Forum: Bronsted Acids & Bases
Topic: Oxoacids
Replies: 4
Views: 254

Re: Oxoacids

Yeah, more electronegative elements can help stabilize and delocalize the charge.
by Justin Chang 2K
Thu Nov 30, 2017 2:08 pm
Forum: Naming
Topic: Trans & Cis Naming
Replies: 3
Views: 186

Re: Trans & Cis Naming

Yeah, you wouldn't know whether or not to add cis or trans unless they give you the structure.
by Justin Chang 2K
Thu Nov 30, 2017 2:03 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Ch 11 #87c
Replies: 1
Views: 131

Re: Ch 11 #87c

I would just look at the moles in the actual chemical reaction.
by Justin Chang 2K
Tue Nov 21, 2017 12:09 pm
Forum: Hybridization
Topic: Sigma Bond
Replies: 3
Views: 226

Re: Sigma Bond

The sigma bond refers to the bond along the internuclear axis, so perhaps trying to fit 2 pairs of electrons along the same internuclear axis would not work since the electrons would want to repel each other as much as possible. Not sure if this reasoning is entirely correct but this is how I think ...
by Justin Chang 2K
Tue Nov 21, 2017 12:00 pm
Forum: Naming
Topic: naming ligands
Replies: 2
Views: 179

Re: naming ligands

oh okay, thank you so much!
by Justin Chang 2K
Tue Nov 21, 2017 11:54 am
Forum: Naming
Topic: naming ligands
Replies: 2
Views: 179

naming ligands

Hey guys!
So in the textbook on table 17.4, it says to use cyanido, fluorido, chlorido, bromido, etc... but in lecture I wrote down "use cyano, chloro, etc. when naming ligands". Maybe I just saw Dr. Lavelle's slides wrong, I'm not sure, but can anyone clarify the exact naming? Thank you!
by Justin Chang 2K
Thu Nov 16, 2017 3:51 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Electron geometry vs molecular geometry
Replies: 2
Views: 183

Re: Electron geometry vs molecular geometry

Yeah, I would definitely be prepared to answer both, especially considering the fact that Dr. Lavelle is continuously asking us how many regions of e- density there are, the shape associated with that, and the molecular geometry as well during class all the time.
by Justin Chang 2K
Thu Nov 16, 2017 3:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar or Non-polar
Replies: 3
Views: 883

Re: Polar or Non-polar

Yeah the bonds between carbon and chlorine are polar, but the whole molecule itself is non polar because the dipole moments cancel out since it is a linear molecule.
by Justin Chang 2K
Tue Nov 07, 2017 4:04 pm
Forum: Bond Lengths & Energies
Topic: Ionic Character and Covalent Character
Replies: 2
Views: 239

Re: Ionic Character and Covalent Character

He will probably give it to us in the problem since we do not normally have the values for electronegativity to determine for sure if it is an ionic bond or covalent bond.
by Justin Chang 2K
Tue Nov 07, 2017 3:54 pm
Forum: Resonance Structures
Topic: How to show a partial resonance structure?
Replies: 1
Views: 192

Re: How to show a partial resonance structure?

I would probably just draw the lone pairs in as if it were for a normal Lewis structure; for example, with the nitrate ion, put dotted lines for the bonds and write in all the lone pairs on the oxygen atoms.
by Justin Chang 2K
Thu Nov 02, 2017 12:07 am
Forum: Lewis Structures
Topic: electron configuration
Replies: 6
Views: 342

Re: electron configuration

I believe the 3d will come first since the d shell is now filled, so it overall is in a lower energy state than the 4s orbital. can someone else confirm this?
by Justin Chang 2K
Thu Nov 02, 2017 12:04 am
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: More Polarizable/Polarizing Power
Replies: 6
Views: 344

More Polarizable/Polarizing Power

bigger anions have higher polarizability and cations with greater charge have higher polarizing power correct? Or is it the other way around
by Justin Chang 2K
Thu Oct 26, 2017 9:04 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ground or Excited State?
Replies: 2
Views: 189

Re: Ground or Excited State?

I'm not completely sure, but I think that if the atom is in the excited state, then the electron configuration would show an electron or two in a higher orbital (higher energy) than its ground state. For example, the electron configuration for oxygen is 1s2 2s2 2p4, which is the ground state of oxyg...
by Justin Chang 2K
Thu Oct 26, 2017 8:59 am
Forum: Trends in The Periodic Table
Topic: d5 and d10 e- exception
Replies: 4
Views: 606

Re: d5 and d10 e- exception

Yeah, all of the elements in those 2 groups have the same exception with the s and d shell, but for the purposes of this class, just memorize copper and chromium.
by Justin Chang 2K
Fri Oct 20, 2017 1:22 am
Forum: Photoelectric Effect
Topic: Quantized Energy Level
Replies: 5
Views: 384

Re: Quantized Energy Level

Yeah, especially when you discuss energy levels of the atom, if the photon does not have the exact amount of energy to go from n=1 to n=2, the electron won't be excited, even if the energy allows the electron to go from n=1 to n=2.5. It must be whole numbers in this case, hence why numbers are quant...
by Justin Chang 2K
Fri Oct 20, 2017 1:19 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Module Q28
Replies: 2
Views: 189

Re: Atomic Spectra Module Q28

Yep! I did:

1m/1,650,763.73 wavelengths = x m/1 wavelength in order to figure out the length of only one wavelength, if looking at the mathematical representation helps at all!
by Justin Chang 2K
Fri Oct 13, 2017 12:40 am
Forum: Properties of Light
Topic: Figure 1.9
Replies: 4
Views: 264

Re: Figure 1.9

Yeah, as long as you have 400-700 nm, 400 is around purple, and 700 in around red all memorized, I think you should be fine.
by Justin Chang 2K
Fri Oct 13, 2017 12:35 am
Forum: Photoelectric Effect
Topic: Problem 1.7 HW
Replies: 4
Views: 294

Re: Problem 1.7 HW

Yeah, I was also confused on that, but the solutions manual does indeed say 150 pm, so you should be good.
by Justin Chang 2K
Thu Oct 05, 2017 6:09 pm
Forum: Balancing Chemical Reactions
Topic: H7 // Book Problem Clarification
Replies: 4
Views: 246

Re: H7 // Book Problem Clarification

Yeah, you reference the catalyst by putting it above the arrow, but you wouldn't include it in the actual chemical equation.
by Justin Chang 2K
Thu Oct 05, 2017 5:57 pm
Forum: Empirical & Molecular Formulas
Topic: Question M19 (Molecular Formula)
Replies: 5
Views: 329

Re: Question M19 (Molecular Formula)

What I did is I found out how many grams of carbon (0.682g * (1 mol CO2/44.01g) * (1 mol C/1 mol CO2) * molar mass of carbon to get grams), hydrogen (same process as carbon), and nitrogen. Then I did 0.376-(mass carbon+mass hydrogen+mass nitrogen) to get the grams of oxygen, and then divided that by...

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