Search found 55 matches

by samuelkharpatin2b
Fri Mar 17, 2017 1:00 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Half-Reaction Voltages
Replies: 1
Views: 295

Half-Reaction Voltages

If you are trying to calculate E°cell using the formula E°cell=E°cathode-E°anode, and one or both of the half reactions provided are in oxidation form with their respective voltage, would you need to flip the sign of the voltage so that the half-reaction would be in reduction form? For example, if a...
by samuelkharpatin2b
Tue Mar 14, 2017 4:01 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Winter 2013 Midterm Q1B
Replies: 2
Views: 345

Winter 2013 Midterm Q1B

I am wondering why for this problem we use Cv instead of Cp, (shown in step 2 of the solution). I ask because the way I understood it is that the volume increases from 3.0 L to 3.5 L, so I thought the volume isn't constant. Please see attached file for the problem.

Thank you!!
by samuelkharpatin2b
Tue Mar 14, 2017 3:31 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: Stability of the Formation
Replies: 3
Views: 333

Re: Stability of the Formation

The most stable conformation is when the "bulkiest" substitutents have a 180° dihedral angle between them, i.e. they are on opposite sides of the Newman projection. By "bulkiest" I mean something other than H.
by samuelkharpatin2b
Tue Mar 14, 2017 12:41 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Oxidation Numbers
Replies: 4
Views: 450

Re: Oxidation Numbers

The problems we are going to see in 14B will have Oxygen with an oxidation number of -2 (if in a compound) and Hydrogen with an oxidation number of +1. Using these known oxidation numbers you can find oxidation numbers of other elements in a compound, say Mn. There is an exception to the -2 rule for...
by samuelkharpatin2b
Tue Mar 14, 2017 12:37 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: Strains
Replies: 2
Views: 307

Re: Strains

It may seem as though steric and torsional strain are very similar, which they in a way are, but the most important distinction between the two is that steric strain is due to actual/physical interaction between atoms in a molecule when they are close to each other while torsional strain is caused b...
by samuelkharpatin2b
Sat Mar 11, 2017 10:38 am
Forum: *Alkynes
Topic: Double or Triple bonds?
Replies: 2
Views: 613

Re: Double or Triple bonds?

Double bonds are named first, but I believe in 14B the compounds we study are going to have either one double bond, one triple bond, or one functional group, etc.
by samuelkharpatin2b
Sat Mar 11, 2017 10:35 am
Forum: *Cycloalkanes
Topic: Constitutional Isomers
Replies: 2
Views: 396

Re: Constitutional Isomers

When you see the term "constitutional isomer", all that simply means is that the problem is asking you to draw out a couple of different configurations of the same molecule. For example, if the compound you need to draw has a total of four carbons, you can draw that as a square, a triangle...
by samuelkharpatin2b
Wed Mar 08, 2017 5:50 pm
Forum: *Cycloalkanes
Topic: course reader page 96 neo and tert
Replies: 3
Views: 506

Re: course reader page 96 neo and tert

You use the prefix neo- when a substitutent has AT LEAST 5 carbons. If the substitutent is composed of fewer than 5 carbons, you cannot use the prefix neo-. Tert-butyl for instance looks similar to neo-(something) in drawings, but due to the number of carbons, you wouldn't use neo-.
by samuelkharpatin2b
Wed Mar 08, 2017 5:45 pm
Forum: *Cycloalkanes
Topic: numbering the carbons
Replies: 4
Views: 701

Re: numbering the carbons

When naming, it is always best (if possible) for the substitutent "earlier" in alphabetical order to get the smaller number as well. Hence, ethyl would receive the number 1 and not 4.
by samuelkharpatin2b
Mon Mar 06, 2017 8:54 pm
Forum: *Alkanes
Topic: Tert- Naming
Replies: 2
Views: 334

Re: Tert- Naming

Tert- would not be considered for alphabetical order, just like sec- too. Iso-, neo- and cyclo- you do consider for alphabetical order.
by samuelkharpatin2b
Sun Mar 05, 2017 7:49 pm
Forum: *Alkanes
Topic: Prefixes & Alphabetical Order
Replies: 2
Views: 269

Re: Prefixes & Alphabetical Order

Thank you.
by samuelkharpatin2b
Sun Mar 05, 2017 7:08 pm
Forum: *Alkanes
Topic: Prefixes & Alphabetical Order
Replies: 2
Views: 269

Prefixes & Alphabetical Order

I know we don't take into consideration the prefixes di- tri- etc. when applying alphabetical order, by do we take into consideration the prefixes iso- and tert- when applying the alphabetical rules?

Thank you.
by samuelkharpatin2b
Sun Mar 05, 2017 1:04 pm
Forum: *Nucleophilic Substitution
Topic: double/single-headed arrows
Replies: 6
Views: 1207

Re: double/single-headed arrows

I believe we can focus mostly on using the double headed arrow for this class, and just know that the single headed arrow simply means that one electron is being transferred. The use of the one headed arrow is really rare and no problems in the organic textbook require the use of a single headed arr...
by samuelkharpatin2b
Sat Mar 04, 2017 9:01 pm
Forum: *Alkanes
Topic: Confusion on naming on page 93 on Course Reader
Replies: 2
Views: 301

Re: Confusion on naming on page 93 on Course Reader

The combination of 4,2,2 is smaller than the combination of 3,5,5. Hence, you use the combination of 4,2,2 and then you arrange the name based on alphabetical order. You ignore prefixes like di- tri- etc when considering alphabetical order.
by samuelkharpatin2b
Fri Mar 03, 2017 8:53 am
Forum: *Alkanes
Topic: Naming
Replies: 2
Views: 356

Re: Naming

Lone pairs do affect the hybridization, however they do and do not affect the geometry of a molecule in a way. For example. The lone pairs in water give it an angular shape but aren't visible in the Lewis structure, (unless of course they're drawn).
by samuelkharpatin2b
Wed Mar 01, 2017 4:37 pm
Forum: Balancing Redox Reactions
Topic: Writing Cell Diagrams
Replies: 5
Views: 793

Re: Writing Cell Diagrams

When writing cell diagrams, we usually write everything that's in a solid form towards the far left/right, while anything other than solid, such as gas, aqueous solution, etc., is placed towards the "inside" of the cell diagram. For example, (s)I(aq)II(aq)I(s) would be a correct way of wri...
by samuelkharpatin2b
Wed Mar 01, 2017 4:32 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: How to write electrode reactions from a cell diagram & write a cell diagram from overall reaction?
Replies: 2
Views: 431

Re: How to write electrode reactions from a cell diagram & write a cell diagram from overall reaction?

Not quite sure what you mean by that first bullet point, but for the second bullet point (2Ag(s) + Br2(g)→2AgBr(s)), both reactants have an oxidation number of zero and the one product is comprised by the Ag+ and a Br-. Using this knowledge, you can now write the two half reactions and proceed to wr...
by samuelkharpatin2b
Wed Mar 01, 2017 4:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Which electrode to use?
Replies: 2
Views: 358

Re: Which electrode to use?

When you are in need of an inert electrode, i.e. one of them isn't present in the original problem, you get to choose whether to use platinum or graphite. Neither one is preferred, however the book tends to use platinum as an example.
by samuelkharpatin2b
Wed Mar 01, 2017 4:24 pm
Forum: *Alkanes
Topic: 4-ethyl-2,2-dimethylhexane vs 2,2-dimethyl-4-ethylhexane
Replies: 2
Views: 517

Re: 4-ethyl-2,2-dimethylhexane vs 2,2-dimethyl-4-ethylhexane

When naming compounds, you are supposed to ignore the prefix. That is, you disregard the "di-" in dimethylhexane and use the first letter "m" when taking into account alphabetical order. This is the same for all prefixes.
by samuelkharpatin2b
Mon Feb 27, 2017 7:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Midterm Problem 1A
Replies: 1
Views: 331

Midterm Problem 1A

Hi, I have a question regarding problem 1A on the midterm. On several practice midterms I have seen problems such as this one be accepted as full credit when the units are either kJ OR kJ/mol. Can someone please explain why that isn't the case here? (Here the problem accepted kJ/mol and not just kJ)...
by samuelkharpatin2b
Sun Feb 26, 2017 7:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Sig Fig Rules (Hess's Law)
Replies: 2
Views: 1044

Re: Sig Fig Rules (Hess's Law)

When using Hess's Law, your final answer would depend on the smallest number of decimal places in your enthalpies for sure. The reason why is because adding/subtracting is the last step you do in order to obtain your final answer. And since adding/subtracting is your final step in calculating the en...
by samuelkharpatin2b
Sun Feb 26, 2017 7:40 pm
Forum: General Rate Laws
Topic: Overall Order of a Reaction
Replies: 2
Views: 300

Re: Overall Order of a Reaction

In order to derive a rate law, you must compare experimental data or pay attention to the slow step in a given mechanism. There is no formula or anything like that where you can simply find the rate law without experimental data or the mechanism.
by samuelkharpatin2b
Sun Feb 26, 2017 7:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When do you add Pt?
Replies: 3
Views: 338

Re: When do you add Pt?

You add platinum to the cell diagrams when it is in need of a solid electrode. There are some times when the anode or cathode situation is comprised of only gaseous or aqueous solutions, so in that case you would add platinum. And when drawing the cell diagram, make sure you write platinum on the ve...
by samuelkharpatin2b
Sat Feb 25, 2017 10:51 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Reaction
Replies: 11
Views: 757

Re: Slow Reaction

When given a mechanism, it should provide you with which step is the slow step and which is the fast step. The slow step, sometimes called the rate limiting step, is what determines the overall rate law.
by samuelkharpatin2b
Thu Feb 23, 2017 9:37 am
Forum: Balancing Redox Reactions
Topic: Oxidation number of oxygen in O3
Replies: 3
Views: 3785

Re: Oxidation number of oxygen in O3

The oxidation number of an oxygen atom in ozone is zero, just like in oxygen gas. So, in O3 -> O2, there are no electrons transferred.
by samuelkharpatin2b
Thu Feb 23, 2017 9:26 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells
Replies: 4
Views: 376

Re: Galvanic Cells

If a redox reaction is happening between two aqueous, two gaseous, or one aqueous and one gaseous states of matter, an inert electrode must be present such as platinum, which is used in most cases, or graphite. There must be some solid electrode present in both the anode and cathode.
by samuelkharpatin2b
Thu Feb 23, 2017 9:23 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Faraday Constant
Replies: 3
Views: 308

Re: Faraday Constant

The Faraday Constant is 96,485 C/mol no matter how many electrons are being transferred.
by samuelkharpatin2b
Wed Feb 22, 2017 6:39 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: What is n? [ENDORSED]
Replies: 8
Views: 817

Re: What is n? [ENDORSED]

n represents the number of moles of electrons transferred, and that number can be found by looking at the balanced half reactions. The coefficient in front of the e- is the value used for n.
by samuelkharpatin2b
Wed Feb 22, 2017 6:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Midterm Q4.C
Replies: 2
Views: 233

Re: Midterm Q4.C

You are correct that the anode information needs to go on the left hand side of the cell diagram and the cathode on the right hand side, however, the order should go as follows: (platinum, if needed)|(anything aqueous or gaseous)|(anything solid)||(anything solid)|(anything aqueous or gaseous)|(plat...
by samuelkharpatin2b
Wed Feb 22, 2017 6:31 pm
Forum: Balancing Redox Reactions
Topic: Balancing equations
Replies: 10
Views: 902

Re: Balancing equations

I would say that knowing the general polyatomic ion charges would be a good thing, but you definitely should know the charges of ions based on their group/family in the periodic table.
by samuelkharpatin2b
Fri Feb 17, 2017 3:10 pm
Forum: Balancing Redox Reactions
Topic: Cell Diagrams
Replies: 2
Views: 276

Re: Cell Diagrams

Yes, platinum is what is used most often and is the inert electrode the textbook uses. There are other electrodes which could be used, such as graphite, but if you use platinum you'll be fine.
by samuelkharpatin2b
Fri Feb 17, 2017 3:08 pm
Forum: Balancing Redox Reactions
Topic: H+ and e-
Replies: 4
Views: 991

Re: H+ and e-

The charges which come from the H+ and e- do cancel each other out, you just have to add an appropriate amount of each so that both sides of the reaction are equal in charge and in the amount of atoms.
by samuelkharpatin2b
Tue Feb 14, 2017 11:00 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: w=-delta(nRT)
Replies: 2
Views: 537

Re: w=-delta(nRT)

The change is in the number of moles, not the temperature.
by samuelkharpatin2b
Sat Feb 11, 2017 9:26 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Faraday's Constant!
Replies: 2
Views: 296

Re: Faraday's Constant!

On the midterm I would use whatever's on the formula sheet.
by samuelkharpatin2b
Fri Feb 10, 2017 6:05 pm
Forum: Balancing Redox Reactions
Topic: OH- H+ and H2O in balancing redox reactions
Replies: 5
Views: 1595

Re: OH- H+ and H2O in balancing redox reactions

You add water when you are in need of more oxygen. The way I balance redox reactions is add H2O when I need additional oxygen, and H+ when I need to add hydrogen, when balancing in acidic solution. When balancing in basic solution, I start off as if I'm balancing in acidic solution, and once I finis...
by samuelkharpatin2b
Wed Feb 08, 2017 5:44 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: pH and the Cell Potential
Replies: 2
Views: 295

Re: pH and the Cell Potential

The Nernst equation uses the concentrations of reactants and products. So if a problem provides you with a pH and you know you need to use the Nernst equation in order to solve the problem, you must first find the concentration of hydronium ions, by evaluating 10^(-pH) and then proceed to plug in th...
by samuelkharpatin2b
Fri Feb 03, 2017 3:18 pm
Forum: Calculating Work of Expansion
Topic: Sign of Work
Replies: 4
Views: 555

Re: Sign of Work

When the system itself is doing work, the sign is negative because it's losing work. When something is doing work on the system, the sign is positive because the system is absorbing the work.
by samuelkharpatin2b
Tue Jan 31, 2017 12:12 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: units for heat capacity
Replies: 5
Views: 814

Re: units for heat capacity

Celsius is the usual unit used in heat capacity. When talking about specific heat capacity though, the units would be J/(degrees C)(g).
by samuelkharpatin2b
Tue Jan 31, 2017 12:06 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: How to interpret ∆H
Replies: 2
Views: 459

Re: How to interpret ∆H

The ∆H listed next to the reaction is the enthalpy of the reaction as a whole. It takes into account the moles of both the reactant and product.
by samuelkharpatin2b
Mon Jan 30, 2017 3:35 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Isothermal Objects
Replies: 2
Views: 350

Re: Isothermal Objects

Any system, whether it be a open, closed or isolated system can be isothermal. Isothermal simply means constant temperature, and that can take place anywhere. Also, remember that under isothermal conditions, the delta(U) of a system is zero, and as a result q=-w.
by samuelkharpatin2b
Thu Jan 26, 2017 7:52 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Standard State Conditions
Replies: 1
Views: 268

Standard State Conditions

I just want to confirm...when talking about temperature in Kelvins in standard state conditions, do we use 298 K or 298.15 K?

Thank you.
by samuelkharpatin2b
Thu Jan 26, 2017 8:41 am
Forum: Calculating Work of Expansion
Topic: Quiz 1 Preparation: Question #3 - Conflicting Information? [ENDORSED]
Replies: 4
Views: 469

Re: Quiz 1 Preparation: Question #3 - Conflicting Information? [ENDORSED]

Sboutros2b, we use the equation for work which includes final and initial volume when the pressure changes. If the pressure is constant, then we simply use w=-Pdelta(V) to calculate work. And since the question states that the process is isothermal, we know that the internal pressure is zero. (For a...
by samuelkharpatin2b
Mon Jan 23, 2017 8:09 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Memorize Values for Quiz?
Replies: 2
Views: 440

Re: Memorize Values for Quiz?

All formulas/constants will be provided to us during quizzes, midterm and final. No need to memorize.
by samuelkharpatin2b
Mon Jan 23, 2017 7:44 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy
Replies: 1
Views: 272

Re: Entropy

The reason why q(rev) and negative delta H are the same thing because as we have learned in Chapter 8, whenever a reaction/process is occurring at constant pressure, (which in most cases that's the case), q(rev)_p, or simply q_p, is the same thing as delta H, or enthalpy. For question 9.3, all you h...
by samuelkharpatin2b
Sun Jan 22, 2017 8:38 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Unit Question [ENDORSED]
Replies: 4
Views: 418

Re: Unit Question [ENDORSED]

By definition, 1 L*atm is equivalent to 101.3 Joules. Units for both work (w) and heat (q) should either be in either Joules (J) or kilo-Joules (kJ).
by samuelkharpatin2b
Thu Jan 19, 2017 9:54 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Values Given on Exams?
Replies: 2
Views: 319

Re: Values Given on Exams?

We will be provided all relevant formulas/constants for our quizzes, midterm and final.
by samuelkharpatin2b
Wed Jan 18, 2017 6:38 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Units [ENDORSED]
Replies: 5
Views: 616

Re: Units [ENDORSED]

Most of the time when working with reaction enthalpy problems the units will be in kJ. However, if a question contains wording such as "enthalpy per mole" or something of that sort, the answer will be in kJ/mol. Answers are in kJ/mol when working with standard enthalpies of formation, alwa...
by samuelkharpatin2b
Sun Jan 15, 2017 11:25 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Sublimation
Replies: 1
Views: 224

Re: Sublimation

That is a very good question. An example of sublimation would be solid carbon dioxide, (also known as dry ice), sublimating at room temperature. A solid block of dry ice will start sublimating at room temperature without transitioning into a liquid state first.
by samuelkharpatin2b
Sat Jan 14, 2017 8:36 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Practice quiz
Replies: 2
Views: 228

Re: Practice quiz

There are three practice quizzes in the very back of the course reader along with a practice midterm and final.
by samuelkharpatin2b
Sat Jan 14, 2017 1:52 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Problem 8.63c typo?
Replies: 2
Views: 216

Re: Problem 8.63c typo?

I was confused by this problem as well, however this link should clear up any confusion:

https://lavelle.chem.ucla.edu/wp-conten ... rs_6Ed.pdf
by samuelkharpatin2b
Sat Jan 14, 2017 10:13 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy
Replies: 2
Views: 239

Re: Enthalpy

Drawing out the correct Lewis structures will help you visually see what bonds are broken and/or formed. You compare and contrast which bonds you see on the reactants side, and which bonds you see on the products side.
by samuelkharpatin2b
Thu Jan 12, 2017 3:26 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Cha. 8 HW Problem #57
Replies: 7
Views: 687

Re: Cha. 8 HW Problem #57

The h sub c does in deed stand for enthalpy of combustion. I have attached a copy of my explanation of the problem. Hope you find it helpful!
by samuelkharpatin2b
Thu Jan 12, 2017 3:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HW Questions #57
Replies: 1
Views: 212

Re: HW Questions #57

It stands for combustion. So delta h sub c means heat of combustion.

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