CHEMISTRY COMMUNITY

samuelkharpatin2b

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...

samuelkharpatin2b

Thank you.

samuelkharpatin2b

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!!

samuelkharpatin2b

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.

samuelkharpatin2b

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...

samuelkharpatin2b

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...

samuelkharpatin2b

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.

samuelkharpatin2b

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...

samuelkharpatin2b

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-.

samuelkharpatin2b

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.

samuelkharpatin2b

Tert- would not be considered for alphabetical order, just like sec- too. Iso-, neo- and cyclo- you do consider for alphabetical order.

samuelkharpatin2b

Thank you.

samuelkharpatin2b

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.

samuelkharpatin2b

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...

samuelkharpatin2b

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.

samuelkharpatin2b

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).

samuelkharpatin2b

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...

samuelkharpatin2b

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...

samuelkharpatin2b

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.

samuelkharpatin2b

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.

samuelkharpatin2b

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)...

samuelkharpatin2b

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...

samuelkharpatin2b

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.

samuelkharpatin2b

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...

samuelkharpatin2b

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.

samuelkharpatin2b

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.

samuelkharpatin2b

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.

samuelkharpatin2b

The Faraday Constant is 96,485 C/mol no matter how many electrons are being transferred.

samuelkharpatin2b

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.

samuelkharpatin2b

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...

samuelkharpatin2b

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.

samuelkharpatin2b

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.

samuelkharpatin2b

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.

samuelkharpatin2b

The change is in the number of moles, not the temperature.

samuelkharpatin2b

On the midterm I would use whatever's on the formula sheet.

samuelkharpatin2b

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...

samuelkharpatin2b

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...

samuelkharpatin2b

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.

samuelkharpatin2b

Celsius is the usual unit used in heat capacity. When talking about specific heat capacity though, the units would be J/(degrees C)(g).

samuelkharpatin2b

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.

samuelkharpatin2b

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.

samuelkharpatin2b

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.

samuelkharpatin2b

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...

samuelkharpatin2b

All formulas/constants will be provided to us during quizzes, midterm and final. No need to memorize.

samuelkharpatin2b

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...

samuelkharpatin2b

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).

samuelkharpatin2b

We will be provided all relevant formulas/constants for our quizzes, midterm and final.

samuelkharpatin2b

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...

samuelkharpatin2b

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.

samuelkharpatin2b

There are three practice quizzes in the very back of the course reader along with a practice midterm and final.

samuelkharpatin2b

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

samuelkharpatin2b

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.

samuelkharpatin2b

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!

samuelkharpatin2b

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

samuelkharpatin2b

The following is my take on #57. Hope you find it helpful!

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