CHEMISTRY COMMUNITY

Albert Chong_1L

Why is surrounding entropy = 0 for an irreversible expansion? The question was posed before, but with no confirmed answer. Thanks.

Albert Chong_1L

Hi,

Is it acceptable to use redundant numbering when naming?
For example, will propan-1-al be accepted for full credit?

Thanks.

Albert Chong_1L

Chem_Mod wrote:Yeah, it has to do with the double bond.

Could you explain what the double bond means in terms of the cis/trans? Thanks.

Albert Chong_1L

Hi,

For this question, which asks for the IUPAC name for a cycloalkene with only one functional group that sticks out of the main chain, how do we decide if it is cis or trans? Does it have something to do with the double bond?

Thanks.

Albert Chong_1L

Hi.

Do the + and - in dihedral angles refer to the back carbon rotating or the front one?
Also, do we have to include signs for the final? or can we simply state the angle?

Thanks.

Albert Chong_1L

Hi,

How do we decide which carbons to draw a Newman projection for if they are not stated?

One example is Self-Test 3.3B in Intro to Organics.
Draw a Newman projection for the gauche conformation of 1-iodobutane.

Thanks.

Albert Chong_1L

Hi,

For the final do we have to memorize the various real-world connections for various functional groups and organic compounds?
For example, that Ethanal is present in plants and their products?

Thanks.

Albert Chong_1L

Hi, I was wondering the priority for double bonds, triple bonds, and other functional groups. I believe double and triple bonds take priority over all other functional groups. I also think that double bonds take priority over triple bonds. These conclusions are derived from various examples. Can som...

Albert Chong_1L

There is an example in the book where a double bond takes precedence over a chloro (halide) substituent...
Maybe halides are are an exception? If so, I would expect ethers to be as well...

Albert Chong_1L

Hi, The unfavorable steric factor in terms of transition states refers to how the specific orientation requirement of a TS causes its change in entropy to be negative, and thus Free Energy change to be positive. In terms of steric strain, this refers to the conformational strain produced when the el...

Albert Chong_1L

Hi,

The products are thermodynamically stable if they have lower Free Energy than the reactants (1&2).
A reaction is kinetically stable if it has a high activation energy, because few reactants will become products at normal temperatures (2&4).

Albert Chong_1L

Hi.

Are Substituents still placed in parentheses for Condensed Structural Formulas?

Thanks.

Albert Chong_1L

Hi, I was wondering if you alphabetize when both alkyls and halogens are included in a structure.

That is, if both chlorine and a methyl group were attached to an alkane, would the structure be for example, 2- chloro-3-methylnonane?

Albert Chong_1L

Nope. Because for triple bonds, there is only one structure possible. A linear one.

Albert Chong_1L

The distance between the reactant potential energy and the potential energy of the transition state is the activation energy needed to cause that reaction to occur.

Albert Chong_1L

I think we prioritize other functional groups over double bonds. Would be great if someone could confirm.

Albert Chong_1L

First of all, cis and trans isomers occur only when there are double bonds in the molecule. To determine cis or trans, look individually at each carbon and what is connected to it. Decide which of the two species connected to each carbon is greater in atomic number, and if they are the same, keep mo...

Albert Chong_1L

In general, does capitalization matter for organic naming?
If so, when do we capitalize?
I've seen things capitalized and not capitalized, so just want to check.

Thanks.

Albert Chong_1L

Hi, I was wondering for condensed structural formulas of Alkenes and Alkynes, do the double and triple bonds have to be shown? For example, would the condensed structural formula of butene be CH2=CHCH2CH3 or CH2CHCH2CH3? Also, just to confirm, the condensed structural formula and structural formula ...

Albert Chong_1L

Hi I was wondering why transition states always have positive enthalpy changes despite TS that involve solely bond formation. One example would be the second step of electrophilic addition of HBr to Propene in which the second step involves a Br anion attaching to a carbocation. Since the formation ...

Albert Chong_1L

Yes. That's right. But what about the example I gave?

Albert Chong_1L

Hi I was wondering why transition states always have positive enthalpy changes despite TS that involve solely bond formation. One example would be the second step of electrophilic addition of HBr to Propene in which the second step involves a Br anion attaching to a carbocation. Since the formation ...

Albert Chong_1L

An external energy source supplies electric current to an electrolytic cell. By introducing an external current, it can drive a non spontaneous reaction. In an electrolytic cell, both electrodes are submerged in the SAME solution. When the positive ions in the solution collide with the negative elec...

Albert Chong_1L

I agree with your first question that the ordering seems strange. To answer your second question, the substituent listed first is always given the lower number if equivalent numbering is possible. However, if lower numbers in general can be obtained by giving the first substituent a higher number th...

Albert Chong_1L

Good question.

I think since we are told to find the initial rate of decomposition and we know that E is consumed at 5 times the unique average rate (which applies without alteration only to species with coefficient 1), we should multiply by 5.

Would double check though.

Albert Chong_1L

I'm not 100% sure what you are asking, but the differential rate law (Rate=k[A]^n) is useful for comparison between data in experiments to determine what the orders are for each reactant.

Albert Chong_1L

Hi, I was wondering if equations should be balanced before rate laws are derived. That is, for Question 3 of Quiz Prep 2, the question states that rate=k[N2O]... However, when the reaction in question is balanced, N2O has a 2 coefficient. Does this not change the rate equation to become rate=k[N2O]^...

Albert Chong_1L

If the question does not specify differently, I would use the time units that are used in the givens.

Albert Chong_1L

The concentration of the reactant being tested has to be small enough relative to the concentration of the other reactants that the concentration of the other reactants will remain essentially constant as the reactant being tested is being consumed.

Albert Chong_1L

You can assume first order with respect to the species in question when the reaction rate doubles due to a doubling of the concentration of that species.

Albert Chong_1L

deltaS represents the entropy change of the exact reaction you are looking at. deltaSo represents the entropy change of the reaction at standard conditions. While deltaS0 might be positive and thus spontaneous at normal conditions, deltaS might not be positive at certain conditions (or visa versa). ...

Albert Chong_1L

For reversible adiabatic process, delta S should be 0. I can see that is true through deltaS=q/T, since deltaS will be 0 when q is 0. However, if V2/V1 can be substituted for T2/T1 in the equation deltaS=nCln(T2/T1), then how does this equation show deltaS as 0 when q=0 (adiabatic)? Is this equatio...

Albert Chong_1L

One instance would be when you find the change in entropy of a monatomic ideal gas due to change in temperature.

Albert Chong_1L

Factors other than heat flow (q) can affect entropy. For example, if volume was increased for a gas, there would be more entropy since the gas molecules have more possible micro states in which to exist.

Albert Chong_1L

I'm not 100% sure, but from what I have seen, the cell notation usually follows the order that the ions are consumed and produced.

If the reaction was Fe(III) + e- --> Fe(II), for example, I think it would be Fe3+, Fe2+ since Fe3+ becomes Fe2+.

Would be great if someone could verify.

Albert Chong_1L

E=Electromotive force=Cell potential. Cell potential is the amount of electrical potential energy created by differences in the charge of two half cells. It is greatest when the current is near 0 and the electrons experience the strongest pull from one half cell to the other. Wmax is the maximum amo...

Albert Chong_1L

Hi.

For the same mass, would fewer, larger molecules have more entropy or more, smaller molecules. Why?

Albert Chong_1L

Diatomic or polyatomic gases have higher molar heat capacities than monoatomic gases because they have more fundamental particles that are able to absorb energy and use it to perform translational/ vibrational/ rotational motion.

Albert Chong_1L

It's a typo. You're right. Use C for entropy calculation.

See link: https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Solution_Manual_Errors_6Ed.pdf

Albert Chong_1L

Isothermal means that the temperature does not change during this expansion. Reversible means that the expansion can be reversed with the slightest push from external forces. Essentially, the system goes to equilibrium with the surroundings at each infinitely small step of the expansion. The pressur...

Albert Chong_1L

Hi.

What coefficients are used when calculating standard enthalpy for a reaction?
Some sources say to make the lowest coefficient 1 in the equation, and others say to make the molecule in question have a coefficient of 1 (with other molecules having fractional coefficients)...

Albert Chong_1L

Use the temperature provided for each substance as its initial temperature.
Then use Tf in your equation to represent final temperature. Tf will be the same for both substances after the temperatures comes to equilibrium.
Finally, you can combine the two Tf's into one variable and solve.

Albert Chong_1L

For the phase change piece, you use the entropy of vaporization of water at 100C, which is 109.0J/Kmol.
For the other pieces, yes, use dS=Cln(T2/T1).
Then, add al the pieces together to get total S change.

Albert Chong_1L

Entropy is an extensive property because it depends on the volume of the substance in question.
When there is more volume, there is greater degeneracy since there are more microstates for the same energy state to be achieved.
Greater degeneracy equates to greater Entropy by the equation: S=kBlnW

Albert Chong_1L

Hi.

What is the purpose of the pressurized oxygen gas in bomb calorimeters?
I presume it has something to do with isolating the sample from the environment?

Thanks.

Albert Chong_1L

A bomb calorimeter provides an isolated system at constant pressure and volume.
A regular calorimeter, such a coffee cup calorimeter, allows pressure to equalize with the environment.
Essentially, a bomb calorimeter is airtight/sealed, while a regular calorimeter is open.

Albert Chong_1L

- A state function refers to an intrinsic property of a substance/object. - Enthalpy is equal to the total heat content of a system. - The total heat content of a system is an intrinsic property. It exists even when the object/substance is not undergoing any action. - Heat on the other hand, refers ...

Albert Chong_1L

- Heat capacity is the amount of heat needed to raise the temperature of a substance/object in question by one degree. - For any gas, an increase in temperature causes it to expand. - For a gas at constant pressure, this expansion causes it to push against the atmospheric pressure of the surrounding...

Albert Chong_1L

See which conjugate bases for the acids will be most stable and most able to withdraw negative charge/electrons after deprotonation.
Generally, conjugate bases with resonance and electronegative atoms will be correspondent to stronger acids

Albert Chong_1L

It means that after the acid is deprotonated, the high amounts of negative charge are withdrawn by other atoms on the conjugate base, and the resonance helps to distribute the negative charge for more stability.

Albert Chong_1L

Greater bond order = stronger bond = shorter bond

Albert Chong_1L

If the x is less than 5% of the quantity it is subtracted by, it may be omitted because it is relatively so much smaller.

Albert Chong_1L

pH of a titration of strong base with a strong acid is 7.
The ions attached to the H+ and OH- do not affect pH and combine to produce a neutral salt.

As for finding volume, calculate how many moles of base need to be neutralized.
Then, calculate the volume of acid that will contain that many moles.

Albert Chong_1L

Hi,

When can one use moles in the ice table?
I assume only when the volume is 1L since Kc is a set value and applies when concentrations are used?
If volume is 1L, moles would essentially be the same as concentrations?

Albert Chong_1L

A salt is used to supply the conjugate acid/base of the weak acid/base that is being used as a buffer.
If no salt is added, the buffer might not be at the optimum level since the amount of acid/base and conjugate are not going to be necessarily equal.

Albert Chong_1L

By definition, a salt is an ionic compound. Thus, its component atoms/molecules are necessarily charged (either positive of negative). When these charged components interact with a polar medium such as water, the ionic components are pulled away from each other. A salt dissolves when the positive en...

Albert Chong_1L

Hi, Since weak acids and weak bases both function as buffers and can act as a sink or source of protons, does that mean that to buffer a solution, it does't matter whether a weak acid or weak base is used as long as the PKa is close to the desired pH? That is, a weak acid can buffer an acidic soluti...

Albert Chong_1L

Hi.

Normally the conjugate acid of a weak base is a strong acid, however, the conjugate acid of the weak base NH3 is a weak acid, NH4+.
Why is this the case?

Albert Chong_1L

If the species is a strong acid or base, it will dissociate essentially completely in water. If it is a weak acid/base, it will only dissociate partially in water, and some will remain in weak acid/base form. To determine if an acid/base is strong, examine the Ka or Kb value. If Ka or Kb is large, t...

Albert Chong_1L

Hi, Since buffers can be weak acids or bases and either will neutralize both strong acids and bases, how does one select the best buffering solution? I assume that adding a salt containing the conjugate of a weak acid or base would be the easiest way to adjust buffering capacity in which case weak a...

Albert Chong_1L

To determine the strength of an Acid/Base, you can calculate and interpret the Ka and Kb values. Remember that Ka = [H+][A-] / [HA] and Kb = [BH+][OH-] / [B]. Ka and Kb are the acid and base dissociation constants respectively. A higher Ka or Kb would mean a stronger acid or base respectively. In ge...

Albert Chong_1L

Hi, When we write the formula for a TM, does it matter the order which the ligands are placed in? I know for naming that the ligands come in alphabetical order before the TM. For example, for tetraamminedichloronickelate(II), would the formula be: [NiCl2(NH3)4] or [Ni(NH3)4Cl2] Also, do we put brack...

Albert Chong_1L

It's alphabetical, so cyano before ethylenediamine.

Albert Chong_1L

Let's clarify first that both the CN- (cyano) and Cl- (chloro) are (anionic) ligands.
From there, we just put them in alphabetical order so chloro is before cyano.

Albert Chong_1L

If concentration of both reactants and products change, you would use the new concentrations as the initials in your ice table and calculate a Q value. Then you would compare the derived Q with the known K value during equilibrium. If Q is smaller than K, the reaction will proceed towards the produc...

Albert Chong_1L

Hi, I know that adding any quantity of inert gas to an equilibrium reaction has no effect on the equilibrium constant and reactant/product concentrations remain the same. However, I don't see why adding an inert gas does not shift the equilibrium towards the side with fewer moles of gas since the in...

Albert Chong_1L

Yes, Lisa. The subscript numbers represent which energy level the (valence) electron(s) are in.
So if an electron was on Pi2px, for example, it would be in the 2nd energy level.

Albert Chong_1L

Hi, If asked to identify the molecular orbital that an unpaired electron occupies in a molecule, are we expected to provide all three of these or only 1 or 2 of them? (If all 3, an example answer would be Pi*2Py) 1. The energy level of the orbital 2. Whether it is bonding or antibonding 3. Shape of ...

Albert Chong_1L

Hi,

I was wondering if a molecule with a fractional bond order of 2.5 is more stable than a molecule with a integer bond number of 2. (It should be since 2.5 is greater than 2?)

Thanks.

Albert Chong_1L

Hi,

For antibonding molecular orbitals, I was wondering why the sigma*s orbitals have a higher energy than the pi*p orbitals. In bonding orbitals, the opposite is true because s orbital electrons penetrate less than p orbital electrons.

Thanks.

Albert Chong_1L

Hi all,

I was wondering why a molecule with Square Planar Configuration (AX4E2) would prefer staying in a 2D plane rather than using 3D space to minimize electron repulsion. Perhaps the 2D shape just happens to be the one that minimizes repulsions?

Thanks.

Albert Chong_1L

In what way do radicals react/interact with DNA to damage it?

Albert Chong_1L

How does one correlate the electrons of a Lewis structure to which orbitals they are in? For example, for oxygen, is one electron pair assumed to belong to the s orbital while the other pair and unpaired electrons are assumed to belong to the p orbitals?

Albert Chong_1L

First recall that subshells with higher “l” (the quantum number “l”) values have greater energy than subshells with lower “l” values. For example, the f orbital (l=3) has more energy than the d orbital (l=2). Electrons of higher orbitals are “less penetrating” (less likely to be found near the nucle...

Albert Chong_1L

How does a photon have momentum p (as in E=pc) if it has no rest mass?
Wouldn't momentum, p=mv=0?
Does that mean that photons have mass but the mass is so tiny it can be considered 0?

Albert Chong_1L

Plank's constant sometimes uses the units "J-s" and other times "m^2 kg / s."
How does one become the other and which should we use for class?

Thanks!

Albert Chong_1L

How does one quickly identify a reaction as redox?
Are there any giveaways to look for in the reaction?

Thanks in advance.

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