CHEMISTRY COMMUNITY

Sandeep Gurram 2E

In the 2013 final question 8c, there is a Newman projection. How do you determine which conformation cyclohexane is by just looking at the newman projection?

Sandeep Gurram 2E

I would assume so. The cyclic structure is a substituent if the straight chain is longer than the cyclic structure.

Sandeep Gurram 2E

An electrophile is a species that wants to gain an electron. Usually this results in a polar bond between two elements. For example, HBr would be an electrophile as the Bromine in this compound pulls on the shared electrons, causing a positive charge around H and a negative charge around Br. A nucle...

Sandeep Gurram 2E

Yes, the species that gets oxidized should have the lower of the two standard reduction potentials.

Sandeep Gurram 2E

Hello,

I just faced a problem where apparently a methyl group has higher priority than a fluorine; is this true? My thought process was that the fluorine should have more priority as it has a higher atomic number over carbon.

Thanks

Sandeep Gurram 2E

For the example on page 17 of the organic chemistry textbook, why is (E)-3,7-Dimethylocta-1,3,7-triene trans and not cis? Doesn't the atom group attached the double bonds indicate that this is a cis stricture?

Sandeep Gurram 2E

Is it possible for a cyclic structure to have another cyclic structure as a substituent? For example is it possible for a cyclopentane structure to have a cyclopropyl substituent?

Thanks!

Sandeep Gurram 2E

When do we know to use the steady state or pre equilibrium approach in determining whether a proposed elementary mechanism matches an observed rate law? Are there definitive clues to look out for?

Thank You

Sandeep Gurram 2E

This is the process where you let the water heat to the vaporizing temperature (100 C), let it vaporize at that temperature, and then let it cool back down to the initial temperature (25 C). Water cannot normally vaporize at 25C, we have to use this special process to calculate the value of it.

Sandeep Gurram 2E

Internal energy is a state function because it doesn't matter how one got to the final state of a certain system. A system could do 100 J of work and end up at a particular internal energy. Another system could do 100,000 J of work and arrive at the same internal energy. Regardless of how much work ...

Sandeep Gurram 2E

Entropy increases with heavier atoms as heavier atoms have more vibrational energy than lighter atoms. Additionally, entropy increases with molecular complexity. Meaning when there are more atoms attached to the central atom of a certain compound, the entropy of that particular compound increases. A...

Sandeep Gurram 2E

U is internal energy.

Sandeep Gurram 2E

The desired reaction for a standard enthalpy of formation of any compound is just a balanced chemical reaction between the constituent elements in their standard states as reactants forming the desired compound as the product. For example, in this problem the desired standard enthalpy of formation i...

Sandeep Gurram 2E

When you are interpreting residual entropies for of a particular compound, how do you know how many orientations it can assume? The example in the textbook showed that FClO 3 had four orientations as it was tetrahedral. Is the molecular shape the only indicator of how many orientations a compound ca...

Sandeep Gurram 2E

Inadvertently, yes. The negative sign basically shows that whatever work a system performs is absorbed by its surroundings. Contrarily, whatever work is performed on the system by the surroundings is absorbed by the system and lost by the surroundings. They are equal and opposite.

Hope that helped!

Sandeep Gurram 2E

I think it is more along the lines of an increase in the expansion of gas will cause an increase in entropy. Entropy is a measure of disorder. Now, there is thermal disorder, disorder from increasing the thermal motion of molecules (heating a substance). There is also positional disorder, which is w...

Sandeep Gurram 2E

For problems involving irreversible expansion you would use w = -P_exΔV.

For problems involving reversible, isothermal expansion, you would use w = -nRT x ln(v_f/v_i)

The problem usually specifies the type of expansion you're dealing with.

Sandeep Gurram 2E

I'm assuming you're referring to 8.43, not 8.41. And you're correct in saying that the right answer is c; the solutions manual confirms this answer.

Sandeep Gurram 2E

You wouldn't use the Hvap= H(vapor)- H(liquid) formula for this question. All you have to do is find the enthalpy of formation in terms of kJ/mol. This involves converting the amount of methanol they gave in grams to mols and then dividing the amount of heat it took to vaporize to this amount by you...

Sandeep Gurram 2E

Heat transferred under constant volume can be calculated by finding the change in internal energy, ΔU. Heat transferred under constant pressure can be calculated b finding the change in enthalpy, ΔH.

Sandeep Gurram 2E

I'll take a mathematical perspective to show why q = Enthalpy at constant pressure: Change in Enthalpy as a state function can be represented by the equation: ΔH = ΔU + PΔV. Where H is enthalpy, U is internal energy, P is pressure, and V is volume. To show that q = enthalpy at constant pressure we c...

Sandeep Gurram 2E

You would use the Heisenburg Uncertainty Equation.

ΔpΔx≥h/4π

Sandeep Gurram 2E

Dr. Lavelle had an excellent explanation of this exact problem in his review session for the final. Basically, CH 3 is a more electron rich species than H is, and therefore has more of a negative charge associated with it. In fact H is basically considered a positive species. Because of this, CH 3 d...

Sandeep Gurram 2E

You use the HH equation when the reaction involves a weak acid and its conjugate base. Usually this implies that the K a value is going to be smaller than 1 x 10 -4 . However if the K a value is larger than that value then it is safer to go with the ICE box. Essentially, the HH equation is an approx...

Sandeep Gurram 2E

The more electronegative a certain atom is in a molecule, the more it draws on the electron density of the overall molecule. This pulling actually results in a higher stabilization state for the molecule. Therefore, the more electronegative a particular element is, the harder it pulls, and the more ...

Sandeep Gurram 2E

Sodium is not included because it is a spectator ion, so we just tend to leave it out.

Sandeep Gurram 2E

In order for acids and bases to neutralize each other, do they have to have the relatively close amounts to one another? Or can you have a lot of base and add a little acid to neutralize the two? (or vice versa).

Sandeep Gurram 2E

This is when calculating reaction quotient (Q c ) is very helpful. Remember, you use the same process to calculate Q c as you do to calculate the equilibrium constant. As Dr. Lavelle has outlined in class, if the reaction quotient is less than the equilibrium constant, (Q c < K c ) then the reaction...

Sandeep Gurram 2E

The ice table is required when the initial molarities of reactants and or products are given, but the equilibrium molarities are not. Typically, the equilibrium constant is provided and using the ice box, you have to solve for the change in concentrations for the reactants and products.

Sandeep Gurram 2E

The roman numerals after the cation name specifies the charge that the cation (central atom has). In the problem that you provided, since NH 3 has a neutral charge, we are left with two chlorines (one inside the coordination complex, and one outside). These two chlorines amount to a net -2 charge. A...

Sandeep Gurram 2E

Hello,

When naming a coordination compound, does a greek prefix play a role in the alphabetization? For example if a compound contained diammine and chloro, would the chloro come first since C comes before D? Or do we disregard the D and say that diammine comes before chloro? Thank You!

Sandeep Gurram 2E

It isn't something we have to calculate, at least for this class. However, there are general rules for which bonds between atoms might be stronger than other bonds. Normally, shorter bonds are stronger than longer bonds (i.e. triple > double > single). Additionally, bonds between atoms that have lon...

Sandeep Gurram 2E

Yes, according to the general rules of formal charge, if sulfur had double bonds with both oxygen atoms, the entire compound would technically be considered in a lower energy, more stable state. However, remember that formal charge is just a general set of rules you can follow, it doesn't mean that ...

Sandeep Gurram 2E

Why is it that in the Lewis structure of the hydrogen sulfite ion, the sulfur is not attached to hydrogen? Instead, the sulfur is attached to three oxygens and the hydrogen is attached to one of the oxygens. Why is this?

Sandeep Gurram 2E

What other properties are examined to determine whether a compound having an electronegativity between 1.5 and 2.0 is more ionic or more covalent? Professor Lavelle mentioned a compound's solubility in water can be indicative its chemical properties. Any other properties we can look at to tell wheth...

Sandeep Gurram 2E

The principle quantum number is always the period the element is located in. In this case, iron would have n=4, as it is in the fourth period. Principle quantum number is unrelated to which orbital electrons are being added to.

Sandeep Gurram 2E

Yes. Another shorthand phrase that is helpful for me to remember which elements are HON and the halogens. Another good one is Have No Fear Of Ice Cold Beer.

Sandeep Gurram 2E

Resonance structures are unique in that the electrons present in the structure are delocalized, meaning that they are not associated with one particular atom or bond in the chemical structure. This state of delocalization is the reason why resonance structures are generally more stable than non-reso...

Sandeep Gurram 2E

For both ionization energies and size there are general trends that have relatively few exceptions within their trends. However, electron affinities seem to be all over the place. Although it is true that the upper right elements generally have high electron affinities, there is not the same constan...

Sandeep Gurram 2E

Bryan did a great job of explaining. Basically, there is a greater electron-electron repulsion force within the oxygen atom than there is within the nitrogen atom because the eighth electron in oxygen is paired with an electron that is already occupying an orbital. This repulsion of electrons in the...

Sandeep Gurram 2E

Question (1.15): In the UV spectrum of atomic Hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line. I understand that you first have to use the λν = c formula to calc...

Sandeep Gurram 2E

There are 1.6022 x 10^(-19) Joules for every electron volt.

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