CHEMISTRY COMMUNITY

Ahmed Mahmood 4D

The question asks you to calculate an irreversible expansion from 4.52 L to 6.52 L under constant external pressure of 1.00 atm for part a. The answer to this should be 2.23, as the change in volume is 2.23 L and the pressure is constant, but the book puts it as 226 J. Why?

Ahmed Mahmood 4D

Please, provide the full question when possible since we don't have full access to the midterms. Thanks in advance! :) “4 Moles of butane (C4H10) are used for cooking. What mass butane id this? Will this combustion do expansion work? Calculate change in internal energy for the rxn. Assume rxn will ...

Ahmed Mahmood 4D

I’d look through the textbook/notes and memorize concepts and formulas relating to third order rxn. Anything that isn’t mentioned probably isn’t necessary.

Ahmed Mahmood 4D

For question six on the midterm, you add work and change in enthalpy to get change in internal energy. I calculated 19.1 kj for work and 11.5 kj for change in enthalpy—how was my change in internal energy -11.5 kj?

Ahmed Mahmood 4D

Since the researcher’s publication was the reverse reaction of the original reaction, wouldn’t her equillibrium constant just be the inverse of the forward reaction’s equillibrium constant? If not, what is it supposed to be, and why did I get points taken off for my answer?

Ahmed Mahmood 4D

What is the reduction reaction and potential of water that we must refer to when covering topic 6.O?

Ahmed Mahmood 4D

"Calculate the potential of a cell constructed with two nickel electrodes. The electrolyte in one compartment is 1.0 M Ni(NO3)2. In the other compartment, NaOH has been added to a Ni(NO3)2 solution until the pH = 11 at 298 K. Use Table 6I.1" I’ve found the concentrations of both nickel ion...

Ahmed Mahmood 4D

Think about it like this: You have two reaction rates, and you want to compare how the factor is affected by the addition of a catalyst. You know that adding a catalyst changes the activation energy; you know that changing the activation energy changes the reaction rate; you know the formula for the...

Ahmed Mahmood 4D

It increases the rate of both of these reactions equally and leaves the equilibrium constant unchanged.

Ahmed Mahmood 4D

Rate depends on concentrations at various points in the reaction, while initial rate depends on the initial concentrations of the reactants.

Ahmed Mahmood 4D

Platinum is an inert conductor added in order to conduct a charge. You add platinum when no other inert solids are able to perform conduction in the cell.

Ahmed Mahmood 4D

They both serve the same purpose and thus have essentially no reasonable difference in this class.

Ahmed Mahmood 4D

Electroplating makes use of redox reactions. For example, when zinc plates iron and this zinc coat is scratched, iron borrows electrons from zinc to keep itself from being oxidized and thus preventing rusting.

Ahmed Mahmood 4D

Yes--after balancing the redox reaction and finding the intermediate electrons transferred, you use this number of electrons as 'n,' as they are the moles of electrons.

Ahmed Mahmood 4D

Intermediate molecules are not a part of the overall reaction, as they are produced and consumed in separate elementary steps of the reaction.

Ahmed Mahmood 4D

Yes. In order to get overall order, you simply add the powers of the reactants--so, two reactants of first order will form a second order rate law for the overall reaction.

Ahmed Mahmood 4D

Different order reactions have different numbers and sequences of steps to form the final product. They also have different powers in the rate law.

Ahmed Mahmood 4D

In question 7.D.5, the solution manual shows that .59 is subtracted. This does not fall into line with the equation ln(k1/k2)=eA/R(1/T1-1/T2). How did they get this value then?

Ahmed Mahmood 4D

You can convert ln(x/y) to ln(x)-ln(y). To obtain x or y, you simply take e and raise it to -x or -y, respectively.

Ahmed Mahmood 4D

The Van't Hoff equation, provided on the equation sheet, was necessary for this. That being said, I did another method where I calculated the K using the relation between E cell and gibbs free energy and got the same answer, but I do not believe that that was the way you were supposed to calculate t...

Ahmed Mahmood 4D

For 6.K.3 part D, how do we know

Ahmed Mahmood 4D

I understand that to balance oxygen, you add water to the side of the equation that is lacking in oxygen. However, how do you know whether to add hydroxide and water or hydrogen when balancing hydrogen in a redox reaction?

Ahmed Mahmood 4D

You assume that temperature is constant in one case and that volume is constant in the other, then you add the results of both of those equations.

Ahmed Mahmood 4D

No, as mentioned the content covered only goes to the end of entropy.

Ahmed Mahmood 4D

Entropy is based on the amount of positions that an object can occupy. Therefore, gasses and complex molecules have the greatest entropies, while solids and simple molecules have lower entropies.

Ahmed Mahmood 4D

Salts can be formed when an acid and base come together and are neutralized, forming water and a salt.

Ahmed Mahmood 4D

Heat can be seen as part of the reaction, with an exothermic reaction having heat in the products and an endothermic reaction having heat in the reactants. Thus, lowering temperature for an exothermic reaction will cause the reaction to sit to the right.

Ahmed Mahmood 4D

Percent protonation is the concentration of the conjugate acid over the initial concentration of the weak base multiplied by one hundred.

Ahmed Mahmood 4D

The reaction's direction shifts to balance out any changes made on the system. Accordingly, if there are more moles of products, the reaction will shift to favor the reactants when pressure is added in order to retain a balanced system.

Ahmed Mahmood 4D

R is a constant known as the gas constant. Its units are represented as Joules . mol^-1 and various other units such as atmospheres.

Ahmed Mahmood 4D

No—K is based on the rate of the forward and reverse reactions, not the concentrations of the products and reactants. Changing concentration will simply cause an imbalance between products and reactants, but this imbalance will be undone as the reaction returns to equillibrium and the equillibrium r...

Ahmed Mahmood 4D

BrOH is a strong base, and thus it will naturally be stronger than most other bases.

Ahmed Mahmood 4D

HOCl's anion is more stable because chlorine is more electronegative and is more stable (via delocalization) than HOI.

Ahmed Mahmood 4D

For one, sigma bonds go directly into one another and have a greater overlap, which makes it stronger than pi bonds, which must go outwards and then connect across a gap. Moreover, I believe interactions w/ multiple bonds are stronger because they have multiple bonds, not necessarily because they ha...

Ahmed Mahmood 4D

Not for naming, but it is important to know that a cis isomer has elements on the same sides of the molecule while a trans isomer has elements on the opposite sides of a molecule.

Ahmed Mahmood 4D

Because HSO4- has sulfur, which has a greater electronegativity than carbon, the anion is more stable (Due to electron delocalization) and thus its acid is stronger.

Ahmed Mahmood 4D

Yes--just because lone pairs are not written in a diagram does not always mean they are not there. As such, they must be accounted for in determining hybridization.

Ahmed Mahmood 4D

Larger molecules with many electrons and a greater surface area can be capable of being stronger than dipole-dipole forces in limited cases.

Ahmed Mahmood 4D

In 6.D.11, we are supposed to identify the pH of the solution when dissolved in water. Part c is KF and has a pH greater than 7. Wouldn’t KF dissociate to form two conjugates of strong bases and acids and thus not affect the solution, leaving it at 7?

Ahmed Mahmood 4D

Polarizing power corresponds to cations, the most polarizing power being found in the smallest cations with he greatest positive charge. On the other hand, polarizability corresponds to anions. The anions with the greater polarizability are the biggest. Whats the relation between polarizability and...

Ahmed Mahmood 4D

When drawing radicals, how do we know which element receives the ‘odd’ number of electrons (i.e which element gets seven electrons instead of eight)?

Ahmed Mahmood 4D

Is the hydrogen atom the only atom with which we will need to use Rydberg’s equation? Also, what is the constant?

Ahmed Mahmood 4D

405112316 wrote:Chelates are basically complexes that have ligands that form a ring of atoms around the transition metal ion. When ligands bond at more than one tie, they are likely to form a chelate.

Solid--what's a tie?

Ahmed Mahmood 4D

I don't exactly understand what chelates are (Beyond definition) or what their implications are--can anybody help me out with this?

Ahmed Mahmood 4D

What are the definitions of polarizability and polarizing power? What are the trends associated with cations and ions? What are the implications/what type of questions may we expect regarding such trends?

Ahmed Mahmood 4D

All molecules contain LDF, but they can also contain additional molecular forces such as hydrogen and dipole-dipole.

Ahmed Mahmood 4D

If other factors such as chemical structure and atoms are controlled for, yes, this is true.

Ahmed Mahmood 4D

As you move down a column, more energy levels are added to an atom, causing increased distance between the nucleus and valence electrons. Due to electron shielding (the interference of inner energy shells in the interactions between outer energy shells and the nucleus), electronegativity decreases a...

Ahmed Mahmood 4D

As many answers have stated, degeneracy refers to the number of possible quantum states on an energy level. A question might ask something like, 'How many degenerate orbitals are there in the p orbital of a carbon atom at ground level?' In this case, there are two degenerate orbitals in the p orbita...

Ahmed Mahmood 4D

Yes. De Broglie's equation is the equation that can be applied to objects w/ mass (Such as base balls and people) to determine their wavelength.

Ahmed Mahmood 4D

The Heisenberg uncertainty equation goes as follows: (mass)x(Velocity)x(Uncertainty in position)>/=h/4pi Using the data from the problem, we can find that the cricket ball is travelling at .042 m/s (Using dimensional analysis). Its mass is given (We use kilograms for mass whenever planck's constant ...

Ahmed Mahmood 4D

The work function can be thought of as the amount of energy required to discharge an electron from a metal surface. As such, the energy of the incoming photon-the work function=the kinetic energy of the discharged electron. The work function is sometimes given, but it can also be algebraically deter...

Ahmed Mahmood 4D

The textbook states that out of BaBr2, BeBr2, and BBr3, BaBr2 is the most ionic bond. Aside from difference in electronegativity/charge, what indicates that BaBr2 is more ionic than BeBr2?

Ahmed Mahmood 4D

Why is cobalt sometimes ‘cobalt’ and other times ‘cobaltate’ ? Moreover, is there a general transition metals list that we can refer to?

Ahmed Mahmood 4D

The question is: Is acetic acid or formic acid stronger?

According to the textbook, formic acid is slightly stronger.

Why is this the case? I figured that since acetic acid has more atoms, it would be more stable if a hydrogen was taken away due to electron delocalization.

Ahmed Mahmood 4D

Is there a set, defined way to find out if a substance is amphoteric?

Ahmed Mahmood 4D

Hi, the review session and exam locations upload states that the final will consist of questions from the homework and the online assessments. Can anybody confirm that this means that only focus questions, assigned homework, and the online assessments for audio-vidual focus topics will appear on the...

Ahmed Mahmood 4D

I personally would memorize the more common acids and bases, especially if they appear on the homework.

Ahmed Mahmood 4D

Memorizing the different strong and weak acids and bases would be the best way to go about solving these types of problems.

Ahmed Mahmood 4D

Given the fact that multiple homework questions necessitate the knowledge of both, it would make sense that you must know both for the final. After all, any one of those homework questions could appear on the final (The Final review session paper states that "Questions will come from the Homewo...

Ahmed Mahmood 4D

Polar molecules, or molecules with a larger dipole moment, have greater differences in electronegativity between atoms.

Ahmed Mahmood 4D

Since intermolecular forces are (far) weaker than intramolecular forces, they are easier to break.

Ahmed Mahmood 4D

You do not need to know the exact bond lengths, but you do need to know general trends that vary across different types of bonds. Exact bond lengths will be given if they are necessary, if I’m not mistaken.

Ahmed Mahmood 4D

Hydrogen bonding is extremely strong. Because of this, it takes more heat to break hydrogen bonds, leading to higher melting points among hydrogen bonds.

Ahmed Mahmood 4D

No. Typically, bonds between hydrogen and nitrogen, oxygen, and fluorine are hydrogen bonds.

Ahmed Mahmood 4D

Determinant factors include strength, molecular size, and electronegativity. London forces are usually weaker. Smaller molecules are primarily dipole-dipole, while the inverse is true for London forces. Greater differences in electronegativity typically indicate dipole-dipole forces.

Ahmed Mahmood 4D

Since electrons in the top right corner of the periodic table are closest to attaining eight valence electrons, they release more energy in order to receive that eighth electron and fill their outer shell.

Ahmed Mahmood 4D

When an electron is removed, the proton:electron ratio heightens. Because of this, the surrounding electrons become more attracted to the protons in the nucleus, requiring more energy to remove said electrons and thus a higher ionization energy.

Ahmed Mahmood 4D

From a premed who has been adjusting to UCLA's curriculum--thank you sm for this post and the advice!

Ahmed Mahmood 4D

As it wasn't covered in lecture, I don't believe so.

Ahmed Mahmood 4D

I don't believe so. Dr. Lavelle mentioned it but explicitly said it was not something we'd need to understand in class, so I don't believe it will be on the test.

Ahmed Mahmood 4D

I think that most equations will be on the cover sheet of the test, but equations that are specifically tied to content in 'The Quantum World' that we are supposed to memorize and/or derive are not.

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