CHEMISTRY COMMUNITY

Abigail Yap 2K

I believe nF = -deltaG/E is derived from the equation deltaG = -nFE. However, I am not sure how we are supposed to know that It = nF. I think we would be given this equation if needed on an exam.

Abigail Yap 2K

I think this is because k and temperature are not directly proportional (they change at different rates), whereas rate and concentration are directly proportional for a reaction that is first order in A (rate = k[A]).

Abigail Yap 2K

I think we always assume standard conditions (298K, 1atm) unless stated otherwise.

Abigail Yap 2K

Hi,

The steady state approximation method assumes that one of the intermediates in the reaction method is consumed as quickly as it is generated. Its concentration remains the same throughout the reaction.

Abigail Yap 2K

How do we know if our proposed reaction mechanism is the correct one?

Abigail Yap 2K

How do we determine the best species to propose as an intermediate?

Abigail Yap 2K

Hi,

I believe the rate of reaction is used to calculate the speed at which the concentration changes over a period of time (delta[A] / delta t), while the instantaneous rate of change is used to calculate the rate of reaction at a single point.

Abigail Yap 2K

Hi,

I believe zero order, first order, and second order all depend on initial concentration when calculating rate laws.

Abigail Yap 2K

Hello,

So far, Dr. Lavelle has never asked for derivations on our exams, so I do not expect that he will for this week's test.

Abigail Yap 2K

The formula for the current (I) is:

I = deltaG / -(Et)

Abigail Yap 2K

Hi,

I think this may actually be a typo in the solutions manual. If I am not mistaken, they should have used the same phase (aq) for both.

Please correct me if I'm wrong!

Abigail Yap 2K

What is the purpose of inert electrodes in galvanic cells? (i.e. Pt)

Thanks!

Abigail Yap 2K

How do we determine which species is the oxidizing / reducing agent?

Abigail Yap 2K

I believe we have to balance the redox reaction and see how many moles of electrons are transferred in the equation.

Abigail Yap 2K

The last step is to balance the charges. You currently have a charge of -2 on the left side of the reaction, and a charge of 2(-2) + 10 = +6 on the right side of the reaction. Adding 8 electrons to the products side will balance the charges. Your final balanced reaction will be: S2O3(2-) + 5H2O -> 2...

Abigail Yap 2K

The vibrational motion causes disorder, so entropy increases. Diatomic molecules would cause greater entropy because the dissolution of polyatomic molecules results in a greater number of particles than the dissolution of monatomic molecules.

Abigail Yap 2K

Hi,

I think we would determine which equation to use based on the information we are given and what we are trying to solve for.

Abigail Yap 2K

Hi,

I believe the first equation is used when the system is at equilibrium (constant pressure) and the second is used when the pressure is changing.

Abigail Yap 2K

Hi,

The system is isolated because the question states that the cooler is "ideal." An IDEAL cooler would be perfectly insulated and would not exchange any matter or energy with its surroundings (we would not find such a cooler in the real world).

Abigail Yap 2K

Hi,

The midterm will most likely cover everything we've learned so far, so that would include internal energy and work calculations.

Abigail Yap 2K

Hi,

Delta S is the change in entropy and delta U is the change in internal energy.

Abigail Yap 2K

Hello, In Friday's lecture, Dr. Lavelle went over the derivation of the formula delta G (standard) = -RTlnK. He then discussed the values of K that make delta G positive, negative, and equal to zero. He also taught us how to derive the equation lnK = (-deltaH/RT) + (deltaS/R) by manipulating formula...

Abigail Yap 2K

It is important to consider the different possible microstates when determining degeneracy (w) because degeneracy is defined as the number of different arrangements that allow for a given energy state.

Abigail Yap 2K

We used integrals to derive the work equations because when systems are at equilibrium, changes within them occur infinitesimally. The integral allows us to sum together all of these small steps to calculate the total work. As mentioned above, the integrals were only used for the formula derivations...

Abigail Yap 2K

Hello!

Positional entropy refers to the number of molecular positions or arrangements that a system can have, whereas thermal entropy refers to the amount of thermal energy that is not available for any useful work.

Abigail Yap 2K

Yes, I think we only use this equation when the system is at constant pressure (delta P = 0)!

Abigail Yap 2K

Hello,

Based on my experience in Lavelle's 14A class, we will be provided with what we need to know.

Abigail Yap 2K

Can someone please clarify the definitions of and differences between reversible and isothermal expansion? Thanks!

Abigail Yap 2K

Hello,

Can someone please clarify the differences between reaction enthalpy and enthalpy of formation? Thanks!

Abigail Yap 2K

Hello,

I am having difficulty understanding the concept of internal energy and its importance in determining enthalpy. Can someone please clarify this for me? Thanks!

Abigail Yap 2K

Hi,

Extensive properties depend on the amount of matter in a sample, whereas intensive properties do not. For example, volume is an extensive property and density is an intensive property. Hope this helps!

Abigail Yap 2K

Hi, I know this question has already been asked, but I am still unsure about this topic. How do we determine whether a molecule is monodentate, bidentate, etc. based on its formula? The examples given in review session were solved using Lewis structures, but I do not understand how we can know the s...

Abigail Yap 2K

Hi,

If I remember correctly, it was said in a review session today that that number indicates the row on the periodic table. C is in the second row, so a 2 is placed in front of the hybridization. Please correct me if I'm wrong!

Abigail Yap 2K

Hi,

For reactions in the gas phase I think it is better to write Q in terms of partial pressures.

Abigail Yap 2K

Hi,

Unless we are given this information, we cannot know the exact angles. It is enough to say that the angle is slightly less than 109.5.

Hope this helps!

Abigail Yap 2K

Hi,

Adding onto the previous reply, you have to find the structure with formal charges closest to zero while also obeying the octet rule. Simply positioning the electrons in a way to get the charges to zero is incorrect. I hope this helps.

Abigail Yap 2K

Hi,

I think we should list all of the bond angles present in the molecule.

Abigail Yap 2K

I think we just draw the most stable structure based on formal charge unless the problem specifically asks for resonance structures. I am not entirely sure, though.

Abigail Yap 2K

Hi,

Radicals have unpaired electrons. To determine which of these species are radicals, we simply calculate the number of valence electrons that each has; those with an odd number of electrons will have an unpaired electron and therefore be a radical species. Answer choices b and c are radicals.

Abigail Yap 2K

Just to confirm, we are not expected to have polyatomic ions memorized for the midterm, correct? Thank you!

Abigail Yap 2K

Hi,

I believe the central atom is the one with the lowest electronegativity, not the lowest ionization energy. In this case, the least electronegative element is nitrogen.

Hope this helps.

Abigail Yap 2K

The g subshell is simply the next subshell and it has nine orbitals for a total of eighteen electrons. I think that there aren't currently any known elements whose ground-state configurations reach the g subshell.

Abigail Yap 2K

Most of the periodic tables I've seen are color coded for these categories. I believe this is just something we memorize or will have given to us.

Abigail Yap 2K

Hello!

I think this is because the three electrons removed from Tl to form Tl3+ are taken from the highest energy orbitals 6s and 6p. Therefore, the Tl configuration [Xe]4f14 5d10 6s2 6p1 will become [Xe]4f14 5d10.

Someone please correct me if I'm wrong!

Abigail Yap 2K

Hello! Yes, the 4s orbital has a higher energy than the 3d orbital.

Abigail Yap 2K

Hello! For this problem, we use the de Broglie equation lambda = h/(mv). If the distance travelled in one second is equal to wavelength, this means that the velocity is equal to wavelength. We figure this out using the formula d = vt (distance = velocity x time): d = vt = v(1 s) = lambda -> v = lamb...

Abigail Yap 2K

I believe these different values for the Rydberg's Constant are equivalent, simply differing in their units. The 3.28 x 10^15 value is in Hz, and the 1.09 x 10^7 is in m-1. We use the first value for the equation E = -hR/n^2.

Abigail Yap 2K

Yes; the electron must gain energy in order to jump up an energy level (i.e. by absorbing light).

Abigail Yap 2K

I converted the 0.512g of CO2 to moles of CO2, converted the moles of CO2 to moles of C, and the moles of C to grams of C. I then calculated the mass of H by going through these same steps for the H2O. This gave me 0.140g C and 0.0234g H. I then calculated for the mass of O by subtracting the masses...

Abigail Yap 2K

It is not necessary to calculate the percent compositions or use a 100g sample. After converting the given masses to moles, you will then divide each one by the smallest value. This will give you a ratio of the atoms relative to each other, which is all you need to write an empirical formula. Hope t...

Abigail Yap 2K

My approach for this problem utilized the key concept that dilutions do not change the number of moles of solute in a solution. Assuming that the amount of X will remain the same after the 90 dilutions, I simply calculated for moles by multiplying the starting 0.10M molarity by the starting .010L vo...

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