CHEMISTRY COMMUNITY

Michael Novelo 4G

alright I understand we subtract them from each other but what values are we plugging in to get the 1.26V? delta G = -(3 x 96,485 x 1.40) - (-1 x 96,485 x -1.69) is what I'm doing and that's wrong.

Michael Novelo 4G

Did anyone who attended Lyndon's review session know how he got E (knot) = 1.26 I know he said to use Delta G = -nFE since it is a state function but I'm confused on the math aspect of it. He said n=3 for the first line and , n=1 for the second line and the total should equal to n=2. are we subtract...

Michael Novelo 4G

Celio_G_Dis2C wrote:I didn't even know he was making one

yea there's one tomorrow on Saturday March 16, 3-6pm, Dodd 147, Lyndon Bui, Hannah Chew, Electrochemistry, Kinetics in case you want to attend. Although I haven't heard about the worksheets being uploaded to chemistry community. Usually they're posted by now.

Michael Novelo 4G

I haven't heard anything yet and it's Friday does anyone have any updates?

Michael Novelo 4G

Philipp_V_Dis1K wrote:1/16= (1/2)^4, so that means 4 times the halflife. 1/4=(1/2)^2 so 2 times the halflife. for part c, use the second order reaction

this method only applies to first order reactions.

Michael Novelo 4G

Usually instantaneous since for graphs we're comparing the concentration vs time. we usually find a concentration at a specific moment in time.

Michael Novelo 4G

it's bimolecular, the coefficient is 2 if it were O3 it'd be unimolecular because there's only one molecule of it.

Michael Novelo 4G

because half life will always taking the form of k1/2 = 1/k[A]o (for a zero order reaction) since k is always on the bottom/denominator for any order if it increases then the value of k1/2 (half life) decreases and vice versa

Michael Novelo 4G

because the integrated 2nd order reaction equation is 1/[A] = kt + 1/[A] where kt is the slope using the equations y = mx + b if mx is a positive then the slope is increasing. The first and zero order have a -kt value in the integrated equation so its slope is negative and is decreasing with time.

Michael Novelo 4G

its going to be a similar format to 14A if you had Lavelle last quarter. The questions are fairly evenly spread out with the material we've learned this quarter. I wouldn't expect a huge emphasis on acid base equilibrium maybe 2 questions max. There probably will be a larger emphasis on midterm mate...

Michael Novelo 4G

Yes initially I believed it had to do with stoichiometric coefficients since it had to do with moles but it has to do with the oxiditation state and electrons transferred in a balanced redox equation.

Michael Novelo 4G

For the unique rate we use the form aA -> bB + cC or can be different depending on how many Reactants and products there are. Regardless of the coefficients it will always have the form of 1/b(coefficient) × d [b]/dt for example. The Reactants form will be have a negative sign and products will not....

Michael Novelo 4G

From the looks of it on his website its just integration and derivatives it doesn't seem that we need to know anything that complex. With the power rule and basic integration and derivatives rules in mind you should be ok. if you know integration "instantaneous rate" may seem familiar.

Michael Novelo 4G

also -PdeltaV refers to the irreversible function and -nRTln(v2/v1) refers to the reversible function. The reversible will always do more work since pressure is changing in infinite small amounts.

Michael Novelo 4G

The previous statement is correct. For Gibbs free energy to be spontaneous it has to be negative so with a high temperature and positive value of delta S and a positive value of delta H the answer will always be negative of delta G which indicates it's spontaneous. Higher temperature increase does n...

Michael Novelo 4G

First make sure the equation is balanced. and then compare reactants to products to form the half-reactions: oxidation and reduction. The oxidation reaction occurs when the Reactants gain a higher + charge. To balance out you add the electrons from the positive charge gained to balance out, for exam...

Michael Novelo 4G

It's commonly used in ΔS=nCln(T1/T2) when the questions states its an ideal gas or monatomic gas, if the question ask to calculate entropy with constant volume (Cv then use 3/2R) if it is constant pressure (Cp then use 5/2R) and R is based on the units of measurement.

Michael Novelo 4G

Hi I was wondering if anyone can assist me on this question I have provided a photo of it. I was wondering why the cis has 12 orientations and why the trans only has 3. I can see why the cis can have 12 orientations but the trans only having 3 orientations is confusing to me. I thought Trans would h...

Michael Novelo 4G

Hi everyone, I was unable to attend professor Lavelle's review session today on Monday on past exam questions and I was wondering if anyone who attended can share their notes through pictures. I would greatly appreciate it, thank you.

Michael Novelo 4G

Usually it'll be given but the biggest difference has to do with the amount of pressure and if it changes "infinitesimal" Its a reversible process if the pressure is being slightly changed like 1 millionth less compared to the pressure of the system. If the pressure change is a large numbe...

Michael Novelo 4G

when a solid becomes a liquid or vice versa the volume isn't really changed. When a solid or liquid becomes a gas then there is a change in volume because the gas wants to expand it has different characteristics compared to a solid or liquid.

Michael Novelo 4G

Outlines 1 through 4. On outline 4 until 4F, entropy. Everything up till entropy. The outlines on the class website go into further detail in what we should focus on.

Michael Novelo 4G

no it simply means heat of the system has been released to its surroundings and should equal one another.

Michael Novelo 4G

In addition to the previous statement we can think about it using the analogy Lavelle gave about using an airpump on a tire. We use energy when pumping air, the energy is lost and the system which is the bike gains the energy. We exert negative work and the bike has positive work.

Michael Novelo 4G

Essentially no energy is lost in the universe since the universe accounts for all matter and everything. There is nothing larger than the universe so no energy is transferred out or in and no matter is added or lost in the universe.

Michael Novelo 4G

In addition to what has been said he defined Enthalpy as the amount of heat released or absorbed at a constant pressure. Exothermic reactions gives off head and loses energy such as a peice of wood burning on a fire and Delta H is negative. Exothermic is he opposite. He also introduced vaporization ...

Michael Novelo 4G

Yes and when solving its Reactants minus the products where the Reactants are always a positive value since there is bond breaking and products are negative since binds are formed.

Michael Novelo 4G

In addition to what has previously been stated if the Reactants - Products equals a negative value then the reaction is exothermic and if it is positive it is endothermic.

Michael Novelo 4G

If you refer to page 402 in the 7th edition of the book and look at Table 5G.2 you can see how the equilibrium constant changes with increased temperature on different equations. Each equation reacts differently so there's no specific rule I believe if you increase temperature. It's more of a concep...

Michael Novelo 4G

often times Kp will be used when the reaction involves gases and ask for the partial pressure. If the question is asking for molar concentration automatically assume to use Kc. Also remember when using Kc use brackets which indicate concentration and for Kp use parentheses to indicate partial pressu...

Michael Novelo 4G

: List of strong acids and bases

this was a list at one of the workshops last quarter.

Michael Novelo 4G

I believe activity is everything that is occurring during an equilibrium reaction. If you look to page 400 on the textbook (7th edition) there is a table that shows activity and then the simplified version. In the activity for an ideal gas substance it is written as Pj/P^o the P^o in this case are t...

Michael Novelo 4G

Neither Kp or Kc is preferred but often times Kp will be used when the reaction involves gases and ask for the partial pressure. If the question is asking for molar concentration automatically assume to use Kc. Also remember when using Kc use brackets which indicate concentration and for Kp use pare...

Michael Novelo 4G

Pure substances can't be separated into other substances. Air for example is a mixture of different gases so it is not 'pure'. Pure substances are also made of the same material throughout so a solid and liquid are physically the same throughout I believe.

Michael Novelo 4G

There should be a double bond between on Cl and O because the overall charge is -1 so the single bond between Cl and O would be -1 for O. Cl formal charge zero and the double bond for Cl and O would have a formal charge of zero for O. O is electronegative so it would want the -1 charge.

Michael Novelo 4G

I believe whatever is in the brackets is what ligands are attached to the metal atom in this case 5 ammonia (if the 5 is the subscript of ammonia) and 1 Chlorine for a total of 6 coordination. The Br3 is left out since it's not being coordinated with Pt

Michael Novelo 4G

Correct when looking at molecular shape we only focus on what's surrounding the central atom and thats when we use the VSEPR Formula such as AX3E to indicate how many bonds and lone pairs (if any) are attached to the central atom. The lone pairs will cause repulsion which will change the bond angles...

Michael Novelo 4G

Hybridization is based on electron densities surround a certain atom, similar to how we view electron density arrangements of molecules, we take a single bond, double bond, triple bond or lone pair as 1 form of electronic density. In other words a triple bond is the same as a single bond in terms of...

Michael Novelo 4G

The lone paired cause repulsion with other atoms. The more lone pairs there are the more repulsion there is causing bond angles in molecular shape to decrease depending on the plane it is in. Lone pairs are the reason why molecules such as H2O have a bent shape, it has 2 lone pairs of electrons whic...

Michael Novelo 4G

The coefficient number in front of the S orbital means the period or energy level it is in. Hydrogen is in period 1 and would be written as H1s and then Carbon is in period 2 and is written is as C2S, that is if it were to have one unpaired electron like Hydrogen does.

Michael Novelo 4G

It has to do with the formal charge stability. In the photo the charge of I is 2 and the charge of O is -1 for a total charge of -1. In the case of double bonds I is a charge of -1 and O is 0 which is a total charge of -1. The reason why Iodine should not have a charge of -1 and is less stable is be...

Michael Novelo 4G

Lone pairs on neighboring atoms repel each other and weakens the bond.

Michael Novelo 4G

All ionic bonds have some covalent character because the anion is attracted to electrons, and electrons are being shared between a molecule. Ionic bonds have higher polarity than covalent bonds do, going down the periodic table increases the distortions of ions which have higher polarizing power, wh...

Michael Novelo 4G

In the example Sulfur Tetrafluoride, SF4 he showed us in lecture S acts as the central atom and the 4 fluorine atoms were each separately attached by a single bond. We know the SF4 has 34 electrons total so the Lewis structure should have 34 total. We know that the first thing we should ensure befor...

Michael Novelo 4G

Delta positives usually give electrons. Delta positives are typically central atoms such as in AlCl3. Al has 3 electrons to give so it bonds with 3 Cl atoms. If you visualize the electron pull it goes towards the delta negative which in this case are the Cl atoms. Electron pull goes towards the delt...

Michael Novelo 4G

You can tell if a molecule is polar or non polar based on its molecular shape. If the shape is symmetric then it is considered nonpolar and if it is not symmetric to the central atom its considered polar. When the molecule is not symmetric it is because the dipole moments do not cancel out with one ...

Michael Novelo 4G

If it were on a test I'd imagine the electronegativity values would be given to each element listed because between 1.5 to 2 the molecule tends to have some covalent character, and to figure out that precise value some number would be given to us I'd imagine. So I wouldn't worry about it too much bu...

Michael Novelo 4G

Also, will hydrogen, ionic, and dipole dipole bonds always have polarizability? Yes, Polarizability is the ability to form instantaneous dipoles. Dipoles form when a molecule has a positive charge and a negative charge such as Na+Cl-. Also in hydrogen bonding it's also important to note that Hydrog...

Michael Novelo 4G

It's important to note that the more Polarizability an element has means the more electrons it has which means it is more distorted and the electrons are less tightly held. An example the professor uses is going from Helium to Xenon, Xenon has more electrons and has more polarizability.

Michael Novelo 4G

The electron configuration for Ga(3+) would be [Ar]3d^10 since the configuration of Ga is [Ar]3d^10 4s^2 4p^1 and we are removing 3 electrons the 4s^2 and 4p^1 are the ones removed.

Michael Novelo 4G

If you see where Cl is on the periodic table, it is on period 2, group 17. If we count how many valence electrons it has, (just counting from period 2) you see it has 7 valance electrons. The 7 electrons can either be lost, all 7 of them to form an octet that results in a charge of +7 or it can gain...

Michael Novelo 4G

Its important to remember that there are two exceptions in the first row of the d block. Cr or Chromium's configuration is [Ar]3d^5 4s^1 and the other exception is Cu or copper which has the configuration [Ar]3d^10 4s^1. I believe one of the TA's mentioned that there are more exceptions further down...

Michael Novelo 4G

Each orbital requires an octet of 8 valence electrons. If for example the element being observed is Ca or calcium its best to lose 2 electrons rather than gain 6 because gaining 6 additional electrons would make it very unstable.

Michael Novelo 4G

In the case of NaCl Na becomes a cation (+) and Cl becomes an anion (-) Na+Cl- to form sodium chloride. With this the ionic bond it is now stable. The - charge indicates that the electron was added and a + charge means a electron was lost. If the charges aren't labeled then the bond isn't considered...

Michael Novelo 4G

On quiz 2 there was a section with orbitals I was confused with what a 5s-orbital entails. How do we know how many electrons it has and how exactly do you get a 5s-orbital?

Michael Novelo 4G

Also if you rearrange the equation to Wavelength = c/v if frequency (v) is larger than we know that wavelength is smaller and if its the opposite where frequency (v) is smaller the wavelength will be bigger. This also woks when Frequency (v) = c/wavelength. Also the units for wavelength are typicall...

Michael Novelo 4G

I believe some fundamentals may show up during calculations such as avogadro's number when converting photons to moles. Or calculating the molar mass of an element. Some examples where this is seen in the textbook are problems 1B7 part B and C. Also the second questions of 1B9 requires converting fr...

Michael Novelo 4G

To answer the second part of the question of 1B9 "How many moles of photons are emitted in that time interval?" you would multiply your number of photons from the first question and multiply that by (1mol/(6.022 x 10^23 photons) to cancel out the photons and get the moles produced of photo...

Michael Novelo 4G

In previous lectures the professor discussed how during a rainstorm, raindrops act as a prism and when light goes through them it displays different colors causing a rainbow. My question is why do we typically only see one rainbow and not multiple ones spread throughout the city if rain is occurring...

Michael Novelo 4G

As the mass increases, the denominator in the equation λ=h/mv increases which in turn decreases its wavelength because λ is a constant. Do you know why 10^-18 specifically? Is it because it is the smallest wavelength that is detectable by most instruments? Thanks It is not 10^-18 specifically but t...

Michael Novelo 4G

If Planck's constant was zero then E=hv would not be possible as well as the De Broglie equation would also not work since they would both equal zero. Researching I found that the Planck constant is a "physical constant that is the quantum of action, central in quantum mechanics."

Michael Novelo 4G

Usually the problem gives you a certain amount of a element or substance to start off with for example 8.00 g of Fe and it would ask you to solve for another variable. In this case use the 8.00 g Fe as a reference point to how many sig figs your answer will be in this case it will be 3 sig figs. It'...

Michael Novelo 4G

I was confused with part c of question E.17 in the Atkins 7E textbook. Which sample in each of the following pairs contains the greater number of moles of atoms. (C) 7.36 x 10^27 atoms of Ru or 7.36 x 10^27 atoms of Fe. I began with trying to convert the atoms back to moles by dividing the 7.36 x 10...

Michael Novelo 4G

What happens when you are dividing the given molar mass by the molar mass of the empirical formula in order to find the molecular formula and get a number like 2.18. Do i just round this to 2 and multiply the empirical formula by 2? Is there a certain problem you are referring to so we could see as...

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