CHEMISTRY COMMUNITY

Chloe Qiao 4C

In class we talked about that when two solid are in the same half cell, we use a vertical line to separate them in the cell diagram. Do we do the same thing if they are two pure liquid species?

Chloe Qiao 4C

I believe they are not the same. Rate of formation depends on the coefficient of the products, but unique rate does not.

Chloe Qiao 4C

log is log base 10, and Ln is log base e. You can use this for conversion though I do not think there will be a problem asking for converting between these two.

Chloe Qiao 4C

For the final, how much do we need to know about ion-selective electrodes such as pH meter?

Chloe Qiao 4C

In a concentration cell, the half cell with higher concentration initially will be the cathode side and the one with lower initial concentration will be the anode side. As the reaction proceed, electrons transfer from the anode side to the cathode side, lowering the substance concentration in the ca...

Chloe Qiao 4C

Under the title "Topic 6O Exercises", it says that for the following questions use E=-0.42 for the reduction of water. I just compared the reduction potential of the ions with that of the water, and the species with higher reduction potential will be reduced.

Chloe Qiao 4C

Another ways will involve a table listing initial reactant concentration and reaction rate. Order of a reaction can also be determined when knowing the mechanism of the reaction and the slowest step in the reaction.

Chloe Qiao 4C

I believe it is not come from a formula. I do not have the sixth edition, but it looks like that the question is asking the concentration A at the time when B is 0.034M. The part after the minus sign is to find how much A has been used to give rise to 0.034M B, and subtract that from 0.153M A(which ...

Chloe Qiao 4C

It is correct. Zero order reaction usually involves a catalyst or enzyme that works at its maximum potential. Increasing concentration cannot increase the rate the catalyst or enzyme works, and therefore zero order reactions do not depend on the concentration.

Chloe Qiao 4C

I believe it is because of the integrated rate laws derived (specific sign because of the math).

Chloe Qiao 4C

Are we expected to know how to derive the integrated rate laws for the final? Or are we just need to know how to use them?

Chloe Qiao 4C

Can someone remind me what is the other inert conductor Dr. Lavelle mentioned in class besides Pt?

Chloe Qiao 4C

A line indicates that the substance are in different phases (e.g. Cu(s)|Cu2+(aq)), and comma representing two substances in same phase (e.g. Fe3+(aq)|Fe2+(aq)).

Chloe Qiao 4C

Consider HCl to be H+ and Cl-. The anode side will be H2 and H+, and the cathode side will be CL2 and CL-.

Chloe Qiao 4C

When writing the cell diagram for a reaction, when do we need to add inert conductor (such as Pt)?

Chloe Qiao 4C

The delta S refers specifically to the hot water and the cold water, and delta S total is the sum of delta S for the cold water and the hot.

Chloe Qiao 4C

I think you are right. Delta G depends on specific conditions the reaction is in, but standard delta G is just under standard conditions, which means that standatd delta G will be constant for a reaction.

Chloe Qiao 4C

Last semester with chem 14A the midterm was given back one week after it was taken.

Chloe Qiao 4C

Can someone explain if work is done on a system, do we use the positive or negative sign? What about for work done by a system?

Chloe Qiao 4C

I do not think there is a formula that always works for degeneracy. But it can be calculated using simple math. For example, if there are three particles and each can be in one of the two directions, then the degeneracy is 2^3=8.

Chloe Qiao 4C

It depends on the conditions that the problem gives. For example, if the question states that there is infinitesimal changes, use the reversible equation. When the change is too large(cannot by reversed by an infinitesimal change), then use the irreversible equation.

Chloe Qiao 4C

I believe that means the delta H is measured in standard conditions.

Chloe Qiao 4C

Athena L 1B wrote:If we have the equations U = q + w, q = H, and w = PV, why does U = H - PV, instead of U = H + PV?

Actually w=-PdeltaV(the negative charge refers to the direction that energy acts on), and this is why we get U = H - PV.

Chloe Qiao 4C

Can anyone tell me what is the SI unit we use for pressure? Is it atm or pa?

Chloe Qiao 4C

I think what Dr. Lavelle meant is that the equation can also be applied to liquids and solids, but the change is too small that we typically do not consider them.

Chloe Qiao 4C

Cellular respiration breaks down the energy contained by glucose and stores the energy in the form of ATP. The heart uses ATP but not the energy from breaking glucose bond directly.

Chloe Qiao 4C

During a chemical reaction, if a bond is broken, it must be broken completely so that new bonds can form. Also, different bonds have different strength and thus nees different amount of energy to break.

Chloe Qiao 4C

This question ask for the pH of 0.055M AlCl3(aq). Could anyone explain how we calculate the pH of a solution with highly charged metals?

Chloe Qiao 4C

The pH of a number is the negative log of that number. For example, pH(10^-1)=-log(10^-1)=1

Chloe Qiao 4C

The bronsted definition of acid is any species that can donate a proton, and a base is any species that can receive a proton. The conjugate acid of a base is a base gaining a proton(for example, the conjugate acid of NH3 is NH4+), and the conjugate base of an acid is an acid losing a proton (for exa...

Chloe Qiao 4C

Le Chatelier's principle is that after a change occurs, the reaction shifts to minimize the change. In the above equation, increasing [N2] would cause the reaction to shift right(forming more products), increasing [NH3] and decreasing [H2] will both cause the reaction to shift left (more reactants w...

Chloe Qiao 4C

Ana Pedreros wrote:If asked for the K expression, can Kc and Kp be used interchangeably?

I think the question will state clearly whether Kc or Kp is asked. If not, it will depend on the states of the substance involved in the reaction or the condition in the question.

Chloe Qiao 4C

Basically, yes; whenever you set up the ICE table, you start by assuming that the reaction hasn't taken place yet. Therefore, there won't be any products formed yet, so their initial concentrations are 0. So if we assume that the reaction hasn't happened yet, is that why for anything that has an in...

Chloe Qiao 4C

Consider "sitting" as describing which side (reactants or products) the reaction favors, and "shifting" only when referring to a change.

Chloe Qiao 4C

When asked to name the ligands of a coordination compound, do we name them as charged or uncharged?

Chloe Qiao 4C

An amphoteric substance is one that can act both as a base and as an acid. An amphiprotic substance is one that can both accept H+ and donate H+. Amphiprotic substance is a part of amphoteric substance. For example, if a molecule act as both lewis acid and lewis base but do not donate or accept prot...

Chloe Qiao 4C

There are two rules to decide the relative strength of two acids: 1. strong acids can lose proton(s) easily: if a acid has a long and weak A-H bond, then it can lose the proton more easily, and therefore making it a stronger acid. 2. strong acids has anions that are stable: 1) typically, if the anio...

Chloe Qiao 4C

Can someone explain why formic acid(CH2O2) is considered stronger than acetic acid(CH3COOH)?

Chloe Qiao 4C

For our final exam, will we be given a ligand name chart like the one on the class website or are we expected to memorize all of them?

Chloe Qiao 4C

Oxalate is a bidentate because the arrangement of its atoms only allows two oxygen to bind to a given metal at a given time.

Chloe Qiao 4C

We use bis, tris, tetakis, or pentakis as prefix if the ligand's name starts with di, tri, tetra, or penta.

Chloe Qiao 4C

For test 3 and the final, do we need to know the VSEPR shapes that are not covered in lectures(like T-shaped)?

Chloe Qiao 4C

Imagine 2 p orbitals side by side to each other, there are two regions of overlapping for each pi bond. If you hold one of the orbitals unmoved and try to rotate the other, at least one of the overlapping regions will no longer exist. Therefore, when you try to rotate a pi bond, it breaks.

Chloe Qiao 4C

You include d when the regions of electron density is higher than or equal to five.
2 regions of electron density=sp
3 regions of electron density=sp2
4 regions of electron density=sp3
5 regions of electron density=sp3d
6 regions of electron density=sp3d2
...

Chloe Qiao 4C

Cl and H have a large electronegativity difference; therefore, when Cl is positioned facing H, there will be an attractive force between them. If there are more Cl on one atom and H on another atom facing closely to each other, the intermolecular force will be stronger.

Chloe Qiao 4C

When there are four regions of electron density, the regions are tetrahedrally arranged. Just think about the model Dr. Lavelle used in class, when replacing a bonded atom with a lone pair, we are basically "taking off a yellow ball". There are no two balls that are arranged exactly opposi...

Chloe Qiao 4C

If a molecule has no dipole moments, it is nonpolar; if it has dipole moments but the dipole moments that cancel out, it is also nonpolar(for example, the two C-O bonds in CO2 are polar, but they are arrange exactly opposite to each other, so the dipole moments cancel out); if the molecule has dipol...

Chloe Qiao 4C

Polarizing power is the ability of a cation to distort an anion(like to which extent an atom can affect another atom), while polarizability is the ability to form instantaneous dipoles(How much the atom itself can be affected).

Chloe Qiao 4C

It means all molecules have Van der Waals forces and the forces are always attractive.

Chloe Qiao 4C

I believe for atomic radius, the element going up and down matters more because when you go down a group, there are additional shells added. For ionization energy and electron affinity, there are less obvious trends.

Chloe Qiao 4C

I believe usually it is the intake of energy that breaks a more stable molecule into parts and cause radicals to form. For example, Dr. Lavelle talked about the energy of photon can cause H2O to separate into H and OH in upper atomsphere while OH is a radical.

Chloe Qiao 4C

I think you need to draw the Lewis structures out to see how many resonance there are for a compound. And for your second question, usually we only choose the best representation(the one with most atoms having formal charge 0 and with the most electronegative atoms having the negative formal charges...

Chloe Qiao 4C

Usually two non-metals bond to form a covalent bond, while a metal and a non-metal bond to form an ionic bond.

Chloe Qiao 4C

I believe usually "shell" is referred to n, "subshell" to l, and "orbital" to ml.

Chloe Qiao 4C

If you mean the magnetic spin quantum number, +1/2 is for the anti-clockwise rotation and -1/2 is for the clockwise rotation.

Chloe Qiao 4C

I believe in the case of lithium and beryllium, lithium has only one electron in its 2s orbital but beryllium has two, which means the 2s orbital of beryllium is already full. Therefore, beryllium is like the noble gases in some way, when you add additional electron to its already full shell, it req...

Chloe Qiao 4C

Can someone explain how De Broglie equation is derived? I have on my notebook that energy is equal to momentum times velocity but I really do not understand this and could not go on.

Chloe Qiao 4C

I do not think h bar will be given as a constant during the test, but the equation of delta x * delta p >=h/4pi will probably on the equation sheet. So don't worry about h bar(unless you really like to use it and if so just remember h bar equals to h/2pi).

Chloe Qiao 4C

I believe it applies to the uncertainty in position. My TA said if we are given a question about an atom or a sphere, we need to pay attention to whether the given value is radius or diameter, and we need to use the diameter value for delta X.

Chloe Qiao 4C

I understand how electrons behave in experiments when energy of the incoming light equals to its threshold energy, but can someone explain what it is like in reality when the ejected electron has no kinetic energy?

Chloe Qiao 4C

In other words, use E=hv when finding the energy of a photon(the inputing energy), and Ek=1/2mv^2 as the energy of the ejected electron(energy left), which is the energy of the photon minus the threshold energy of the electron.

Chloe Qiao 4C

"I cannot conceptualize light being both photon (PACKETS) of energy and wavelengths. I find it difficult to exercise this into equations when I do not understand how it can be both and have one number. Please explain and possibly use equations in your explanation if possible. If not that is ok...

Chloe Qiao 4C

Don't worry about charges so much for now because we are not balancing ions but mostly molecules. Pay more attention to the charges and electrons when doing problems with redox reactions later.

Chloe Qiao 4C

I believe empirical formula does not directly refer to the mass percent composition of a molecule because mass percent composition is based on the mass of each type of atom over the total mass(and different atoms have different masses) while the empirical formula is more about the relative ratio of ...

Chloe Qiao 4C

I believe it's better to use 3 sig figs for your answer in part C even though the answer in the book only gives 2 sig figs because all numbers given in the question have 3 sig figs.

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