CHEMISTRY COMMUNITY

Andrew Liang 1I

I will attend!!! This is exactly what we need when all the other review sessions are cancelled

Andrew Liang 1I

I think when the question asks greater deltaT we need to assume that it is looking for the greatest reaction. 50 mL of 2 M HCl with 50 mL of 2 M NaOH is the answer because the volume is the smallest out of all the choices and the concentration for both species are the highest. In other words, they a...

Andrew Liang 1I

I think it will be given most of the time but if not I think we can determine the slow or fast step by: 1) Looking at the value of k. The smaller k is probably the slower step. 2) Looking at the activation energy for each step. The step with larger activation energy is the slower step. Both of these...

Andrew Liang 1I

I think we can determine the slow or fast step by: 1) Looking at the value of k. The smaller k is probably the slower step. 2) Looking at the activation energy for each step. The step with larger activation energy is the slower step. Both of these can be determined by the Arrhenius equation:k = A * ...

Andrew Liang 1I

It means that in the reaction we are assuming all the reactants except 1 to be large excesses, and therefore, constants.
For example: A+B+C --> P
we assume B and C are large excess and so the pseudo 1st order rate law would just be kprime[A], where kprime = k[B][C]

Andrew Liang 1I

Dr. Lavelle said that in unimolecular reactions the molecule does not have to collide with other molecule. The molecule can collide with the side of the beaker or with solvent that is not a part of the chemical reaction. These collision can cause bond breaking in that one molecule resulting in unimo...

Andrew Liang 1I

I don't think the unit matters too much in Q because we learned that K (equilibrium constant) does not have unit. Q and K are essentially very similar where they both are the reaction constant.

Andrew Liang 1I

If the standard reduction potential is negative it means that the reverse reaction is favored, which I think it means that the reaction is spontaneous if it is oxidized.

Andrew Liang 1I

Yes. The aqueous solution needs to be closer to the center, next to the double line slat bridge. Solid compound/element is usually put at the outermost ends of the cell diagram. Also keep in mind that cathode is usually on the right side of the cell diagram, while anode is usually on the left side.

Andrew Liang 1I

In acidic solution, we usually use H+ to balance out the H in the reaction; therefore, in a cell diagram there will most likely be H+ somewhere. In alkaline solution, we usually use OH- to balance out the H2O on the opposite side; therefore, in this kind of cell diagram there will most likely have O...

Andrew Liang 1I

Yes look at their oxidation states on the left and the right of the chemical reaction. I believe this is how you would usually determine whether something is oxidized or reduced.

Andrew Liang 1I

When drawing cell diagram do we need to put the coefficient of the molecules? Do we put H2O?

Andrew Liang 1I

I was confused on this question as well but I just assumed it's a typo. I assumed the reaction is Cl2(g)->HClO(aq)+Cl-(g) because the reaction given on the textbook is not balanced.

Andrew Liang 1I

My TA told us to add Pt(s) when there is no solid metal in the reaction. If there is a solid metal in the reaction given then that can be used as electrode and you wouldn't need to add Pt(s). I am not too sure though...

Andrew Liang 1I

I am not sure if you can tell by just looking at the oxidation number, but I'm sure that if a reaction is favorable/Galvanic cell, the E naught value has to be positive which means the delta G naught value is negative and the equilibrium constant is greater than 1

Andrew Liang 1I

The E naught value I think should be 0.27 because: The cathode is Hg2Cl2 + 2e- --> 2Hg +2Cl- (0.27V) The anode is 2H+ +2e- ---> H2 (0V) E naught = cathode (0.27V) - anode (0V) = 0.27V After using Nernst equation you should be able to find that Q is 0.009397.... since Q is (conc(H+)^2 (1)^2)/((1)^2) ...

Andrew Liang 1I

For the reaction quotient, the products go on top and in that case it would be the anode which is the left side of the cell diagram. The bottom would be the reactants, which are the cathode given in the the right side of the cell diagram. In other words, the quotient is (anode/cathode).

Andrew Liang 1I

In discussion we went over balancing redox reaction in acidic vs. alkaline condition. I think my TA said something about using OH- to balance out H+ but I wasn't too sure when and how exactly do we need to do that. Thank you in advance if someone can explain briefly.

Andrew Liang 1I

Galvanic cells are essentially used to produce electric work from chemical reaction or redox reaction.

Andrew Liang 1I

I think so because Cl is being both oxidized and reduced

Andrew Liang 1I

If the E cell value is positive it means that oxidation-reduction reaction is spontaneous. If the E cell value is negative it means that the reverse reaction is spontaneous, which is reduction at anode and oxidation at cathode.

Andrew Liang 1I

The TA in my discussion said that cathodes are usually on the right and anodes are usually on the left of the salt bridge in a diagram

Andrew Liang 1I

In an isolated system, the reaction can't really be affected by any outside sources In an open system, the reaction can be affected by many outside sources such as heating/cooling or by add or decreasing the substances in the reaction In an closed system, the reaction can also be affect by a few out...

Andrew Liang 1I

I want to say the unit would be mol/L. But the equilibrium constant wouldn't have any unit though.

Andrew Liang 1I

In reversible reaction, we were told that delta S = 0, but in reality it's the delta S total that is 0, meaning that the change in entropy of the surrounding and the change in entropy of the system is the same with opposite sign.

Andrew Liang 1I

Delta S is usually referred to the change in entropy of the system. Change in entropy of the surrounding is written as delta S(sur).
Delta S total is the sum of delta S and delta S(sur)

Andrew Liang 1I

Yea Dr. Lavelle doesn't curve any tests. He only adjusts the total points at the very end of the quarter.

Andrew Liang 1I

Can someone explain what is Cp and Cv? What is their relationship? Are there any equation that has Cp and Cv in it?

Andrew Liang 1I

Are we expected to memorize any equations for the midterm or are they going to give all of them to us on the cover sheet?

Andrew Liang 1I

The total number of moles in the system will be 0.045 because 0.030 mole of product 2SO3 and 0.015 mole of left over O2. Between 0.030 mole of 2SO2 and 0.030 mole of O2, we figure out that 2SO2 is the limiting reagent and O2 is the excessive. After the reaction is complete, all 0.030 mole of 2SO2 wi...

Andrew Liang 1I

You use q=mCdeltaT when you want to find the energy it takes to raise the temperature of something from one point to another. However when the thing is undergoing phase changing we then use Hvap etc. It wouldn't make sense to use q=mCdeltaTto find the energy in phase change because the temperature i...

Andrew Liang 1I

The main difference between reversible and irreversible reactions is their speed of reaction. Reversible is very slow and therefore in this type of reaction the temperature will be constant. On the other hand, Irreversible reaction is very fast and therefore the temperature will be different from th...

Andrew Liang 1I

The system loses energy by expansion because the internal energy is greater than the surroundings. To balance out the energy difference, the system will apply energy on the pistol and push it outwards, losing energy to the surroundings.

Andrew Liang 1I

Yes. You can increase the energy by:
1. Adding/removing substance
2. Heating the system
3. Doing work on the system

Andrew Liang 1I

How did Dr. Lavelle derive this equation: delta U = delta H - (P delta V)?

Andrew Liang 1I

delta T is measuring the temperature outside of the system. While delta H is measuring in terms of the system inside. So in an exothermic reaction, delta H would be negative but delta T would be positive. And in an endothermic reaction, delta H would be positive, but delta T would be negative.

Andrew Liang 1I

Yes a +q means that the system is taking in heat therefore endothermic. a -q would mean that the system is losing heat and therefore exothermic. a +w means that the system is increasing energy by being compressed. a -w means that the system is losing energy through expansion.

Andrew Liang 1I

What is the difference between pKa and pH?

Andrew Liang 1I

small pKb = more basic
small pKa = more acidic
large Kb = more basic
large Ka = more acidic

Andrew Liang 1I

Steam has a lot of energy compared to liquid water because of its high vaporization energy. Liquid water needs to obtain a lot of energy in order for it to break the bonds and change phases from liquid to gas

Andrew Liang 1I

Test 1 only covers chemical equilibrium and acid and base equilibrium.

Andrew Liang 1I

Other molecules also have plateau points in between phases. I would assume the graph would look somewhat similar, but the energy it takes to change the phase would definitely be different compared to water.

Andrew Liang 1I

It does not matter which unit is given, ICE table works as long as we keep the unit the same through out the calculation. Bar or atm are usually used for pressure of a gas.

Andrew Liang 1I

You use ICE table when the question asks for the equilibrium composition of the reaction system. In other words, the system given in the question is usually not at an equilibrium so the question is basically asking us to find what is the concentration of each molecules when the system is finally at ...

Andrew Liang 1I

Ka and Kb have an inverse proportional relationship. Ka x Kb = Kw. Kw is a constant therefore when Ka increases Kb must decrease in order to maintain the same constant value for Kw.

Andrew Liang 1I

You wouldn't need to divide the initial partial pressure with the volume as long as you keep the unit the same for all the other molecules. However, I think if the question gives you a molecule in the unit of bar and another molecule with molarity then I think you would need to convert bar into conc...

Andrew Liang 1I

I think the key idea is that bond is being broken during the reaction, and it takes energy (heat) to break bonds. In this case the reaction is endothermic; therefore, increasing the temperature will favor product formation.

Andrew Liang 1I

Chemical activity = activity coefficient x concentration of the compound
Equilibrium constant = Chemical activity of product / chemical activity of reactant
The units basically cancel out therefore equilibrium constant does not have unit.

Andrew Liang 1I

We calculate Q and K the same way (product/reactant). However we use Q when we are unsure whether the chemical reaction is at equilibrium yet. If Q is greater than K then it means that there is still more product that need to be reacted; therefore, it is a reverse reaction going from product to reac...

Andrew Liang 1I

K alone usually works for any phases because it just means equilibrium constant unless the problem tells us to specify either Kc or Kp.

Andrew Liang 1I

Wait I don't think Kc will equal to Kp since they are technically measuring different things. One is concentration while the other is partial pressure. When I looked it up it says that Kc will not always equal to Kp. The only time Kc and Kp are going to be equal is if the number of gas molecules on ...

Andrew Liang 1I

I think in that case we would need to convert the gas to molar concentration using the equation: concentration= P/RT.

Andrew Liang 1I

I want to assume that it is talking about the different types of ligand dentates and chelating ligands.

Andrew Liang 1I

I don't think we will be asked to find the Ka and Kb because they are for weak acid and weak bases. I don't think we will be asked to find those until 14B. I'm not too sure though. Kw was never in the lecture slides, so I doubt that it will be in the exam

Andrew Liang 1I

Oxalate (C2O4 2-) can only be a bidentate because when you draw the lewis structure there are only 2 lone pairs in the molecule (one on each farthest oxygen atom). In order to be a tridentate, the ligand must have at least 3 lone pairs.

Andrew Liang 1I

I think the best way is to draw out the lewis structure of the ligands. If the molecule has 3 lone pairs then it can potentially be tridentate and if the molecule has 2 lone pairs then it can potentially be bidentate and so on. However, a thing to keep in mind is the spacing of these lone pairs. If ...

Andrew Liang 1I

KF is a salt that comes from strong base KOH and weak acid KF. When added with water, KF becomes K+ and F- and F- is not stable as an ion because of its strong electronegativity. The F- will attract the H+ from water forming OH-. On the other hand, KBr comes from strong base KOH and strong acid HBr....

Andrew Liang 1I

In naming coordination compounds, why is Iron, Fe, called ferrate and not ironate if the complex has negative charge? Are there any more unique ones other than Iron?

Andrew Liang 1I

When naming a coordination compound, do we put the molecule outside of the coordination sphere before or after the name?

Andrew Liang 1I

Are ligands usually bases because they donate electrons to form covalent bond with the central atom?

Andrew Liang 1I

Is there are way to identify a strong/weak acid or base by just looking at the compound?

Andrew Liang 1I

The dipole cancels out when they are exactly opposite of each other and that they are the same atom because different atoms have different dipole force. The only way for a tetrahedral to have no dipole is when all 4 atoms are the same because based on the VSEPR model none of the atoms are points dir...

Andrew Liang 1I

Yes polar molecules will have higher boiling point than nonpolar molecules because polar molecule involves in dipole-dipole interaction, while nonpolar molecules involve in london dispersion. In intermolecular forces, london dispersion is weaker than dipole-dipole interaction; therefore, nonpolar mo...

Andrew Liang 1I

yes 180 would be present in C-C-N bond because the there are 2 electron density around the central atom with no alone pairs. The lone pairs on N would not affect the structure of the C-C-N.

Andrew Liang 1I

Instantaneous dipole moment happens when a polar molecule distorts the electrons in a nonpolar molecule, causing an uneven distribution of electrons which led to a temporary dipole.

Andrew Liang 1I

Ionic bond can happen between alkaline earth metals (the column next to the alkali metal) and nonmetals as well because the differences in electromagnetically between these two groups are also large enough to form ionic bonds

Andrew Liang 1I

Since there are 2 double bonds in this molecule we know that there must be 2 sigma and 2 pi bonds because double bond always consists of 1 sigma and 1 pi bond

Andrew Liang 1I

Yes lone pairs on central atoms are also regions of electron densities because they affect the molecular shape significantly. Lone pairs have strong repulsion that push bonds away.

Andrew Liang 1I

Another tip that I learned from my TA today was that most of the time when the central atom has lone pairs then the molecule is most likely to be polar.

Andrew Liang 1I

Interaction potential energy is always negative because it is an attractive force. The equation is [-(alpha 1)(alpha 2)]/r^6
alpha represents the polarizability of the atom or molecule and r represents the distance between the two interactive atoms or molecules.

Andrew Liang 1I

Bent and angular refer to the same molecular shape. Those words can be used interchangeably.

Andrew Liang 1I

Dashes and wedges are just another way of drawing the structure of the molecule that allows us to visualize its depth and its 3D shape. I think the quiz will most likely still asks us about tetrahedral, trigonal bipyramidal or octahedral shapes

Andrew Liang 1I

I don't think the bond length difference implies the actual physical length difference. I believe the bond length suggests the strength of the bond. So triple bond does not necessarily means that it is 1/3 the length of the single bond, but rather it suggests that this kind of bond is shorter and st...

Andrew Liang 1I

Dipole is induced when an charged ion approaches a non-dipole atom/molecule. The charged ion will disturb the electrons of the atom causing one side to be more negative and the opposite side more positive, inducing dipole.

Andrew Liang 1I

More negatively charged anions are more polarizable especially larger anions at lower periods of the periodic table, such as Iodine. The reason is because there are more electrons in the outer shell that are more likely be attracted to the positive charge of the cation.

Andrew Liang 1I

Ionic character often involves around an atom donating its electron for the other atom, while covalent character involves 2 or more atoms sharing electrons. You can tell whether a molecule has covalent bond or ionic bond by finding the difference in electronegativity of the atoms. If the difference ...

Andrew Liang 1I

All halogens exist as diatomic molecules. The inter-molecular attractions between one molecule and its neighbors are called van der Waals dispersion forces. As you move down the group, the molecule gets larger, thus more electrons to move around to form this van der waals attraction. The more attrac...

Andrew Liang 1I

If in reality the bond length in resonance structure is the same how to people observe that triple bonds are shorter than double bonds and that double bonds are shorter than single bonds?

Andrew Liang 1I

A coordinate covalent bond is when an atom provides both electrons to another atom to complete the octet rule.

Andrew Liang 1I

Do we need to know how to use this equation: ((q1)(q2))/r to calculate the electrostatic potential energy? I have not seen any of those question in the homework or from discussion sessions.

Andrew Liang 1I

Ionic bond is when an electron is fully transferred to an atom and the two atoms are linked by electrostatic forces. Covalent bond is formed when two atoms share electrons. Ionic bond is stronger than covalent bond.

Andrew Liang 1I

# 57 Lanthanum actually belongs to the d-orbital and elements 58-71 belongs to the f-orbital. That's why f-orbital can hold up to 14 electrons and Tungsten have 4 electrons in the d-orbital

Andrew Liang 1I

P, S , and Cl are the common exceptions to the octet rule. They can hold more than 8 valence electrons because atom in period 3 or higher have d-orbital in valence shell that allows them to hold additional electrons

Andrew Liang 1I

Yes with Dr. Lavelle we do need to write 3d before 4s because 3d actually comes before 4s in electron configuration. 3d is in 3rd principle energy level and 4s is in 4th principle energy level. I'm not too sure about the second part of the question.

Andrew Liang 1I

The ionization energy to remove the second electron is always higher than removing the first because without 1 extra electron there is less electron repulsion and electrons are more attracted to the positive charge of the nucleus.

Andrew Liang 1I

During the discussion today, our TA said that it is not necessary to write px, py, pz unless it is specifically asked for in the question.

Andrew Liang 1I

I think the threshold energy can be calculated. I believe the equation is (E of photon) - (Threshold energy) = (Kinetic Energy) so if we rearrange the equation a little bit it will be: (Threshold energy)=(E of photon) - (Kinetic Energy). However, if the question is asking for the kinetic energy or t...

Andrew Liang 1I

The standard electron configuration for a neutral Ag atom is [Kr] 4d^10 5s^1, not 4d^9 5s^2, because the outermost electron moves to the 4d orbital, filling it up and making the atom more stable. Therefore, the Ag cation loses its outermost electron, which is in the 5s energy level, making the elect...

Andrew Liang 1I

The "m" in De Broglie's equation refers to the mass of the object with momentum, P, and has wavelike properties with wavelength. However if the mass is large then the object most likely does not have detectable wave-light property and acts more like a particle.

Andrew Liang 1I

When the light intensity is increase, the only thing that is changing is the number of photons. In that case, each photon still does not have enough energy to knockout an electron. In EM waves, intensity does not increase the energy of the photon. Frequency is the one that affects the energy of the ...

Andrew Liang 1I

I am quite confused with the idea of principle, angular, and magnetic quantum numbers (n,l, and ml). How do you determine the the state of the electron with those quantum numbers? During lecture I saw a chart in the slide that can help us determine the state of the electron, but are we suppose to kn...

Andrew Liang 1I

A lot of reactions or system cannot be 100% efficient because there are always something that is lost to the environment, uncontrollable variables that can alter the result, side reaction, and impurities. Those are just some of the reasons why actually yield is almost always less than the theoretica...

Andrew Liang 1I

On my solution manual, it says 150 pm. You are right and maybe it is a typo in the textbook.

Andrew Liang 1I

In high school I learned something about the refraction index of a medium. The equation is n = c/v. n is the index, c is the speed of light constant, and v is the velocity of light in the medium. To answer your question, i think the question will have to do something with the index.

Andrew Liang 1I

When the experiment changed the intensity of the light on the metal, it is only changing the amount of photons in the light. Lower intensity means less photons and thus dimmer light. Electromagnetic wave does not behave the same as sound wave or ocean wave. When we increase the intensity of an EM wa...

Andrew Liang 1I

Limiting Reactant is the substance that is completely used up in a chemical reaction. Limiting reactant determines how much product is produced in a chemical reaction. Identifying Limiting Reactant: 1. Identify reactant and products 2. write a balanced equation for the reaction 3. Calculate molar ma...

Andrew Liang 1I

An angstrom is a unit of length usually used to measure the bond length of atoms. It has the symbol of Å. 1Å = 1x10^-10 m

Andrew Liang 1I

K = C +273.15 -----> C = K - 273.15
F =(1.8)(C)+32
Kelvin to Fahrenheit = F = (1.8)(K - 273.15) + 32

Andrew Liang 1I

We cannot really change the frequency of a wave unless we completely change the type of the electromagnetic wave. Frequency of an electromagnetic wave normally remains the same because each electromagnetic wave has its own unique driven oscillation. When we increase the intensity of the light, we ar...

Andrew Liang 1I

You can check out the class website and you'll see there are a lot of discussion sections, peer learning sessions, exam review sessions, and Step-Up Sessions you can attend. Online learning modules are also a great help!

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