CHEMISTRY COMMUNITY

Sharon Kim 2A

In a way they are connected but I remember Lavelle talking about the differences more. In thermo, this will tell us if the reaction is favorable or not. While in kinetics, it will tell us how fast the reaction is going.

Sharon Kim 2A

I am assuming that you add the Pt when you don't see a solid in one of the half reactions. This will not change the reaction and will show you cell diagram where it won't only have ions on one side.

Sharon Kim 2A

The reason why the catalyst wouldn't change the enthalpy is because it is a state function function. The catalyst changes the pathway of the reason thus lowering the activation energy and increasing the rate constant. So it is just making the reaction go faster to its final state.

Sharon Kim 2A

The order of the reaction would be 2 because in an inverse relationship. The easiest way to tell if this is a second order is by plugging values and rearrange k to see which fits. We know that this half-life is dependent on [A] initial so that automatically cancels out the first order!

Sharon Kim 2A

In this question, they give you a chart! You cannot tell if the order of a reactant unless you do the calculations by dividing each initial rates and cancelling out constants to find each order.

Sharon Kim 2A

The concept of "kinetic control" is saying that the reaction is determined of how fast or slow the reaction is taking place. The difference with thermodynamics is that it analyzes if the reaction is forward/reverse (favorable/not favorable). Kinetically stable reactions occurs when the rea...

Sharon Kim 2A

If we are balancing redox reactions, the problem would have to tell you if it is either an acidic or basic solution. That way we know how to balance our reaction according to the solution. Meaning knowing when to leave the reaction with H+ or add OH-'s.

Sharon Kim 2A

Lavelle says that it is possible, however, determining the rate law with even 3 molecules is already difficult as it is. It is less common to see 4, 5, etc. molecules and be able to determine the rate law. I would say not to worry too much about that. Hope this helps!

Sharon Kim 2A

I believe so, the list Lavelle had in his lecture states that A+A would be a bimolecular which I am assuming is the same thing as 2A. So 2A+B would be termolecular.

Sharon Kim 2A

I think when it says k', it is referring to when you had to manipulate the reactants to be in higher excess so that you can focus on the reactant that has a lower concentration. I believe you are able to obtain the value of k' from the slope after manipulating the reaction and getting the rate law. ...

Sharon Kim 2A

Usually you can approximate "X" to be zero when the K value is 10^-4 and less. Sometimes it can be in the 10^-3 range if it is a very small value. But a higher 10^3 value would not be as accurate so I think that's why Lavelle said values 10^-4 and on are the safest bet.

Sharon Kim 2A

Hello! For this question would be using the E=-(0.0592V)/2*logQ because the standard reduction potential would be 0. You would plug in the values like you normally would. For Q, it would be (1.4/0.89^2) (according to the reaction equation). The rest you just plug it in, hope this helps!

Sharon Kim 2A

Usually the case would be that the anode is the left side of the system and cathode is the right. So that the electrons are flowing from left to right. The anode side would be losing mass, so you would see that there is a release of anions into the solution. In the cathode side, anions are being tak...

Sharon Kim 2A

When the question is taking for oxidizing/reducing agents, think of the opposites of them. So the molecule going through oxidation is the reducing agent and vice versa. The easiest way to think of it is to think of the opposite.

Sharon Kim 2A

The purpose of a salt bridge is to keep the solutions neutral so there is no buildup of charges on one side. This can also be done with a porous disk, where cations and anions are able to pass through. Keeping a neutral solutions will help keep the electrons flowing.

Sharon Kim 2A

E naught represents the system under standard conditions. Just regular Ecell represents the system when concentrations aren't standard like in 1M or 1 atm. The system would not be in standard conditions.

Sharon Kim 2A

The potential is referred to as the measure of the voltage difference between the anode and cathode. He says that the maximum potential occurs when the switch is open because there is no electrical current flowing. I am assuming that it is the maximum because there is no added flow, so whatever is l...

Sharon Kim 2A

Work with compression on the system would be positive because the system isn't doing work, it is some outside force that is doing the work to compress the piston. Work would be negative if the system is expanding and there is a change in volume. This would be negative because the system is doing wor...

Sharon Kim 2A

correct, you will be using that equation and ignore thermal disorder. usually residual entropy would be associated with more complex molecules.

Sharon Kim 2A

when work is done ON the system the value will be positive and when work is done BY the system it is a negative value. When positive, the system is being compressed and when work is negative the system is expanding. Usually, in the problem it mentions that the system is doing work, which means that ...

Sharon Kim 2A

State function does not depend on the path taken. Meaning that the only thing that matters is the final and initial state of the property. That's why when you are given the standard values of Gibb's free energy, you are able to do products - reactants.

Sharon Kim 2A

When it said Cp, this is at constant pressure. In this situation, the system is allowed to expand and have a volume difference. Work is done in this situation but not in systems with constant pressure. There should be different equations associated with the two.

Sharon Kim 2A

Using the "integral" involved work being done in a reversible reaction. This is when the volume different between V2 and V1 is very little and basically at equilibrium. Wee don't actually use the integral, is was shown how to derive this equation we use: w=-nRTIn (V2/V1)

Sharon Kim 2A

There is no need to convert when dealing with temperature change because the difference is the same. The time when you need to convert is when you're dealing with a temperature that is a fixed value.

Sharon Kim 2A

Usually the R constant that is 0.0821 L·atm/(mol·K) is used when dealing with PV=nRT. The other gas constant 8.314 J/(mol·K) when dealing with equations like w=-nRTIn(T2/T1). But of course, make sure you are using the units corresponding to the question.

Sharon Kim 2A

No temperature is used! All you need is the sum of all the delta G's from products - reactants. Make sure to take into account of the coefficients.

Sharon Kim 2A

Usually specific heat are not memorized and often for the problems I've seen it either gives it to you or you have to solve for it. Also for the equation Delta U, it should be U=nC(change of T). In the problem they gave specific as 5R/2 (R=8.134), so from there you can plug in the values and should ...

Sharon Kim 2A

For reversible expansion the external pressure and the internal pressure are nearly the same, however, the external pressure is slightly larger (by a millionth). If you see a distinct difference between the external and internal pressure (2 atm and 1 atm), then that gives you a clue that the system ...

Sharon Kim 2A

Yes, you are breaking bonds in the reactions but you are still forming bonds to make CO2 and H2O. I'm thinking that since there are both processes of forming bonds and breaking bonds, the energy released from forming bonds is much larger than the energy needed to break the bonds.

Sharon Kim 2A

I think what Professor Lavelle meant is that gas will occupy any space that is available. So I think of it as gas filling up as much room it can in a container. This is what he meant by not having to put in work for the gas molecules to do that process because it is favorable (spontaneous) it does i...

Sharon Kim 2A

I would say understand how work is used when deriving the equation for entropy and for reversible expansion. Also that in gases, there is not work for a spontaneous process but work for compression.

Sharon Kim 2A

Usually you go by what the problem gives you. In most cases the reactant side is -X because the problem gives you initial concentrations of the reactants since you are adding in reactants which will then form into products. But to be safe, always refer to the direction of the reaction by the Q value.

Sharon Kim 2A

Adding inert gas will not change anything. The moles of reactant & product and volume remains constant. Consider it to be negligible.

Sharon Kim 2A

We can tell if the reaction is exo or endo depending if the reaction is forming bonds or breaking. In an exothermic reaction, heat is being released and bonds are being formed. But in endothermic reactions, bonds are being broken because energy is being put in to break the bonds. The reaction that y...

Sharon Kim 2A

Even though liquid and steam are at the same temperature, there is a difference in energy release to get to one phase to another. In the graph Professor Lavelle showed in the lecture, liquid and steam (gas) were at the same temperature but the flat line part of the graph was must longer going into t...

Sharon Kim 2A

Usually it would be when the K value is 10^-3 but sometimes those values might be a little too high to the point reaching to 10^-2. So to be safe we start from considering X values that are 10^-4 and smaller to be insignificant.

Sharon Kim 2A

I think the chart Lavelle showed in the lecture was really helpful because it showed how much energy it took to get to the gas phase. Even though they are at the same temperature, it took different amounts of energy to get to different phases. Also, since the H-bonds are strong, the high amount of e...

Sharon Kim 2A

This entire problem you're working backwards especially on the stoichiometric level. You first need to get the initial concentration of OH- by taking the pOH (0.75) and do the inverse log of 0.75 (10^-0.75), which gives you 0.178M. This is the concentration at the volume of 500ml when it was diluted...

Sharon Kim 2A

Yes, water will not always be the solvent. In one of the example problems, water was included in the expression since it was in aqueous form. Denote that all liquids are the solvent even if it's not water.

Sharon Kim 2A

When the problem says the system is at constant pressure, do we assume that the pressure is the standard 1 atm?

Sharon Kim 2A

I'm pretty sure the Le Chatelier principle will still apply in this case. If the partial pressure of the reactants increase, then the system will shift forward and vice versa.

Sharon Kim 2A

I like to think of it by referring back to the pH scale which was out of 14. Since half the pH scale is either acid or base, [H30+] and [OH-] would be 1x10^-7. Multiplying both the K values gives 1x10^-14. Kw comes into play especially in problems where it gives you the Kb value and need to convert ...

Sharon Kim 2A

If water is not part of the reaction then look for molecules that are in liquid phase. Just know that in K expressions, only molecules that are either in gas phase or aqueous can be included. Not solids or liquids. In some problems, water was actually included in the K expression and ICE table becau...

Sharon Kim 2A

The change in temperature still refers to the Le Chatelier's principle because adding heat still shifts the system. Think of heat being on the reactant side when the reaction is endothermic and heat is on the product side when the reaction is exothermic. Increasing heat in an exothermic reaction wou...

Sharon Kim 2A

This is sort of unrelated to the topic (I don't know how to make a topic on here), but in relation to Friday's lecture if the concentration of the hydronium ion is really small then do you just assume that the pH is 7? What that was Lavelle was saying? Because he gave an example of [H30+] being arou...

Sharon Kim 2A

Usually in order to know where to put the -x/+x would be what the question is giving you. If the question says it is adding more reactants then you know that in the reaction the reactants are going to lose some value of x and the products will gain some value of x, vice versa. It comes does to the L...

Sharon Kim 2A

I'm not sure about it having more moles on the left. Decreasing the volume should increase the concentration but not the amount of moles. Since the reactants have a higher concentration, the reaction will shift to the right (forward) to make Q=K again. Hope this helps!

Sharon Kim 2A

Adding more reactant shouldn't have any effect on the overall reaction itself. When adding more reactant, the reaction will temporarily be out of equilibrium and the excess reactant will be used to form more products to reach the attained ratio. During that process there would be a reaction and then...

Sharon Kim 2A

In the lecture, Lavelle mentioned that even with the pressure changing, if the volume itself isn't changing then it will have no effect on the reaction. Change in volume causes the change in concentration which changes the EQ to adjust back to the attained ratio.I am assuming if the question mention...

Sharon Kim 2A

For ICE tables in this class, I think it would be best to stick with molar concentration because sometimes you can forget to convert it back to M since most problems want it in those units.

Sharon Kim 2A

Does anyone know what Lavelle meant when heating exothermic reactions it favors the endothermic reactions?

Sharon Kim 2A

Elements starting from the 3p orbital on and elements that are able to have d-orbitals can have expanded octets. Elements that have less than octets are Group 13 elements common ones are (Al, B), free radicals (CH3), any sort of Lewis acid/base molecules. Hope this helps!

Sharon Kim 2A

We know if the ions have a larger radius is they have a less positive charge. If they have a high positive charge then that means the ion lost electrons and electrons is a key part that makes the size of ions and atoms because of repulsion. Which is the electron cloud.

Sharon Kim 2A

To determine is a salt is acidic or basic, what I do is look at the compound and see if either the cation or anion came from either a strong acid or strong base. For example NH4ClO4, CLO4 is an anion that came from a strong acid. It would be best to memorize the list of strong acids and bases and re...

Sharon Kim 2A

Usually for determining whether something is acidic or basic look for charges and protons that it accept or donate. So for acids, you should look for any hydrogens it can give away and look for positive charges. For bases, usually the it is Group 1 and 2 elements and seeing any OH- is a good indicat...

Sharon Kim 2A

I think what you are saying is correct! What I usually like to think for determining the acidity or how basic a salt is is seeing the the formula which element is usually from a strong acid or base because they will dominate over the element that is "weaker". They are usually the determine...

Sharon Kim 2A

Make sure that bond angles will be smaller because of lone pair repulsion for the more complicated structures. They won't be the standard 120, 109.5 angles.

Sharon Kim 2A

Since there are two chlorines in the compound, it would have to be "dichloro". So the negative charge would add up to be -3 instead of -2. Since the overall charge of the coordination compound is 0, we know that the oxidation number of cobalt would have to be +3.

Sharon Kim 2A

Yes, going off of the previous post. Coordination number corresponds to the number of BONDED atoms to the transition metals.

Sharon Kim 2A

An easy way for me to find the oxidation number is to find the anion charge first and determine what the overall charge of the coordinate compound is. Whether it is 0 or -2, -1, etc. Using that to find the oxidation number so that the charges in the compound matches the overall charge.

Sharon Kim 2A

Usually with HF, it is considered to be a weak acid since the bond length is shorter. Meaning it will not dissociate as easily. I think Dr.Lavelle used HCl since it was a better example to use. I would just think with HF, it may not be as easy but I wouldn't say it is impossible.

Sharon Kim 2A

To find the coordination number is the number of bonded atoms to the transition metal. In other words, look for the number of bonds the coordination compound has. Hope this helps!

Sharon Kim 2A

We know that there are octet exceptions starting from the 3rd p-block. An element that is able to attain a d-orbital usually starting from P and on are expanded octets. Elements that have less than an octet would be Group 13 elements, radicals, H, He, Li, and Be.

Sharon Kim 2A

So far we have seen many ring structures with multiple carbons. So if there is a molecule that has a lot of carbons and you know that there is resonance, maybe that is a clue that there might be a ring structure.

Sharon Kim 2A

The number of ligands would correspond to the number of atoms (Lewis base) that are attached to the cation (central atom). So the number of bonds that molecule has.

Sharon Kim 2A

I was thinking of when Professor Lavelle mentioned the cis and trans molecule. How one cancels out and one causes a dipole moment. So I am assuming yes? Considering if the molecule only had sigma bonds. If there are pi bonds I am assuming no because structure will remain how it is because it cannot ...

Sharon Kim 2A

In today's lecture 11/23, does anyone know why in the example of ethene (C2H4) after explaining the unhybridized p-orbital he wrote sp^3 around carbon. Was it no longer sp^2 even though carbon still only has 3 electron densities?

Sharon Kim 2A

Usually you should look for symmetry and atoms that have different electronegativities within the structure. If dipole moments do not cancel it is safe to assume there are polar bonds.

Sharon Kim 2A

Can I3- can be bent as well? I was thinking that since lone pairs have a stronger force in repulsion that it will cause the structure to have a bent shape. Can someone explain more as to why it is linear?

Sharon Kim 2A

The higher the boiling/melting point indicates that it takes more energy to break the bonds (stronger intermolecular forces).

Sharon Kim 2A

Usually when referring to the strength of the bonds, it relates to the length of the bonds. However, the larger the difference in electronegativity the stronger the attraction. I am assuming that it will resemble more of an ionic character.

Sharon Kim 2A

I didn't see one electron from the s orbital go to the p orbital. In the lecture he included all the 4 valence electrons of carbon. He combined the one s orbital and the 3 p orbitals to make 4 atomic orbitals. In the 4 atomic orbitals, he fit all the 4 valence electrons in each orbital. All of this ...

Sharon Kim 2A

Yes! It is more favorable for the charges to be 0 or at least very close to 0 like a charge that it is -1. The formal charges should add up to the overall.

Sharon Kim 2A

As far as I know, I am assuming no. Usually they would give the formula already with the charges so that we will know how to draw the lewis structures and relate them to formal charges.

Sharon Kim 2A

Technically, London Dispersion forces are always present. It is a matter of what forces are dominating in those interactions. Such as London Dispersion forces being present in ionic bonds but the ionic forces are more dominant.

Sharon Kim 2A

I would put the atoms with the least ionization energies in the center and go based on the formula given in order. Carbon should be in the center as a row and be attached the H and O.

Sharon Kim 2A

When writing the electron configurations, I understood it to be written as 3d orbitals before the 4s. Is that the same thing as saying 3d orbitals are filled before 4s?

Sharon Kim 2A

The difference induced dipole-dipole and dipole-dipole is that with induced dipole-dipole interactions have non polar and polar molecules interacting such as HCL and N2. Induced dipole- dipole have a temporary dipole moment where there is a distortion with the electron cloud. While dipole-dipole are...

Sharon Kim 2A

Since he is giving an introduction to acids and bases, he didn't go as far to talk about the amount of hydrogen ions. For now he mainly focused on the concept of Lewis acids accepting electrons and Lewis base donating electrons.

Sharon Kim 2A

We usually use them to see which lewis structure is best to use because the formal charges tells you which ones are the most stable. Finding the structure that have zero charge or close to zero is preferable.

Sharon Kim 2A

Usually, by looking at one structure you can recognize where certain bonds can be placed or replacing a lone pair to make a double bond. I think by practicing with many Lewis structures, overtime you'll just remember which structures have resonance. However, I wouldn't say there's a definite shortcut.

Sharon Kim 2A

Yes, even in polar covalent in the sharing region there is an unequal sharing of electrons making one side partial negative and partial positive. As Professor Lavelle said, it is very unlikely to ever find a pure covalent bond. I think it goes for both concepts too like distortion. Such as ionic bon...

Sharon Kim 2A

Usually, I think of it as electronegativity, ionization, affinity gets stronger an arrow goes diagonally up right of the periodic table. Then for atomic radius (size) increasing, I think of an arrow going diagonally down to the left of the table. That has helped me through the years I took chem!

Sharon Kim 2A

Yes, I was having a lot of trouble with that problem as well because I didn't understand exactly what the problem was asking. But you have to count up the number of wavelength cycles that are complete/whole. The ones that cut short are not compatible.

Sharon Kim 2A

For this question, it gave the energy value of the ejected electron in eV. To get the unit into eV/atoms do we just multiply by 6.022E23? I don't know if I would do that though because it is over moles. Is doing that technically making the units over atoms?

Sharon Kim 2A

I think my TA said that for this class, there are no competition between students so there won't be a curve for exams.

Sharon Kim 2A

Are nodal planes basically the "axis" lines in the model?

Sharon Kim 2A

I was thinking that if the light has a higher frequency, the energy emitted would be the same as long as the the energy (frequency) is reaching the energy threshold. The same energy would be emitted that was initially absorbed.

Sharon Kim 2A

Does anyone know the concept of 4s being a higher energy level? I was thinking that ground states have higher energy since it is the closest to the nucleus, but why does 4s or any level higher than the ground state have the title of "higher energy level"? Is there a difference between ener...

Sharon Kim 2A

Was the midterm review session schedule posted anywhere on the website? The link was there before and the date still had to be posted, but now it's not there.

Sharon Kim 2A

I still do not understand how the energy level at 5, n = 5 and l = 0. I am still going off go how l is based off of n values like "n-1". I can't seem to find the connection.

Sharon Kim 2A

Usually the final answer should in nm? It's just in the problem the wavelength comes out be in m initially.

Sharon Kim 2A

The speed of light equation (c = lambda * frequency) was used to derive the De Broglie equation. With that equation, it was derived by the combination of Energy = pc and E = hv. The speed of light equation was rearranged to be v = c/wavelength. From E=hv (substituting v), we get E=hc/wavelength. Mak...

Sharon Kim 2A

Usually the SI unit for the wavelength that comes from the speed of light formula is in m. However, for most of the questions, I've found they want the answer to be in nm. When going to from m to nm, multiply by 1E9 and from nm to m multiply 1E-9.

Sharon Kim 2A

For these series, basically do we need to know that for UV it has longer lengths for Lyman series going from n=1 to n=2 and for Balmer it is shorter and starts from n=3 to n=2 to n=1. Not completely sure about this concept.

Sharon Kim 2A

Not completely related to this topic but will the question tell you if light is acting like a particle or wave? Or do we have to figure it out somehow?

Sharon Kim 2A

Not sure either but I'm pretty sure for visible light we should know that it ranges from about 400nm to 700nm.

Sharon Kim 2A

I was confused as to why there were two separate energies in this problem. For the formula E=hc/l is E the total energy from the light source or the energy per photon? I was confused since there was the 32 j/sec and then the formula was used to find another energy value.

Sharon Kim 2A

To add on, even though it may seem obvious, I think it is so important to take advantage of the office hours and peer sessions opportunities! But not just show up. Do the textbook problems, Sapling hw, and review over the lectures. Come prepared with questions that target weak areas of understanding.

Sharon Kim 2A

To change it to integers, normally wouldn't you multiply the entire equation by the denominator of the coefficient that's not a whole number

Search found 104 matches