CHEMISTRY COMMUNITY

Quinton Sprague 1A

Quinton Sprague 1A

In friday's lecture, Dr. Lavelle mentioned how in some scenarios an inert conductor such as platinum is added to transfer e-. I am bit confused as to why this is necessary is a given reaction? What exactly does this addition do? How can we know when an addition of an inert conductor is necessary?

Quinton Sprague 1A

Wondering why the standard reduction potential is not changed when a half reaction is balanced. I know the sign changes, but why do we not multiply the Enaught by the balancing coefficient as we would in Enthalpy of Entropy.

Quinton Sprague 1A

Wondering if someone could explain this diference to me?

Quinton Sprague 1A

Today in lecture Dr. Lavelle mentioned this concept. The limit as i approaches 0 gives the potential as a electromotive force of the cell. What is i in this concept?? Am I thinking about this correctly?

Quinton Sprague 1A

The question is as follows:

Consider the following reaction at 298 K.

C(graphite)+2H2(g)⟶CH4(g) ΔH∘=−74.6 kJ

I was able to find the change in S sys but cannot figure out how to find the S surr and univ. Wondering if anyone can offer some help as to where I can go from here.

Quinton Sprague 1A

The question is as follows: Calculate the standard change in Gibbs free energy for the reaction at 25 °C. 3H2(g)+Fe2O3(s)⟶2Fe(s)+3H2O(g) Confused how to answer this. I know I will need to incorporate the temperature but not sure where, should I recalculate the deltaG for each molecule with the diffe...

Quinton Sprague 1A

Was wondering the same thing, does Liters x Kpa = Joules? This would be my only guess as to why we use this constant because kPa is present in the question instead of atm.

Quinton Sprague 1A

Hey! I think on the slides during his lectures, it shows K in comparison to 1 (that is, >1, <1, or =1). In this case, we would know that when you put any value less than 1 as the input to ln(x), it will be a negative number so negative times negative would be positive. Yep, not sure why I missed th...

Quinton Sprague 1A

Dr. Lavelle says in lecture that when K<0, deltaG should be a postive number. Initially this made sense to me as the K side of the equation is already negative (thus a negative times a negative equals a positive) however, I was under the impression you could not take the natural log of a negative nu...

Quinton Sprague 1A

Why in the equation DeltaStandardG = -RTlnK is the K value represented by a natural log. I understand the application discussed in lecture but I am unclear where this natural log came from...

Quinton Sprague 1A

These are the same, just often represented differently depending on textbook, lecture, website, etc..

Quinton Sprague 1A

Having trouble on the following question: A 0.513 mol sample of SO2(g), initially at 298 K and 1.00 atm, is held at constant pressure while enough heat is applied to raise the temperature of the gas by 18.1 K. Calculate the amount of heat q required to bring about this temperature change, and find t...

Quinton Sprague 1A

Struggling on this problem: A sample of an ideal gas in a cylinder of volume 2.73 L at 298 K and 2.01 atm expands to 8.19 L by two different pathways. Path A is an isothermal, reversible expansion. Path B has two steps. In the first step, the gas is cooled at constant volume to 1.14 atm . In the sec...

Quinton Sprague 1A

The question is as follows: An ice cube with a mass of 55.0 g at 0.0 ∘C is added to a glass containing 441 g of water at 45.0 ∘C . Determine the final temperature of the system at equilibrium. The specific heat capacity of water, Cs , is 4.184 J/g⋅∘C , and the standard enthalpy of fusion, ΔH∘fus , o...

Quinton Sprague 1A

Today in lecture, Dr. Lavelle was expressing the change in internal energy (/\U) as equal to /\H - (-P x /\V). Shortly after this he rewrote the equation as /\U= /\H - P x /\V . Wondering which equation we use, should we assume P x /\V to be negative? Only in some circumstances? I figured both of th...

Quinton Sprague 1A

Chloe Little 3K wrote:I'm not sure what most people do, but I'm taking 14BL right now and I'm planning on taking 14CL next quarter with chem 14C.

Has it been hard to manage 14BL with 14B? Nervous about taking 14C and BL together next quarter but feel like I don't have much a choice.

Quinton Sprague 1A

This is called Carboxyl group and often makes up Carboxylic Acids. These acids have a general formula of R–COOH, with R representing a Alkyl, Alkenyl, Aryl, or other group. These are very common in nature but most associated with Amio and fatty acids.

Quinton Sprague 1A

Any ideas when we should know our grades? Shouldn't expect any curve right?

Quinton Sprague 1A

I am still confused on how exactly these two effect chemical equilibrium and the value of K. I know this is dependent on what physical state the compounds in the reaction are in, but say there is a gas in both the product and the reactant, and a liquid in the reactant and a aqueous solution in the p...

Quinton Sprague 1A

Wondering if someone can help me understand the difference between these two.

Quinton Sprague 1A

If B is a monoprotic base and the equation is set up as H2O + B -> BH+ + OH-, then yes [BH+] and [OH-] should be the same because of the ICE table. If anything else affects the equation such as coefficients then you would have to set up an ICE table for the new equation. Does this rule hold true fo...

Quinton Sprague 1A

In Lavelle's most recent lecture he referred to calculating enthalpies through adding the bond enthalpies up and making a change equation for the total enthalpy (Method 2 in lecture). This being the case, I believe he referenced a chart/table that had these bond enthalpies given. Is this table somet...

Quinton Sprague 1A

Wondering if anyone could help me calculate this, looked in my notes but can't figure it out. I see on Sapling that you are supposed to use the formal concentration for the reactant, does this mean initial or final? Is the equation essentially concentration of H+/OH- divided by the concentration of ...

Quinton Sprague 1A

Being that Ka is the acidity constant and measures concentration of hydronium ions, I am wondering if pKa is always equal to pH? In the case of a base I guess it would not be likely that you could find the pKa so maybe this is a time where the pH is relied on, but in other circumstances are these tw...

Quinton Sprague 1A

"Because heat is required during the melting or boiling (phase transition), temperature of sample remains constant even though heat is being supplied" CHEM DELETE.jpg **Thought this was pretty cool and the first time I heard about this.** EDIT: Just watched further in lecture and see he us...

Quinton Sprague 1A

An exothermic reaction will release heat, while an endothermic reaction will absorb heat. If an exothermic reaction occurs the surrounding area may be made warmer. If a endothermic reaction occurs the surrounding area may be made cooler.

Quinton Sprague 1A

To determine the answer you must know where the salts are derving. The acidity of the compounds they come from determine these properties of the subsequent salt.

Quinton Sprague 1A

I believe this may only occur when the concentration of the conjugate base and the concentration of the conjugate acid are equal. But I am pretty sure this is the case in many reactions.

Quinton Sprague 1A

Hi! So you are correct that the change for both reactants would be +1 while the change for the product would be -2x. However, the initial concentrations of the reactants should be .1, because you were at equilibrium and it was disturbed, so you need to find the new equilibrium values. So the initia...

Quinton Sprague 1A

In the Sapling due tonight, a question gives you the equilibriium concentrations of .1M for both reactants, and .6M for the product in the reaction N2 + O2 > 2NO. Then, the concentration of NO is modified to .9M and it asks you to find NO's equilibrium concentration with this modification. I started...

Quinton Sprague 1A

Quinton Sprague 1A

I believe temperature will soon become a big deal, though with what we are working on at the moment it does not seem that we are expected to identify its effect and how to attribute for that.

Quinton Sprague 1A

For the Sapling problem that gives multiple reactions and asks for you to find the Equilibrium constant, how to you set this up? Are there only 2 reactions specifically that can help one solve for this? I have attempted to find x in some reactions but no luck, wondering if I am choosing the wrong on...

Quinton Sprague 1A

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Quinton Sprague 1A

I believe the ICE table would go as follows: Since the Carbon is a solid it will not be included. Then you may look for their initial concentrations, the only one given is for water, but it was given as a mol figure with a specified volume. To find this concentration divided the H2O moles by the lit...

Quinton Sprague 1A

The reaction will go out of equilibrium to begin, but later will return to equilibrium as the products/reactants decrease to make up for the increase in the other. I believe volume and pressure are inversely porportional, though I am not sure why.

Quinton Sprague 1A

In previous lectures, Dr. Lavelle discussed the corelation between lowering a volume and increasing a pressure, or decreasing a pressure and increasing a volume. I may have missed his explanantion, but wondering why this are porportional in this way? Having trouble conceptually understanding why doe...

Quinton Sprague 1A

If asked on the final to determine the molecular shape of NO2- or rather NH3, would the shape be bent, as we often say in H2O, or angular? Are the technically the same thing? Is one VESPR and the other molecular?

Quinton Sprague 1A

I am reviewing what bond angles are associated with each VESPR structure and was curious why tetrahedral compounds have bond angles of 109.5 or less. Since linear, 180 x 2 = 360, trigonal planar, 120 x 3 = 180, but tetrahedral, 109.5 x 4 = 438??

Quinton Sprague 1A

Dr. Lavelle used the example today of how HCl + NH3 -> NH4Cl, making the solution acidic because of the acidic ions. Wondering if he is referring to the NH4Cl as the acidic ions? How do we determing that NH4Cl would be an acid being that it does not have a formal change? Do we just assume it would l...

Quinton Sprague 1A

In today's lecture, Dr. Lavelle discussed how H2CO3 can actually donate both of its H+ in a reaction with water. In calculating the Ka, he showed how you multiply the products in the numerator and divide this by the solvent. Wondering if actually calculating ourselves, what numbers we put into this ...

Quinton Sprague 1A

Still a bit confused with the difference between pH and pKA values. Since pKa is the -logKa I thought this meant it was the pH. It is also shown in a similar format as the pH, a number between 1-14. Can pKA be considered like the pH of a single compound, and pH be considered the acidity of the entir...

Quinton Sprague 1A

Nonpolar compounds share electrons equally, you can sometimes tell these from lewis structures in which forces cancel eachother out. Polar compounds share electrons unequally, resulting in a dipole moment where one atom is turned slightly electronegativite while the other electropositive.

Quinton Sprague 1A

Quinton Sprague 1A

You name the ligands before the metal atom/ion and do so in alphabetical order.

Quinton Sprague 1A

Believe I heard this as well. Also would make sense because I do not believe that we have worked with anything past an octahedral.

Quinton Sprague 1A

In today's lecture, Dr. Lavelle discussed how anions are stabilized by resonance or increased electronegativity. He used the example or ClOH to demonstrate how the chloride's electronegativity 'stabilizes' it by pulling on the oxygen. Wondering if anyone can describe what he means by the anion stabi...

Quinton Sprague 1A

Anyone know if the table for naming ligands in coordination compounds (on Dr. Lavelle's website) is a sheet we will be permitted to have with us on the final?? Wondering if this is something I should attempt to memorize or can simply have with me.

Quinton Sprague 1A

Bit unclear which problem you're are refering to but important to note that when Phosphorous has four electron domains, say 3 bonds to separate atoms and one lone pair, the hybridization of the phosphorous atom is sp^3. Wondering if anyone can answer: Is this the case for any atoms, four electron do...

Quinton Sprague 1A

By knowing how many single/double bonds the compound has. Every single bond is considered a sigma, while every double is considered a pi bond.

Quinton Sprague 1A

A delocalized pi bond is just a pi bond in which the electrons are free to move over more than two nuclei.

Quinton Sprague 1A

You can determine the intensity of the dipole moment through the difference in electronegativites of two atoms. If one atom present is very electronegative (say Fluorine) and the other is fairly electropositive (say Potassium) you know the dipole moment will be more severe since the Fluorine will pu...

Quinton Sprague 1A

In Wednesday's lecture, Dr. Lavelle discussed how a salt like NiCl2 can disolve in water by accepting electrons from H2O and forming new bonds. Short after, he discussed the example of the drug Cisplatin that loses its chlorides to bond with DNA. Wondering how we can tell, when looking at a coordina...

Quinton Sprague 1A

Bit confused on how these two differ regarding their position on the internuclear axis. Believe Dr. Lavelle said Sigma bonds occur on the axis while Pi bonds are around the axis. What does this really mean about the electron interaction between two atoms? For Pi bonds one electron is above the other?

Quinton Sprague 1A

Should be linear, otherwise I believe you could not discern the answer with only that info.

Quinton Sprague 1A

I don't believe there is a specific time they are set to be released. However we received the grades to our last midterm around two weeks after taking it so figuring we may know by the end of this week.

Quinton Sprague 1A

: Chem Community Joke.jpeg (10.48 KiB) Viewed 772 times

Quinton Sprague 1A

In friday lecture Dr. Lavelle discussed the mixing of s and p orbitals to create hybrids so certain atoms may form more bonds. I was wondering if such hybridization can occur all along the periodic table, as in between d and f orbitals potentially, or other variations as such? Are hybrid orbitals on...

Quinton Sprague 1A

I believe you are correct in that a double bond can be considered just a pi bond, however, as I am sure we will get questions regarding how many of each bonds are present and others along these lines, I would air on the side of caution and label every double bond as one sigma and one pi, rather than...

Quinton Sprague 1A

Anyone know if we are permitted to use a periodic table with electronegativity values on it?

Quinton Sprague 1A

Though I know this midterm will likely have far less mathematical problems on it, should we expect any printable sheet that we may use on the test? Could include periodic trends, exceptions of electron rules, formal charge equation and various principles as such. Assuming the periodic table will be ...

Quinton Sprague 1A

I am struggling on a problem that gives the experimental bond lengths and contrasts them with expected bond lengths. The question then asks whether the single bonds are overwhelming C-O or C-N bond character, or if they are ample C--O or C--N bond character. I am not sure how to figure what is the c...

Quinton Sprague 1A

Wondering the same thing... also, will we be required to know various exceptions as such on the upcoming midterm? Is there a way to figure the configuration simply given the periodic table or rather are these cemented rules for the elements?

Quinton Sprague 1A

Today in lecture Dr. Lavelle went over the dissasociation energy for a hydrogen bond and described how an Oxygen's lone pair of electrons will link to an hydrogen atom. Because in the case of water molecules the H-atom has already given up its single electron to make a covalent bond with the Oxygen ...

Quinton Sprague 1A

Another way of telling deals with Hydrogen atoms. If an compound donates a hydrogen ion than it is an acid, if it gains an hydrogen ion then it is a base. Hope this helps a bit more.

Quinton Sprague 1A

Did you know that oxygen went for a second date with potassium?
How did it go?
It went OK2!

Quinton Sprague 1A

Looks like your answer should be correct, the 3d subshell is filled and the remaining two electrons go onto the 4s shell. If you are ever really unsure on a problem there is also a textbook answer key on sapling that you may refer to. Hope this helps!

Quinton Sprague 1A

I believe the atomic radius actually decreases across a period. Since the effective nuclear charge increases across a period, there is a greater nuclear attraction to the electrons across a period, subsequently pulling the electron cloud closer in and lowering the atomic radius. Hence, a transition ...

Quinton Sprague 1A

Higher charged cations exert stronger electrostatic attraction on anions which distorts the anion's electron cloud. The larger the electron cloud of the anion the more easily it becomes distorted. What gives distortion covalent character is when a cloud is distorted there is electron density shared ...

Quinton Sprague 1A

A release of energy correlates to a transition to a more stable state. An element that is most likely to gain an electron, one closest to filling its valence shell, will release the most energy. On the other hand, a gain in energy correlates to a transition to a less stable state. Adding an electron...

Quinton Sprague 1A

Hi, I believe the main difference between the ground and excited state is that the ground is representative of the configuration with the lowest energy and most stable environment, while the excited state represents the configuration with a higher energy arrangement. Because of this, I think the gro...

Quinton Sprague 1A

Thank you both! I finally solved the complete question after my eleventh try. I was unclear that it was asking specifically for each subshell, I appreciate the help!

Quinton Sprague 1A

On the Sapling homework I have been having trouble solving these two questions. Both ask you to find the maximum number of electrons that could have the sets of quantum numbers. The first is n=4 and l=2. My thought was that regardless of the principal shell, theres atleast 2 electrons. Then since l=...

Quinton Sprague 1A

When posted, I imagine we will receive an email notifying us of their completion, whether that be on ccle or myucla.

Quinton Sprague 1A

The uncertainty equation is given as P(change)*X(change) is greater than or equal to h/4pi. Due to the greater than or equal to, any value for position(x), momentum(p), velocity(v), or mass(m) that satifies the equation given the other variables, will already be the minimum possible value for that v...

Quinton Sprague 1A

I was curious of the same thing but it from what I have heard you may print out and use the constants and equations sheet Dr. Lavelle has listed on his website. It sounds like he was planning on updating it so I may wait till a day before the midterm to print it and make sure you have the most updat...

Quinton Sprague 1A

I was wondering the same thing. If you check out the post titled "Midterm Nomenclature" it appears to be answered by a TA who says that we will not be expected to know/balance formulas like nitric acid, phosphoric acid, or other compounds as such.

Quinton Sprague 1A

Hi, While I know this is probably irregular, given the unconvential test taking environment, does anyone know if our written work on the midterm will be taken into any consideration? Additionally, if this is the case, will we be expected to write the correct number of significant figures for the wor...

Quinton Sprague 1A

Hello,
The value 2.998 x 10^8 m/s is the most precise so although it is easy to remember 3.0 x 10^8, if the grading is very picky, it is likely best to go with the figure closest to its exact value, that being the 2.998 x 10^8 representation of the speed of light.

Quinton Sprague 1A

This is great! Thank you for sharing!

Quinton Sprague 1A

Hello! I believe the Lyman series starts at n=1 because one of the light energy sources (or lines on the series) used by Lyam has a frequency and wavelength equipped to excite an electron from the ground state to n=2. This gap from n1 to n2 is the largest in all the electron levels therefore require...

Quinton Sprague 1A

Hello everyone, Being that our midterm is coming up I am looking for ways to really review the fundamentals that will be on the exam. I have already completed the bookwork and been through all the modules, but I would love to hear what peers are doing to study these chemistry basics. Any great video...

Quinton Sprague 1A

The exact appearance and properties of light are still somewhat unknown. Like the peer before me stated, to truly perceive how the photons appear and interact one must be able to view a light source from a incredibly small scale (quantum). Because of this, the idea of photons as small packets of ene...

Quinton Sprague 1A

I have recently been working on some empirical formula practice and noticed in some instances a molar ratio with values close enough to zero are often accepted while others seemingly just as close are multiplied out to find the next whole number ratio. For instance, I just found the ratio for sucros...

Quinton Sprague 1A

Hello, It is also important to keep in mind the vast unknown regarding these concepts. Because humans can only see visible light, it is increasingly hard to scientists to identify what exactly quanta and photons look like, being that they are both symbolic of this so called 'packet' of energy. Dr. L...

Quinton Sprague 1A

Also, does anyone know which we will be using most frequently? What is the significance in using Kelvins if they are simply an addition to Celsius and proportional?

Quinton Sprague 1A

Hello, Hearing of the uniqueness each atom and molecule holds within their spectral fingerprint had me curious of the logistics in deriving each absorption line in the atomic spectra. I understand that these lines can be discovered by harnessing the energy electrons put out when they lose excitement...

Quinton Sprague 1A

Using the given density, you want to first convert the .20mL of 2-butanoe into grams. Then you'll need to lookup the molecular equation to calculate for the molarity of 2-Butanoe. Once the molarity has been derived, convert your grams of 2-Butanoe into moles. Using the 1:1 ratio of moles of 2-B: mol...

Quinton Sprague 1A

Because 950,000 has no decimal placed, the four zeros following 95 are considered trailing and therefore insignificant. This is the same case with the final zero in 80,060, because of no decimal place it is insignifant, while the two zeros between the very much significant 8 and 6 are considered sig...

Quinton Sprague 1A

Hi!

Molecules are simply groups of atoms bonded together.

Moles, on the other hand, are units of measurement we use to define quantities of molecules/atoms. Moles represent 6.02x10^23 (Avogrado's Number) of a chemical unit, just as a half-dozen represents 6 of something.

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