CHEMISTRY COMMUNITY

Jordi M 2I

I doubt that there will be the option to go fully remote. I know UCR is going for maximum in person classes next fall.

Jordi M 2I

Does anyone have an idea when they will take 14CL? I wanted to take it in the summer but I can't enroll yet.

Jordi M 2I

I thought the final was pretty simple. Not as many calculations as I expected.

Jordi M 2I

You have to do a qualitative analysis of the scenario in the problem. Since half life increases when the initial conc. decreases, we can infer that the reaction is second order since the 2nd order half life formula has initial conc. in the denominator.

Jordi M 2I

Once again, thank you Dr. Lavelle for another amazing quarter in general chemistry. I'm confident that taking 14A and 14B with you has thoroughly prepared me for future courses, exams, and studies in STEM.

Jordi M 2I

Intermediate species are those which are produced from one elementary step and consumed in the next step. They should not appear in the overall reaction since they cancel out. The same goes with a catalyst although I'm unfamiliar with the exact differences between the two.

Jordi M 2I

Understanding the conceptual reasoning behind each problem will be of great help. Its one thing to know how to plug in numbers to an equation and another thing to know when to apply it. Thermodynamics is perhaps the best example of this at work.

Jordi M 2I

If the solution concentrations at the anode and cathode are equal for a concentration cell, does $E_{cell}^{o}=0$ or $E_{cell}=0$ .

Jordi M 2I

We include H+ when the redox reaction occurs in acidic conditions. Similarly, we use OH- when the reaction in is basic conditions.

Jordi M 2I

The electromotive force or (emf) is what causes a flow of electrons. It occurs when there is a electric potential difference between 2 points, in our case the anode and cathode. Emf is synonymous with voltage and it is measured in volts (joules/coloumb). Think of voltage/emf as the work/energy neede...

Jordi M 2I

The anode and cathode will be solid state unless they are dissolved in the solution, then they are aqueous. OH- in basic conditions and H+ in acidic conditions will both be aqueous as well. Finally H20 will be liquid in galvanic cells.

Jordi M 2I

The anode is shown with a negative charge and the anode dissolves into the solution by releasing cations through oxidation. The cathode grows in size due to the accumulation of metal on its surface from the reduction reaction.

Jordi M 2I

Lavelle mentioned in lectured today that the process from diamonds into graphite is thermodynamically favorable but doesn't occur due to a high energy barrier. Therefore is it still possible that diamonds can turn into graphite at standard conditions (room temp and 1 atm) over many many years?

Jordi M 2I

So E naught does not equal zero at equilibrium correct?

Jordi M 2I

I believed Lavelle mentioned before that charging a cell is a non spontaneous process, which makes sense since my phone doesn't recharge itself. But mathematically, how is this proven?

Jordi M 2I

I was a little confused after watching the lectures why the salt bridge is needed in a cell/battery. Also, how do the ions move from one side to another with the bridge?

Jordi M 2I

I believe it can be used for both since we approximate systems as being reversible.

Jordi M 2I

What are some thermodynamic properties that are considered extensive aside from entropy?

Jordi M 2I

Oh my gosh, I made the same mistake by using Cp. Thank you!

Jordi M 2I

I believe the person above is a little mistaken. The delta S of the SYSTEM is not equal to 0 but delta S TOTAL is in fact equal to zero since for a reversible reaction (which phases changes are since they use qrev) the delta S total is always equal to zero.

Jordi M 2I

Daniel Huynh 2J wrote:RdeltaT represents the work done on the system, n just represents the amount of moles that does that amount of work.

I thought when change in volume = 0, there is no work done. I'm a bit confused why this term is necessary then?

Jordi M 2I

This equation can be used to calculate the heat required to perform a phase change of a particular substance. The number of moles of the substance multiplied by the enthalpy change for fusion or vaporization will give you how much heat is required to fully change that amount of a substance into a di...

Jordi M 2I

For this problem, I approached it by calculating the change in entropy due to the change in volume and then added the change in entropy due to the increase in temperature. However, I didn't arrive at the correct answer of +11.2 J/K and I'm not sure why.

Jordi M 2I

When I was reviewing the answers to some textbook problems I found this equation for the change in enthalpy at a constant volume: \Delta H=\Delta U + nR\Delta T Where does the second term in this equation come from? I understand that when the volume is constant, work=0 but I do not understand why th...

Jordi M 2I

I believe you are correct. A positive value for heat means there is an input of heat into the system from the surroundings. A negative value means the system released heat into the surroundings.

Jordi M 2I

So assuming that the standard entropy and free energy of the products and reactant is given in the table, all you need to do is follow this formula to calculate the change: (Sum of all standard entropies of the products) - (standard entropy of the reactant) The same applies with Gibbs free energy: (...

Jordi M 2I

When the temperature is higher, the molecules have more kinetic energy and therefore can occupy more micro-states. This is the reason why gases have higher entropy values. If the temperature is already high, adding more heat to the system will not lead to a dramatic increase the kinetic energy since...

Jordi M 2I

If you know both the change in enthalpy of vaporization and the change in entropy of vaporization you can use the equation \Delta S=\frac{q_{rev}}{T} Since enthalpy is just the heat at constant pressure you can replace q with the value of the change in enthalpy and solve for T which will be the temp...

Jordi M 2I

The rest of thermochemistry and up until the end of the thermodynamics outline I believe but Lavelle will let us know for sure.

Jordi M 2I

In class, we discussed that the change in entropy is lower when adding heat to a substance already at a high temperature. I think you may be confusing this concept with changing entropy of substances at low vs high entropy. Changes in temperature mostly have to do with changing the kinetic energy o...

Jordi M 2I

I was confused on the solution to this problem which listed the increasing change in entropies as B<C<A. I thought the order would be C<B<A since molecules in C are already vibrationally active thus start out with a larger entropy value. Wouldn't this mean that their change in entropy when raised to...

Jordi M 2I

I believe that is correct. That's how I understood it.

Jordi M 2I

In lecture today Lavelle gave an equation of how to calculate entropy of surroundings: \Delta S {surr}=-\frac{\Delta H_{sys}}{T} Is the temperature T in this equation the temperature of the system or of the surroundings? I was confused because when he was showing an example of thermal equilibrium it...

Jordi M 2I

You have to use context clues that are given in the question. Often in Thermodynamics problems, you are supposed to draw your own conclusions based on "hidden" information in the problem. For example, when pressure is constant, q becomes the definition of enthalpy so you could replace it w...

Jordi M 2I

I was planning on taking Chem BL and CL together over the summer. Is this a bad idea to take two lab courses at once?

Jordi M 2I

What is an example where work is done on the system, resulting in a positive value for work?

Jordi M 2I

Molar heat capacity can be thought of as a form of specific heat capacity. Specific heat capacity is the energy required to raise the temperature by 1 degree for a GRAM of that substance. Molar heat capacity is the energy required to raise the temperature by 1 degree for a MOLE of that substance.

Jordi M 2I

I've been seeing a lot of examples which mention the standard entropy of vaporization for a substance. What does this term exactly mean? Is this just the entropy when the liquid is vaporizing?

Jordi M 2I

I believe this has to do with the space the gas molecules can now occupy which is similar to the 2 chamber vial example Lavelle showed us when he defined degeneracy. In Lavelle's example, the gas molecules could either be split between the two chambers or in one of the chambers. Doubling the volume ...

Jordi M 2I

I should clarify. The degeneracy is after you evaluate the expression and is the number of possible arrangements. Like in todays lecture, the 2 states of left and right with 2 particles has 4 possible ways to arrange it.

Jordi M 2I

I believe the terms are synonyms for one another. You can say arrangements, microstates, etc. It just means the number of possible outcomes/final states. For example left or right or on or off.

Jordi M 2I

In lecture today, Dr. Lavelle showed an example of an O2 molecule having a residual entropy of 0 since it only has one state. Does this mean all diatomic molecules like F2 and Cl2 will also have a residual entropy of 0? What about BF3? or CH4?

Jordi M 2I

In the lecture today Dr. Lavelle substituted work as the function $-P\Delta V$ . Does this mean we can substitute in the formula for a reversible reaction under conditions of constant pressure? The one with the integral.

Jordi M 2I

Yes if the change in enthalpy is negative, it is an endothermic reaction and heating the system will produce less product. :)

Jordi M 2I

What context are you asking your question for? Like what problem?

Jordi M 2I

Think of a closed water bottle for a closed system and a closed thermos/canteen for an isolated system.

Jordi M 2I

Yes, look at the units the problem gives you. Most of the time though it will be atm. Your equation sheet will have all of them though.

Jordi M 2I

You need to know whether the salt has the anion of a conjugate base from a weak acid or an anion of a conjugate acid from a weak base. Remember that halogens do not affect the pH nor do alkali earth metal cations.

Jordi M 2I

Neutralization is where an acid and a base combine to form a salt in water. The pH will be neutral in such cases. Combining HCl and NaOH will result in the formation of NaCl and water, neither of which will affect the pH of the solution.

Jordi M 2I

When I calculated the volume of N2 gas in the airbag, I use the 1 atm as my pressure in the ideal gas equation. So in the next step where I use the equation $w=P \Delta V$
, what value do I use for my pressure? I can't seem to get the right answer.

Jordi M 2I

In an acid-base reaction such as NH4+ giving off a proton to turn into NH3. Would 1/Ka of this reaction be equal to the Kb for the reverse reaction where the conjugate base NH3 accepts a proton?

Jordi M 2I

From what I understand, Sulfuric acid can be considered completely disassociated/ionized in its first K value as it is on the list of strong acids. As to how close K1 and K2 need to be, I am not sure.

Jordi M 2I

To use Hess's Law, you need to be given equations (and their corresponding enthalpies) that can be related to your equation of interest. To use standard enthalpy, you need to have a table of the enthalpies of common compounds such as CO or H20. As for which one is more accurate I am not quite sure.

Jordi M 2I

Try setting up your Kb expression now. Since you know your OH- concentration, you know that your NH4+ concentration must be the same which will allow you to solve for the NH3 concentration. Once you find NH3, that is your EQUILIBRIUM concentration so you still need to find your initial in order to c...

Jordi M 2I

The enthalpies for bonds that are not diatomic are averaged across all the other molecules they are found in. Therefore, using bond enthalpies is the least accurate method of the three ways Dr. Lavelle showed us.

Jordi M 2I

He gets them from a pre made table which lists the enthalpies of known bonds. He changes the sign for the enthalpies in the products since forming a bond releases energy and is exothermic.

Jordi M 2I

Yes drawing out the lewis structures is necessary in more advanced cases. It helps visualize bounds that were broken and reformed such as the double bond of carbon in today's example in class.

Jordi M 2I

Why is carbon's most stable state graphite? Is the graphite In my pencil pure carbon lol?

Jordi M 2I

I go for walks with my girlfriend and play with my cat Lucy :)

Jordi M 2I

You have to combine the equations it gives you to make the correct equation in the question. You can inverse their equations and even multiply them by stoichiometric constants .

Jordi M 2I

If you are not given the formula or if it is already balanced then I think so.

Jordi M 2I

The concentration of H30+ or OH- should never surpass 1 or go lower than 1x10^-14. The autoprotolysis of water explains that at 25 degrees C, the product of H30 and OH is always 10^-14 (hence the pH scale). You shouldn't have a H30 concentration above 1.

Jordi M 2I

Sometimes an x value will be too large when subtracting x from the reactants and would give you negative reactants which isn't possible.

Jordi M 2I

Based on a given enthalpy (usually seen as delta h)

Jordi M 2I

Lindsey_Su_3A wrote:Does anyone know how long the midterms will be?

90 minute midterms

Jordi M 2I

Begin by finding the Kc (equilibrium constant) based on the given concentrations. After, make an ice table with the initial concentration of NO2 being 0.8 M while O2 and N2 remain at 0.2 M. Since more product was added to the system, there will be a shift toward the reactants. Therefore you can crea...

Jordi M 2I

TJ Lai 2H wrote:
Nick P 3D wrote:H2O is water and H2O2 is hydrogen peroxide.
What is H2O4?

Drinking

Can someone explain this joke? I don't get it :(

Same with this from lecture yesterday:

Screenshot 2021-01-14 103034.png

Instead of saying “what is H204?”
Say it as “what is H20 for”

Jordi M 2I

What do Switzerland and H20 have in common?
They always remain neutral!

Jordi M 2I

What do Switzerland and H20 have in common?
They are always neutral!

Jordi M 2I

My understanding is that monoprotic acids forms only one mole of H30+ per molecule of the acid. Therefore in the Ka equation, there should be no exponents on the concentrations of H30+. Would this mean that in a diprotic acid such as H2SO4, would there be a 2 on the exponent of the H30+ concentratio...

Jordi M 2I

Adding an inert gas does not affect the concentration of the reaction because concentration is determined by the equation moles/volume. Adding the inert gas into the reaction chamber does not affect the moles of reactants nor the volume of the chamber since the volume will be fixed. All it does is i...

Jordi M 2I

One important thing to note is that many will refer to an equilibrium as shifted or leaning to the right or left. This does not mean the reaction is not at equilibrium, this means the forward reaction either favors products or reactants more. A Q value on the other hand can physically lay right or l...

Jordi M 2I

It depends on what the question gives you and what it is asking for. If it gives you the concentration of a reactant or product, use Kc. If it gives you a pressure, use Kp.

Jordi M 2I

I am having trouble understanding where to begin on this question. Since no concentrations are given for any of the products or reactants, I know that the solution will have to involve using the other chemical equilibriums but I am unsure how to relate them. Any advice? Screen Shot 2021-01-07 at 4.3...

Jordi M 2I

Sorry, I never expected it to be a problem with the browser given that I used Safari all last quarter and ran into no issues. My apologizes for the inconvenience.

Jordi M 2I

Strange because I always used Safari last quarter and had already disabled my pop up blockers and it always worked but now it just refuses.

Jordi M 2I

Jazlyn Romero 1I wrote:This same issue happened to me when I tried accessing sapling through safari so I tried it on google chrome and it worked. Maybe try on google chrome or another browser?

Yes thank you that worked! For some reason Safari doesn't like Sapling lol

Jordi M 2I

Chem_Mod wrote:I contacted Sapling over the weekend and they said today (Monday) it should be fixed. Try again and it should work.

Im still receiving the same error that reads: "You must sign up for this through your instructor's course on your University's learning management system."

Jordi M 2I

I have not been able to access the Sapling Learning homework for Chem 14B even though I bought a 24 month access last quarter for Chem 14A. I contacted the sapling support and they said it must be a issue on Lavelle's or UCLA's part. Has anyone also been getting an error when trying to enroll with y...

Jordi M 2I

Good to remember the short list of strong acids and bases

Jordi M 2I

Thank you Dr. Lavelle for making this course very well adapted for online learning! The review sessions and Chemistry community were of great help! I look forward to taking Chem 14B.

Jordi M 2I

Thank you! I had the impression it was Hund's rule but I never saw this type of violation where an electron was in the opposite spin state.

Jordi M 2I

: Screen Shot 2020-12-12 at 6.29.27 PM.png (2.12 KiB) Viewed 357 times

Which rule does this configuration violate? Is it Hund''s rule?

Jordi M 2I

Take the -log of 12% to get 0.92
-log(0.12)

Jordi M 2I

I believe the stronger acid is H3PO4 since the resulting anion is more stable due to the xtra oxygen which increases electronegativity. PO4-3 also has resonance structures which delocalize its electrons to disperse the negative charge across the molecule.

Jordi M 2I

In this example, you would divide the product of the concentrations of the products over the concentration of the solvent: AH <—> A- (aq) + H+ (aq) leads to Ka =( [A-][H+] )/[AH] Concentrations, if they aren't given, would be calculated through our molarity formula M = n/V, where n=moles and v= vol...

Jordi M 2I

Is that all the information the question gives?

Jordi M 2I

When comparing two weak acids, you can determine their relative strength to one another by examining the hydrogen bond. If the bond is longer, it is also weaker and thus the hydrogen can easily dissociate (stronger acid). If the bond lengths are the same, you want to look at the stability of the res...

Jordi M 2I

It is technically possible but it is very uncommon for these shapes to occur in coordination complexes. I was also confused at first since the see saw shape also has 4 bound atoms. Square planar and tetrahedral are just more common.

Jordi M 2I

Often conjugate bases can be made out of atoms that are metalloids such as Si, P, As, etc. HPO4- is one example of an amphoteric compound.

Jordi M 2I

Yeah the things we have to remember in this course are the name of ligands - charge and conformation. - (monodentate, bidentate etc.) and the strong acids/bases.

Jordi M 2I

I'm not quite sure. I know the most stable structure for molecules spread their electron densities as far away as possible, so the bond angle is always the largest possible angle. I know bond strengths are determined on their bond order and their length. They can also be weakened by atoms with large...

Jordi M 2I

The order when examining the strength of an acid goes:
1.) Bond length of hydrogen
2.) Stability of resulting anion
a. Has an atom with a large electronegativity which pulls and disperses the negative charge
b. Has a resonance structure which delocalizes the electrons

Jordi M 2I

Why do we have to take the pKa value for some acids when we can take the pH for others? Do we only use the Ka value for weak acids? I know that a large pKa value means a stronger acid and a smaller pKa value means a stronger acid as well.

Jordi M 2I

I like to make quizlet flashcards to help me remember :)

Jordi M 2I

Is there a pOH scale that would also go from 0 to 14 like pH?

Jordi M 2I

Also remember that the product between the concentration of H30+ molecules and the concentration of OH- molecules will always be 1*10^-14. Some questions may ask you to find the H3O+ conc. by giving you the OH- conc. Just useful to know (:

Jordi M 2I

CH2Cl2 is a polar molecule because of its tetrahedral shape. No mater where you place the chlorine atoms, there will be a net dipole moment. C6H4Cl2 on the other hand is a cyclic structure meaning it forms a ring. In this structure, the chlorines are position are opposing ends which would cancel the...

Jordi M 2I

First thing to remember is that the coordination number is the number of bonds or attachment points to the metal cation (in this case Cobalt) within the coordination sphere. The coordination sphere is indicated by the brackets so Bromine would not be included when finding the coordination number. No...

Jordi M 2I

Yes you should definitely be ready to name the ligand if you are given its formula or abbreviation such as (en) or (edta). Also make sure you know the oxidation of the ligand so you can calculate the oxidative state of the metal cation. If you can't remember this, try quickly drawing the ligand to f...

Search found 152 matches