CHEMISTRY COMMUNITY

Jonathan Batac - 2D

We would use the equation k=e^(-Ea/RT); you don't need to worry about the "A" value because mathematically it will cancel out. We are given activation energies, we know the R constant (use 8.314 J.K-1.mol-1), and we know temperature (294K). Since we are looking for the ratio of k(cat)/k(un...

Jonathan Batac - 2D

Since it is a first order reaction, we would use ln[N2O5]=-kt+ln[N2O5]0. First, identify what is the initial concentration and what is final concentration; that would be .0651 and .0187, respectively. Your equation should look like this: ln[.0187]=-kt+ln[.0651]; you did not give the rate constant, k...

Jonathan Batac - 2D

There was a graph that Lavelle introduced in lecture that shows two lines (representing the same reaction under different temperatures) with activation energy marked somewhere along that graph. I think he said that it's not that big of a deal, but can someone help me try to interpret what's going on...

Jonathan Batac - 2D

Parks and Rec is elite.

Jonathan Batac - 2D

Intermediates are not included in rate laws. Therefore, you have to find a way to substitute the intermediate with the reactants that form that intermediate. There is a great Sapling HW problem for this (they can explain it way better than I can); if our numbers are the same, it should be Sapling We...

Jonathan Batac - 2D

A textbook problem gives this notation: "Pt(s)|Sn^+4(aq), Sn^+2(aq)||Cl−(aq)|Hg2Cl2(s)|Hg(l)." Can someone help break down the components for me? For example, which are the actual electrodes, why use a comma instead of a vertical line, and what is the salt meant for neutralizing the soluti...

Jonathan Batac - 2D

Molecular shape and structure. VSEPR theory is elite.

Jonathan Batac - 2D

Lavelle mentions how we would use the integrated rate laws and look at graphs to determine order. What is the method in doing that? Are we just given values like initial concentration and k and plot a graph ourselves? If someone can clarify this that would be amazing. Thanks!

Jonathan Batac - 2D

Can someone clarify Lavelle's example in lecture about a catalyst being saturated and how that relates to how increasing reactant concentration does not affect the rate of reaction?

Jonathan Batac - 2D

ln(2)

Jonathan Batac - 2D

Given experimental data, is there a simpler way to find the order of a reaction (and the order of certain concentrations (finding n and m)) without doing the mathematical analysis like Lavelle did in lecture?

Jonathan Batac - 2D

I was having a bit of trouble following what Lavelle was saying about the ion-selective electrodes. Can someone explain the purpose of it and how the Nernst Equation ties into it? Thanks!

Jonathan Batac - 2D

There are a few rules that you can follow. First, any neutral element that is not a part of a compound (such as O2 in this problem) will always have an oxidation state of 0. Second, oxygen and hydrogen usually have oxidation states of -2 and +1, respectively, when attached to any compound. So for th...

Jonathan Batac - 2D

The actual anode is written on the far left of the notation while the cathode is written on the far left. For this problem, the Pb(s) (the anode) would be on the far left. The metal chlorides (such as the PbCl2) that correspond to their metal electrodes are placed right next to the electrodes; in th...

Jonathan Batac - 2D

What are the basic steps to balancing any redox reaction in either a basic solution or acidic solution?

Jonathan Batac - 2D

n will be the moles of electrons transferred. Remember to balance your redox reaction to get the correct number of moles of e- transferred.

Jonathan Batac - 2D

I'm not sure that this is the correct way of thinking, but this is how I visualized it. Mn+2 is a reactant and since we are increasing its concentration (using LeChatelier's Principle), the forward reaction will increase to produce Mn(s). Since the flow is from anode to cathode (the Mn(s) being the ...

Jonathan Batac - 2D

I have in my notes that deltaS(total), for a reversible process, will be equal to 0; likewise, deltaS(surroundings), for an irreversible process, will be equal to 0. I hope I wrote that down right. If so, can someone explain this concept? Thanks!

Jonathan Batac - 2D

I think it's because during phase changes (vaporization, for example), the system is at equilibrium. Therefore the energy required for the vaporization of a liquid (the enthalpy) is cancelled out by the increase in entropy.

Jonathan Batac - 2D

Vibrationally active means that there is vibrational motion of particles in container C; this means that there is more "chaos" or "disorder" or "entropy." Since container B does not have vibrational motion of particles, C has a greater change in entropy.

Jonathan Batac - 2D

Degeneracy(W) is equal to the number of positions (let's call it "x") raised to the power of the number of particles, molecules, etc (let's call it "n"). Therefore "W = x^n". The "NA" that you wrote down is Avogadro's number; so that "2^NA" would be ...

Jonathan Batac - 2D

I forgot what lecture it was but Lavelle used the "deltaG = deltaH - T*deltaS" formula to derive "-deltaG/T = -deltaH(sys)/T +deltaS(sys)." Since "deltaS(surr) = -deltaH(sys)/T" and "deltaS(surr) + deltaS(sys) = deltaS(tot)" it would make sense that if deltaS(...

Jonathan Batac - 2D

Can someone explain the 2nd Law of Thermodynamics in words? And maybe connect it to the equation "deltaS = q/T."

Jonathan Batac - 2D

I was checking out how Lavelle derived the equation "deltaS = nR*ln(V2/V1)." I understood up to when he got "deltaS = kb*ln(V2/V1)" but then I didn't understand why he could substitute kb (Boltzmann's constant) for nR. Can someone clear this up? Thanks!

Jonathan Batac - 2D

From last week and this week, I think I count three different equations for deltaS: deltaS = q/T; deltaS = nR*ln(V2/V1); and deltaS = nCp*ln(T2/T1). Can I just get some clarification on the difference between the three and in what situations I would use them? Thanks!

Jonathan Batac - 2D

Hi, sometimes in lecture I get a bit confused on the difference between q and deltaH. I understand q is heat and deltaH is enthalpy, but is there any reason why we would use one to represent heat flow instead of the other? Sometimes I think Lavelle uses them interchangeably but I'm not sure if that'...

Jonathan Batac - 2D

The molar heat capacity for carbon monoxide at constant volume is CV,m =20.17 J/(K·mol) . A 5.00 -L fixed-volume flask contains CO(g) at a pressure of 10.00 kPa and a temperature of 25.0 °C. Assuming that carbon monoxide acts as an ideal gas and that its heat capacity is constant over the given temp...

Jonathan Batac - 2D

Can someone explain the concept that when work is being done by the system, it should be a negative value; and while when work is being done to the system it should be a positive value?

Jonathan Batac - 2D

Can someone explain the difference between irreversible expansions and reversible expansions. Along with that, can someone explain how a given problem would present such information and what equations we should be using to calculate work for either expansion.

Jonathan Batac - 2D

I did question 20 and somehow got it right, but I was confused on the table given. Can someone explain the difference between gas atoms, linear molecules, and nonlinear molecules and how their specific heat capacities at constant volume relate to one another?

Jonathan Batac - 2D

Delta H should be positive if the reaction is absorbing heat and negative if releasing heat. You might be thinking of q being negative or positive? If the delta H is positive and the reaction is absorbing heat, q(system) should be positive because the system is gaining heat while q(surroundings) sho...

Jonathan Batac - 2D

Can someone explain the difference between constant volume and constant pressure when solving a question in which you have to calculate deltaU? What situations would be given and how would be be able to tell if the system is under constant pressure or volume?

Jonathan Batac - 2D

A 0.773 mol sample of NO2(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 10.1 K. Calculate the amount of heat q required to bring about this temperature change, and find the corresponding total change in the inter...

Jonathan Batac - 2D

Usually a week.

Jonathan Batac - 2D

There is a difference between the system being exothermic and the surroundings of the system increasing in temperature. While the system itself is giving off heat (that is why it is exothermic), that heat must be released somewhere. That "somewhere" is the surroundings. The surroundings wi...

Jonathan Batac - 2D

The reaction started at 25 degrees Celsius and ended at 31.9 degrees Celsius. From this, we can tell that the reaction is exothermic (the system is releasing heat, making the surroundings warmer and raising the temperature). Delta T is change in temperature, so the +6.9 is simply 31.9 - 25 (final te...

Jonathan Batac - 2D

What are the key differences between a calorimeter under constant pressure versus one under constant volume?

Jonathan Batac - 2D

I don't think there are any that you must memorize. If you look at the constants and equation sheet on Lavelle's website, specific heat capacity of water (ice, vapor, liquid) is listed. I think any question about substances other than water will give their heat capacities.

Jonathan Batac - 2D

What is the purpose of using Cv and Cp for molar heat capacity?

Jonathan Batac - 2D

As per the outline for Equilibrium on Lavelle's website: "Use Le Chatelier's principle to predict how the equilibrium composition of a reaction mixture is affected by: adding or removing reagents; compressing or expanding a gaseous mixture; and by raising or lowering the temperature." Basi...

Jonathan Batac - 2D

Method 2 (side note: which is usually an inaccurate way of calculating enthalpy of reaction) says that we can take the enthalpies of bonds that are broken in the reactants and subtract them from the enthalpies of bonds formed in the products. Remember that breaking bonds is endothermic and enthalpie...

Jonathan Batac - 2D

There are two reactions that must happen to get nitrogen dioxide: formation of NO from N2 and O2 and formation of NO2 from NO and O2. These two separate reactions have two different enthalpies of reaction (180kJ and -112kJ, respectively). Hess's law says that when we combine the two reactions (which...

Jonathan Batac - 2D

You first have to determine how the reaction will proceed; towards the products or towards the reactants? You figure this out either through a description of the problem or through calculating Q and comparing that to the K value. Once you find out how the reaction will proceed, you assign positive o...

Jonathan Batac - 2D

The outlines on Lavelle's website give a clear picture as to what material can possibly be on the midterms. As for this midterm, many students expect this one to be calculation heavy; it will be best to attend workshops and do ALL textbook and Sapling problems. If you are looking for other resources...

Jonathan Batac - 2D

The first midterm should only cover weeks 1-3 (that's how Lavelle did it last quarter for 14A), unless there are things that Lavelle specifically says otherwise. As for an outline, on Lavelle's website there are outlines for equilibrium, acids/bases, and thermochem that are definitely worth going ov...

Jonathan Batac - 2D

Hi, can someone clarify why we can get the equation "enthalpy(sublimation) = enthalpy(fusion) + enthalpy(vaporization)" and how that ties into to how enthalpy is a state property?

Jonathan Batac - 2D

Aliya Roserie 3I wrote:I did not have this issue. Try emailing your TA to ensure that your grade is accounted for !

Thanks! I'll make sure to do that.

Jonathan Batac - 2D

I'm confused about this too. I think I have the same problem. I finished today and on sapling it shows I have a 100% but on ccle it shows I have a 97%. Does it take a while to load or update frequently? CCLE does take a while to catch up to Sapling; to make sure, I would take a screenshot or have s...

Jonathan Batac - 2D

I was just checking CCLE and looked at my grade for Week 1's Sapling HW. I completed it during Week 1; I remember because I remember seeing the cute little hopping bunny. Anyways, my grade was a 90% and I was confused as to why. I also faintly remember logging onto CCLE and checking my grade about a...

Jonathan Batac - 2D

Endothermic reactions require heat while exothermic reactions release heat. In a given problem you can look for those words or look for the enthalpy of the reaction (denoted by the change symbol/triangle with H). A positive enthalpy is endothermic and negative enthalpy is exothermic.

Jonathan Batac - 2D

"Favors" or "lies to" the right/left side refers to the K value by itself (either more reactants or more products are present at equilibrium. "Shifts to" the right/left refers to when there is a change in parameters or concentration since the system has to "shift&q...

Jonathan Batac - 2D

You are right in that amphoteric substances can act as an acid or a base. Amphiprotic substances, I think, are just a bit more specific because amphiprotic means that a substance (such as water) can either donate or accept H+ ions. Amphiprotic substances are always amphoteric, but not all amphoteric...

Jonathan Batac - 2D

Is it correct to say that we pKa should only be used for measuring the dissociation of weak acids (and pKb for weak bases) while using pH for strong acids (and pOH for strong bases)? If not, what would be the correct way to define pKa vs pH. I was just a bit confused on the distinction between pKa v...

Jonathan Batac - 2D

I was doing a textbook problem and wrote the K expression in terms of concentration but the answer key puts it in terms of partial pressure. Looking back at the reaction, all species are in gas phases so it makes sense why use partial pressure. Is there any instance where we could use Kc instead of ...

Jonathan Batac - 2D

Only temperature will change the K value. Any other change in parameters such as pressure/volume will result in a change in concentration.

Jonathan Batac - 2D

To find which side has more moles of gas, you just need to look at the coefficients of all gas species. Take for example N2(g) + 3H2(g) <-> 2NH3(g). By counting the coefficients there are 4 moles of gas on the reactant's side (one N2 and three H2) and 2 moles of gas on the product's side (two NH3). ...

Jonathan Batac - 2D

When using the quadratic formula, there should be two values of X if solved correctly. Is there a general rule to which one we should use and the reasoning for why that particular one?

Jonathan Batac - 2D

If H20 was a pure substance in the reaction (either a liquid or solid) it should not be included. But as a gas (water vapor), always include it in the ICE table.

Jonathan Batac - 2D

a. Remember that when a system reaches equilibrium, there is a constant, K. This constant is the ratio of products and reactions ([P]/[R] or P(products)/P(reactants)). Since the forward and reverse reactions are the same at equilibrium, there should be no instance in which products increase or decre...

Jonathan Batac - 2D

I would always check what units are given. As you stated, if given concentration (Molarity) usually you would be calculating for Kc, and if given atm/bars usually you would be calculating for Kp.

Jonathan Batac - 2D

I guess the safest way to figure out a problem like this is to draw it out. In Lavelle's last lecture, he drew out the Lewis structure of the acid H2SO4. When placed with water, the hydrogens will dissociate and form hydronium with water, then you will first have HSO4^-1 then SO4^-2. These are the c...

Jonathan Batac - 2D

I'm not sure what you mean by polyphonic, but I am going to assume that you mean polyprotic acid. To tell if the acid is completely deprotonated, you just have to look for H+. Take for example carbonic acid, H2CO3. The neutrally charged species is obviously not deprotonated because it has two H+. Li...

Jonathan Batac - 2D

I am trying to understand the concept of chelates, so please correct me if I'm wrong. All chelates must be polydentate, but not all polydentates can be chelates? If so, why is that? And what are some major chelates that we should be aware of?

Jonathan Batac - 2D

Though used interchangeably, the textbook distinguishes the two. If I recall correctly, the complex consists of the ligands and transition metal (or as the textbook says "one or more of the ions or neutral species present in the compound") while the compound is the overall neutrally charge...

Jonathan Batac - 2D

I was doing a textbook problem that asks to write the formula of "sodium bisoxalato(diaqua)ferrate(iii)". I almost got the right answer, but the "bis" confused me a bit. I ended up writing "Na [Fe(C2O4)2(OH2)4]" instead of "Na [Fe(C2O4)2(OH2)2]". I was under t...

Jonathan Batac - 2D

Can someone explain the significance of having a stable anion in order to have a strong acid? Why does it matter if it is stable or not?

Jonathan Batac - 2D

The prefix "ferr" comes from Latin. "Ferrate" is used because the coordination complex is an anion (has a negative charge). There are other elements that share this characteristic: Silver (Ag) becomes argentate, gold (Au) becomes aurate, and copper (Cu) becomes cuprate.

Jonathan Batac - 2D

All you can really do is memorize the strong versus weak acids. There doesn't seem to be a clear trend in identifying them . For example, HCl and HBr are both strong acids and halogens, but HF is a halogen but not a strong acid. The same goes with strong bases and weak bases.

Jonathan Batac - 2D

The ligand itself is tetradentate (it can form 4 bonds with the metal (iron). The iron, you are correct, likes to form an octahedral structure (6 bonds). The other two bonds come from the histine and the O2 molecules.

Jonathan Batac - 2D

I was doing some Sapling learning problems and I came across this coordination compound. It's name is barium tetrabromoferrate(iii). I'm a bit confused on the process on how to name it. Can someone tell me how they would approach naming this compound? Thanks.

Jonathan Batac - 2D

Two adjacent carbon atoms with a double bond between then will cause the hydrogens to be parallel to each other (on the same plane). Attaching another carbon to either end of the two carbon chain will cause the new carbon and its hydrogens to become perpendicular to the previous two carbons; this th...

Jonathan Batac - 2D

As Lavelle mentioned, it does not really matter. It will be accepted either way.

Jonathan Batac - 2D

Whenever I hear "delocalized" I immediately think resonance. So if a structure has resonance (the double or triple bond can be "placed" between some other atom and the central one), it should have delocalized pi bonds (pi bonds appear in double and triple bonds).

Jonathan Batac - 2D

Since cisplatin has the chlorines on the same side and transplatin has the chlorines on the opposite sides, is there a reason why the difference in structure happens? I remember that the difference in cis-/trans-dichloroethene from the VSEPR section is due to the double bond and the restrictive forc...

Jonathan Batac - 2D

Hi, I think I understand the concept of ligands and chelates, but can I get some clarification on why the example at the end of the 11/25 lecture (the EDTA -4) is a hexadentate as opposed to a tridentate or any other polydentate?

Jonathan Batac - 2D

I think Lavelle said something about how sigma and pi bonds have an effect on how a molecule like dichloroethene can be either in a fixed shape (cis-dichloroethene = polar) or loose shape (trans-dichloroethene = nonpolar). Are there any other kind of molecules that can help further emphasize and vis...

Jonathan Batac - 2D

Yes VSEPR notation definitely helps with figuring out the shape of a molecule. A is the central atom and X & E are the two different types of electron regions. Counting the number of Xs and Es, you can find the arrangement (tetrahedral, octahedral, etc), but to find the exact shape you got to ta...

Jonathan Batac - 2D

I'm having a bit of trouble visualizing the shape of sigma and pi bonds. In Friday's lecture, Lavelle's slides said that sigma bonds allow bound atoms to rotate and pi bonds don't allow rotation. What does that mean and how does that relate to the shape of the bonds?

Jonathan Batac - 2D

I was wondering, are there only three situations we will be getting in identifying the sigma and pi bonds? Like single = one sigma, double = one sigma & one pi, triple = one sigma & two pi. There wouldn't be any other combination?

Jonathan Batac - 2D

Boiling point is the transition of matter from a liquid to a gas while melting point is the transition from a solid to a liquid. I wouldn't worry too much about the difference at the moment, but in relation to intermolecular forces, they trend mostly the same way.

Jonathan Batac - 2D

I'm not sure if dissociation energy is a trend like the way we think of electronegativity and atomic radius (someone please correct me if I'm wrong). But generally, dissociation energy increases as the bond between two atoms becomes shorter and therefore harder to break; single bonds are weaker than...

Jonathan Batac - 2D

Dipoles refer to polar covalent bonds, which is the unequal sharing of electrons between two atoms in a molecule. This occurs when you have an atom (take for example F) has a higher electronegativity than another atom that it is covalently bonded to (for this example H). When F pulls the electrons c...

Jonathan Batac - 2D

Putting delta positives or delta negatives indicate that something has a partial positive or negative charge. Something with a delta negative is the more electronegative atom and therefore electrons from the atom it is covalently bonded to will be attracted to the partial negative atom. The best exa...

Jonathan Batac - 2D

Yes. Hydrogen atoms must be polarized by F, O, or N in order for a hydrogen bond to occur.

Jonathan Batac - 2D

Although we haven't learned this yet, BCl3 has a symmetric shape (trigonal planar). You can kind of think of each Chlorine equally pulling Boron in separate directions, so therefore there is no polar movement of the molecule. You can also apply this thinking to I2; the Iodines are equally repelling ...

Jonathan Batac - 2D

There doesn't seem to be a clear requirement to memorize all the molecules and compounds that Lavelle uses, but it is very useful to memorize quite a bit of them. For example, theres a big difference between nitrate and nitrite. I personally think everyone should know how to derive a chemical formul...

Jonathan Batac - 2D

I personally just count the number of lone pair electrons (or dots) and the individual bond. After added those two up, I subtract the valence electrons by that number.

Jonathan Batac - 2D

L stands for the actual number of electrons (or dots, if you will), not the total amount of lone pairs. For example, there may be two lone pairs of electrons, but L will be 4 because there are four individual electrons.

Jonathan Batac - 2D

I don't know if this is too much to ask, but can someone provide a comprehensive list of the octet guideline exceptions. No detail is needed, but just to kind of wrap my head around everything, a list would be greatly appreciated :) Thanks!

Jonathan Batac - 2D

Given the formal charge of each atom in a Lewis structure that has resonance, how do you tell which structure will be more/less stable than the other?

Jonathan Batac - 2D

Can someone explain why elements in the top right of the periodic table (like group 17) have high electron affinity?

Jonathan Batac - 2D

Rydberg's equation can only be used for H-atoms. Since the whole experiment with exciting an electron to a higher energy level takes into account only a single electron, that is what the equation is modeled after. There would be more complex mathematical equations to deal with multi-electron systems.

Jonathan Batac - 2D

Elements with a low ionization energy have low ionization energy because electrons on their outer shells are easily removed from the atom. For example, Na has a single electron in its outer shell, and because of electron repulsion that electron is easily removed; it does not take a lot of energy to ...

Jonathan Batac - 2D

Lavelle emphasized that c is a constant. In the equation c=wavelength.frequency, c is the constant and should always be the speed of light.

Jonathan Batac - 2D

Professor Lavelle always mentions that orbital and state are sort of interchangeable. What is the distinction between the two?

Jonathan Batac - 2D

Electron density (which is represented as psi^2) refers to the probability of finding an electron in a certain area.

Jonathan Batac - 2D

So what I'm doing is going through all my notes that I've been taking during Lavelle's lectures and modules, making sure I am highlighting the things he emphasizes. For practice problems, Sapling questions are a good way of studying the types of questions could be on the test (the hints and full sol...

Jonathan Batac - 2D

This may have been answered already, but I just wanted clarification because I am a bit uncertain (hehe :D). If a question gives you +/- (a number) m/s as delta V, do you use that exact number and plug it into the equation or do you multiply it by 2 to account for both the positive and negative valu...

Jonathan Batac - 2D

Since there are numerous d- orbitals, is there a good way to, not necessarily memorize them, but distinguish them from each other. For example, what would the difference be between d-yz and d-xz and d-xy, both conceptually and on a diagram?

Jonathan Batac - 2D

What is the significance of the Hamiltonian in Schrodinger's equation? I understand that E is the energy of the election and the psi symbol represents the wave function (or the orbital) of the electron, but how does the Hamiltonian relate to any one of these variables?

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