CHEMISTRY COMMUNITY

Anisha Chandra 1K

It is also a different pathway because atoms in the transition state complex may have a different orientation, so the reactants take a different pathway to become the final products.

Anisha Chandra 1K

Activation energy can change for the reaction but I think free energy stays the same regardless of whether the activation energy is lower or higher.

Anisha Chandra 1K

For the first part you can just use the numbers for [A] with the above equation. For part b, you would use the fact that delta[A]/delta t = 1/2 delta[B]/delta t. using that you can find out how much [A] changes as [B] increases to 0.19M. You can then use the above equation using [A]0 and [A] when [B...

Anisha Chandra 1K

Make sure to convert from mmol to mol before getting the final answer in mmol.

Anisha Chandra 1K

Can the whole reaction have a negative overall order or only certain steps?

Anisha Chandra 1K

k doesn't have to have units M/s, but the overall rate does.

Anisha Chandra 1K

I think the book said something like this:
- if the slow step is the second step, the rate law for that step determines the rate law for the reaction
- if the slow step is the first step, the rate law for that step must match the rate law for the reaction

Anisha Chandra 1K

Yes, I think the negative is just because we flipped the final and initial. Also, remember that it's ln[final/initial] and not ln[final]/ln[initial].

Anisha Chandra 1K

A higher concentration of initial reactant usually indicates higher k as well.

Anisha Chandra 1K

I think O2 is an intermediate that we see cancels out of the final chemical equation.

Anisha Chandra 1K

The problem: When a pH meter was calibrated with a boric acid-borate buffer with a pH of 9.40, the cell potential was +0.060V. When the buffer was replaced with a solution of unknown hydronium ion concentration, the cell potential was +0.22V. What is the pH of the solution? My question: When using t...

Anisha Chandra 1K

For the reaction AgBr (s) <-- --> Ag+ (aq) + Br- (aq), why do you separate Ag(s) and AgBr(s) by a line in the cell diagram if they're both solids?

Anisha Chandra 1K

Yeah I was a bit confused about how the oxidation numbers don't change, but it can be broken down to reduction and oxidation half reactions:

reduction: 4e- + O2 + 2H2O --> 4OH-
oxidation: 2H2O --> 4H+ + O2 + 2e-

Anisha Chandra 1K

What are some common solutions that are used to form salt bridges?

Anisha Chandra 1K

What was Dr. Lavelle saying in lecture about showing an exponential relationship vs. a linear relationship using the Nernst equation? I think it was right after he talked about log/ln.

Anisha Chandra 1K

An example of some half reactions would be:

Zn(s) --> Zn2+(aq)
Cu2+(aq) --> Cu (s)

Anisha Chandra 1K

If you keep each half-reaction as it is and just flip the cell diagram, then you know:
- if the right-hand electrode in the cell diagram is the cathode, you have a positive cell potential
- if the right-hand electrode in the cell diagram is the anode, you have a negative cell potential

Anisha Chandra 1K

The element/compounds are expected to be written in a state that is in accordance with how it exists in nature. For instance, if you need to write H2, you know it will be a gas.

Anisha Chandra 1K

A positive voltage is associated with a positive Ecell, which means that a reaction has more pushing and pulling power to generate a high potential difference.

Anisha Chandra 1K

I think it means to reduce H+ to H2 gas.

Anisha Chandra 1K

Is the delta U of an isothermal irreversible reaction also equal to 0, like it is for an isothermal reversible reaction? If it's not equal to 0, why is that?

Anisha Chandra 1K

You can then calculate the delta H of this reaction using enthalpy of formations and the fact that zinc is the limiting reactant. This delta H will be equal to the heat gained/lost from the HCl solution, and from there, the only variable you are missing is the final temperature, so you can directly ...

Anisha Chandra 1K

Usually it should be given, but if it's an ideal gas, Cv = (3/2)R and Cp = (5/2)R

Anisha Chandra 1K

If the problem only gives temperatures and doesn't specify anything about constant volume or pressure, how do you know whether you should use Cp or Cv?

Anisha Chandra 1K

For the reaction 2SO2(g) + O2(g) --> 2SO3 (g), part c says to assume that temperature of the reaction remains constant. Part D asks to calculate work and Part E asks for enthalpy. Since temperature is constant, wouldn't the change in internal energy be zero? That's what I thought but the solutions m...

Anisha Chandra 1K

I think delta(entropy of system) tells us about the spontaneity. If the entropy change is positive, it's spontaneous, but if the entropy change is negative, it isn't spontaneous. delta(entropy total) doesn't tell us about spontaneity because the total entropy should usually be positive since the ent...

Anisha Chandra 1K

You can use the pressures to determine the ratio of V2/V1, which is all you need to plug in to the equation.

Anisha Chandra 1K

The first equation is for a process where temperature changes and for the second equation, I think you mean volume instead of temperature, so that would be for an isothermal process.

Anisha Chandra 1K

Entropy doesn't decrease with temperature, but the entropy change decreases with higher temperature. This is because a change to a lower temperature system will affect it more drastically than it would affect the higher temperature system, since it already has a higher entropy.

Anisha Chandra 1K

For an ideal gas, Cv = (3/2)R and Cp = (5/2)R.

Anisha Chandra 1K

During a reversible reaction, a small infinitesimal change can immediately affect the movement of the piston and reversing that small change would also reverse the movement of the piston.

Anisha Chandra 1K

Why do reversible processes do the greatest amount of work?

Anisha Chandra 1K

I think you should just know that an integral is used to sum a series of steps, and in this case infinitesimal changes. It's basically the area under a curve, so the reason we use it to sum up infinitesimal changes is so we can sum the change in a pressure/volume curve.

Anisha Chandra 1K

In what cases would we have thermal equilibrium, where temperatures of system and surroundings are the same and energy flows as heat in both directions at the same rate?

Anisha Chandra 1K

Yeah, you can do (Tfinal - 100) and then add a negative sign to the other side with water to show that the heat lost by copper is that gained by water.

Anisha Chandra 1K

Not sure what context you're referring to, but maybe orderly vs. disorderly is just a way to assess the phase the molecules are in. So a solid would have more orderly motion of atoms, while a gas would have more disorderly motion of atoms.

Anisha Chandra 1K

Based on the outlines, in thermochemistry it seems like we'll mostly be discussing enthalpy, heat, and work in reactions, while in thermodynamics we'll also start learning about entropy and free energy.

Anisha Chandra 1K

Technically, yes. Use whichever is most convenient considering the units you have in the rest of your equation.

Anisha Chandra 1K

A good way to think about it is with the mountain example Dr. Lavelle presented in class: - altitude is a state function, as the height of an object does not depend on the path taken to get there - work is not a state function, as it depends on the energy taken to get there, so someone who took a lo...

Anisha Chandra 1K

Closed systems cannot exchange matter, but can exchange energy with their surroundings. Isolated systems are completely isolated and both matter and energy are constant.

Anisha Chandra 1K

Since N2 is more stable, it's triple bond is pretty strong. Breaking that bond requires the addition of heat, while forming bonds releases heat. In this example, the product has a higher enthalpy (or energy) so the enthalpy change is positive, and thus, the reaction is exothermic.

Anisha Chandra 1K

Yes, remember that when we were learning about Kc and Kp, when we were asked to find just K in general we could use concentration or pressure depending on what was given. The same goes here.

Anisha Chandra 1K

We add the two expressions together so that we are left with the equation for the autoprotolysis of water. Prof. Lavelle used NH3 and NH4+ to demonstrate the relationship between Ka and Kb for a base and its conjugate acid, and ultimately he derived the equation that relates Ka, Kb, and Kw. This is ...

Anisha Chandra 1K

Yes, because as we see in Kc vs. Kp, concentration and pressure work about the same way. Just like how moles make up a certain fraction of total moles, partial pressure make up a certain fraction of total pressure.

Anisha Chandra 1K

Use it any time you think you need to obtain anything included in the equation (pressure, volume, moles, temperature), but aren't given values for one or more of the components of the equation.

Anisha Chandra 1K

Hg is in pure liquid form and we've been told to only use what is aqueous or gaseous for Kc and Kp, as changes in amount of liquid are usually not quantitatively significant.

Anisha Chandra 1K

I'm not completely sure about my reasoning for this, but the balanced equation might be 2A <-- --> B + 2C. A and C decrease and increase respectively at the same rate, and C increases twice as fast as B. Then you would just use the pressure where they each end on the graph and insert that into the K...

Anisha Chandra 1K

I believe it still would because multiplying a chemical equation by any factor should raise K to that power.

Anisha Chandra 1K

If you manipulate the equation to solve for P or concentration, then you can use the resulting pressure or concentration in when calculating Kc (concentration) or Kp (pressure).

Anisha Chandra 1K

I think it does mean that the concentration of products is increased at equilibrium, so yes the reaction would shift to the left to reach equilibrium.

Anisha Chandra 1K

How do you decide if a coordination compound is tetrahedral, octahedral, square planar, etc. when you have a compound that is the result of a transition metal reacting with water? For example, in 6D.11, Al3+ and Cu2+ form octahedral coordination compounds, but how do we determine this?

Anisha Chandra 1K

In the solutions manual, why is SO3 drawn as having 1 double bond and 2 single bonds instead of 3 double bonds?

Anisha Chandra 1K

005162520 wrote:How does EDTA remove deadly metals from the bloodstream?

EDTA is a hexadentate ligand that can bind to metals, so by binding to metals, the metal cations are no longer floating freely in the bloodstream.

Anisha Chandra 1K

How does the lone pair of the guanine bind to cisplatin? Does it bind to the chlorines of cisplatin? Or is the chlorine displaced by nitrogen or water?

Anisha Chandra 1K

The coordination number is just the number of bonds formed. So for A, the answer would be 4 bonds because 4 chlorines are bonded to one nickel atom.

Anisha Chandra 1K

Monodentate means a ligand can bind at one site and donate one electron pair. In the structure of water, both electron pairs are on a single central oxygen atom. That same oxygen atom cannot simultaneously bind to two sites, so water must be monodentate.

Anisha Chandra 1K

brennayoung wrote:Does anyone know if this will be on the final?

I don't think we discussed it in class, so I don't think so.

Anisha Chandra 1K

In addition to what's on the outlines, also the examples he introduced in lecture. Like cisplatin, hemoglobin, myoglobin, etc.

Anisha Chandra 1K

How should we take molecular shape into account when deciding how many binding sites a polydentate ion has?

Anisha Chandra 1K

If we do use the -ate, would be cobate or cobaltate?

Anisha Chandra 1K

K4 [Ni(N)4] The potassium is outside the brackets, so the name will start with potassium. The transition metal name goes at the end. Did you intend for the ligand to be CN or is it just N? Not sure how to do it with N, but for CN, you would do potassium tetracyanidonickelate(IV). Try going about the...

Anisha Chandra 1K

I'm not completely sure about this, but won't s orbitals never be unhybridized? S orbitals seem to always be involved in hybridization - sp, sp2, sp3, sp3d, etc. so extra electrons will go in unhybridized p orbitals.

Anisha Chandra 1K

How does hybridization work for elements where some or all of the valence electrons are paired? Do the paired electrons get promoted to d orbitals?

Anisha Chandra 1K

I think you should also know what types of orbitals form each. For example, in ethene (C2H4), there are 4 sigma bonds between 1s and 2sp2, 1 sigma bond between 2sp2 and 2sp2, and 1 pi bond between the unhybridized p orbitals.

Anisha Chandra 1K

A pi bond is formed when two p-orbitals overlap side to side. When C double bonds with C as in ethylene, the C atom has sp2 hybridization, leaving one unhybridized p-orbital with 3 hybridized sp orbitals. These sp orbitals form sigma bonds with other atoms while the unhybridized p-orbital of one C ...

Anisha Chandra 1K

How come when you have a double or triple bond, there is only one sigma bond and the rest are pi bonds?

Anisha Chandra 1K

Why are induced-dipole-induced-dipole forces just as strong as dipole-dipole forces in a gas?

Anisha Chandra 1K

For 26b, how does size of the atoms impact bond angles?

Anisha Chandra 1K

If you have 2 molecules with hydrogen bonding, how can you tell which one is stronger?

Anisha Chandra 1K

To expand upon @Brittney Hun 1K and clarify a couple of things, both CHF 3 and CHI 3 exhibit dipole-dipole forces, so this doesn't matter in determining the melting/boiling points. What matters, therefore, is the LDFs of each molecule. CHI 3 is a larger molecule/has a higher molar mass, and this co...

Anisha Chandra 1K

I was also confused about this. On the test, should we be drawing all resonance structures or just the most stable structure?

Anisha Chandra 1K

The boiling point of pentane - CH3(CH2)3 CH3 is 36.1 C, whereas that of C(CH3)4 is 9.5C. The solutions say that pentane has a higher surface area and thus stronger London forces than C(CH3)4 because C(CH3)4 is spherical and more compact, but how do you draw the lewis structure of C(CH3)4 to determin...

Anisha Chandra 1K

Also the interactions between the atoms in the molecule. Pay attention to electronegativity to determine strength of dipole-dipole forces and whether hydrogen is in the molecule to determine if there are hydrogen bonds.

Anisha Chandra 1K

Just to clarify, does high vapor pressure indicate higher boiling point?

Anisha Chandra 1K

Make sure you aren't looking at each option as different angles of one molecule - that's why I was confused at first until I realized I needed to pay attention to intermolecular attractions and not intramolecular attractions!

Anisha Chandra 1K

How do you determine which forces to prioritize when dealing with a molecule that has a halogen? For example, for 3F.5 part c, it says CHI3 has a higher melting/boiling point than CHF3 because of London forces. However, doesn't CHF3 have stronger dipole-dipole forces and aren't dipole-dipole forces ...

Anisha Chandra 1K

Hydrogen bonding is the dominant intermolecular force whenever N, O, or F is bonded to a hydrogen atom.

Anisha Chandra 1K

Yes, the 4s orbital is lower energy than 3d, but once 4s is filled, it becomes higher energy than 3d, which is why electrons will be removed from 4s before 3d during ionization. So to clarify, if we need to remove electrons we would go to 4s before 3d, because this confused me. Yes, that is correct.

Anisha Chandra 1K

How would you draw dipole moment arrows for H2SeO4? Is this molecular polar and does the presence of the two hydrogen atoms affect its polarity?

Anisha Chandra 1K

Why can't a central atom have more than 6 bonds/lone pairs? This allows for 12 electrons which is already an expanded octet, but why can't it expand more if the d subshell has 10 electrons and s, p, and d together have 18 electrons?

Anisha Chandra 1K

You could try different orders of the atoms in the molecule and see which structure has the most favorable formal charges. For particularly long molecules, sometimes they group atoms attached to one another together. For example if you see CH3 or NH3 in a long molecular formula, you can likely assum...

Anisha Chandra 1K

Chemical bonds store potential energy, so the higher the potential energy of a chemical bond (determined by the stability of the molecule --> lower potential energy = more stable molecule), the greater the dissociation energy because it will take more energy to break a higher energy chemical bond.

Anisha Chandra 1K

The reason polar bonds are stronger is because the more electronegative atom attracts electrons of the other atom, shortening and strengthening the bond. As for coordinate covalent bonds, I think they are just as strong as any other covalent bond, but if someone else could confirm this that would be...

Anisha Chandra 1K

It's important to note that the atoms in a molecule may have large differences in electronegativity, but the molecule itself still isn't polar because the dipole moments cancel. An example of this would be CCl4.

Anisha Chandra 1K

Yeah, I have the same question because I would think you'd multiply by 2 but I saw in one of the textbook question answers that they didn't...

Anisha Chandra 1K

No, because if we know the mass of the object the uncertainty in velocity will be VERY miniscule.

Anisha Chandra 1K

For anyone confused about how the negative sign comes into play, you basically use the Rydberg equation to do Efinal - Einitial. So if an electron was going from n=1 to n=3, you'd do: -hR/9 - -hR/1
This would become positive, which makes sense because the electron is gaining energy.

Anisha Chandra 1K

It is not a constant value and may come with units like kJ/mol, so you can change it's value by changing the units.

Anisha Chandra 1K

Sometimes the work function is given with units kJ/mol so you know to convert to J/atom, but what if no units are given? Should you assume you're given the energy to eject a mol or one electron?

Anisha Chandra 1K

Yes, the 4s orbital is lower energy than 3d, but once 4s is filled, it becomes higher energy than 3d, which is why electrons will be removed from 4s before 3d during ionization.

Anisha Chandra 1K

What if the central atom is the most electronegative atom? (Ex. chlorine in the center in ClO4-) Would you want chlorine to be 0 or more negative than the oxygens since chlorine is more electronegative? What would the correct structure be for Cl04-? I've seen two different answers - one with 3 doubl...

Anisha Chandra 1K

How come d electrons usually aren't considered part of the valence shell? How come we usually just regard s2p6 as the valence electrons?

Anisha Chandra 1K

So we discussed that chromium and copper have exceptions in that they become 3d54s1 and 3d104s1. Does this also happen to elements in the same group as these two, like in 4d, 5d, etc?

Anisha Chandra 1K

Since neutrons also show diffraction patterns after passing through a crystal, do they also have dual wave-particle properties? What about protons? How come their wave-particle duality isn't emphasized and we always focus on electrons?

Anisha Chandra 1K

How do you determine if an object has wave-like properties based on its mass and velocity? I know objects of high mass don't have significant wave-like properties, but for questions where you're asked to justify if a particular subatomic particle has wave-like properties, how would you justify it?

Anisha Chandra 1K

Yes, the formal charges on each atom adds up to the charge of the compound. I think it's a good way to check that your Lewis structure is correct. For example, if you have a chlorine in the center with a formal charge of +3, that is very unstable - especially since chlorine's usual anion has a -1 ch...

Anisha Chandra 1K

What are the similarities and differences between electron affinity and electronegativity?

Anisha Chandra 1K

so s electrons are found close to the nucleus and are therefore more tightly bound to the nucleus but p electrons (assume same principal energy level) have higher effective nuclear charge than s electrons because they have more protons and electrons Both of those statements seem contradictory, so co...

Anisha Chandra 1K

Yeah, I saw that in the textbook too but he never mentioned it in class so I doubt it.

Anisha Chandra 1K

For b, why are s electrons better at shielding than p electrons?

For d, how come effective nuclear charge is lower for p electrons than s electrons in the same shell? Doesn't higher effective nuclear charge = more protons, and p-orbital elements have higher atomic numbers?

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