CHEMISTRY COMMUNITY

Lorena Zhang 4E

Basically, you will use the equation to solve for the rate, temperature, or activation energy. Also, you may use the equation to compare the reaction under different temperature. When using Arrhenius equation, typically all but one conditions would be given.

Lorena Zhang 4E

Intermediates exists to show the reaction mechanism and it cancels out if you combine the separate steps together. However, catalyst is consumed and will be regenerated in the next step, and it functions to lower the activation energy.

Lorena Zhang 4E

Usually, we use a pre equilibrium approach when the reaction is separated into a few steps in which the a fast step is followed by a slow step. In this case, we can assume that the faster step reaches equilibrium.

Lorena Zhang 4E

Depending on what reaction's happening, the change of temperature would affect the rate of reaction. Therefore, we can conclude that since the concentration stays the same, k has to change.

Lorena Zhang 4E

Essentially, the final unit for all reaction is M/s or mol/(L*s). Therefore, you can start from the end and make it back to the unit of k based on the orders.

Lorena Zhang 4E

The final rate would always be M/s or mol/(L*s). Therefore, if the order of the reaction changes, in order to reach the final unit of M/s, the unit of k will have to change.

Lorena Zhang 4E

Yes. To add on that, when adding catalyst, you increase the rate of reaction because the activation energy barrier is lowered so that the reaction can proceed faster.

Lorena Zhang 4E

Kinetic control means that even the reaction is favorable in terms of thermodynamics(gibbs free energy is zero), but kinetics trumps that because there is a huge activation energy barrier between the reactant and product.

Lorena Zhang 4E

Kinetically stable means that the reactants need a lot of activation energy to turn into products. Thermodynamically stable means the reaction is favorable(gibbs free energy would be negative).

Lorena Zhang 4E

Technically, if the galvanic cell is running properly and measured correctly, the cell potential should always be positive. This also means that the reaction would be spontaneous according to the equation since delta G would be negative.

Lorena Zhang 4E

Anode is oxidation while cathode is reduction. When trying to identify them in the galvanic cell, preferably, you would write down the half reactions and identify the transfer of e-.

Lorena Zhang 4E

e- transfer from one "reaction beaker" to another will stop due to charge buildup. Therefore, a salt bridge is necessary to allow ion transfer so that the two solutions would stay neutral.

Lorena Zhang 4E

When the gibbs free energy is zero, the reaction is at equilibrium because neither the forward nor the reverse reaction is favored.

Lorena Zhang 4E

For a specific compound, if it's gibbs free energy of formation is negative, then it's relatively stable.

Lorena Zhang 4E

This is the gibbs free energy equation: deltaG = deltaH - TdeltaS
when deltaG is negative, the reaction is spontaneous; when it's positive, the reaction is non spontaneous.

Lorena Zhang 4E

Without performing any calculations, predict whether there is an increase or a decrease in entropy for each of the following processes: (a) Cl2 (g) + H2O (l) --> HCl (aq) + HClO (aq) The answer says that entropy decreases because there's not as many moles of gas on the right side of the equation. Do...

Lorena Zhang 4E

The mass is definitely a determining factor. However, we usually consider degeneracy first then the mass of the molecule.

Lorena Zhang 4E

Which would you expect to have a higher molar entropy at T=0, single crystals of BF3 or of COF2? Why?

Lorena Zhang 4E

During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5 degrees Celsius was compressed suddenly and irreversibly to 0.500 L by driving in a piston. In the process, the temperature of the gas increased to 28.1 degrees Celsius. Assume ideal behavior. What is the change in entr...

Lorena Zhang 4E

For example, the volume of the gas inside the container would not be fixed. It would increase/decrease depending on the pressure. We calculate the work of reversible expansion by using integral since the pressure keeps changing. The final equation would be w=-nRTln(V2/V1).

Lorena Zhang 4E

In order to calculate work, do we use internal or external pressure? For example, in the case of irreversible expansion, when the external pressure is smaller than the internal one, do we use the external or the internal? Do we always use the external/internal pressure when calculating the work?

Lorena Zhang 4E

Why that the maximum work is done by the reversible expansion?

Lorena Zhang 4E

The heat is used in breaking the bonds. In order to break the bond, a lot of energy would be required. Therefore, the temperature will not increase since all the heat is used up.

Lorena Zhang 4E

The change in enthalpy would be positive in this case because in order to have the liquid water change phase into vapor, the process requires heat. The final enthalpy minus initial would generate a positive change of enthalpy.

Lorena Zhang 4E

Because the steam undergoes condensation, a phase change, in which it releases a lot of energy. This energy would burn a lot more than just, for example, boiling water dropped on the skin because boiling water would only under go temperature change.

Lorena Zhang 4E

The conjugate parts are usually the products. In order to identify the conjugates in the products, you need to know if the reactants are acids or base. In terms of that, you should see whether the reactants accept or donate protons. Acids generally lose protons, therefore, having conjugate base in t...

Lorena Zhang 4E

First of all, you should turn all the mass into concentration. Then you should set up an ICE table. The initial concentration of ammonium carbamate can be calculated, and we know at initial point, there's only ammonium carbamate in the flask. For the change of concentration, it should be -x, +2x, +x...

Lorena Zhang 4E

We'll have to use the quadratic formula to calculate the exact value of x.

Lorena Zhang 4E

You need to write out the balanced equation. Then you can calculate Kc out of it. After, you set up an ICE table in which the initial for PN2, PH2, and PNH3 should be 3.11+1.57=4.68 bar, 1.64 bar, and 23.72 bar respectively. I 4.68 1.64 23.72 C -x -3x +2x E 4.68-x 1.64-3x 23.72+2x You will be able t...

Lorena Zhang 4E

If you are calculating Kp, then you need to write P subscript to indicate you are using the partial pressure. However, when you are calculating Kc, you can simply use the bracket to show the concentration.

Lorena Zhang 4E

When calculating Kp, do we have to change the unit of pressure into a standard one (bars or atm) or just use the unit that the question gives?

Lorena Zhang 4E

So I know that salts that contain conjugate acids of weak bases produce acidic solution, and salts that contain conjugate bases of weak acids produce basic solution. But how do you know when the salt is neutral? For example, KBr is a neutral salt. Is it that if it doesn't fit into any of the categor...

Lorena Zhang 4E

When writing the complete ionic equation for a salt produced from the acid-base neutralization reaction, do we write all acids/bases in dissociated form(ions) or just the strong acids/bases? For example, homework J9 in 7th edition, I believe phosphoric acid, bromous acid, and hydrosulfuric acid are ...

Lorena Zhang 4E

Why that CO3 2- can be either mono or bidentate ligands? Why that it can't be tridentate with the third oxygen atom?

Lorena Zhang 4E

A single electron will affect the shape. However, because there's only one electron, the lone electron repulsion generated would be much smaller than the lone pair(two electrons). Therefore, the degree of angle distortion would be less significant.

Lorena Zhang 4E

Angular shape is the same as bent shape. So it would be slightly less than 120 degrees.

Lorena Zhang 4E

For the molecules that have resonance structures, for example SO3 2-, how many sigma and pi bonds does it have?

Lorena Zhang 4E

For assigned problem 3F.9, it asks us to place ion-dipole, dipole-induced dipole, dipole dipole in the gas phase, ion-ion, dipole-dipole in the solid phase in order of increasing strength. The answer shows that dipole induced dipole is similar to dipole dipole. I don’t quite understand why.

Lorena Zhang 4E

When we are talking about ionic or covalent compounds/bonds, is it that we are saying the compound/bond has more ionic/covalent characters? Is it that essentially, there’s no clear cut between ionic/covalent?

Lorena Zhang 4E

I believe we need to predict the bond angle based on the lewis structure as well as hybridization.

Lorena Zhang 4E

There is no formula for determining bond angle. A lot of the times we can only know the approximate bond angles because it differ based on the electron pair repulsion.

Lorena Zhang 4E

If the lewis structure of a molecule, for example ClO2+, has a lone pair, does it make the shape a trigonal planar or bent? I thought it would be bent, since the lone pair repulsion would make the bond angle slightly less than 120 degrees, but the answer says it should be trigonal planar.

Lorena Zhang 4E

How to distinguish between dipole dipole and london forces?

Lorena Zhang 4E

I don't think we need to memorize any bond length. However, we do need to understand how to calculate the average bond length based on the lewis structure(such as resonance structures) and the value of bond length given.

Lorena Zhang 4E

Polarizability gets higher as the number of electrons increases. This is because the nuclear charge has less control over the electrons due to the shielding effect. Therefore, the outer electrons are more easily distorted.

Lorena Zhang 4E

When the molecule has resonance structures, you need to find the average bond length. For example, if the molecule has a single bond in one form of resonance and a double bond in the other, you need to calculate the average of the two.

Lorena Zhang 4E

I have the same question too. I think one possible reason would be that oxygen has a higher electronegativity, therefore pulling the electron to it. But I'm not sure if this explanation is right. I went to a chemistry drop in session today and the tutor there wasn't sure either.

Lorena Zhang 4E

In order to know the most stable lewis structure, you should calculate the formal charge. The most stable lewis structure has the least formal charge on each atom.

Lorena Zhang 4E

The problem asks what element of each of the following pairs has the higher electron affinity: gallium or indium; beryllium or magnesium. The answer for both is equal. I don't quite understand how that works.

Lorena Zhang 4E

For multi-electron, orbitals with same l but different ml are said to be degenerate. For hydrogen, orbitals with different n are degenerate because it only has one electron. This rule would not apply to multi-electron model because multi-electron model is more complicated and need to take the electr...

Lorena Zhang 4E

The shape of s orbital is spherically symmetrical and there is no point of region where you can find that the electron probability density is zero.

Lorena Zhang 4E

It is just to show the orbital orientations. X, Y, Z can be used to show different planes.

Lorena Zhang 4E

Does this rule also apply to the uncertainty in position? For example, when it's +-5m, is it that we should use 10m in the equation for uncertainty in position?

Lorena Zhang 4E

These are from homework 2C 5. The solution manual shows that for ClO, the lewis structure would be a single bond between Cl and O, however, leaving five valence electrons on Cl. I don't understand why there are only five valence electrons left in this lewis structure for Cl since Cl has seven valenc...

Lorena Zhang 4E

So according to the definition, the radicals have unpaired electrons. When it comes to odd number of electrons, the molecules would be seen as a radical while those have even number of electrons are not radicals. However, there's also the concept of paramagnetism and diamagnetism. What is the differ...

Lorena Zhang 4E

This problem is asking for the energy required to remove an electron from ONE sodium atom. The work function given is the threshold energy needed to remove the electron from one mole of sodium atom. Therefore, in order to get the energy required to remove an electron from one sodium atom, you need t...

Lorena Zhang 4E

Thank you. This helps a lot!

Lorena Zhang 4E

How does interacting waves give rise to diffraction patterns? Also, does the diffraction experiment(the slit experiment) need to be conducted under vacuum condition?

Lorena Zhang 4E

In the class, Dr. Lavelle talks about how increasing the intensity of light would increase the number of photons. I am little confused about the concept of light intensity. Is it related to the amplitude of wavelength? Does increasing/decreasing the amplitude of wavelength result to the increase/dec...

Lorena Zhang 4E

For some of the multistep problems, I got answers that are slightly off from the ones on the solution manual due to significant figures. For example, 0.001-0.002 off for a three significant figure problem. I am wondering if my answer would be acceptable. What is generally the accepted range for the ...

Lorena Zhang 4E

Some of the solutions give the answers that convert units like kg or mg into grams. Do we have to convert the units for answers in the homework/test into more frequently used units or it is fine as long as the significant figure are right?

Lorena Zhang 4E

For example, E 25 asks for the number of KNO3 formula units in 0.750 mol KNO3.

Lorena Zhang 4E

There are several practice problems that ask for the formula unit of a molecule or ion. I am not sure what that means.

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