CHEMISTRY COMMUNITY

Selena Yu 1H

No, not all zero order reactions is dependent on a catalyst. A zero order reaction could also occur with an enzyme or a surface. It's just that most commonly you would find a catalyst with a zero order reaction.

Selena Yu 1H

For E cell, I got 2.05 V because the Ce is the cathode and Fe is the anode so it will be 1.61V - (-0.44V) = 2.05V. Since my E cell is different than yours, I also got a different delta G and K. For delta G, I got -396 kJ/mol and for K I got 2.6 x 10^69

Selena Yu 1H

You would use ICE to solve this problem and use 0.22 bar for HCl as the initial partial pressure. The initial partial pressure for H2 and Cl2 would be 0. Then for equilibrium you would use -2x for HCl and x for H2 and Cl2. Then you would set it equal to K and solve for the equilibrium partial pressu...

Selena Yu 1H

Yes, the rate constant can change. It can change due to temperature. The rate constant is related to temperature through the Arrhenius equation.

Selena Yu 1H

Yes, a dead battery means that the reaction is at equilibrium so E potential is 0 and so is delta G.

Selena Yu 1H

How can determine which step is a slow step or fast step? What does fast step of a reaction mean?

Selena Yu 1H

The A stands for the frequency of collisions that occurs with the correct orientation or is the pre-exponential factor which is a constant for the reaction

Selena Yu 1H

One way to determine the order of the reaction is to look at the differential rate law. The general form for the differential rate law is k[R]^n and n is the order of the reactant or how many reactants are needed to form a product. So, if n = 1 then it is a first order reaction and if n = 2 then it ...

Selena Yu 1H

The K' for multi step reactions would be the reverse rate of the overall K that we get at the end. For instance, in class the K overall we got was [D] /[A][B]. Then at equilibrium, it would be k[A][B] = k'[D] and then you could solve for k'.

Selena Yu 1H

The slope of a zero order reaction is always negative because the equation we derived in class is equal to -k and since k must be positive all the time the slope of a zero order reaction is always negative since a zero order reaction doesn't depend on reactant concentration there's nothing to change...

Selena Yu 1H

First you would add H2O to balance your oxygens. Then you would add H+ to balance your H and then you would add OH- to both sides because of alkaline or basic solution

Selena Yu 1H

No because the charge of Mn in MnO4- is +7 and so Mn is going from a +7 charge to a +2 charge which means that it is gaining electrons for the charge to be less positive. So Mn is being reduced. You have to look at the charges individually if it is a compound and not the overall charge of the compou...

Selena Yu 1H

You add H2O to balance the amount of oxygens and you do this step first. Then you add H+ to balance the amount of hydrogens.

Selena Yu 1H

It's going to cover the second page of thermodynamics and electrochemistry!

Selena Yu 1H

So if we start off with an equation: 2KMnO4 + 8FeCl2 --> 2KCl + 2MnCl2 + 8FeO + 5Cl2. Through this equation you would see that your potassium value doesn't change, its charge is still +1. You also notice that the charge of Cl doesn't change and that it is still -1. That means MnO4 and Fe are your ca...

Selena Yu 1H

Cl2 would have a charge of -2 because one Cl would have the charge of -1. So therefore one Hg would have the charge of +1 and Hg2 would have the charge +2 because overall the compound is neutral

Selena Yu 1H

So the order of a cell diagram would be solid|gas|aqueous || aqueous|gas|solid. The two lines in the middle represent the salt bridge and the left side represents the anode and the right side represents the cathode. A cell bridge is just another way to represent the transfer of electrons from an an...

Selena Yu 1H

Since the standard reduction potential is an intensive property, does that mean after we complete the reaction it stays constant and never changes again? If it does change again, what causes that change?

Selena Yu 1H

The half reactions would be O2 + 2H2O + 4e- --> 4OH- and O2 + 4H+ 4e- --> 2H2O. You would just ignore the Pt because we add the Pt in the cell diagram because we needed a solid.

Selena Yu 1H

Yes, because the units for Gibbs free energy is J/mol or kJ/mol and you cancel out the K with temperature.

Selena Yu 1H

So the order of a cell diagram would be solid|gas|aqueous || aqueous|gas|solid. The two lines in the middle represent the salt bridge and the left side represents the anode and the right side represents the cathode. A cell bridge is just another way to represent the transfer of electrons from an ano...

Selena Yu 1H

I'm pretty sure the answer key is wrong because I also got -2.7 kJ/mol and the other people I asked also got -2.7 kJ/mol. Also, in my answer key, someone added a decimal point.

Selena Yu 1H

For 5G.15, for the standard GFE I got -12.35 kJ and for my final answer, I actually got -2.7 kJ/mol instead of -27 kJ/mol How did you get -12.35 kJ? I used the one for NH3 in the back of the book that was -32.9 kJ/mol since the standard GFE for the reactants are zero. For this question, you also us...

Selena Yu 1H

For 5G.15, for the standard GFE I got -12.35 kJ and for my final answer, I actually got -2.7 kJ/mol instead of -27 kJ/mol I also got -2.7 kJ/mol, did you happen to figure out what went wrong? Thank you!! I'm not sure I think the book just made an error but I checked with other people and they also ...

Selena Yu 1H

For G, I got -19.124 kJ instead of 19.33 kJ. You would use the equation G = -RTlnK to find what G is. So, you use G=-RTlnK to find the standard GFE and not the ones in the back of the book? Yup! You would use the ones in the back of the book if they didn't give you equilibrium and values to find Q.

Selena Yu 1H

For the Van't Hoff Equation, if we assume the change in standard entropy and standard enthalpy to be constant, then is the change in standard Gibbs free energy also constant because deltaG = deltaH + TdeltaS?

Selena Yu 1H

You could also think of it this way, where 1 mL = 1 cm^3 so therefore 1 L = 1000 cm^3 and 1L = 0.001 m^3

Selena Yu 1H

Yes as long as the two pressures given are the same units then it doesn't matter because when we did chemical equilibrium we also used bars for pressure. So it will continue to be the same here. Hope this helps!

Selena Yu 1H

For 5G.15, for the standard GFE I got -12.35 kJ and for my final answer, I actually got -2.7 kJ/mol instead of -27 kJ/mol

Selena Yu 1H

For G, I got -19.124 kJ instead of 19.33 kJ. You would use the equation G = -RTlnK to find what G is.

Selena Yu 1H

What is the 3rd Law of Thermodynamics and why is it important? How does it relate to entropy or enthalpy?

Selena Yu 1H

The molar heat capacity is given as a specific value for a compound when it is not an ideal gas. When the compound is an ideal gas, depending on whether or not it is mono, linear, and non-linear and whether or it is constant volume or constant pressure there would be different ratios.

Selena Yu 1H

Since entropy is a state function, it doesn't matter if the reaction is reversible or irreversible. We would just do everything separately.

Selena Yu 1H

Heat energy is still being transferred into or out of the system if work is being done on or by the system because in order for deltaU to be equal to zero then there must be heat energy to balance out the amount of work done for the deltaU = 0 because deltaU = heat energy + work. However, if no work...

Selena Yu 1H

You use the ideal gas constant for monoatomic ideal gases when you have constant pressure or constant volume. Some examples of monoatomic ideal gases include all the noble gases on the periodic table, like Xenon, Neon, etc.

Selena Yu 1H

When you have a constant volume or pressure, it means that the volume and pressure is fixed and won't change during the reaction.

Selena Yu 1H

Yes it is because a change in temperature is the same no matter the units and so a change in temperature of 7.32 C is the same as a change in temperature of 7.32 K

Selena Yu 1H

You would use the equations qp = nCpΔT and qv = nCvΔT to find the final temperature. Make sure to know that Cp = 5/2R and Cv = 3/2R

Selena Yu 1H

The first work equation is the one with the integral and you would use that if pressure isn't constant. However, if pressure is constant then you would use w = -P ΔV.

Selena Yu 1H

Extensive property is something that depends on the amount of material. For instance, since heat required depends on the amount of substance there is, heat capacity is an extensive property. Other examples of extensive property include volume, mass, weight, and etc.

Selena Yu 1H

You use Hess's Law when you are giving the enthalpy change of the total reaction. You use bond enthalpies when they give you the enthalpy change based on bonds, for example C-H 413KJ/mol. And you use standard enthalpies of formation when they give you the enthalpy of a compound. Hess's Law is for th...

Selena Yu 1H

Are there any phase changes from vapor --> liquid, liquid --> solid, or vapor --> solid? Are these changes just the exothermic process of the ones we talked about in class?

Selena Yu 1H

KNO2 is the salt in the reaction, and as a salt it dissolves into K+ and NO2-. That's why 0.15M KNO2 is assigned to NO2- because KNO2 dissolves into NO2-.

Selena Yu 1H

A reversible reaction means that it could occur both ways. Either a forward reaction (reactants --> products) could occur or a reverse reaction (products --> reactants) could occur.

Selena Yu 1H

Yes, Ka and Kb are only assigned to weak acids and bases because Ka and Kb are the equilibrium constants for the dissociation of acid or base in the water and if you have a value for Ka and Kb that means that the acid or base isn't fully dissociated yet and not being completely dissociated is relate...

Selena Yu 1H

Yes, it's okay to do problems from Acids and Bases for homework 3 because we just started thermochemistry

Selena Yu 1H

The lower pKa and pKb, the stronger the acid and base. Does that mean the higher the kA and kB, the stronger the acid and base? Since, they are inversely related.

Selena Yu 1H

Why is it that if X is less than 5% of initial then approximation is okay? Like why is the cut off 5%?

Selena Yu 1H

You would look at the pKb values in Tables 6C.2 to determine the strength of the base. The lower the pKb, the stronger the base.

Selena Yu 1H

The dissociation reaction is AlCl3 + H2O --> Al(OH)3 + HCl. H2O would always be added because it is a solvent and then with that you could figure out the products. The equation above is not balanced and then HCl would dissolve into H+ and Cl- and you would use that to calculate the pH.

Selena Yu 1H

It says in the problem that compound A decomposes into compounds B and C. So the chemical equation would be A (g) --> B (g) + C (g)

Selena Yu 1H

Why is the quick way to know whether or not the reaction shifts to the right or left for change in pressure not exactly correct according to Dr. Lavelle?

Selena Yu 1H

Why is K = 1 considered rare to achieve?

Selena Yu 1H

Part c is asking for the amount of each product and reactant at equilibrium. So you would use the ICE method to figure out the concentrations of the reactants and products.

Selena Yu 1H

What function you use is determined by the amount of products you have. You have to use the ICE rule to determine the equation and exponents used.

Selena Yu 1H

Yea, there can't be any reactions that only contains pure substances because two solids wouldn't mix together to create another solid as there needs to be a solvent for the reaction to occur. In most cases, the solvent would be H2O and since the concentration amount is insignificant, it is often not...

Selena Yu 1H

Yes, I'm pretty sure you can use abbreviations.

Selena Yu 1H

The most stable form of a Lewis structure is when all the formal charges on the molecules are zero.

Selena Yu 1H

No, a strong acid will have a weak conjugate base and it is the same for bases.

Selena Yu 1H

Yea, everything you said is correct and additionally all polar molecules form dipole-dipole

Selena Yu 1H

Hemoglobin is made out of 4 myoglobin-like molecules. The hemoglobin binds to the 4 O2. While myoglobin is the heme complex + protein and the heme complex is Fe bound to porphyrin ligand.

Selena Yu 1H

What are some examples of weak acids and bases?

Selena Yu 1H

No, cisplatin should be all we need to know for industrial examples of coordination compounds. But remember that we also need to know biological examples of coordination compounds.

Selena Yu 1H

You use aqua for water when the ligand has no charge and you use dihydrate when the ligand is either a cation or anion.

Selena Yu 1H

The number of bonds don't affect the hybridization because we see double and triple bonds as one region of electron density just like how we did when we determining shape using VSEPR.

Selena Yu 1H

For coordinate covalent bonds, a lone pair is donated from the atoms, while in an ionic bond, the valence electrons are donated from the atoms. That is the difference between coordinate covalent bonds and ionic bonds.

Selena Yu 1H

What is the difference between coordinate covalent bonds and covalent bonds? Or is there no difference? But if there is no difference why can't we just call them covalent bonds?

Selena Yu 1H

What is the difference between bronsted acids and Lewis acids? Why do we need to classify acids differently?

Selena Yu 1H

You should also be aware of the function of cisplatin. And other biological applications include the importance of chromium and how it assists insulin in control of blood sugar, cobalt and how it helps with vitamin B12, and how Mn, Ni, Cu, Zn are critical for enzyme function.

Selena Yu 1H

Yes, the d comes from the s and p orbital

Selena Yu 1H

A ligand that is polydentate can form many bonds

Selena Yu 1H

I'm confused about homework question 3F.3. How can you determine when dipole-dipole interactions are important? What does that even mean?

Selena Yu 1H

The formula, kq1q2/r, refer to the electric potential energy which finds the potential energy between two charges. While the formula, Dr.Lavelle talked about in class refers to the interaction potential energy which finds the potential energy between two atoms.

Selena Yu 1H

It might be mentioned during lecture tomorrow. I heard from my TA that the lecture tomorrow would still be included on the test

Selena Yu 1H

For b, a radical is a lewis structure that has an unpaired electron. So when you draw the Lewis structure and you find that you have one unpaired electron, which is usually on the central atom, then it is on a radical. Then for the increasing HCH bond angles you would have to do VSEPR theory to figu...

Selena Yu 1H

My TA said that test 2 would be everything that was not on midterm up to what we learn in class on Friday. So, things such as like dipole-dipole, intermolecular forces, and VSEPR theory.

Selena Yu 1H

First, you would try to figure out what atoms correspond to which color. So looking at the diagram, the dark grey atom would be carbon because it is the central atom. Then, the light grey atom would be hydrogen because hydrogen is smaller than chlorine. So then that leaves the green atom to be chlor...

Selena Yu 1H

Why is the interaction potential energy always negative? What makes the interaction potential energy negative?

Selena Yu 1H

Molecules are polar when electrons are not equally shared and that means that there is a big difference in electronegativity between the two molecules, making one molecule more negative and the other more positive. Below, I have attached a picture showing H2O being polar. http://upload.wikimedia.org...

Selena Yu 1H

No, we won't be tested on the shapes of pentane and dimethylpropane. We just need to know that the rod-shaped molecules are closer together and therefore they are stronger than a spherical-shaped molecule.

Selena Yu 1H

Hydrogen and covalent bonds are different things because hydrogen bonds are between molecules, while covalent bonds are between atoms. Hydrogen bonds are intermolecular forces, while covalent bonds are intramolecular forces. So we can't really compare the two for bond strength and length

Selena Yu 1H

Hydrogen Bonding explains a higher melting point because they are a very strong intermolecular force, which means that more energy is needed to break the bond leading to a higher melting point.

Selena Yu 1H

You also make the change in energy negative because we can't have a negative energy of a photon. So instead, we make the change in energy negative.

Selena Yu 1H

No, you don't always have to write out the full electron configuration because you just have to know the periodic trend for ionization energy, which is that it increases from bottom to top and left to right. As for the exceptions we need to know, they are oxygen and nitrogen, where nitrogen is great...

Selena Yu 1H

The electronegativity is the e- pulling power of an atom. So, the stronger the e- pulling power of an atom, the electronegativity, the stronger the bond strength.

Selena Yu 1H

The Schrodinger's wave function equation is to show that there are many solutions, which means that there are many different orbitals. I think that's all you need to know about it.

Selena Yu 1H

You would most likely get the formula, so you wouldn't have to just know the name. But in a situation, where you would have to know the name, you would start by looking at the periodic table for the charges or you have to remember the polyatomic ions.

Selena Yu 1H

You can identify that a bond is ionic because electrons are being transferred from metal to nonmetal atoms, while a bond is covalent because electrons are being shared instead of being transferred.

Selena Yu 1H

Is there ever an exception where you won't choose the atom with the lowest ionization energy as the central atom?

Selena Yu 1H

No, we weren't suppose to know the mass of electron. You can look it up. We would be provided this information on the test.

Selena Yu 1H

Dr. Lavelle was saying that you shouldn't put more charges on a lower electron affinity molecule because that would make the whole lewis structure less stable, which is what you don't want.

Selena Yu 1H

The bond energy is lower because it is no longer just double bonds, but rather a mixture between double bonds and single bonds, so the energy would would be lower.

Selena Yu 1H

Why is the spin magnetic quantum number only either +1/2 or -1/2? Was this found through experiments? Is it possible for it to be any other number?

Selena Yu 1H

For a, you would use the Rydberg equation to find frequency, v. The Rydberg equation would be v = R((1/(n1)^2) - (1/(n2)^2), with R = 3.29x10^15 Hz. After finding the frequency, you would use the c = λv to find wavelength. For b, you would look at the wavelength you got in part a and then look at th...

Selena Yu 1H

The arrows that he draws in class is called the spin magnetic quantum number and they are telling us which way the electrons in the orbitals are spinning, which is either up and down. As for how you would determine whether or not the arrows are spinning up or down there will always be spin up and sp...

Selena Yu 1H

No, we would be giving an equations and constants sheet. It should be the first page of the test.

Selena Yu 1H

A particle in a box has zero potential energy inside the box because it has kinetic energy. Since, the particle is inside the box it's constantly moving around because it keep hitting the walls/sides of the box giving it kinetic energy and since it has kinetic energy it would have zero potential ene...

Selena Yu 1H

I was wondering how do you know the right wavelength to have the electrons ejected. How do we figure out the right wavelength? Is there an equation for that?

Selena Yu 1H

I'm still confused on the difference between the photoelectric effect and atomic spectra. I know that for both a higher frequency is better as there is more energy to eject the electron. So, what is the difference? Is it just the way the experiments are conducted?

Selena Yu 1H

You would use the equations E=hv and c=λv to first find the energy of the photon and then you would multiply the energy of the photon by Avogadro's number.

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