CHEMISTRY COMMUNITY

Cecilia Lei 3K

Does all reaction follow Arrhenius behavior?

Cecilia Lei 3K

I think whenever you see reversible/isothermal/isothermal reversible, you can assume it is isothermal reversible expansion.

Cecilia Lei 3K

q should be the heat, it can be positive or negative depending on whether the reaction is endothermic or exothermic. And when it is under constant pressure, q=delta H.

Cecilia Lei 3K

Ice melting will be endothermic since the phase change from solid to liquid requires energy. And when you freeze water into ice, you get the opposite since ice is more stable than water, energy and heat have to be released, which makes it exothermic.

Cecilia Lei 3K

I think it's when you have a phase change, it will absorb more energy, and you can use the value of delta H (phase change) to obtain the answer.

Cecilia Lei 3K

Can someone help explain the difference between these two?

Cecilia Lei 3K

Are stoichiometric coefficients and reaction rate order related?

Cecilia Lei 3K

I actually remember how we talked about the order of the reaction can only be determined from the experimental data. But I saw that the reaction order of a single-step matches with the molecularity of the reaction. Can someone help explain why stoichiometric coefficient is coming into play again?

Cecilia Lei 3K

Corrosion occurs when water oxidizes a metal. If you have a metal that has a lower reduction potential, it will be oxidized since higher reduction potential will have the tendency to be reduced.

Cecilia Lei 3K

If we take a look at the equation for E cell, while E naught will equal 0, we still have the other half of the equation we have to deal with ([RT/nF]lnQ). Unless Q is equal to 1 (which in many cases, is not), you will find the E cell will, in fact, not equal to 0. Hope this helps! I understand what...

Cecilia Lei 3K

WiIl E cell be smaller than 0 for electrolytic cells?

Cecilia Lei 3K

We talked about how at equilibrium, E cell will be 0 because no work is down. Also, we said for concentration cells, the E naught will be 0. I am just wondering, for a concentration cell at equilirbrium, will both the E cell and E naught be 0?

Cecilia Lei 3K

Can someone clarify the relationship / difference between them?

Cecilia Lei 3K

Wait, I am so sorry I think I made a mistake. We said delta G=0 at equilibrium, that's true, but K doesn't necessarily have to be 1. So the question would be why delta G equals to 0 at equilirbium, but at equilibirum there's also the maximum work done. Wouldn't these two be contradictory?

Cecilia Lei 3K

The textbook talks about how work done at non expansion system means delta G=w maximum. But we learned that for a reversible process, w should be at maximum. Does that mean non expansion work include reversible process?

Cecilia Lei 3K

I understand that by this equation: delta G=-RTlnK, the system is not doing any work since delta G is 0. But we also talked about how at equilibrium, w=-nRTlnV2/V1 before. Wouldn't these two be contradictory?

Cecilia Lei 3K

Why delta S is equal to qrev/T? I think it should be that delta S=delta H/T, and under constant pressure, delta H=q, so delta S would be q/T. But under equilibrium, the pressure would not be constant, so why would delta S equals to q/T?

Cecilia Lei 3K

We discussed how at equilibrium, delta G will be equal to 0, and how the E not for concentration cell will also be 0. I am a little bit confused about these two. Since the concentration cell is 0, we get the E not equals to 0. But when we have equilibirum, wouldn't that mean E not and delta G will b...

Cecilia Lei 3K

Happy Valentine's day!

Cecilia Lei 3K

Why does wmax=delta G the maximum work done at constant P and T?

Cecilia Lei 3K

What if the Ka/Kb value is less than 10^-4 but the percentage ionization is larger then 5%? Is it still possible to use the approximation of [HA]=the concentration of the initial solution here?

Cecilia Lei 3K

I am just wondering can we generalize amphiprotic species to be amphoteric? Since species that are amphiprotic are able to accept H+ and donate H+, they can act as Bronsted base and Bronsted acid at the same time, but I am not so sure about it. Can anyone help explain this?

Cecilia Lei 3K

For a reaction that only involves solids and liquids, can we assume that the volume doesn't change; thus, delta V should be 0, and no work is done on or by the system?

Cecilia Lei 3K

When calculating the equilibrium constant for part b, I am confused why the solution manual divided the partial pressure by 100 for each term. Can someone help explain this?

Cecilia Lei 3K

All reversible reactions are isothermal, but not all isothermal reactions are reversible (there are some irreversible isothermal reactions). In isothermal reactions, all heat added to the system does work right? I think this should be the case since the internal energy change equal to 0 for isother...

Cecilia Lei 3K

When we are talking about entropy change of the surrounding, we mentioned that the equation would be -delta H/T. What does the T stands for here? Can we only use this formula when it is in isothermal reversible reaction since the T hot and T cold would be different if it is not in a reversible condi...

Cecilia Lei 3K

When having a reversible reaction, does it always mean that it will be in isothermal condition? Meaning that isothermal reversible conditions always go long with each other?

Cecilia Lei 3K

I think delta H can have units of kJ or kJ/mol based on the questions asked. So it's like the standard enthalpy of reaction have unit kJ but the enthalpy of combustion, formation will be kJ/mol since they are measuring the enthalpy of per mole of compounds or elements.

Cecilia Lei 3K

How can delta H equal to Q when they have different units? I think the unit for delta H should be J*mol^-1 whereas the unit for q should be J?

Cecilia Lei 3K

Do we need to know what is talking about in this chapter..? I think we didn't cover that in the lecture and I feel it difficult to understand.

Cecilia Lei 3K

Basically we understand that in the change of internal energy equation, ΔU = q-PΔV, that if the volume of the system is constant (or no change in the volume), then that means ΔV = 0, thus PΔV is just equal to 0. In the end, the equation we are left with is ΔU = q(v). That's the question I have here...

Cecilia Lei 3K

Can we calculate the value of Qv? In this way, how can we obtain the internal energy of a system if it's under constant volume rather than constant pressure?

Cecilia Lei 3K

Can we only calculate Qp=cmTV but not Qv? Which means it is only possible to obtain Qp rather than Qv? And relate this to internal energy, would it be impossible for us to calculate the change in internal energy of a system that is not under constant pressure since delta U is only equals to Qp+w and...

Cecilia Lei 3K

Is irreversible expansion work only happens in constant pressure? And is reversible expansion work only happen at pressure that is not constant? I think I understand what reversible and irreversible means, but not so sure about how they are related to constant and non-constant pressure.

Cecilia Lei 3K

Does Q have negative value or positive value? Or it will always be positive since Q measures the transfer of heat. However, enthalpy of reaction can be positive or negative depending on whether the reaction is endothermic or exothermic. Is that correct?

Cecilia Lei 3K

Because the energy is added to turn the phase from one to the other.

Cecilia Lei 3K

It requires more energy to change from boiled water to steam than from cold water to boiled water.

Cecilia Lei 3K

When you break the bond, there's only one type of bond to be broken, and when you measure it, it will be exactly what you are looking for as the bond enthalpy.

Cecilia Lei 3K

Are bond enthalpy measured at the gas phase?

Cecilia Lei 3K

Can someone please explain Hess Law more in detail? I think I didn't quite get that.

Cecilia Lei 3K

Can some one explain Le Chatelier's Principle again> Does it have something to do with Q and K?

Cecilia Lei 3K

-logKa=pKa

Cecilia Lei 3K

At a given temperature, there's only on K. However, Q can change base on different concentrations of the products and reactants and can be different from K.

Cecilia Lei 3K

They will be solved using the same way. They are different because Kp is used in gas, while Kc is used in solution concentration.

Cecilia Lei 3K

Do we need to memorize the ideal gas equation?

Cecilia Lei 3K

Are we still having multiple choice questions for exam this quarter?

Cecilia Lei 3K

Yes. Temperature is the only factor affecting Kc, and you should look at it with thermodynamics.

Cecilia Lei 3K

What is the units for the component in ideal gas law equation?

Cecilia Lei 3K

Is there any examples where ideal gas law can be used together with equilibrium constant Kc?

Cecilia Lei 3K

I think K doesn't have units since the units for concentration has been canceled.

Cecilia Lei 3K

What's the difference between Kp and Kc?

Cecilia Lei 3K

NO3 2- is the conjugate acid of a strong base, meaning that it won’t affect the pH of the salt solution produced. Also, Cu2+ is a highly electronegative small ion, meaning that it will increase H3O+.

Cecilia Lei 3K

The concentration of OH- times the concentration of H+ will be 10^-14, and that’s the reason why pOH+pH=14.

Cecilia Lei 3K

The conjugate base of a weak acid will affect the pH of the salt solution.

Cecilia Lei 3K

I think what we should know is only about at the equivalence/ stochiometric point, the titrant will change color.

Cecilia Lei 3K

I think they won’t affect pH because Na+ is in group now and Cl- is the conjugate base of a strong acid.

Cecilia Lei 3K

Is Mg(OH)2 a strong acid or weak base? Because in the textbook, it says that the conjugate acid does not affect pH, so it should be a strong acid. However, other websites says that it should be a weak base.

Cecilia Lei 3K

I had a serious illness last week and wasn't able to catch up with the achieve assignment for week9. Is there a way that I can make up for those points?

Cecilia Lei 3K

When Ka is larger, it means that the acidity of the solution is larger as there are more H+ present in the solution.

Cecilia Lei 3K

The pH scale should be between 0 and 14, and it is rare for a solution to have pH below zero.

Cecilia Lei 3K

I think we should understand that pH=-log[H+] and when calculating the pH of strong acids and bases, this equation can be used directly.

Cecilia Lei 3K

I think Professor Lavelle mentioned that acids are more readily lose H+ is the resulting anion is stabilized by resonance and/or electron withdrawing atoms which delocalize and stabilize the negative charge. What does that mean? Can someone give an example?

Cecilia Lei 3K

What's the difference between Ka and pKa?

Cecilia Lei 3K

How to determine pKa and acidity?

Cecilia Lei 3K

Are all polydentates chelates? Or polydentates form a rings structure called chelates?

Cecilia Lei 3K

The PDF on class website lists NAME* and NEW IUPAC CONVENTION. Which exactly shall we use in naming those coordination coumpounds?

Cecilia Lei 3K

When we are drawing lewis structures, there may be several different ways we can think of regardless of formal charge and lowest energy required. Shall we always calculate the formal charge and think of different ways to draw the molecule and pick the one with the lowest energy? If not, there might ...

Cecilia Lei 3K

Sristi Palimar 2E wrote:Bonds with electronegativity differences:
<0.4 are nonpolar covalent
between 0.4-1.8 are polar covalence
>1.8 are ionic

I think that >2.0 should be ionic? It was what Dr. Lavelle said in class.

Cecilia Lei 3K

Why can't IO3- have three double bonds to O? I think Iodine can have d-orbitals to incorporate more electrons, and the electron added should be distributed to the central atom I rather than O?

Cecilia Lei 3K

How to determine the polarity of bonds based on electronegativity? Is there a specific value of electronegativity difference in which we can separate from polar bonds and nonpolar ones?

Cecilia Lei 3K

What's the difference between molecular geometry and electron geometry? Can someone help me clarify this by using examples?

Cecilia Lei 3K

Are we given the electronegativity table while we are having the exam? If we are not given. how can we determine the ionic character and covalent character based on pure periodic table?

Cecilia Lei 3K

London dispersion forces always present since it is caused by the movement of molecules or gravitational force, and it is temporary.

Cecilia Lei 3K

Hydrogen bond can occur when a slightly positive Hydrogen interacts with another electronegative (N O F) on another molecule. And as long as the N O F has a lone pair, hydrogen bond can occur.

Cecilia Lei 3K

Ion dipole interaction happens when an ion and a polar molecule interact with each other, and dipole induced-dipole happens when a polar molecule interacts with a non-polar one, causing the electron cloud to be attracted to the more positive side of the polar molecule.

Cecilia Lei 3K

Dipole-dipole interactions only occur for polar molecules since they need a dipole to occur, which happens when atoms with different electronegativities bond with each other in a molecule.

Cecilia Lei 3K

You can determine them by looking at their column (vertically). Eg. B is in the 13 column, so it has 3 valence electrons. Note: valence shell is the shell that can lose or gain electrons for the atom.

Cecilia Lei 3K

We put the atom that has the least ionization energy in the middle, and that is, the atom with the lowest electronegativity since they tend to lose electrons.

Cecilia Lei 3K

Formal charge has the formula of FC=V-(L+(S/2)., where V stands for valence electrons of the original atom, L stands for lone pair electrons, and B stands for bonding electrons for the atom. It is slightly impossible for atom with high electronegativity to receive a positive value of formal charge s...

Cecilia Lei 3K

When do we know that a molecule includes radicals?

Cecilia Lei 3K

Does the central atom need a formal charge to be 0 when drawing lewis structures? Or is it the most stable when the central atom of the molecule has a formal cahrge of 0?

Cecilia Lei 3K

Do we need to know the coordinate covalent bond and when to include coordinate covalent bond for the second midterm?

Cecilia Lei 3K

Why expanded octet fill the d subshell rather than the s subshell first? For example, PCl5 tends to fill the 3d orbitals first than to to fill the 4s orbital.

Cecilia Lei 3K

The strongest bond should be giant covalent structure.

Cecilia Lei 3K

They can be used to predict the electron configuration of atoms and ions.

Cecilia Lei 3K

Ionic bond I stronger than the covalent bond in some circumstances. Because ionic bond is formed between the positively charged cation and negatively charged anion, they are hold closer between the two. Covalent bond are only shared electrons. But Ionic bond is not stronger than covalent bond in the...

Cecilia Lei 3K

They are exceptions to the octet rule because they have too less electrons in the outer shell, making them impossible to fulfill the 8 electrons in their outer shell. Also, they don’t have the orbitals enough to hold 8 electrons.

Cecilia Lei 3K

Because after removing the first electron, the other electrons are pulled closer to the positive nuclear charge, making them harder to remove.

Cecilia Lei 3K

You have to close CCLE before using it.

Cecilia Lei 3K

ml determines the orientation of the angular momentum, and it is dependent on l so that the label of it says ml. When the element's electron is in the d bloock, the number of l should be 2. So, ml should be -2, -1, 0, 1, 2.

Cecilia Lei 3K

The direction of spin is determined by the sign of 1/2. + means spin up and - means spin down. The reason why electrons are opposite in spin in one orbital is that electrons repel each other in one orbital. Actually, when filling orbitals in the same block, electrons tend to occupy empty orbitals fi...

Cecilia Lei 3K

To write electron configurations, I think the best way is to see whether it can be write in a simplified form or not, because it will be easier for you to construct a configuration with the help of inert gases like helium. The second step is to see where is the element locate in the periodic table a...

Cecilia Lei 3K

Lavelle mentioned that the energy of empty 3d orbital is actually higher than the energy of 4s, but after element 20, the energy of 4s will be higher than that of 3s. Can someone explain why?

Cecilia Lei 3K

What exactly do we need to know about Schrodinger's equation? Do we need to learn how to use the equation to calculate? Or we just need to know the square of wave function is related to the probability of finding e-?

Cecilia Lei 3K

Do we really have to remember specifically which wavelength corresponds to which region of radiation (eg: ultraviolet, visible light)?

Cecilia Lei 3K

Lyman series are the series for UV light, and Balmer series are for the visible lights.

Cecilia Lei 3K

We are supposed to know the mass of electron because we have to use the formula E=1/2mv^2 to calculate the energy of the electron. However, the mass of the electron can be found on the class website in the Equations and Constant file. Our TA told us that you should be allowed to bring your own copy ...

Cecilia Lei 3K

The velocity of an electron that is emitted from a Metalllic surface by a photon is 3.6*10^3 kms^-1. (A) what is the wavelength of the ejected electron? (B) no electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50*10^16 Hz. How much energy is required ...

Cecilia Lei 3K

The answer is shown in the below attachment. And for the first question, I used the formula E=1/2mv^2.

Cecilia Lei 3K

Do all particles have wavelike property and particle property combines? Or it’s just electron that have these two properties?

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