CHEMISTRY COMMUNITY

melissa_dis4K

I know that when we have two aqueous we write the one with the higher oxidation state first, but what if they have the same oxidation state? Example: S2O8^-2 and SO4^2-. Thanks!

melissa_dis4K

Why do we have to convert the standard potential of half reactions into delta G and add them to convert it to the total standard potential of the reaction. Ex: U^4+ + 4e- ---> U. Why can't I just add the standard potentials of U^4+ e- ---> U^3+ and U^3+ + 3 e- ----> U? Thank you!

melissa_dis4K

When given a question like the one attached, where the given reactions have H+ like part c, how do I know on which equation to write the H+ on when doing the half reactions?

melissa_dis4K

When there are two solids how do you decide how to put them in the cell diagram? Thank you!

melissa_dis4K

I can see clearly from the given equation that Fe loses 6 e- but I do not see how Cr gains the 6 e-. Is this seen after the reaction occurs?

melissa_dis4K

Thank you!!! :) That makes sense now I was looking at it wrong.

melissa_dis4K

For part b, n is equal to 6 but I do not understand why. I thought n was how many electrons were transferred and here we have a charge of 24+ and 24+ on both sides so why isn't n=0? Also, am I doing the charge counts wrong? Thank you!

melissa_dis4K

For basic solutions, how do you know what side to add the OH- on? Is there a guide to how to balance basic solutions in the textbook? Thanks! I really appreciate it.

melissa_dis4K

But then for 3C(subscript 2)H(subscript 5)OH -----> 3C(subscript 2)H(subscript 4)O how would I know that C was oxidized since they have zero charge. So should I always have to calculate the charges like mentioned above or can I assume that because in the redox reaction the Cr was reduced then the C ...

melissa_dis4K

I notice that to determine which element was oxidized or reduced you need to find the charge of the atom. For example, Cr(subscript2)O(subscript 7)^2- being turned into Cr^3+. I found that it was being reduced from 6+ to 3+ but my question is: If we have the final redox reaction instead of finding t...

melissa_dis4K

Nvm! Delta S of universe = delta S (system) + delta S (surr) and if this is greater than 0 then it is spontaneous!

melissa_dis4K

This is regarding Karen's Gibbs Free energy worksheet question 2. It says:
Use the following values for entropy, determine if a reaction would be spontaneous for each case.
a. delta S system= 30J/K ; delta S surroundings= 50 J/K
Thanks

melissa_dis4K

Can someone pls explain how to do #3 from the Gibbs Free Energy worksheet.Thanks!

melissa_dis4K

How can I determine whether a reaction is spontaneous or not from given delta S of the system and delta S of the surroundings? Thanks!

melissa_dis4K

Can someone pls explain how to calculate the equilibrium constant for Gibbs Free Energy wkst #1d? Thank you!

melissa_dis4K

In class why did Professor Lavelle change the Cu^2+ + 2 e- ---> Cu reaction to the reverse reaction?

melissa_dis4K

Why do the carbons have different charges? Thank you!

melissa_dis4K

Why does an endothermic (positive delta H) not favor the forward process?

melissa_dis4K

The maximum amount of work is theoretical, meaning that we can calculate the maximum amount of work but in reality we never get to the maximum amount of work, The maximum amount of work is when this work has the potential to do USEFUL work. In reality, there is energy lost as thermal energy which is...

melissa_dis4K

A salt bridge is important to allow anions to diffuse through. Without it, over time there will be an accumulation of electrons on the right side, so use anions like Cl- to diffuse to the other side to keep the two solutions neutral.

melissa_dis4K

Because E is an intensive property, meaning that it does not depend on the amount of material, therefore you do not multiply by the number of moles.

melissa_dis4K

Is delta U equal to zero for irreversible processes?

melissa_dis4K

How is the pressure changing?

melissa_dis4K

Can someone please explain why molecules do have entropy at 0 Kelvin and what that entropy is? Thank you!

melissa_dis4K

How can we calculate the entropy of vaporization for water at room temperature?

melissa_dis4K

Why do we use constant volume heat capacity instead of constant pressure? Isn't the volume changing? Thanks

melissa_dis4K

During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5 C 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 C. Assume ideal behavior. What is the change in entropy of the gas? So I know ...

melissa_dis4K

I know that for a reversible, isothermic process delta U is zero because there is no change in temperature. Is delta U =zero for irreversible process as well? And if so, why? Thank you!

melissa_dis4K

Why do weak acids have to go in the forward direction?

melissa_dis4K

In class, Professor Lavelle said that there are times when we need to take into account that 10^-7 [H3O+] but other times it is negligible. I am confused on what he meant and when we do take it into account. Thank you!

melissa_dis4K

How can I know that CH3COOH wants to donate its proton to create H3O+ and CH3COO- without memorizing that it is an acid from the table in the book? I want to know how to identify them so I can write chemical equations when needed to do ICE tables for weak acids and bases. Thank you? Also will it alw...

melissa_dis4K

When a bond is broken, energy is required. When a bond is formed energy is released.
Breaking Bonds → Energy Absorbed
Forming Bonds → Energy Released

melissa_dis4K

How can you determine whether work was done by or on a system? Thank you.

melissa_dis4K

How do you know when work is positive or negative. I know that when F and displacement are in the same direction work is positive but in the homework 8.3b.) 6th edition I got confused. Thanks!

melissa_dis4K

I am confused on increasing and decreasing the temperature of an endothermic reaction. Why does decreasing the temperature favor the reactant? I thought that it always favored the endothermic (requiring heat) reaction.

melissa_dis4K

On worksheet 1 how exactly did they get the answer for number 3 because I am confused. I just thought it was Kc=[products]/[reactants] so Kc=x^5/1.0-x. Thank you

melissa_dis4K

Can someone please explain why we need to square the Kc for worksheet 1 question #2a? I thought that the same molecules under the same conditions (same temp (973 K) would have the same Kc even if one has more "material" used. Why do I need to square it?
Thank you!

melissa_dis4K

On Worksheet 2, why is the concentration of CO3 the same as Ka2 for problem 4b? In the second ICE table, the concentration of CO3 is x, and because x is so small, it is essentially Ka2.[/quote] I still don't understand this, I'm sorry could someone please explain more? I'd greatly appreciate it. Wh...

melissa_dis4K

How do you know when the autoprotolysis of water doesn't significantly affect the pH? Is this different for different acids and bases or should it always be assumed? Thanks!

melissa_dis4K

How do I answer the following question. All I know is that Kw=[H3O+][OH-]
Estimate the concentrations of (a) [H3O+] and (b) [OH-] at 25 C in
6.0 x 10^-5 m HI(aq).
[Answer: (a) 60. mumol/L; (b) 0.17 nmol/L]
Thank you

melissa_dis4K

I've noticed that when all the species are in the gas phase, the book has been using partial pressures and then converting them into concentrations using the ideal gas law and the ice table, so my question is when calculating the equilibrium constant for a reaction with all species in gas phase shou...

melissa_dis4K

For the following question how am I supposed to find the temperature to convert the given partialpressures into concentrations knowing that concentration= P/RT? Self-Test 11.10A The initial partial pressures of nitrogen and hydrogen in a rigid, sealed vessel are 0.010 and 0.020 bar, respectively. Th...

melissa_dis4K

I see.. thank you so much!

melissa_dis4K

Do we need to know how to write the equilibrium constant for net ionic equations? It is on the sixth edition, after Chapter 11.2 but under self assessment 11.3. Thank you!

melissa_dis4K

In the following question I did not understand why they used both concentration and partial pressure for the equilibrium constant. I thought that you only used either concentrations or partial pressures, not both. Can someone explain to me please? This is from the sixth edition. Self-Test 11.2A Writ...

melissa_dis4K

In the 1/16/19 lecture, he explained towards the end that because x was less than 5% of the initial value it was okay, since in that calculation it was 1.3%. He got the 1.3% from calculating the % ionization of aceitic acid. I was also confused on what he meant but I think that he means that if the ...

melissa_dis4K

Are Ice tables only for molarity? Or can we use them for partial pressures as well? I saw a question on Chemistry community about using partial pressures in ICE table but I thought it was only used for molarity. Thank you!

melissa_dis4K

I am confused on how to identify an acid from a base and when it is best for it to gain/ get rid of its proton? Thank you.

melissa_dis4K

I did the same thing as explained above and I get Kc=[BrCl]^2/[Br2][Cl2]=[3.37 x 10^-5]^2/[7.52 x 10^-5][7.52 x 10^-5].
My answer: 0.199637845, however, is not an answer choice can someone please explain what I did wrong?
Thank you!

melissa_dis4K

So both in the module video and in class, Professor Lavelle mentioned that we should not think of equilibrium being shifted, rather that it sits on the right or left. However, when I was completing the first module I came across two questions: With respect to equilibrium constants what does it mean ...

melissa_dis4K

This is a question from the module, I just would like an explanation for why equilibrium constants are useful. I know that the equilibrium constant is equal to the [products]/[reactants]. But I don't understand what the answer would be if the choices are: A. One number that gives us information abou...

melissa_dis4K

Can someone pls explain how to draw the Lewis structure for KOH and how to determine if its a bronsted acid or a base? Thanks!

melissa_dis4K

Would it be because it is already stable since the formal charge of Sulfur with the lone pair is 0?

melissa_dis4K

Can someone pls explain how H2SO3 is a bronsted acid? I thought the sulfur could accept a proton with its lone pair making it a bronsted base but that is not correct. Thank you!

melissa_dis4K

Why is HBr a bronsted acid?

melissa_dis4K

Why does changing a hydrogen in CH4 to CH3F change the angle of the molecule? Is it because the F has lone pairs and repels the bonding pairs thus changing the angle?

melissa_dis4K

How can you determine which has a higher boiling point and why between C5H12 and C3H8? Thank you!

melissa_dis4K

It's helpful to draw the lewis structures to see if the structure is stable enough to either donate or accept a hydrogen. For example, NH4+ is a base because it can only donate a hydrogen. If it accepted a hydrogen, Nitrogen would have 5 bonds, which we know is not possible. Another example is OH-....

melissa_dis4K

Thanks!

melissa_dis4K

Thank you! That makes sense, so to clarify the Pt is the central transition metal atom therefore I shouldn't have included it as a seventh ligand. I got confused because it was inside the brackets. May I ask what the Br3 is then?Is it just another molecule attaching to it not part of the coordinatio...

melissa_dis4K

When drawing lewis structures any negative charges should go on the most electronegative atom and I thought the negative charge should go on nitrogen rather than carbon.

melissa_dis4K

Between carbon and nitrogen which is more electronegative? I thought it was Nitrogen but according to a review session I went to, it's actually carbon?

melissa_dis4K

What are the valence electrons of elements in the d block?

melissa_dis4K

How does one solve this question can someone pls explain how there are 6 ligands? Vitamin B12 is an essential nutrient containing Cobalt (Co). Cyanocobalamin, shown at right, is one form of B12 in which the cobalt center has a cyanide ligand. In addition, the cobalt is coordinated by a ring structur...

melissa_dis4K

To find the molecular shape of [Pt(NH3)5Cl]Br3 do I have to find the coordination number? And if so, isn't it 7? And the answer for this is octahedral does this mean that anything above 6 is octahedral? Or am I doing this wrong? Thanks!

melissa_dis4K

How do you know when the molecule is best accepting or donating its hydrogen?

melissa_dis4K

Between atoms like chloride and oxygen how do you determine which has a higher electronegativity given that electronegativity increases as you go up and across to the right?

melissa_dis4K

Between atoms like chloride and oxygen how do you determine which has a higher electronegativity given that electronegativity increases as you go up and across to the right?

melissa_dis4K

When would you use bis, tri, tetrakis? And are we using it instead of di, tri, tetra, etc?

melissa_dis4K

Are chloro and chlorido the same?

melissa_dis4K

When finding the oxidation number do I need to do the Lewis structure to find the charge of Cl, for example in [Fe Cl(OH2)5]^+ Or how can I find the charge of chloride to be able to find the oxidation number of the central atom? Thank you!

melissa_dis4K

Is it safe to assume that because all the atoms besides the central atom of ClF3 is polar because they are the same element or should the charges always be taken into consideration when determining polarity?

melissa_dis4K

Can someone please explain polarizing power and polarizability in an easy way for me to understand? I don't understand the definition. Thank you

melissa_dis4K

Just to clarify, when looking at the greater ionic character, the difference between the electronegativity of the two atoms, do the number of atoms, the subscripts make a difference? For example, comparing the molecules H (subscript 2)S and HCl. I know that HCl has the greater ionic character, but d...

melissa_dis4K

Nvm to that^ that makes sense thanks!

melissa_dis4K

Thank you! Regarding the dipole moment is there only one from the N to the O without the double bond? And if so do the formal charges "give it" its partial charge. I'm basing this idea off from the worksheet posted for "ch3; Chemical Bonds"

melissa_dis4K

I'm having a lot of trouble understanding polarity, can someone please help and explain how it is that we identify polar molecules. I know that polar is the unequal sharing of electrons and that if the dipole moments cancel it is nonpolar. However, I am just having trouble applying it to the actual ...

melissa_dis4K

Can someone please explain why NO2 is polar? Is it just because they are the same atoms and have an unequal sharing of electrons? Do the dipole moments not cancel out? If not, is this because the molecule is bent due to the unpaired lone electron on the N atom? Thanks

melissa_dis4K

I believe that we should know which angles are associated with the types of shapes. I'm not sure that we will necessarily be calculating them, I think that knowing them will be very helpful.

melissa_dis4K

Hello! I believe that see saw shape is one in which the central atom has 5 regions of electron density, 4 being bonds between the atoms and the 5th being the lone pair. For example, in the Lewis structure for TeCl(subscript 4), Te is the central atom and when all formal charges equal 0, Te has five ...

melissa_dis4K

I understand that Sulfur can have an expanded orbital, thus it has a d orbital. But if you do the electron configuration for Sulfur it is [Ne]3s^2 3p^4. I don't understand how it has a d orbital. Can someone please explain?

melissa_dis4K

does anyone know how to solve 8b? i am having trouble with it. First convert the work function from kJ/mol into J and convert lambda into meters. Then using E(photon)- work function =kinetic energy, we will be solving for E(photon). But first we need to know the kinetic energy to do so use Ek=1/2 M...

melissa_dis4K

For the electron configuration of Pd I get [Kr]4d^8 5s^2 but it is [Kr] 4d^10. My question is do we change it to [Kr] 4d^10 because we should fill in the entire d orbital before continuing to the 5s orbital? Is this always?

melissa_dis4K

Could someone explain 13c to me? -13c is a Heisenberg Uncertainty Principle problem. The equation for this problem is ΔPΔX=>h/4pi. For this equation we need the mass, the velocity(these two values multipled together are ΔP), and we need ultimately to find ΔX. -We are given the mass which is 2.8 gra...

melissa_dis4K

Thank you! So does this only happen for ions and elements like Cu and Cr?

melissa_dis4K

For number 11, part b why would delta E be a negative value? If the problem is asking for the change in energy from n = 6 to n = 4, and the formula is E = -hR(1/n1^2 - 1/n2^2), the energy released from n = 6 to n = 4 equals 7.5689 x 10^-20 J. So, why is the answer negative? Remember that the change...

melissa_dis4K

The abbreviated electron confuration of Ni3+ is [Ar]3d^7. Just to clarify even though while I did this I got [Ar]3d^5 4s^2, the electrons in the 4s orbital will move to the 3d orbital to fill that up first. Is this always true or an exception. I.e. will electrons always fill in the previous levels f...

melissa_dis4K

For 8B I understand that we need to use E(photon) - work function = kinetic energy. We are given the wavelength and work function. However, I don't know where to use the wavelength since E(photon)=h*frequency and we have the given work function and Kinetic energy= 1/2 Mass* Velocity(unknown). Can so...

melissa_dis4K

This may be very simple, but I am trying to understand why it is that when an atom is excited it gains energy? Is there an easier visual way for me to understand this?

melissa_dis4K

To calculate the uncertainty in kinetic energy you need to use the uncertainty of velocity from the previous problem: delta v=3.3*10^10 m/s. Then use the formula for kinetic energy= 1/2 Mass * Velocity^2. Plug in the mass of an electron (given) 9.11*10^-31 and the velocity from the previous problem ...

melissa_dis4K

When finding the electron configuration for Cerium, it is [Xe] 4f^1 5d^1 6s^2, I understand the 5d^1 and 6s^2, however I am confused on where and how we get 4f^1. I'm just confused on how to find it for the f-block. I know that for the d-block we have to take the period and subtract one is there som...

melissa_dis4K

This is from the sixth edition.. I'm having trouble understanding the difference between ground state and excited state can someone pls explain? Thank you!

melissa_dis4K

I realized my answer is wrong can someone explain what I did wrong? Thanks!

melissa_dis4K

34. B. If molybdenum is irradiated with 194 nm light, what is the maximum possible kinetic energy of the emitted electrons? For the previous question part a I got E=7.22 x 10^-19. However, I am not sure how to solve this problem. I think I should use Kinetic Energy=1/2Me*Ve^2. But, I don't know how ...

melissa_dis4K

Thank you, it did help! I was overthinking the equations. But, now I got 150.6 J for question 29b when I added the work function plus my answer from 28a. I then used frequency=E/h and got 2.27 x 10^35. However, the answer seems to be to the power of 38. Do you know why I get the wrong power sometimes?

melissa_dis4K

When I am calculating sometimes I get the wrong power on my calculator and was wondering if anyone knew why this is? I do make sure I input everything correctly and that I use parentheses.

melissa_dis4K

The question asks "Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 10^5 m.s-1. The work function for sodium is 150.6 kJ.mol-1. What is the frequency of the incident light on the sodium metal surface?" I began by doing E=h*v(frequency). However, I don't ...

melissa_dis4K

For this question, "Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 10^5 m.s-1. The work function for sodium is 150.6 kJ.mol-1. What is the kinetic energy of the ejected electron?" I know that E(photon)-E(energy remove e-)=Kinetic energy of the electron...

melissa_dis4K

For question 27 it asks "Calculate the energy per photon of ultraviolet radiation of frequency 3.00 x 1015 Hz." What I did was, using E=h*frequency(v) and c=lambda*frequency(v) I solved for E by rearranging the equations to give E=hc/lambda =(6.626*10^-34 Js)(3.00 x 10^8 ms^-1)/3.00 x 10^1...

melissa_dis4K

How do you know when to multiply the molar mass by the coefficients? Or we do always?

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