CHEMISTRY COMMUNITY

JulieAljamal1E

The x-axis would be 1/t for this Arrhenius plot. What would the y-axis be?

JulieAljamal1E

Is the slope of a plot of a first order negative?

JulieAljamal1E

How do you calculate the change of internal energy given heat capacity of a calorimeter and the final and initial temperatures?

JulieAljamal1E

From test 2, problem 4 wants us to construct a cell diagram of the balanced cell reaction NO3-(aq)+4H+(aq)+Fe(s)->NO(g)+2H2O(l)+Fe^3+(aq). I know the anode goes on the left and cathode on the right. Is Fe(s)|Fe3+(aq)||NO3-(aq)|NO(g)|Pt(s) correct? Or do you need to put H+ and H2O in there too??

JulieAljamal1E

In lecture on Friday, Dr. Lavelle showed us an example and asked us which step was the slow step. How do we identify which is the slow step?

JulieAljamal1E

Are there any textbook problems involving zeroth order that we can do as examples?

JulieAljamal1E

5I.13 asks to determine if Cl2 or F2 is more thermodynamically stable relative to its atoms. The answer is Cl2. How is that so? We solved that the F2 reaction has an equilibrium constant of 1.2x10^-4 and the Cl2 rxn had 1.3x10^-7 Kc.

JulieAljamal1E

In part C, we’re asked to calculate the rate constant for the rate loss of A from 2A->B+C given that [A]0=0.153 mol/L and that after 115s give the the concentration of B rises to 0.034 mol/L. To do this, I know we have to uses ln([A]t/[A]0)=-kt. But first we need to come of with [A]t. The solutions ...

JulieAljamal1E

In 7A.17 from the 7th edition, part c asks us to determine the value of the rate constant. In the examples from the book, it seemed like they just picked one of the experiments and plugged that into the rate law reaction and it worked. For 17 though, it seems like you have to choose “the right” expe...

JulieAljamal1E

The book says a reaction with a large positive Ecell°has K>>1. What does this mean?

JulieAljamal1E

Does temperature always have to be in kelvin for the Nernst equation?

JulieAljamal1E

How do you distinguish what to plug in for Ecell versus Ecell°? How do you know which one is which?

JulieAljamal1E

in part a) Ni|Ni2+||Ag+|Ag we need to write the balanced equation. I understand how to do this, but the solution manual shows for each half reaction what the E°(cathode) and E°(anode) is. How did they come up with these values?

JulieAljamal1E

Sarah Kiamanesh 1D wrote:reducing agents bring about reduction by becoming oxidized and giving up their electrons
oxidizing agents bring about oxidation by becoming reduced and accepting electrons

So whatever is oxidized is the reducing agent? And whatever is reduced is the oxidizing agent?

JulieAljamal1E

For part a) we need to balance the skeletal equation O3+Br- ---> O2+BrO3- using oxidation and reduction half reactions taking place in a basic solution. Would O3-->O2 be oxidizing or is that a reduction? I think it's oxidizing, but later when the solutions shows the half reaction, it gives H2O+O3+ 2...

JulieAljamal1E

Is the element that's being reduced the reducing agent or the oxidizing agent? What is a reducing or oxidizing agent?

JulieAljamal1E

In class on Friday, we covered an example that asked what temp Br2(l)->Br2(g) would be spontaneous at 1 ATM? The professor said that this is the same thing as asking what the boiling point is. Can someone explain this? I understand going from a liquid to a gas would involve boiling, but why does tha...

JulieAljamal1E

For one of the questions on the midterm, did we need to use approximations when calculating x? I got confused because I thought the problem needed it but I remember in class we were told there would be no approximation based questions.

JulieAljamal1E

Is test 2 going to be covering thermodynamics? Or is it going to be on electrochemistry?

JulieAljamal1E

Are we going to need to know how to derive certain formulas on the midterm? In class Dr. Lavelle seemed to spend some time deriving them out but only the final equation helps solve the question?

JulieAljamal1E

In the end, it shouldn't matter which equation you use to find the change in entropy. I believe that ΔS=nR ln(T2/T1) was used over ΔS=Cv ln(T2/T1) simply because it you can derive the number of moles (using PV=nRT) more easily than trying to find the heat capacity. If you can find the heat capacity...

JulieAljamal1E

For question 4F.11 we're asked to calculate the change of entropy of a gas where there was 3 L of N2 at 18.5 degrees Celsius compressed to 0.5 L. In the process the temp increased to 28.1 degrees Celsius. I know we have to calculate the change of entropy for both the volume and temperature change an...

JulieAljamal1E

On the class website, it says the midterm will cover content to the end of entropy, does that mean the material till the end of section 4F (titled entropy) in the Textbook, or all the sections passed that that involve more information about entropy as well?

JulieAljamal1E

On problem 4E.5 part a, it asks to calculate the reaction enthalpy using bond enthalpies for the reaction 3C2H2->C6H6 The table in the book gives what I’m assuming is a resonance bond enthalpy for benzene's Carbon single and double bonds. Before noticing that, I did 3(348)+3(612) which is for the si...

JulieAljamal1E

The question asks to calculate the standard enthalpy formation of dinitrogen pentoxide from the info: 2NO+O2–>2NO2 delta H= -114.1kJ 4NO2+O2->2N2O5 delta H= -110.2 kJ I’m confused on how to do this. The solutions show to add the first reaction with half of the second, but why are you allowed to mult...

JulieAljamal1E

The lectures seem to be out of order compared to the Textbook outlines. By now, which sections of the Textbook (7th edition) have we read, and which homework problems should we be able to know how to do? There seems to be a lot of jumping around even within the sections.

JulieAljamal1E

As mentioned in class, a burn from 100 degree steam is more severe than that of 100 degree water. Is the reason for that because it takes longer for the steam to cool compared to water?

JulieAljamal1E

When you have a chemical equation and you take the reverse reaction, why does delta H change sign to negative if it was originally positive and vice versa?

JulieAljamal1E

Can someone explain how to do problem 4d.19 from the 7th edition step by step? It asks to calculate the reaction enthalpy for H2 + Br2 -> 2HBr given the following data: NH3 + HBr-> NH4Br delta H= -188.32 kJ., also given N2+3H2->2NH3 delta H=-92.22 kJ, and given N2+4H2+Br2->2NH4Br delta H= -541.66 kJ...

JulieAljamal1E

I have two questions about 6D.3. It asks to find the Ka and pKa values given the information that you have 0.10 M HClO2 with pH 1.2. In the solutions it shows that the concentration of H3O is 0.06 mol/L which is solved by taking 10^-pH in this case 10^-1.2. I understand that, but then they say that ...

JulieAljamal1E

Can someone explain how to solve number 20 on the post-assessment 3? I understand how to set up the table but why in the given table for the equilibrium concentration do they say c+2x for 2SO3 and not just 2x. How do you solve for the c? A vial of SO2 (0.522 mol.L-1) and O2 (0.633 mol.L-1) react and...

JulieAljamal1E

On 6B.3 part B (7th ed) it asks what the actual pH of a solution would be when a lab technician wants to prepare 200 mL of a 0.025 M HCL solution but uses a volumetric flask of 250 mL by mistake. The solutions show that you take the -log((200mL x 0.025M)/250 mL)= 1.7. Can someone explain this work o...

JulieAljamal1E

Autoprotolysis, as defined in the book, is a type of reaction where one molecule transfers a proton to another molecule of the same kind. Is this specific to just H2O or is it any of the same two molecules?

JulieAljamal1E

On question 5I.17 in the 7th ed., there is a step in the solutions manual that goes from 2x=(3.16x10^-3)(0.114-x) followed by the step 2.00316x=3.60x10^-4. Can someone explain the work process in between those steps or how to get from that first step to the next?

JulieAljamal1E

How do I convert from Kc to Kp or vice versa?

JulieAljamal1E

For the last question on module 2, “The reaction 2 SO2 (g) + O2 (g) ⇌ 2 SO3 (g) occurs in a 1.00 L flask at 312 K and at equilibrium the concentrations are 0.075 mol.L-1 SO2 (g), 0.537 mol.L-1 O2 (g), and 0.925 mol.L-1 SO3 (g). Calculate their respective partial pressures at 312 K using R = 8.206 × ...

JulieAljamal1E

K is the equilibrium constant. It represents the concentration of products at equilibrium over the concentration of reactants at equilibrium. At equilibrium the reaction is still occuring and products and reactants are still being formed/ the forward and reverse reactions are stil occuring but at eq...

JulieAljamal1E

How do you know whether to add -o -ido or -ato to the end of an anions name vs leaving it as is?

JulieAljamal1E

I believe it is determined by the number of atoms which can body to the central atom.

JulieAljamal1E

How do we know that H2Se has a greater boring point than H2S considering that they both have LDF and dipole dipole?

JulieAljamal1E

In problem 6D.11 7th edition, it asks to decide whether an aqueous solution off each of the following salts has a pH equal to, less than 7, or greater than 7. If pH>7 or pH<7 then write a chemical equation to justify the answer. a) NH4Br b) Na2CO3 c) KF d) KBr e)AlCl3 f)Cu(NOs)2.Can someone please e...

JulieAljamal1E

How can I tell if something is polydentate? And how do I decide if it's mono dentate, bidentate, trident ate etc.? I understand polydentate means that the ligand binds at multiple sites but, how can we figure out how many sites it binds to?

JulieAljamal1E

On part c) given [Co(CN)5(OH2))]2- the name is aquapentacyanocobaltate(iii) ion. Why is it cobaltate and not just cobalt, while on the next part d) we have [Co(NH3)5(SO4)]+ the name is pentaamminesulfatocobalt(iii) ion. here we have Co written as cobalt not cobaltate. How do you know which one to use?

JulieAljamal1E

When would I name something Cyano vs Cyanido?

JulieAljamal1E

Can anyone explain how to know what the oxidation number is when naming a coordination compound? I think it has to do with the overall charge of the compound, but then how do you also know what the charge of the compound is?

JulieAljamal1E

Will we need to know how to draw the hybridized orbitals for the test?

JulieAljamal1E

Are there any other elements or examples like Boron Trifluoride where the central atom can have an incomplete octet like boron does? Besides the first four elements of the periodic table (which never have a complete octet)

JulieAljamal1E

When drawing the Lewis structure for Boron Trifluoride, why do we allow it to have an incomplete octet? I get that adding a lone pair to the Boron would mess up its formal charge, but why can it then have an incomplete octet? This impacts determining the molecular shape because it involves regions o...

JulieAljamal1E

When you have a molecule that doesn't really have a central atom i.e. N2H4, how do you determine the shape?

JulieAljamal1E

Do we need know the notation for vsepr (AXE)?

JulieAljamal1E

What is the difference when asked for molecular shape versus electron geometry?

JulieAljamal1E

I believe it must be at least three posts per week due by Sunday nights. I don't think posting more in one week will compensate for posts you've missed in the past.

JulieAljamal1E

How do you figure out the shape of a compound? Is it just based off of the number of bonding pairs on the central atom?

JulieAljamal1E

I believe you subtract the electronegativity of Phosphorus from that of Chlorine since chlorine is more electronegative. Thus it would be 3.16-2.19=0.97 electronegativity difference.

JulieAljamal1E

In the 7th edition 2C.3 the question asks, draw the lewis structure including typical contributions to resonance structure for (b) hydrogen phosphate ion, (c) chloric acid. I am confused as to why in part (b) the solution shows the hydrogen connected/bonded to an oxygen as opposed to bonding to the ...

JulieAljamal1E

In the 7th edition question 2A.13 part D asks to predict the type of orbital from which an electron will need to be removed to form the +1 ion of Cu. The answer is supposed to be the 4s orbital. Can someone explain why? I would've thought it would lose it from the 3d orbital?

JulieAljamal1E

I'm confused as to why the lewis structure of BrF3 permits 10 electrons surrounding Br (3 single bonds with each F for a total of 6 electrons) and then two pairs of lone pairs (4 electrons). I understand Bromine needs 7 valence electrons, but why are we allowed to add those extra lone pairs and brea...

JulieAljamal1E

On question 1F.11 (edition 7 of the textbook) the question asks for you to choose which element of a given pair has the higher electron affinity. How do you distinguish which element has the higher electron affinity if they are in the same group? Beryllium and magnesium (which are in the same group)...

JulieAljamal1E

Is there a difference between electron affinity and electronegativity? Or can these two terms be used interchangeably?

JulieAljamal1E

Would we be expected to memorize/know the charges of polyatomic ions/molecules for the test/midterm?

JulieAljamal1E

When going across the periodic table ionization energy tends to increase. Nitrogen would have the tendency to gain electrons while Lithium would tend to lose an electron. What about elements in group 4 of the periodic table? Would they "rather" lose 4 electrons or gain 4 electrons?

JulieAljamal1E

Hi, I believe Professor Lavelle mentioned that the 4pi results from a long derivation process for the Heisenberg Indeterminacy Equation but that we won't need to know it. As long as you know the equation you should be fine, and it may even be given on the test.

JulieAljamal1E

In my discussion section, we went over a problem asking us to calculate the wavelength of light emitted in the n=3 to n=2 transition in the hydrogen atom. When the solution was put up, the equation used to solve this was v= -R(1/n^2 - 1/n^2). I am confused as to why we put a negative in front of the...

JulieAljamal1E

Hi, I was wondering if chapter 1F will be included on the test on Tuesday because in class, Dr. Lavelle mentioned the test would only include information taught up to Friday's lecture, but the outline on his website shows that we should also know 1F.

JulieAljamal1E

I used the second equation you listed that was shown in the book. This method was more efficient to me.

JulieAljamal1E

I believe we receive our homework back in our discussion sections and I'd assume we'd find out our test grades in the discussion section as well.

JulieAljamal1E

Whatever numbers are given in the problem allow you to determine sig figs. If you are multiplying or dividing numbers, you limit your sig figs to the smallest number of sig figs in the calculation. If it is addition or subtraction, you limit sig figs to the term in your calculation with the smallest...

JulieAljamal1E

Test 2 will be given in our discussion section during week 4. If you go on the chem 14A class website, under test and exam schedules you can see a list of dates for all the upcoming tests.

JulieAljamal1E

Fundamentals D touches on naming compounds, so that could be helpful to review prior to the test. However I think we will be given the formulas for the compounds on this first test.

JulieAljamal1E

So you know the left side is fixed with 9 atoms of gallium and you want the scale to be balanced. So find the mass of 9 gallium atoms by multiplying 9 by the molar mass (70 g/mol) which gives you 630 grams. Then to balance the other side you need to have 630 grams of astatine. So multiply the molar ...

JulieAljamal1E

You start by solving for the molarity of Sodium Carbonate by first dividing the given mass of Na2CO3 (2.111g) by its molar mass which is 105.99 g/mol to get grams into moles. Then you take the number of moles you just calculated (.01992 mol) and divide that by the given volume of 0.25 L (I converted...

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