CHEMISTRY COMMUNITY

sonalivij

Does a higher enthalpy indicate a higher stability?

sonalivij

Does k have restrictions on which phases are included? Like if a reactant or product is in the solid or liquid phase, do we not consider it?

sonalivij

A good way to check if your approximation was valid is to see if x is less than 5% of the initial concentrations

sonalivij

how do you solve for worksheet 9 number 6? I used the half-life equation for a first-order reaction and solved for k when the half-life was 6 days. my k value was 0.1155. In order to find the percent of Hg(II) left in the body, would I have to find the k value for the 30-day half-life and divide th...

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Emily Tam 1k wrote:for number 5 of karen's 9th worksheet (kinetics), it says that the rate constant is 7.0x10^0 M.s. Does M stand for molarity or for minutes?

M stands for molarity, or mol/L

sonalivij

Quick question for Worksheet 1 ques8: When I2 is added, neither products nor reactants is favored as I2 is a solid. What happens when I2 is removed, does the reaction not shift too? Yes! Because it is a solid it is not included in the equilibrium equation so any change in concentration would not af...

sonalivij

when we write the rate laws, do we write it as "rate=..." or ""d[A]/dt=..."? Specifically in question #3 of the Reaction Mechanisms worksheet, could we replace "d[F]/dt" with "rate"? Yes they are synonymous. Writing it as d[A]/dt is just better because i...

sonalivij

On Worksheet 9, how would you solve for #7? For a first order reaction, you can use the equation (1/2)^n=whatever fraction of A is left because the half life is constant throughout the reaction. For this problem, use (1/2)^n=1/8 which means n is 3 (n is the number of half lives). We know the length...

sonalivij

How do you do #8 on worksheet 9? I tried to do .99[A]=.5^n[A] and solving for n by ln(.99)/ln(.5)=n, but this didn't work.

sonalivij

For worksheet 8 #4d I am getting 144 M/s instead of 140 M/s. Am I doing something wrong?

sonalivij

A section in the textbook is on corrosion. Do we need to know this?

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You add Pt(s) on the left side of the oxidation reaction or the right side of the reduction reaction in the cell diagram when there is no metallic solid in the half reaction. Pt(s) can appear in one, both, or neither half reaction.

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Remember, Ecell is different than the standard potential - Ecell is calculated using standard potentials, E knot

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K. If given C you should convert using K=C+273.15

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When given an experiment table, you choose the two experiments in which one concentration is the same and one is changing. In this case, the concentration of one of the reactants is double so we divide the rates on one side and set it equal to the concentrations divided by each other, which is 2.0, ...

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The half reaction with the most negative standard potential is the strongest reducing agent, and the half reaction with the most positive standard potential is the strongest oxidizing agent

sonalivij

We get our tests back in our discussion section or you can ask your TA to bring it to office hours if you can't make it to discussion.

sonalivij

I was confused on this as well. My thinking is that once you find the K2 for the equation you take the square root of it then the -log of it. The answer would be the neutral value. Anything below it is acidic and anything above is basic. This is just a guess though.

sonalivij

You can find n by balancing both Half reactions so the same number of electrons are transferred in the oxidation and reduction reactions. n is then the number of electrons transferred

sonalivij

I'm still confused on #6 for worksheet 4. I get the same answer for work as the answer key if I used -nRT (n=31.9, R=.0821, T=38) but not if I use -PV (P=1, V=L). Why aren't they the same?

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On Lavelle's midterm information schedule, he said class will be a review session, In which he goes over problems from old midterms or similar to old midterms. No new information is learned on these days

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Michelle Nwufo 2G wrote:Which of the reactions requires you to take the integral of the change in volume when calculating work?

The equation for an isothermal reversible expansion/compression requires you to take the integral of the change in volume when calculating work

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KarlaArevalo2F wrote:also, does any one know where we can get more practice problems besides Lyndon's?

Karen's worksheets are always very helpful!

sonalivij

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? I know th...

sonalivij

While I am not sure about this equation specifically, on his syllabus it says we should know how to derive pKw=pH+pOH so we might also have to know how to derive this.

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Keep in mind that x is only considered to be 0 when it is being added or subtracted to a number, not when it is alone and being multiplied

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005199302 wrote:For #5 on worksheet 1, don't we need the value of R to calculate the volume?

R is a constant and since P is in atm, use the R constant that has atm in its units.

sonalivij

Can someone please indicate the main steps to solve worksheet 1 problem #5? First you would use PV=nRT to find the volume of the container, and then divide the .05 mol PCl5 by the volume to get the initial concentration of PCl5. Once you have that, you can do an ice table like u normally do and sol...

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Can someone explain how to do Worksheet 1 #4d? My friend did it with initial concentration of NH3 as 0 and she got the right answer. Why doesn't the initial concentration of NH3=5.82*10^-3 ? I did this problem using the initial concentration of NH3 and ended up getting 11.6*10^-3 which is pretty cl...

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If the pKa is given for an acid, and we are told to find the pKb, are we technically finding the pKb of the acids conjugate base if we use 14-pKa=pKb?

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Why do solutions of weak acids have higher pH values than solutions of strong acids at the same concentration? Is it because a higher pH indicates a less acidic solution because the weak acid has not fully dissociated?

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Its given that the concentration of H3O+ ions is 1.5 mol/L. When I try to find the concentration of OH- ions by doing (1*10^-14)/(1.5) I get 6.6*10^-15 which is not the right answer. What am I doing wrong?

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In part c, it says the concentration of H3O+ ions is 3.1 M, except in the solutions manual they use 3.1 x 10^-3 to find the concentration of OH- ions. Why is that?

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Claudia Luong 3G wrote:This is because you want the positive charge to be on Cl instead of O (due to Cl being less electronegative than O).

Isn't Cl more electronegative than O?

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Why is the lowest energy resonance structure not one O double bonded to the Cl and one O triple bonded to the Cl, with one lone pair on the Cl, which would give the Cl a formal charge of 0 and the O a formal charge of +1. It's actually both O's double bonded to the Cl, with one lone pair on the Cl, ...

sonalivij

Which compounds do we need to know the function of for the test?

sonalivij

Find the formula for sodium bisoxalato(diaqua)ferrate (III).

I was confused as to why (OH)2 came before (C2O4)2 in the formula, isn't it alphabetical by the symbol?
Also, what do the parenthesis in the name mean?

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Consider the bonding in H2C--CHCHO. Identify the composition of the bonds and the hybridization of each lone pair.

How would you determine the hybridization of a lone pair? Also why is the formal hybridization of the pi bond between the double bonded carbon atoms pi(C2p,C2p)?

sonalivij

How do radicals influence the shape of a molecule?

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In this unit, bond type is mainly important when determining sigma and pi bond, but not when counting regions of electron density.

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Sigma bonds overlap end to end at the internuclear axis and mainly occur when a 2pz and 2pz, 2s and 2pz, or 2s and 2s orbital overlap. Pi bonds are perpendicular to the internuclear axis and overlap side to side and occurs mainly when a 2px and 2py orbital overlap. The important thing to remember ab...

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Carbon has a single bond with both the hydrogen atoms and a double bond with the oxygen atom (which has two lone pairs on it but we don't need to know that, just to help you visualize the lewis structure). CH2O would have three bonding domains, making its hybridization sp2 There are two single bonds...

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Is there any way two molecules with a hydrogen bond could also have van Der Waals forces because they would also have dipole moments?

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Also, the C-Cl bond is polar and since they are unable to all cancel each other eat (because there are C-H bonds thrown in there), the whole molecule becomes polar

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I post bad chemistry jokes because all the good ones Ar(gone) :)

sonalivij

You can do any of the homework problems since all of the information we learn will always be pertinent to this class, as long as you haven't already turned them in before.

sonalivij

Electronegativity does follow a trend. Atoms tend to decrease in electronegativity as you move down a group because the shells get farther and farther from the nucleus. Atoms tend to increase in electronegativity when they move from left to right across a period because of an increased effective nuc...

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Kunseo Yook 2E wrote:Is this the same for every element below copper and chromium? And are there any other elements with this kind of exception?

As you go down the periods, the elements are farther away from the nucleus and stop adopting this rule

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Joussie Camacho 4I wrote:For #8, which asks for the full electron configuration of Nitrogen, would 1s^22s^22p^3 be wrong? Do we have to write out 2px^1 2py^1 2pz^1?

I don't think so, I believe thats just an easier way to write it to visualize unpaired electrons

sonalivij

Could someone explain 13c to me?

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Why would gallium not have a full s-shell instead by losing one electron, instead of trying to get a full d shell by losing 3 electrons?

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Why is the most likely charge of Gallium Ga3+?

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The 4p orbital would have one more nodal plane than the 4s orbital. The number of nodal planes increases as l increases. So s orbitals have 0 nodal planes, p orbitals have 1, d orbitals have 2, and f orbitals have 3.

sonalivij

Why are cations smaller than their parent atoms if the loss of an electron would move them further to the left in a period. Wouldn't this make them larger? Also why are anions larger than their parent atoms if gaining an electron would move them further to the right in a period, which would make the...

sonalivij

Why is the electron configuration for tungsten [Xe]4f^14 5d^4 6s^2 instead of [Xe]4f^14 5d^5 6s^1 because doesn't the d-orbital want to be half filled?

sonalivij

In the first quantum world worksheet for #7, I don't understand where she got .0278 from, because wouldn't you have to add 1/16 to .03456?

sonalivij

Which equations in quantum use kg and which ones use grams?

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In this question it states "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 to remove the electron from the metal surface?" We were also given velocity in this problem. I figured this question me...

sonalivij

So will chapters 1E and 1F not be on the test? (7th edition)

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Does anyone know which chapters in the textbook this test covers?

sonalivij

Why is it that its impossible to know the position if the momentum is known precisely?

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No, the number of photons would not affect the energy. The only thing the number of photons would affect is the intensity of the light.

sonalivij

I always thought light worked in such a way that all the wavelengths absorbed were not seen, and the wavelengths reflected were seen. How is it that the absorption spectrum and the emission spectrum have the same absorption and emission lines? Am I understanding this wrong...?

sonalivij

How do you use E=hv to calculate the number of photons emitted from a light source?

sonalivij

Objects larger than that typically don't have wavelike properties because their momentum and mass are far too large.

sonalivij

Would someone be able to explain to me what the difference between molecules and formula units are?

sonalivij

In order to get your answer in scientific notation, you have to move the decimal place until it is in a place that creates a number between 1 and 10. In order to figure out what power you have to put ten to, count the number of places you moved the decimal place. If you moved it to the right, it wil...

sonalivij

This typically is not a problem as most periodic tables have slightly different molar masses so being .01 or .02 of is to be expected.

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Molarity is basically the measure of the concentration of a solution in moles of a solute (which is the substance being dissolved) over the liters of solution (which is the substance the solute is being dissolved in). Something helpful about molarity is that if it is given, it can be used to find un...

sonalivij

Typically, when I balance chemical equations I count how many of each element is on the reactants side and the product side and then start off by balancing the element that is in the least amount of compounds. After that I balance the next compound that has the least amount of an element and so on u...

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