CHEMISTRY COMMUNITY

Tatum Keichline 2B

mol/Ls zero and first
1/mol/Ls second order

Tatum Keichline 2B

Zero order is time vs concentration
First order is time vs ln concentration
Second order is time vs 1/concentration

Tatum Keichline 2B

I’m having trouble understanding what a unique rate is. Can someone clarify please?

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You'd have to use the experimental data still because coefficients don't determine order

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How does the graph for second order look? Will it ever be exponential, or only linear?

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Does the 1/2 life for first order depend on the initial concentration like it does for zero and second-order reactions?

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I believe it should be a straight line with decreasing slope

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The units must cancel out. K cancels with the other units, so use K.

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There was a problem on test 2 asking whether the compound was acidic or basic using K and the other values given. I'm pretty sure we had to use the Van't Hoff equation as well. Does anyone know how to approach this problem?

Tatum Keichline 2B

I am confused on this as well, but I think 50% is the minimum and it goes in increments of 10-20% for the rest of the letter grades.

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More negative E for reducing and more positive E for oxidizing I believe

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deltaG must be negative for a spontaneous reaction, so T deltaS must be a positive term to make sure the number subtracted from deltaH in deltaG=deltaH-TdeltaS has deltaH as a large negative number.

Tatum Keichline 2B

I don't think the test will be cumulative because it will mainly focus on Gibb's Free Energy and electrochem, but Lavelle told me you need to know thermodynamics prior to this for the test.

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There should be a link on the class website saying what is on the test, but it will cover thermodynamics, mainly in chapter 9 of the outline.

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I would focus on connecting the equations to each other because they will all be on the equation sheet. Know the main equation for enthalpy and entropy, then focus on manipulating the variables for each when needed. Basically, focus more on when to use what, not memorizing the formula itself.

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n and r are constant if T changes, but r and T are constant if the system is isothermal (same temperature)

Tatum Keichline 2B

How do we know which value of R to use because aren't there two values? I know we usually use 8.3145, but when would we use the other value?

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What does C represent in the entropy equation for ln of temperature change?

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When do we use the Boltzmann equation? Do questions specifically ask for it. I've been gone for the past week, so I am lost. Thank you.

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Do we need to memorize the constants like 3/2, 5/2..etc. for tests?

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the slanted lines are in their own/same state, while the straight lines represent the phase change (sol->liq->gas)

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The irreversible wouldn't be doing the maximum amount of work because the outside pressure was only 1 atm compared to the inside pressure of 2 atm, so this doesn't represent the work against maximum pressure. On the other hand, the reversible pressure is at equilibrium, so it is expanding against th...

Tatum Keichline 2B

I don't think so, but I'm not sure. I think you have to know the lewis structures on your own.

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for 8.9, use 8.206e-2Latm/kmol and 8.314J/kmol then convert to kJ and subtract that answer from kJ given.

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I'm not understanding how to approach problem 8.3 in the 6th edition textbook. I was sick during this lecture, so I am behind on this section and I'm not understanding how 24J is the answer.

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Averages are going to be least exact and inaccurate, which is why bond enthalpies is the least accurate way to measure reaction enthalpies.

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acid+base-->conj. base+ conj. acid. The conjugate base is an anion so that will help you identify it.

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Kc is specific to concentration while Kp is for gases and partial pressures. Kc can be used for gaseous mixtures I believe, but it's more likely for Kp to be used.

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Ok that makes sense, thank you!

Tatum Keichline 2B

I am confused on how to do 6th edition 11.27 and solving for the partial pressure of PCL3 using the given partial pressures. Can someone help please?

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There are more products, meaning that the reaction favors the products since products are on the right.

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Q=K, meaning that the forwards and back reaction rates are equal

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If q is less than k, the reaction moves towards the products. If q is greater than k, the reaction moves towards the reactants. K is just equilibrium.

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A bronzed acid must be the proton donor in the chemical equation. It's dissociation determines the strength of the acid.

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Strength is determined by the how readily acid/base dissociates into H+ and OH-.

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the number in front represents the period the element is in. S is the orbital.

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I think Dr. Lavelle said either way is acceptable in lecture because it's whatever you prefer.

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A sigma bond is a single bond, a double bond is a sigma and pi, a triple is a sigma and 2 pi. Single is the longest, double is medium-length, and triple is the shortest.

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X is the bonds formed and E is the lone pairs

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I think it's because the electrostatic forces hold ionic bonds together tightly and because they are between metal and nonmetal, while hydrogen bonds consist of hydrogen and an element of a higher electronegativity. Ionic bonds are when electrons are transferred from one element to the other. Hydrog...

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B, Be, Li, H all exceptions to octet rule because they don't complete valence shell

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Atoms that can hold electrons in the d-orbital (P3 and below)

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Polarity: Charge distribution causing polar or nonpolar molecules due to differences in electronegativity
Polarizability: How easily an electron cloud can be distorted

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Polarizability is how easy it is to cause distortion to an electron cloud. Anions are highly polarizable because they have more electrons/are larger. Cations are small/less electrons and have high polarizing power, but low polarizability.

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You just have to know the bond angles from VSEPR, and Dr. Lavelle was saying 360/# of bonds, but that doesn't always work.

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Just try to get formal charges to equal zero or match the charge that the molecule is supposed to have.

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I believe so because it doesn't specify that you need 50% on any one assignment category, so it would be 250/500 in the course.

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Lone pairs on the Iodine lead to repulsion making it t-shaped

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Trigonal bipyramidal, trigonal bipyramidal, octahedral/square planar, trigonal pyramidal

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Count the valence electrons you can have for the molecule, determine how many you've used. If you used too many, you create a double/triple bond and it can be on either side of the central element between the other elements that are the same as each other (ex. NO2) (resonance structures). The amount...

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You determine the valence electrons it needs to lose or gain to reach an octet.

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You have to lose 7 (+7) to reach an octet or gain 1(-1) to reach an octet (electrons).

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I would go to the review session talked about in beginning of lecture on Friday/look up the “garlic bread” review topic because it has mock midterm problems. It seems very useful and the review session date should be posted on there soon. https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=157&t...

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Sulfur has higher electron affinity because oxygen electrons experience more repulsion between each other, since the valence shell is held closer to the nucleus. The repulsion causes more energy to be consumed when an electron is introduced than with sulfur due to the repulsion of electrons being im...

Tatum Keichline 2B

Ground state would be the lowest energy state of the atom. So the electron configuration has to show the lowest energy state.

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I would know these just because we had practice problems on these topics in lecture and in the text. It's better to have a basic understanding.

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The midterm from last year is also on ccle :)

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If something has a high electron affinity, it means it has a higher ability to attract other electrons. This will in turn make the bond stronger because of the greater pull.

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px, py, and pz correlate to the ml=-1,0,+1. px and pz can be either -1 or +1, but pt must be the middle number for the list of ml values is what I understood.

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Joule is kgm^2/s^2, but multiplying my 1/s cancels one of the s units, making kgm^2/s

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h bar is h/2pi, but in uncertainty problems you use deltap*deltax is greater than or equal to h/4pi

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You should definitely use the most accurate molar mass given. I wouldn't worry about sigfigs until the end. Either way with rounding, your answer won't be too far off from the answer you should have, but it is more accurate to use the most digits given on your periodic table for molar mass. It's bes...

Tatum Keichline 2B

Sigfigs should always match the lowest significant number given in the problem. For example, if a problem has 3.2+4.88=?, your answer should be rounded to two sigfigs.

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I would personally try to match the sigfigs given in the problem, but you can use however many sigfigs between calculations. Just round at the end :).

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