CHEMISTRY COMMUNITY

Daniel Yu 1E

For an ATP to be made, you would need an ADP molecule to collide with a Pi molecule. You can see why this is affected by kinetics. In biology, there would be catalysts (enzymes) which speed up the process, but you still need the ADP and Pi to find their way to the enzyme's activation site.

Daniel Yu 1E

The higher the activation energy, the lower the reaction rate, as a general rule.

Daniel Yu 1E

The axes label for a first order reaction is ln[A] vs time.
For a second order reaction, 1/[A] vs time.

Daniel Yu 1E

You can look at arrhenius' equation to see the relationship between reaction rate and temperature.

Daniel Yu 1E

You aren't multiplying rate 1 and 2. You are assuming that Step 2 is the slow step. Using the pre-equilibrium approach, we treat reaction 1 as if it is in equilibrium. Since reaction 1 is in equilibrium, the forward rate is equal to the reverse reaction rate. Using this, we can get rid of the interm...

Daniel Yu 1E

It's for ideal gases, and if they're monatomic, diatomic, and so on. For Chem 14B we are only concerned about monatomic and diatomic ideal gases.

Daniel Yu 1E

W for the system is negative when the system does work. W for the system is positive if work is done on the system.

Daniel Yu 1E

It should result in the same value.

Daniel Yu 1E

Thank you Dr. Lavelle for the two quarters of Chem 14A and 14B. You've been a very caring professor and provided many resources for your students. You put in lots of time and energy and we appreciate that!

Daniel Yu 1E

A Pseudo First Order Reaction is reaction which is not first-order reaction naturally but made first order by increasing or decreasing the concentration of one or the other reactant is known as Pseudo first order reaction. Pseudo means 'fake'.

Daniel Yu 1E

What are the units for k in a zero order reaction? What are the units for the reactants of a zero order reaction? I don't understand why the units are what they are can someone help me?

Daniel Yu 1E

But just to be clear, you do not have to worry about steady state approach for Chem 14B

Daniel Yu 1E

The steady state approach is something we don't need to know for this test but is still a very relevant kinetics concept. It is an approach where you measure the rate of the reaction within a very, very small time frame: the moment the reaction starts, you take a quick snapshot of the atoms in react...

Daniel Yu 1E

How do you do 7A.15? How do you find the order each reactant? If they are different orders, don't the units change? Can you still use the given table to solve?

Daniel Yu 1E

The order of the reaction can vary depending on the equation and the number of reactants. If you have 3 first order reactants, the order of the reaction is 1+1+1 = 3. If If you have a first order reactant and a second order reactant, the order of the reaction is 1+2 = 3. If you have the rate law, an...

Daniel Yu 1E

What are the units for first order reactions? Why are they mol*L^-1*s^-1?
What about for second order reactions?

Daniel Yu 1E

How does the temperature affect the reaction rate? I see that it is in the denominator of the Arrhenius equation but what is it meant to do? Are catalysts affected by temperature?

Daniel Yu 1E

What is the pre equilibrium approach? How do you use it? What does it mean for kinetics?

Daniel Yu 1E

Can someone explain the concept behind the steady state approach? Why do chemical engineers use lasers?

Daniel Yu 1E

What is a general rate law? What is the equation for a general rate law? Is it k[a]^m*[b]^n...? How do you interpret this?

Daniel Yu 1E

Look at the table of experimentally obtained standard reduction tables. Metals that are higher up (more positive) are more likely to be reduced.

Daniel Yu 1E

Finding an oxidation number is essential to balancing Redox reactions. It will tell you whether an element is being reduced or oxidized. You can find the number by finding the typical oxidation state of the most electronegative nonmetal. There are rules for finding the oxidation state of nonmetals.

Daniel Yu 1E

The electrochemical series is just a list of experimentally obtained reaction cell potentials. The more positive the value, the more likely the molecule will be reduced.

Daniel Yu 1E

Today in lecture, Dr. Lavelle played the song Hazey (Stripped) by Glass Animals.

Daniel Yu 1E

When you are doing thermodynamic calculations with solutions in calorimeters, why doesn't the mass/mol matter sometimes?
I've seen in some equations you need to use mass/ moles but in others it is ignored. Why is that?

Daniel Yu 1E

For part b, constant volume means that no work is done. Therefore Delta H = q+ nR*Delta T.

Daniel Yu 1E

If it's isothermal you know Delta T is 0. Volume therefore must change, and the problem will most likely tell you the initial and final volume. Just use the formula Delta S = nRln(V2/V1) to solve for Delta S.

Daniel Yu 1E

W is equal to 'a', the number of possible ways to achieve a specific energy state, raised to the 'n' power where n is the number of particles in the system.

Daniel Yu 1E

Dina 2k wrote:how soon does he usually have it graded and back to us?

Dr. Lavelle said in an email that he would have them back for us by Wednesday, 2/19 after lecture.

Daniel Yu 1E

If Delta H is kJ.mol^-1, then multiplying Delta H by n, mol, would result in an answer in kJ. kJ is the units that work is in, so n*Delta H = q.

Daniel Yu 1E

How would you calculate Delta H for an isolated system if q=w=0? Or will it always be 0?
What about for Delta S? If the system doesn't interact with its surroundings, will entropy increase?
What about for W, degeneracy?

Daniel Yu 1E

If you had an irreversible expansion that had changes in volume as well as changing temperature, how would you find the overall change in Entropy, given everything you need to calculate for it?

Daniel Yu 1E

W is the degeneracy of the system. Entropy is a measure of disorder and thus is related to degeneracy. This equation helps quantify and define this relationship. W is measured by the number of possible states all the molecules in a system could have. If you had 'a' possible configurations and 'n' pa...

Daniel Yu 1E

If you were given the K_A or K_B of an acid/base, and the pH of the solution it was in, how would you find the actual dissociation/ protonation of the acid/base in the solution?

Daniel Yu 1E

What is the significance of Van't Hoff's Equation?
In lecture Dr. Lavelle mentioned something about how it relates the K, chemical equilibria, to S, entropy, but how is that useful?

Daniel Yu 1E

What are the different types of Delta S? You have change in entropy resulting from work being done on the system, change in entropy due to temperature change. What else? What is the difference between Delta S_total, Delta S, and Delta S_system and how do you calculate them based on the formulas we'v...

Daniel Yu 1E

I'm assuming you are talking about the Ideal Gas Law, PV=nRT.
P stands for pressure
V stands for volume
n stands for moles
R is a constant that you use to convert your answer into useful units. Based on your units for your other variables you would have a different R value.
T stands for temperature.

Daniel Yu 1E

I'm pretty sure it really doesn't matter whether you leave it Joules or KJ, as long as you convert correctly. I'm assuming if the quantities are given to you in KJ you would leave it as KJ, and the same for Joules, but it doesn't really matter as long as you have the same answer.

Daniel Yu 1E

I'm confused can someone explain to me how the internal energy of an ideal gas changes? Does doing work on the system affect it at all?

Daniel Yu 1E

Hess's Law states that the total enthalpy is independent of the intermediate reactions. This means you can add up the enthalpy changes of intermediate reactions to find the overall enthalpy change of the reaction. You use it for enthalpy change questions.

Daniel Yu 1E

Steam causes burns because when it comes into contact with your skin, it'll transfer its energy. It has a lot of energy since water requires lots of energy to undergo the phase change from liquid to gas.

Daniel Yu 1E

Rita Chen 1B wrote:In something like N2 + 3H2 —> 2NH3, if we increased N2, does it affect H2 as well?

Yes, it would decrease the [H2]. Because you increased the reactants, the forward reaction would be favored. In order for the forward reaction to occur, H2 will be used.

Daniel Yu 1E

Dr. Lavelle was talking about Le Chatelier's Principle when he posed these types of questions during lecture. Since the system will try to balance itself and keep itself at low energy, if you remove the product then the forward reaction will be favored. Leftover reactants are not efficient, so in th...

Daniel Yu 1E

So in one or two of his lectures, Dr. Lavelle mentioned the pH of water and how adding a small concentration of H+ ions, for example, wouldn't change the pH of the solution since it is significantly smaller than the already present 10^-7 [H+] in water. When are we supposed to use the water pH level ...

Daniel Yu 1E

Maya Pakulski 1D wrote: This might be a dumb question but you calculate all of these the same way right, with products/reactants?

Yes, although you might have to do some other calculations to get everything in the same units.

Daniel Yu 1E

It technically doesn't matter, at least for Test 1, the difference between bars and atm. It will result in different answers in different units because you use different R constants, but the answers should be interchangeable with a bit of conversion.

Daniel Yu 1E

Why is the activity of water equal to 1 when you are calculating the Kw with [H3O+][OH-]/[H2O]^2?

Daniel Yu 1E

The Q and K inequality is exactly that: an inequality. K is the ratio of the concentration of products and the concentration of reactants. Q is the exact same equation, [p]/[r]. Given a certain set of physical conditions, the K will always be the same number for a given reaction. This is because K i...

Daniel Yu 1E

The equilibrium will shift to whichever side has less moles. That way, the molecules take up less space and the pressure is minimized. I agree with this but I am not very clear on why this is. Why would balancing the moles result in less pressure? If you had .2 mol of Cl2 and it was undergoing a re...

Daniel Yu 1E

I can't figure out how to get the correct answer for part a) of this problem. Where did the 5.5 x 10^-6 come from?

Daniel Yu 1E

H2N group because it can become H3N, which means it is basic (takes H+ away and creates OH-). Just remember that NH3 is amphiprotic.

Daniel Yu 1E

How would you know that the coordinator for hydrated Al is 6? Most coordination complexes with first row metals want 6 coordinate covalent bonds with the metal. I think most coordination complexes in general tend to have 6, if they can. It has to do with the shape, octahedral. If Cu^2+ were surroun...

Daniel Yu 1E

The bases formed by metals in the first in second groups are strong bases. Therefore, they fully dissociate in water and don't affect pH. Basically, the conjugate acids of strong bases are nonreactive with water.

Daniel Yu 1E

Because the CH3 methyl group is a destabilizing group that makes the post-reaction anion (conjugate base) less stable.

Daniel Yu 1E

How can a solution with equal acidic and basic properties have a pH unequal to 7? Like we went over in lecture, how come some stoichiometric / equivalence points don't have a neutral pH?

Daniel Yu 1E

If you were to draw the CCl2H2 as a tetrahedral, you would see that the Chlorines were not opposite of each other, meaning their dipole moments wouldn't cancel. Remember the bond angles that we learned for tetrahedrals.

Daniel Yu 1E

I don't think there can a trend on the periodic table for isoelectronegativity since it's comparing the amount of electrons for different molecules. O^2- is isoelectric with Neon because they both have 10 electrons. In terms of atomic size in an isoelectric series, the more protons there are the sma...

Daniel Yu 1E

Alison Trinh 1A wrote:To further elaborate, Bronsted acids are considered proton donors. It is a Lewis acid if an electron pair is accepted. A Bronsted base is considered a proton receptor. A Lewis base is considered an electron pair donor.

So do acidic salts contain a bronsted acid or a conjugate acid?

Daniel Yu 1E

Conceptually, how are Ka and Kb related to Kw? High Ka means strong acid and low Kb means weak base and vice versa, but why do they have to balance out to be equal to Kw?

Daniel Yu 1E

If an atom is said to be amphiprotic then that means that the atom has the ability to donate or accept protons whereas amphoteric is the ability of an atom to act as an acid or base. I'm confused about the difference here between amphiprotic and amphoteric. Bronsted acids are substances that can do...

Daniel Yu 1E

Kehlin Hayes 4C wrote:Ligands donate electron pairs

So are all ligands Lewis Bases?

Daniel Yu 1E

If a salt contains a conjugate acid, how will it react in water? Will it raise the pH and make the solution more basic because the acid takes a hydrogen ion?

Daniel Yu 1E

Bronsted acid: a species that donates a proton Bronsted base: a species that accepts a proton Conjugate base: what is left over after an acid donates a proton Conjugate acid: what is formed when a base accepts a proton Bronsted acids have conjugate bases and Bronsted bases have conjugate acids. In ...

Daniel Yu 1E

Bond strength helps to determine how easily an acid gives up a hydrogen ion. H-F (strong, short bond) is a weaker acid than H--I (long, weaker bond) because it doesn't give up its hydrogen atom as easily.

Daniel Yu 1E

Based on the Brønsted–Lowry acid–base theory, a conjugate acid is formed by a base receiving a proton. A conjugate base is the opposite - it is the base formed when the acid donates a proton. So can a molecule become both a conjugate acid and base? If it gains a proton does that make it a conjugate...

Daniel Yu 1E

Higher molar mass means more protons and neutrons. More protons and neutrons means more electrons. More electrons means more movement of electrons. More movement of electrons means a potential for a greater disparity in the distribution of electrons-- a stronger dipole moment. Stronger dipole moment...

Daniel Yu 1E

Dipole-Dipole is a describing two molecules, each with an individual dipole, interacting. Thus it is an intermolecular force. A dipole itself is a separation of charge in a molecule, resulting from an uneven distribution of electrons.

Daniel Yu 1E

Coordinate covalent bonds relates to Lewis acids and bases because they can bond to form a coordinate covalent bond. A Lewis acid is missing a full octet since it has an empty orbital and a Lewis base has a free lone pair to share, thus forming a coordinate covalent bond. A metal ion binding to a ch...

Daniel Yu 1E

Heisenberg's Indeterminacy principle states that we cannot know the exact velocity and position of an object at any given time, even in theory. This is why we have electron density regions.

Daniel Yu 1E

Octet expansion only occurs when a period 3 element utilizes a d orbital.

Daniel Yu 1E

Ground state means that none of the electrons are excited. They included that in the test to make sure there was no misunderstanding about how to write the electron configuration of the atoms they listed. All the electrons are in their lowest energy state.

Daniel Yu 1E

I think the size of the atom also matters, as do lone pairs and electronegativity.

Daniel Yu 1E

Is Ep the measure of the strength of the bond or how much energy it takes to break the bond or are they the same thing?

Daniel Yu 1E

Will test 2 contain problems verbatim from the homework like the midterm did?

Daniel Yu 1E

Do formal charges give any information on the resonance of a molecule?

Daniel Yu 1E

So does this mean that the oxidation number is basically the sum of the formal charges of all atoms within a molecule?

Daniel Yu 1E

Formal charge is what you calculate with your FC= V - (LP + B/2) formula and it helps you understand the distribution of charge when making bonds by showing the gain or loss of electrons for that atom. Partial charge is talking more about electron distribution in the molecule as a whole, generally a...

Daniel Yu 1E

What do you do for exceptions? Such as in an atom consisting of N and O, which would be the central atom? O technically has the lower ionization energy than N. Does the number of desired bonds matter when considering the central atom more than the electronegativity?

Daniel Yu 1E

When calculating formal charge, you would count each e- in lone pairs as individual e- but shared e- as a whole because their charge is not solely distributed to one atom.

Daniel Yu 1E

What is an oxidation number and how is it calculated? Is it just the charge of the molecule as an anion?

Daniel Yu 1E

A dipole moment is what is caused by a difference in electronegativity. Thus, unless it is a bond between two identical atoms, a dipole moment will exist. Dipole moments are defined as an unequal sharing of electrons, which results in slight differences in charge within the molecule. An instantaneou...

Daniel Yu 1E

I think in Chemistry it's pointing toward the δ- but in physics it points toward the δ+.

Daniel Yu 1E

What about drawing like curves and circles? I've seen those on the internet.

Daniel Yu 1E

Can someone explain metals a bit? About the bonds they form and their lowest energy state. Especially those in the lower rows of the periodic table I don't really understand.

Daniel Yu 1E

What did you all put as your response to #8 part a on the Midterm Review?
Q: Write an equation using words only that captures the conservation of energy in the photoelectric effect. Describe the conceptual change that arose from the photoelectric experiment and discuss how intensity plays a role.

Daniel Yu 1E

Where can I find the review problems? Also, how do I download the problems?

Chem Mod: Please simply scroll up and read the post! Everything you've asked is there.

Daniel Yu 1E

Will we need to know how to use Shrodinger's Equation on the test or just understand it conceptually, like what an allowed energy level and a not allowed energy level looks like?

Daniel Yu 1E

Z is the measure of the number of protons right? The radius of a helium atom is smaller than that of a hydrogen atom because there is a greater positive charge pulling the electrons tighter. Maybe that's what the book is trying to get at?

Daniel Yu 1E

So what exactly is the relationship between Schrodinger's Equation, wave functions, and orbitals?

Daniel Yu 1E

If you rounded your sig figs/ used a different periodic table and showed that through your work on a problem that you got incorrect because of rounding would you lose points?

Daniel Yu 1E

Is there a specific way that we should be showing our work to maximize partial credit like showing unit conversions and stuff? Also, since Dr. Lavelle didn't explicitly go over Sig Figs how impactful are they going to be on the test grading?

Daniel Yu 1E

Electronegativity is affected by the amount of valence electrons and the amount of orbitals. The more orbitals there are, the farther the electrons are from the positive nucleus. And since elements want to exist in their ideal state, they want to get as close as the a filled outer shell. That means ...

Daniel Yu 1E

Ionic bonds are stronger than covalent bonds. However, in water, ionic bonds are weaker. This is why you might hear that covalent bonds are stronger in your biology classes.

Daniel Yu 1E

Increasing the amplitude will increase the intensity, but it does not affect the number of protons.

Daniel Yu 1E

Wavelike properties is talking about things like amplitude, frequency, and wavelength. Only particles with small enough mass will exhibit wavelike properties, which can be proven by DeBroglie's equation. Things with wavelengths less than 10^-15m are widely considered to not exhibit wavelike properti...

Daniel Yu 1E

It means super-duper cold. 0 Kelvin, or absolute zero, is a temperature that we can never actually reach (limit).

Daniel Yu 1E

I think generally converting moles to grams before you have determined the limiting reactant makes the equation a little more complicated and leaves more room for error. Maybe in an equation where you can't determine the moles for every singe element, using grams would be the easiest method. E.g. if...

Daniel Yu 1E

Aside from YouTube channels and videos on that platform, Bruincast is also very valuable resource. If you learn best through video, maybe watching some lectures from our UCLA professors will be a good way to review.

Daniel Yu 1E

For test 1, I've been told that as long as you do the homework, go to class, and attend discussion, you will succeed :) But as far as I know, no homework questions will be there verbatim on test 1. You won't be tested on the stuff we learned in lecture today about Quantum Mechanics and light. Don't ...

Daniel Yu 1E

The vectors are just there to indicate the direction and intensity of the fields as they travel. I think the answer to the second part of this question is probably a lot more complicated than what we would be learning in class. From what I've seen (very little), the magnetic field and electric field...

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