CHEMISTRY COMMUNITY

Annalyn Diaz 1J

I would probably also know any industrial and and environmental examples that Dr. Lavelle has gone over in class just in case. I think it's safe to assume there might be a small question on them.

Annalyn Diaz 1J

Additionally, catalysts speed up the rate of reaction by lowering the activation energy, which changes the reaction mechanism. Although this occurs, adding a catalyst doesn't affect reaction enthalpy or the equilibrium position and neither does it alter reaction yields at equilibrium.

Annalyn Diaz 1J

How do homogeneous catalysts play a role in the formation of ozone in the lower atmosphere?

Annalyn Diaz 1J

Why is the straight-line plot for second-order reactions have a positive slope rather than a negative one like zero-order and first-order reactions?

Annalyn Diaz 1J

Why is it that the half-life of a first order reaction doesn't depend on initial concentration?

Annalyn Diaz 1J

To add on, we only consider reactants with the integrated rate law because if we consider products, we also have to keep into account the reverse reaction, which complicates the math. We only consider reactants to "keep the math simple".

Annalyn Diaz 1J

The 0.0592 comes from changing the natural log in the original equation ( E=E(standard)-(RT/nF)lnQ ) to log base 10, which yields E=E(standard)-(2.303RT/nF)logQ. At standard temperature (298K), 2.303RT/F = 0.0592, which gives you the representation of the Nernst equation that first mentioned, E = E ...

Annalyn Diaz 1J

Why is determining the order of a reaction important?

Annalyn Diaz 1J

Michelle Lee 2E wrote:What if the n value we calculate using the method of initial rates was not a whole number but some weird decimal?

Dr. Lavelle also said in lecture that he wouldn't give us any fractional orders or anything that you couldn't round to a whole number.

Annalyn Diaz 1J

Why is recharging a battery considered to be an unfavorable reaction?

Annalyn Diaz 1J

Basically the Van’t Hoff equation is used to calculate the equilibrium constant when the temperature is different as long as you know dH. It shows the temperature dependence of K, the equilibrium constant.

Annalyn Diaz 1J

I believe that Gibbs free energy is 0 at phase changes because there’s an equilibrium that exists during that phase change and dG =0 at equilibrium.

Annalyn Diaz 1J

Why is Gibbs free energy 0 at equilibrium?

Annalyn Diaz 1J

Also in relation to the change in internal energy, heat under constant pressure is dH, which could help with the manipulation of dU=q+w.

Annalyn Diaz 1J

It also tells us the free energy of a system at any point in time. The fact that it a state function makes it easier to calculate as you would with dH° and dS°.

Annalyn Diaz 1J

I'm not entirely sure, but it may be negative because the question is asking how body heat affects the entropy in your surroundings?

Annalyn Diaz 1J

I understand that in a closed system, energy can be exchanged with its surroundings but matter cannot. If this is the case, why is it that in a closed system, q=0 is always true? Isn't heat a form of energy? Just some clarification for question 4B.9 in the 7th edition of the textbook.

Annalyn Diaz 1J

To address the spontaneity, think of the example he mentioned about the boulder on the mountain; it will roll down the side by itself (spontaneously), but it won't roll up the mountain itself. Energy through the form of work is needed to push that boulder up the mountain. If something can occur by i...

Annalyn Diaz 1J

I understand Avogadro’s number can be used when calculating degeneracy, but I’m confused as to when we would use it. Can someone clarify that please?

Annalyn Diaz 1J

Why is the universe considered an isolated system?

Annalyn Diaz 1J

The integral equation is used when calculating reversible expansion done by a gas, since in this case it is set up so that the change in pressure occurs in small increments till it reaches the volume it should be at in equilibrium. In reversible expansion, the external and internal pressures are ne...

Annalyn Diaz 1J

Additionally in a closed system, internal energy relates to work in this equation:

delta U = q + w

Annalyn Diaz 1J

I know that the standard state for a gas is 1atm. How do you determine standard states of something other than a gas, such as a liquid or solid, or an element?

Annalyn Diaz 1J

In lecture, Dr. Lavelle mentioned that using bind enthalpies is the least accurate method. Why is that so?

Annalyn Diaz 1J

I don't think there will be any video modules on thermochemistry. I believe that the video modules stop after chemical equilibrium.

Annalyn Diaz 1J

Le Chatelier’s Principle is applied to equilibrium reactions in trying to determine the direction in which a reaction will go when changes are introduced to the system.

Annalyn Diaz 1J

As mentioned above, you would be able to calculate Q in the same manner in which K is calculated. The only difference in its application is that Q represents any point in the reaction that is not at equilibrium.

Annalyn Diaz 1J

Is there a reason why we can “bypass” the quadratic equation when calculating for x with weak acids?

Annalyn Diaz 1J

I know that the combined gas law has more restrictions than the ideal gas law, such as the fact that moles (n) has to stay constant. In this sense, this is why the ideal gas law is used more often in regards to equilibrium.

Annalyn Diaz 1J

I understand that K is often used to represent either Kc or Kp and that they are found in the same manner. Why do we use Kp for gases when we could also use Kc? Is one more preferred than the other?

Annalyn Diaz 1J

It’s to my belief that any liquid or solid in its pure form is negligible in calculating the equilibrium constant because their change in concentration during the equilibrium reaction is so small that it’s not counted.

Annalyn Diaz 1J

For Gail's review session she recommended that we do know both just in case.

The chemical formula of EN is C2H8N2.
The chemical formula of EDTA is C10H16N2O8.

Annalyn Diaz 1J

I’ve seen that Kw=Ka*Kb, but I’ve also seen Kw=10^-14. Can someone clarify that concept for me? Thanks.

Annalyn Diaz 1J

What is the importance/function of polyprotic acids and bases?

Annalyn Diaz 1J

Dr. Lavelle said something about nitrogen in the compound needing a lone pair or else it can’t act as a base. Can someone remind me why that lone pair is necessary?

Annalyn Diaz 1J

To add on, because hemoglobin has 4 myoglobin-like molecules, it therefore has four times the carrying capacity of myoglobin, which is very important for the transport of oxygen in blood.

Annalyn Diaz 1J

I believe that transition metals can have multiple oxidation states because of their electrons in the 3d orbitals.

Annalyn Diaz 1J

Quick question, are we going to have to know in-depth about radicals or just know a basic application of it for the final?

Annalyn Diaz 1J

I would have to agree, having the most stable molecule possible would be the priority over the octet rule (especially since the octet rule becomes violated in and after period3 due to expanded octets) although for the most part having the octet for elements before period 3 does contribute to the ove...

Annalyn Diaz 1J

when (if) this happens how can we differentiate between the two characters? I think Dr. Lavelle mentioned a rough guideline based on the difference in electronegativity: if difference is >2, ionic character if difference is <1.5,covalent character It's tougher to determine the character if the elec...

Annalyn Diaz 1J

I believe that for the most part what you are saying is correct but I’ll clarify just in case. Lone pair electrons do repel the other electrons on the substituent atoms, which cause the bond angle to be slightly greater than what’s normally expected; in the same case, as a result, the bond angle bet...

Annalyn Diaz 1J

It’s pretty easy to see the trends when it comes to VSEPR models with three or even four bonding regions (lone pairs included) but why does having five bonding regions make these trends harder to see? Or rather, why does having 5 domains somehow break the trend?

Annalyn Diaz 1J

So I understand that in drawing VSEPR diagrams (or even just a 2D representation with Lewis structures) we use the wedges to represent distance from the central atom. For my question, I was confused on which type of wedge indicated a further distance: the completely shaded or the hatched wedges?

Annalyn Diaz 1J

Don’t quote me on this, but I believe that if the shape is tetrahedral, the bond angle should be 109.5° for the most part.

Annalyn Diaz 1J

There was a question on the midterm about determining the bond length for N-O in NO2, given that the a single bond is 140Å(?) and a double bond is 120Å(?) (I don’t quite remember the units). Any clue on how to determine that?

Annalyn Diaz 1J

I believe that having a higher polarity increases the chances of the distortion of electrons because the electrons from one atom are being pulled/attracted more strongly by another atom. In a sense, I think having a larger atomic radius would also increase the chances of electron distortion.

Annalyn Diaz 1J

I think the central charge only contributes to the overall net charge of the atom, so as long as the charge of the central atom in addition to the other atoms equal the overall charge, it'll be fine because that's what you're looking for.

Annalyn Diaz 1J

I remember from high school chemistry that double bonds are shorter than single bonds. If that's the case, could someone explain why the bond lengths in resonance structures are experimentally the same bond length? I didn't quite get that.

Annalyn Diaz 1J

I would think that the first four elements on the periodic table don't need an octet because they would rather lose electrons than gain them. It would be very difficult and unstable if they were to somehow try to get an octet.

Annalyn Diaz 1J

You can write the shorthand configuration of elements by going back to the nearest noble gas before it (in atomic number), then account for the electrons after that noble gas. Say, for example, you have Arsenic (As). The shorthand would be As: [Ar]4s^2 3d^10 4p^3.

Annalyn Diaz 1J

Although both are correct, I believe that Dr. Lavelle prefers 1s^2 2s^2 2px^1 2py^1 over the 1s^2 2s^2 2p^2 because it gives better insight on whether or not the electrons are paired.

Annalyn Diaz 1J

Although I'm not entirely sure which SPECIFIC orbitals the f subshell would have, I do know that it should have 7 orbitals.
(s=1 orbital, p=3 orbitals, d=5 orbitals, f=7 orbitals)

Annalyn Diaz 1J

This has become a string of questions for now, but to (hopefully) answer most of the questions, one of the UAs told me that Dr. Lavelle prefers that we use the En = -hR/n^2 equation over the other one because it makes more sense conceptually. In this manner, we won't learn the other version but I th...

Annalyn Diaz 1J

I understand that the two are the same, but I don't quite remember why Dr. Lavelle prefers "indeterminacy" over "uncertainty"... Can someone clarify that really quick for me?

Annalyn Diaz 1J

During lecture Dr. Lavelle said that the De Broglie equation only works if the particles have “rest mass”. Can someone clarify what that means?

Annalyn Diaz 1J

I believe the original problem (part (b)) asked for the final wavelength to be in picometers, which is 10^-12. Hope that clears it up!

Annalyn Diaz 1J

The work function is also called the "threshold energy", so watch for that too! The way I remember how the threshold energy function is by relating it in my mind as something similar to "activation energy" because in both cases, if the minimum requirement is not met, then nothing...

Annalyn Diaz 1J

To add on, don't forget that the Balmer series represents the visible region and that the Lyman series represents the ultraviolet region!

Annalyn Diaz 1J

Per Dr. Lavelle, over time you'll pick up how to name compounds through working through more problems just like this. To add further elaborate on the post above: -ite : used when the same compound has lesser amount of oxygen (ex. phosphite, PO3) -ate: used when the same compound has the larger amoun...

Annalyn Diaz 1J

For an empirical formula, the numbers must be whole numbers, not numbers like 1.33 or 2.5, etc. In such case that you don't get a whole number, you would multiply that by another number to make it whole. But to address your question regarding the threshold for rounding, I believe Dr. Lavelle mention...

Annalyn Diaz 1J

From my understanding, I think you are correct in regards to finding the formula units. I believe you would have to find the amount of moles first, then multiply by Avogadro's number.

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