CHEMISTRY COMMUNITY

David Zhou 1L

For this though, couldn't the Fe be oxidized into Fe²⁺? Why does it have to be Fe²⁺ oxidized into Fe³⁺?

David Zhou 1L

Remember that multiplying my L/mol is the same thing as dividing by M, or multiplying by M^-1.

David Zhou 1L

Rate laws are determined experimentally generally rather than by analyzing the chemical equation, so it's often a difficult task to figure out the specific mechanism for a specific rate law.

David Zhou 1L

Since there can't be a negative amount of products or reactants that exists in a chemical equilibrium, the rate constant must be positive.

David Zhou 1L

It's the rate that's unique to that reaction, separate from the coefficients you multiply to get to the reaction rates with regards to species in the reaction.

David Zhou 1L

Looking over the hw problems and chapter outlines will always give a good overview of what we need to know.

David Zhou 1L

Any idea how those work though? Does it have something to do with the reduction potentials of different ions?

David Zhou 1L

This common type of process is called electroplating, in case you wanted to read more about it!

David Zhou 1L

Know that Cv = 3/2 *R, because the v and the 3 make a heart! <3

David Zhou 1L

It's always useful to be very familiar with all the equations you might use, so that you don't have to spend time flipping to the first page and searching for them!

David Zhou 1L

It's more stable because the electrons are delocalized.

David Zhou 1L

Problems will supply you with the constant external pressure if that's the case. Often times that value is 1 atm.

David Zhou 1L

Many of the reaction pathways that are taught in biology are long chains of these connected reactions, like in glycolysis, the Krebs/Citric acid cycle, and the Calvin cycle. These metabolic pathways are crucial to the survival of an enormous number of organisms, and are happening all the time.

David Zhou 1L

Infinitesimal doesn't necessarily have to do with time, it's just denoting a mathematical value smaller than anything measurable. A change that's infinitesimal can refer to time, pressure, volume, temperature, or anything you want to assign it to since it's unitless.

David Zhou 1L

It doesn't take too long to learn it, it's just the combination of a couple equations for delta G that are given to you.

David Zhou 1L

Isothermal, reversible processes would be an example of this.

David Zhou 1L

It's just algebraic manipulation; flipping the numerator and denominator will give you the negative log value.

David Zhou 1L

Gases spread to fill the entire container that they're housed in, unlike liquids and solids. So if the volume of the vessel they're in is .75 L, that's their volume.

David Zhou 1L

Attoseconds are much faster than what's controllable by a stopped syringe - they're 10^-18 seconds. That's a unit of time that's completely unheard of in science, except at quantum level.

David Zhou 1L

Activation energy has to do with kinetics. Thermodynamics is concerned with the difference in internal energy before and after the reaction, which is a different concept, and mathematical value from the activation energy for the same reaction.

David Zhou 1L

Why is reaction rate given the units M/s? Why not something like moles/s or g/s? Or even %mass/s? Is this just an arbitrary decision or is there some deeper meaning baked into this definition?

David Zhou 1L

What do you do when you find a questionable amount of sulfur, tungsten, and silver in your backpack?

Keep calm and SWAg on!!!!!!!11!!!11!!!!!

-- Andrew Nguyen

David Zhou 1L

If you're not a part of the solution, you're a part of the precipitate.

David Zhou 1L

It's generally better to use more sig figs in your constants so your final answer is more accurate, but if the number of sig figs are low (<3) for any other value that you plug into the problem, then you'll be fine as well since your final answer won't have a lot of sig figs anyways.

David Zhou 1L

Is enthalpy a state function?

David Zhou 1L

Bonds in the cyclopentane can't rotate freely in any way since that would break the ring. However, in 1-pentene, the molecules aren't bound into a shape, and are relatively free to rotate while still maintaining the same structure.

David Zhou 1L

Also, with q/T, if there's any heat transfer, there must be some change in entropy.

David Zhou 1L

9.99 doesn't have a part b, maybe you were referring to 101?

David Zhou 1L

Intermolecular forces also play a large role in determining heat capacity; for example, water has a pretty high specific heat due to hydrogen bonding between the atoms. This is somewhat related to molecular complexity.

David Zhou 1L

It's convenient also to think of reversible processes as the ideal situation; the system should be thermally insulated from its surroundings.

David Zhou 1L

What's the difference between Gibbs Free Energy and Potential Energy? Is there a general equation for Potential Energy? In physics, $\Delta$ U = mgh is used very often to represent it, so I'm curious if there's any unifying equation for Potential Energy...

David Zhou 1L

Heat transfer always involves something getting hotter and another thing getting colder so that the first law of thermodynamics is obeyed and the universe stays functioning. When water turns into ice, it's getting colder, and so the surroundings must get warmer to balance out the heat transfer. When...

David Zhou 1L

1 atm = 1.01325 bar
1 bar = 100,000 Pa

For most questions that don't require extremely accurate measurements, though, there's not enough difference to necessitate this distinction.

David Zhou 1L

Also, if you're ever unable to find the enthalpy value or any other kind of experimental value, you can always Google it. There's another earlier homework problem in which you needed to use the specific heat capacity of Cu, and for that I just Ok Google'd it because that's really the fastest way to ...

David Zhou 1L

I just think of the exhaust pipes and the exhaust fumes that come out of the car; instantly then it becomes obvious that the car engine is an open system.

David Zhou 1L

For the purposes of doing HW and acing tests, I don't think this is very pertinent to the scope of this class. However, if you're interested, take a look at these links:

https://en.wikipedia.org/wiki/Superheating
https://en.wikipedia.org/wiki/Supercooling

David Zhou 1L

So long as the problem doesn't tell you to disregard the container the water is in, it's a good idea to incorporate the given mass of the container into the problem-solving process. Everything has a specific heat capacity; in fact, glass has a higher specific heat capacity than copper. Copper: 0.385...

David Zhou 1L

It's also of note that standard enthalpy refers to when the pressure is at 1 atm and 25 degrees C (298 K).

David Zhou 1L

No gas behaves completely like an ideal gas; however, in many situations, especially those with relatively low pressure and small gas particles, gases behave close enough to ideal gas behavior that the ideal gas law is a very good approximation for the situation.

David Zhou 1L

Isothermal expansion is when a system remains at the same temperature. It's in contact with a heat reservoir like a water bath, which keeps the temperature constant, and this process is done slowly enough that the system can continually adjust to maintain the right temperature.

David Zhou 1L

The methyl group of acetic acid has greater electron donating power than the single H in formic acid, meaning it destabilizes the carboxylate anion - the anion already has a negative charge on it, and so the slightly higher electron donating power of the methyl group repels against that.

David Zhou 1L

Wouldn't the answer be something electronegativity of the oxygens, because they want to keep hold of their electron pairs? I still don't understand what's going on here.

David Zhou 1L

Then will we have to know solubility rules at any point? Like memorizing how soluble nitrates, sulfates, carbonates, etc. are?

David Zhou 1L

But the actual amount of substance has in fact increased if you define the amount of substance as the number of molecules. The number of atoms doesn't change because it's a closed container, but because some of the gas molecules break down, there is an increase in the number of molecules in the cont...

David Zhou 1L

Increasing the concentration of gases also decreases the ideal nature of gases; this also causes inter-molecular forces to become more of a factor.

David Zhou 1L

Yes, since the s orbital can only hold two electrons due to the Pauli Exclusion Principle, only the first bond will be a sigma bond.

David Zhou 1L

Elements that are more electronegative will attract the electrons more so than less electronegative elements. Therefore, the single unpaired electron will tend to be on the less electronegative element, since the more electronegative elements will likely attract full valence shells. Also, it's alway...

David Zhou 1L

Does this mean that radicals can also have resonance structures, and thus have delocalized electrons?

David Zhou 1L

Also, shorter bond lengths will result from smaller ions bonding together.

In the example with HF<HCl<HI, because atomic radii increase down the periodic table, the larger the halogen, the longer the bond length.

David Zhou 1L

Due to Hund's Rule, the electron configuration isn't the ground state. One of the electrons in the single filled 2p orbital should move to an empty p-orbital, with spin up or down, whichever the one remaining in the first orbital is oriented in; they should be parallel. Excited doesn't have to mean ...

David Zhou 1L

In the textbook on page 37, it states that at "l = 0, there is no orbital angular momentum to fling the electron away from the nucleus." This, of course, corresponds to the s-orbital, which means that the probability density of s-orbitals is closer to the nucleus than other orbitals. Then,...

David Zhou 1L

Lanthanides and Actinides tend to be confusing because they're usually shown all on their own at the bottom, seemingly separate from the rest of the periodic table when in reality the periodic table is just made that way so that it has a nice aspect ratio that can be easily printed/copied. If you ta...

David Zhou 1L

If it's I3-, it's because of the 3 lone pairs in the middle and 2 bonds, making it trigonal bipyramidal. The 3 lone pairs around the central I atom make it linear.

David Zhou 1L

Particles are thought of as point sources of mass. In math, particularly geometry and calculus, you've probably learned that points are defined as a very specific location on a line or on a plane or surface. They are of zero dimensions and thus have no length, area, or volume; they are just that ver...

David Zhou 1L

Electromagnetic radiation can't have a negative frequency because that would mean it oscillates negative times a second, which doesn't make sense; the least it could oscillate is zero times a second. Frequency isn't like velocity, where a negative sign implies movement in the opposite direction, it'...

David Zhou 1L

Also for the purpose of problem-solving in this unit, it's extremely helpful to keep the kg*(m^2/s^2) definition of the Joule in mind in order to make error checking much easier. If at the end of a problem you see that your units are wrong, you know somewhere along the line something went wrong. For...

David Zhou 1L

What does it intuitively mean when we find the wavelength of large everyday objects? For example, in problem 1.35, what does it really mean when we compare the wavelengths of a 60kg person vs an 80kg person? Or if we calculate the wavelength of a baseball traveling 92 mph in problem 1.39? Do these h...

David Zhou 1L

Oops sorry guys! Wrong topic... I'll move this over.

David Zhou 1L

What does it intuitively mean when we find the wavelength of large everyday objects? For example, in problem 1.35, what does it really mean when we compare the wavelengths of a 60kg person vs an 80kg person? Or if we calculate the wavelength of a baseball traveling 92 mph in problem 1.39? Do these h...

David Zhou 1L

I've found there's no need at all for a complicated mnemonic to memorize which gases form diatomic molecules; that just makes things harder, because you have to recall the entire string of elements in your word or phrase to pick out the single one you need. To me, it's far easier to just look at the...

David Zhou 1L

Incomplete combustion just means that instead of your reactant, in this case heptane gas, reacting with oxygen gas to form carbon dioxide and water, it forms carbon monoxide and water. Complete combustion skeleton equation: reactant + O2 --> CO2 + H2O Incomplete combustion skeleton equation: reactan...

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