CHEMISTRY COMMUNITY

Jacob Puchalski 1G

What's the difference between galvanic and electrolytic cells?

Jacob Puchalski 1G

The third law of thermodynamics is basically as the temperature reaches absolute zero (0 Kelvin) then entropy will also decrease to zero.

Jacob Puchalski 1G

Why do we graph ln[A] against time instead of just [A] against time?

Jacob Puchalski 1G

I'd think that if they propose certain mechanisms then one of them would have to match the given rate law?

Jacob Puchalski 1G

What's an example of a zero order reaction? I still don't completely understand how they would work

Jacob Puchalski 1G

I think so yeah

Jacob Puchalski 1G

We work with initial reaction rates because they're more clear and easier to measure.

Jacob Puchalski 1G

Thermodynamics tells us whether the forward or reverse process is favored. Kinetics touches more on the energy during the reaction itself.

Jacob Puchalski 1G

Basically the activation energy (the hump part of the graph) is high enough so that under normal conditions the reaction won't proceed.

Jacob Puchalski 1G

it tells you how the concentration of the reactants affects the rate.

Jacob Puchalski 1G

It has a linear rate

Jacob Puchalski 1G

I think a galvanic cell just has a negative Gibbs free energy value.

Jacob Puchalski 1G

If they occur in basic solutions, the steps are the same, except for when you balance one side with H+ you need to balance both sides with the same amount of OH-, so that there is H20 on one side and OH- on the other side.

Jacob Puchalski 1G

You use a single line to differentiate between phases. If they're both in the same phase then you list them using a comma.

Jacob Puchalski 1G

I think we might be provided with half reactions but also it would be good to practice coming up with them on our own?

Jacob Puchalski 1G

I also keep getting the same as you so it might be an error

Jacob Puchalski 1G

Oxidation is the transfer of electrons in a reaction; the oxidizing agent is the reactant that is reduced.

Jacob Puchalski 1G

If a reactant in one reaction is the same as a product in the other then you can cancel them both. For example if 5O2 is a reactant in the first and 3O2 is a product in the second then you can subtract the difference so that in the final reaction there is 2O2 on the reactant side.

Jacob Puchalski 1G

I think the point was to relate K to the temperature? I might be wrong

Jacob Puchalski 1G

The standard entropy of a reaction is found in lab conditions.

Jacob Puchalski 1G

It's just easier to understand what's happening; you don't really need to if you don't want to.

Jacob Puchalski 1G

I'm pretty sure the heat released is measured by the calorimeter as the surroundings rather than the system. So since it's exothermic, Q is negative and heat is released into the surroundings, raising the temperature.

Jacob Puchalski 1G

Since they give you the specific amount of moles then you're able to find the specific reaction enthalpy.

Jacob Puchalski 1G

If F2 dissociates more then Cl2 would be more stable

Jacob Puchalski 1G

It's mentioned that the ice took 10.5 (10 hours and 30 minutes) hours to reach 5.00 degrees. If it takes 30 minutes for water to increase five degrees in temperature, it's safe to say that the ice took ten hours to melt, and as water also took thirty minutes to reach 5.00 degrees.

Jacob Puchalski 1G

I'm sure that if that's something we need on the test then they'll provide it

Jacob Puchalski 1G

Pretty sure the manual's solution is correct. Did you use w=-nRTln(V2/V1)? Or maybe make sure you're using the right units?

Jacob Puchalski 1G

With gas you can compress or expand the volume which changes the concentration, and with aqueous solutions the concentration of dissolved molecules can also increase or decrease. However, for the most part it's extremely difficult for the concentration of solids and liquids to change so it remains c...

Jacob Puchalski 1G

I'm pretty sure there's technically no such thing as a completely isolated system. However, some experimental systems are close enough to be considered isolated since the changes are negligible.

Jacob Puchalski 1G

I think what the question is saying is that the technician meant to produce 200 ml of a .025M HCl solution, but since he accidentally used a 250mL flask he added 50mL more water than he meant to. So he didn't actually produce a .025M HCl solution. If he made it right you would just find -log(.025) =...

Jacob Puchalski 1G

To find Ka, you find the concentration of the products and divide that by the concentration of the reactants. They gave you .10 M for the initial concentration of HF. pH is -log[H3O+] = 2.63, so [H3O+] = 2.34 x 10^-3. Since one mole of HF dissociates into one mole of H30+ and one mole of F-, you kno...

Jacob Puchalski 1G

If the acid or base isn't completely dissociated then it's probably weak.

Jacob Puchalski 1G

Yeah you'd include it if it was a gas.

Jacob Puchalski 1G

I think that in general the more complex a molecule is the higher the capacity will be, because more energy would go into the bonds. So I think NO2 would have a higher capacity?

Jacob Puchalski 1G

It's the ideal gas law so you just use it for gases.

Jacob Puchalski 1G

It measures the heat of chemical reactions

Jacob Puchalski 1G

For part a, since M is moles per liter, the [OH-] of the original solution would be 100 times stronger, since the 5.0 mL solution was diluted to 500 mL. So the original [OH-] would be 18M. For part b, you use the equation you have to convert the 18M OH- to grams of Na2O. 18 mol/L x .2 L x 1 mol Na2O...

Jacob Puchalski 1G

a) pH = 5.00
b) pH = 5.63
c) pH = 2.72
d) pH = 8.97

Jacob Puchalski 1G

So ultimately we're trying to get from pH to pKb. Since propylamine is a base we know it's best to deal in terms of OH-, so we should convert the pH to pOH (2.14). Since pOH is just -log[OH-], we can find [OH-] through 10^-2.14, which comes out to be 7.2 x 10^-3. We know that Kb is the molarity of t...

Jacob Puchalski 1G

So I think you might have tried to find the concentration of H30+ by setting up the equation x^2/.2 = Ka? I don't think that would work out because the reactant is a base? If you wanted to find and use the concentration of H30+, you would need to first find the concentration of OH- by using Kb. Once...

Jacob Puchalski 1G

I'm pretty sure it's just a typo, and should just be in the denominator. If you carry out the problem as normal without the typo, you get the same answer it provides.

Jacob Puchalski 1G

Opposite charges attract!

Jacob Puchalski 1G

The reaction quotient is the proportion of the molarity of the products to the reactants at any given time of the reaction. It's pretty much the same as Kc and Kp but those two are measured specifically at equilibrium.

Jacob Puchalski 1G

R is a constant used in the ideal gas law, 8.314 J/(K.mol)

Jacob Puchalski 1G

Not sure which is the default but 1 bar = 10^5 Pa (1 kilopascal is 1,000 pascals).

Jacob Puchalski 1G

I think what you're talking about is whether the reaction shifts left or right? If the volume decreases and more moles of gas are added to the reactants, then the reaction shifts right. If the volume decreases and more moles of gas are added to the products, then the reaction shifts left.

Jacob Puchalski 1G

Yeah I think it could be bidentate

Jacob Puchalski 1G

Water can act as an acid in the presence of a base, and can act as a base in the presence of an acid.

Jacob Puchalski 1G

The pH scale is a log scale, so if you reduce the molar concentration to .1, or 10% of the original concentration then the resulting pH will raise by 1; -Log(.1) = 1. So if molarity of HCl is reduced to 12% of the original concentration, then -log(.12) = .92. So all you need to know is the differenc...

Jacob Puchalski 1G

I think it's just that polydentate ligands happen to form a chelate with the central atom.

Jacob Puchalski 1G

I'm pretty sure the pi bonds in double and triple bonds aren't hybridized.

Jacob Puchalski 1G

For a dipole bond to be considered a hydrogen bond, does the hydrogen atom have to be both bonded to a N, O, or F atom within the same molecule, and then form the hydrogen bond itself with a N, O, or F atom with a lone pair in another molecule?

Jacob Puchalski 1G

Yep. Nonpolar molecules could have dipole moments as well that happen to cancel each other out.

Jacob Puchalski 1G

I would think so because they make kind of a big difference in many cases.

Jacob Puchalski 1G

At what point is an acid (or base) weak or solid? Where do you draw the line?

Jacob Puchalski 1G

I think either would be fine since they're both correct.

Jacob Puchalski 1G

Acids release H+ ions in water, while bases release OH- ions in water.

Jacob Puchalski 1G

In lecture today Dr. Lavelle mentioned something about the prefixes bis-, tris-, tetrakis-, and pentakis-... can someone explain what he was talking about?

Jacob Puchalski 1G

What's the difference between a Lewis and Bronsted acid and base?

Jacob Puchalski 1G

I think it depends on your TA but you could probably just turn it in the week after

Jacob Puchalski 1G

I'm pretty sure it's just a molecule attached to a central metal ion.

Jacob Puchalski 1G

It's the central metal atom and the ligands attached to it.

Jacob Puchalski 1G

The Be atom is central, forming a 180 degree angle with the two bonded C atoms. But there are also three H atoms bonded to each C atom. Because of this there are four regions of e- density around the C atoms, so they are the center of a tetrahedral structure. The structure of the entire molecule is ...

Jacob Puchalski 1G

I'm pretty sure there should be two lone pairs on each of the bonded nitrogen atoms while the central nitrogen has a formal charge of +1. The overall charge is still -1 and that way the angle would be 180.

Jacob Puchalski 1G

Which type of bond is strongest, between polar, non-polar, and coordinate covalent bonds?

Jacob Puchalski 1G

I think he mentioned something about how since xenon has a low electronegativity, its electrons are more easily distorted by atoms with stronger electronegativity, like fluorine.

Jacob Puchalski 1G

Are there ever any exceptions to the VSEPR formula? Or can we always rely on it?

Jacob Puchalski 1G

Why is the SI unit of mass kg, not g?

Jacob Puchalski 1G

Why is that preferred?

Jacob Puchalski 1G

Do ionic bonds ever have dipole moments?

Jacob Puchalski 1G

When given the velocity, is the actual velocity important at all or just the change of velocity?

Jacob Puchalski 1G

When would we ever see l>3?

Jacob Puchalski 1G

Are atoms with expanded valence shells stable?

Jacob Puchalski 1G

Are partial charges found only in covalent bonds or also in ionic bonds?

Jacob Puchalski 1G

So basically, whether a bond is ionic or covalent depends on the difference of the electronegativities of the atoms involved?

Jacob Puchalski 1G

I asked my TA about the valence electrons of elements in the d-block, and the short answer was that any electrons in shells that aren't included in the noble gas notation would be considered valence electrons. So for Mn, after [Ar] there are seven electrons. Hope that helps

Jacob Puchalski 1G

Are we expected to know specific values or just the general trends?

Jacob Puchalski 1G

I'm pretty sure the energy shell is the principle quantum number (n), the orbital is the angular momentum quantum number (l), and the subshell is the magnetic quantum number (ml).

Jacob Puchalski 1G

Is it ever possible to have more than 8 valence electrons?

Jacob Puchalski 1G

So do most d-block elements have only a couple of valence electrons?

Jacob Puchalski 1G

Are we going to need to know the chemical formulas of compounds in order to create the lewis structure, or will they be given?

Jacob Puchalski 1G

Are there any exceptions to the octet rule besides H, He, Li, & Be?

Jacob Puchalski 1G

You can use De Broglie's equation : λ=h/p (p=mv).

Jacob Puchalski 1G

That helps! What I don't understand is if it's arbitrary, why did Dr. Lavelle say in his lecture today that when n=2, l=1, and ml=-1, the e- is in the 2Px state?

Jacob Puchalski 1G

It means the electron is located in the p orbital of the second energy level, and is located somewhere along the x plane.

Jacob Puchalski 1G

How are we able to determine whether a p orbital is px, py, or pz?

Jacob Puchalski 1G

For a, you know it's the second period and a p orbital. There's six elements in the second period with a p orbital, so there's six possible orbitals. That's how I'd go about each question.

Jacob Puchalski 1G

Ashley explained it well, here's part a written out. .5 grams KCl x (1 mole KCl)/(74.55 g KCl) = .0067 moles of KCl. For every molecule of KCl, there is one K atom. So there are .0067 moles of K. .5 grams K2S x (1 mole K2S)/(110.27 g K2S) = .0045 moles of K2S For every molecule of K2S, there are two...

Jacob Puchalski 1G

Yep, electrons will only move up an energy level if that specific requirement is met. That's why there's distinct spectral lines on an atomic spectrum.

Jacob Puchalski 1G

So if electrons have both wave and particle properties, does that mean that anything with mass have both wave and particle properties as well?

Jacob Puchalski 1G

He means that each electron can only hold specific amounts of energy. That's why the energy levels are n=1, n=2, n=3,... instead of any random number like n=1.74.

Jacob Puchalski 1G

If you look at electromagnetic radiation as individual photons, a higher intensity basically increases the number of photons - each photon still contains the same amount of energy.

Jacob Puchalski 1G

What's the difference between percent yield and percent error?

Jacob Puchalski 1G

It's a unit of measurement (micrometer) which is 10^-6 of a meter.

Jacob Puchalski 1G

I think it's best to round throughout the steps to an extent; we should round enough so that it's easier to keep track of the numbers but not so much that it'll affect the final answer. Maybe around four sig figs?

Jacob Puchalski 1G

Even if it isn't accurate, precision can be helpful because you know that at least your calculations are consistent. It can then be easier to fix any errors.

Jacob Puchalski 1G

Later in the course we'll need to, but for now anything uncommon will be provided for.

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