CHEMISTRY COMMUNITY

Joseph_Armani_3K

N, in this case, would be the number of electrons transferred in a redox reaction. It would make sense; in a way, they're the number of moles of electrons in a balanced equation. You'll be able to get that number if you balance a redox reaction by balancing the half-reactions!

Joseph_Armani_3K

Yes, either by changing the temperature, or by changing the activation energy via a catalyst, as per the Arrhenius equation:

$k = Ae^{-E_{a}/RT}$

Joseph_Armani_3K

An enzyme is a biological catalyst, responsible for synthesizing and breaking down compounds in living organisms. So, in essence, all enzymes are catalysts, but not all catalysts are enzymes. Hope this helps!

Joseph_Armani_3K

The collision theory is basically that in order for molecules to react, they have to collide with enough speed and in the right orientation (the way the molecules face each other) to cause a breaking of bonds.

Joseph_Armani_3K

The concentration does affect the rate of the reaction, but NOT the rate constant. Things like temperature change and the presence of a catalyst do affect the rate constant.

Joseph_Armani_3K

Hello! When Dr. Lavelle showed us the pre-equilibrium approach, in the 2kK[NO]^2[O2] rate law, where did the 2 constant come from, and where did the 1/2 in 1/2(d[P]/dt) come from?

Joseph_Armani_3K

When the fast equilibrium step is the first step, and the slow step the second, we need a substitution equation for the intermediate, the reactant of Step 2 that was the product of Step 1. A + B <=> C + D (fast eq) D + E ==> F + G (slow) We need a substitution for [D]. Luckily, since Step 1 is fast ...

Joseph_Armani_3K

The equation is actually ln(k2/k1) = -(Ea/R)(1/T2 - 1/T1). When we substitute that negative into the temperature change equation, the two temperatures get reversed, and it becomes (Ea/R)(1/T1 - 1/T2). Hope that helps!

Joseph_Armani_3K

0.693 = ln2

Joseph_Armani_3K

Algebraically, the order is the sum of the reactant concentrations' exponents. So if the rate = k[A][B], the reaction order would be 2 because 1+1=2

Graphically, the graph that is the most linear out of the three (A vs time, lnA vs time, 1/A vs time) is the reaction's order.

Joseph_Armani_3K

k will be constant no matter the concentrations or the rates resulting from them; that's why you can use any experiment in a rate law problem to solve for k. It could, however, change depending on temperature.

Joseph_Armani_3K

Kinetics is for how fast a reaction goes, and thermodynamics is for how favorable a reaction is, how much entropy changes, or how much heat is transferred. Hope this helps!

Joseph_Armani_3K

Kinetic stability refers to the energy barrier for the reaction. Because the energy barrier for diamond to graphite is so large, the reaction, although spontaneous, is extremely slow that diamond virtually doesn't change. So, while diamond may be thermodynamically unfavorable, it's kinetically stable

Joseph_Armani_3K

Hello! I'm wondering what percentage range corresponds with grades in this class. For instance, a B+ is from what percent to what percent? Is there a guide I can consult?

Joseph_Armani_3K

Courtney Situ 2B wrote:Hello!

The problem specifies copper (I), and I believe you used the standard reduction potential for copper (II).
To save you the search, here it is:
Cu+(aq) + e– → Cu(s)
+0.52
Hope this helps!

Yes! Be sure to keep track of which ion variant's reduction potential you're using.

Joseph_Armani_3K

I don't think there's a way around it; you'll have to know the reduction potentials. I'm sure they'll give you that kind of information should you be tested on this.

Joseph_Armani_3K

As the redox reaction progresses in the cell, there would start to be a more positive side and a more negative side, and that would persist if it weren't for the salt bridge. The salt bridge is meant to keep the charges balanced across the whole cell.

Joseph_Armani_3K

I make sure to remember that it's swapped. The substance that is gaining electrons (and is being reduced) is the oxidizing agent, and the substance that is losing electrons (and is oxidized) is the reducing agent.

Joseph_Armani_3K

Delta n is just the change in moles of gas, since it's the ideal gas law. Hope this helps.

Joseph_Armani_3K

The anode is where oxidation happens, and electrons are released, which will flow to the cathode. The cathode is where reduction happens.

Joseph_Armani_3K

How do we know what charge (or oxidation number) an ion will have after a redox reaction? For example, how would we know that Mn 2+ is formed and not any other charge? Or would they tell us from the get go?

Joseph_Armani_3K

That helps plenty! I remember both LEOGER and OILRIG.

Joseph_Armani_3K

Yes, pressure is inverse to volume, so for all other conditions being constant, if pressure decreases, volume increases, and so does entropy.

Joseph_Armani_3K

I believe it has to do with the size of the substance/molecule as well as the number of atoms bonded that the molecule has. C4H10 is more complex and will have a higher entropy than C2H6. Intermolecular forces may also play a role, but I'm not sure. Hope this helps!

Joseph_Armani_3K

Cp and Cv are the pressure-constant molar heat and the volume-constant molar heat, respectively.

I haven't used Cv for the delta U portion, though. I just got the change in volume from PV=nRT, then plugged that into w = -P(delta V) and converted that into joules. Afterwards, I did the q + w equation.

Joseph_Armani_3K

For the moles part, use PV = nRT to get n because the rest of the variables have been given to you.

Now, for Path A, use -nRT ln(V2/V1) where V1 and V2 are the two volumes mentioned, and for Path B, use -P(delta V). Hope this helps!

Joseph_Armani_3K

I'm stuck on question 5 of the Sapling homework due tomorrow (W3 and W4) about 2M + 3Cl2 => 2MCl3. Help would be appreciated!

Joseph_Armani_3K

If an equation is spontaneous then it will happen all by itself, without the need for you to add some kind of energy to make it happen. For example, a gas has a disposition to expand to the full volume of the container, so a gas taking up full volume is a spontaneous process.

Joseph_Armani_3K

Q is negative when heat is released, but positive when heat is absorbed.

W is negative when work is done by the system, but positive when work is done on the system.

Joseph_Armani_3K

Entropy is the measure of disorder in a system, and you can really observe entropy in, for example, a gas. A gas won't stay in a small cluster; it will spread out and take up the entire volume of its container, thus indicating an increase in disorder (randomness)

Joseph_Armani_3K

The external pressure, I presume since work has to do with the pressure exerted on the system.

Joseph_Armani_3K

It depends on the units you're using, for example, for pressure (It differs whether or not you're using atmospheres, bar, Pascal, etc.)

Joseph_Armani_3K

What the other comments said. I believe it's mc(delta T) of the liquid water = fusion heat of ice + mc(delta T) of the ice

Joseph_Armani_3K

Can somebody help me clarify how pressure works depending on the type of system (open, closed, isolated)?

Joseph_Armani_3K

Extensive properties are dependent on the amount of the substance, such as the mass or number of moles. Intensive properties are not dependent on the amount of substance; you divided it by the amount, so it's a measure of heat capacity per 1 gram or 1 mole. Specific heat capacity stays the same thro...

Joseph_Armani_3K

The textbook talks about the conversion between K and Kc, but I'm having trouble understanding the difference between the two, how to convert from one to the other, and which one I should use. Any help would be appreciated!

Joseph_Armani_3K

For diatomic elements, the diatomic molecular form is the most stable form; thus, they naturally exist that way, and the bond connecting them doesn't change. However, in other elements, the bond's strength and properties may change depending on what molecule it's in or what state it is; that's why t...

Joseph_Armani_3K

I believe Hess's law is used when working with a multi-step reaction, and standard enthalpy of formation is used for calculating the enthalpy of a one-step reaction. I'm sure the latter could also be used for multi-step though.

Joseph_Armani_3K

I believe so; endothermic reactions will always have a positive enthalpy and exothermic reactions will always have a negative enthalpy.

Joseph_Armani_3K

I believe it's because of the enthalpy of vaporization in reverse that comes from the vapor condensing into a liquid. The heat is being released when a gas condenses into a liquid (phase change); that's why the temperature wouldn't change at that time. A larger difference in heat released (more nega...

Joseph_Armani_3K

The higher the Ka, the stronger the acid, and the higher the Kb, the stronger the base!

Joseph_Armani_3K

pKa is defined as -log(Ka), Ka being the acidity constant, and "log" being log base 10.

If you were given pKa you would probably have to find Ka, in that case, it would be 10^(-pKa). Hope this helps!

Joseph_Armani_3K

The stronger the acid, the weaker the conjugate base, and the stronger the base, the weaker the conjugate acid. This is because, for example in strong acids, the proton transfer equilibrium favors the formation of H3O+ ions, therefore, the splitting of the H+ ion from the strong acid. Thus, the conj...

Joseph_Armani_3K

It's always best to convert to molar concentrations first. Divide 0.920 by 5 and 0.150 by 5 and you get Initial concentration of SO3 = 0.184 M Equilibrium concentration of O2 = 0.030 M When you do ICE for the reaction, 0.184 <---> 0 0 -2x +2x +x ---------------------------------- 0.184-2x 2x 0.030 y...

Joseph_Armani_3K

If there are multiple gases in one container, partial pressure is the pressure of a single type of gas. Total pressure is the combined pressure of all gases in a container. So if there was a jar filled with nitrogen, oxygen, and carbon dioxide, the pressure of oxygen in the jar would be a partial pr...

Joseph_Armani_3K

Yes! I've tried it out with a calculator, and when the volume is increased, the reaction will begin to favor the side with more moles of gas.

Joseph_Armani_3K

P = pressure
V = volume
n = moles
R = gas constant (around 0.08206 I believe)
T = temperature in Kelvin

Joseph_Armani_3K

Is it just about PV equaling nRT, or is there a property about those gases that makes them ideal? I must have forgotten from the last time I did chem.

Joseph_Armani_3K

I believe we plug in the moles of that specific gas into the ideal gas law, along with the total volume of the container, to get the partial pressure.

Joseph_Armani_3K

Solutes and solvents' molar concentrations are capable of changing; however,
for pure substances such as solids and pure liquids, their concentrations would not change. That's why we leave them out of the equation.

Joseph_Armani_3K

I don't like getting acid all over me. Nothing really happens; it just gets under my skin.

Joseph_Armani_3K

It's all in whether or not the ions can form a strong acid/base or a weak acid/base. If both the acid and base are strong, the ion is neutral. If one's a weak acid and the other a strong base, the salt is basic. If one's a strong acid and the other a weak base, the salt is acidic.

Joseph_Armani_3K

These points just represented the pH at different volumes; they're supposed to demonstrate the change in pH before and after the stoichiometric point

Joseph_Armani_3K

Some salts are neutral salts, and they generally come from the reaction between a strong acid and a strong base. In addition, the ions of a neutral salt in water aren't effective in changing the pH of a solution.

Joseph_Armani_3K

That's how I've been comprehending it! I usually think of neutralization reactions between strong acids and strong bases in this formula: Acid + Base -> Salt + Water. It makes sense that strong acids and strong bases would produce water because all the strong bases have OH and the strong acids have...

Joseph_Armani_3K

HBr would be the stronger acid. The longer the bond in a binary acid, the stronger it will be. When the bond is weaker, the H+ ion is easier to remove, meaning the acid would release more H+ ions into a solution by dissociating. Hence, the acid would be stronger.

Joseph_Armani_3K

All amphiprotic substances are amphoteric, because they all act like either acids or bases depending on the situation. However, not all amphoteric substances are amphiprotic, because amphiprotic substances donate or accept hydrogen ions, and some amphoteric substances don't have to donate or accept ...

Joseph_Armani_3K

HCl, as a strong acid, will dissociate in water, and the H+ ion will be accepted by H2O to create H3O+. The acid-base interaction is as follows: HCl + H2O <--> H3O+ + Cl- All it takes from here is stoichiometry. The ratio of HCl to H3O+ is 1:1, same with HCl to Cl-. That's why there is 0.1 M H3O+ an...

Joseph_Armani_3K

Myoglobin transports oxygen in muscle tissue, whereas hemoglobin transports oxygen in blood. In addition, hemoglobin transports more oxygen than myoglobin because hemoglobin has four myoglobin-like structures that can carry oxygen. Hope this helps!

Joseph_Armani_3K

Are there any naming rules for polyatomic ions that are ligands in a coordination compound? I'm talking about chlorite, chlorate, phosphate, etc. They wouldn't just be called "chloro", right? That's the ligand name of chloride ions. What are the naming conventions besides adding "o&qu...

Joseph_Armani_3K

I'm still not sure as to why, for example, when carbon bonds with 3 atoms and one of the bonds is a double bond, how the unhybridized orbital forms. Are there simply not enough hybridized orbitals for four electrons?

Joseph_Armani_3K

If it were linear and the two lone pairs cancel its forces out, then the angle between the lone pair and the bond would be 90 degrees, and electron repulsion wouldn't allow that. When there are four regions of electron density, the electron geometry is tetrahedral and the bond angles are 109.5 degre...

Joseph_Armani_3K

What is it about transition metal cations specifically, that are responsible for them binding to ligands, and how can it bind with 6 ligands? Does it work the same way as an ionic compound?

Joseph_Armani_3K

The number of regions of electron density has to do with how many lone pairs and bonding areas there are (single, double, and triple bonds are counted as one bonding region). CH 4 has 4 bonds, therefore, 4 regions of electron density. Likewise, NH 3 has 3 bonds and 1 lone pair on nitrogen, making up...

Joseph_Armani_3K

I'm having trouble understanding the connection between the presence of sigma VS pi bonds, and the hybridization of orbitals. Assuming, of course, there is one.

Joseph_Armani_3K

I'm a little confused as to how stronger polarizing power (cation) and higher polarizability (anion) could result in the bond having more covalent character. If those forces are greater, I'd have assumed it would have more ionic character.

Joseph_Armani_3K

Generally smaller, highly-charged cations, such as Al 3+ , will have a greater polarizing power because of a greater effective nuclear charge, whereas larger anions will be more polarizable (i.e. their electron cloud will be more distorted), because their nuclei have a weaker pull on their valence e...

Joseph_Armani_3K

I understand why oxygen is the exception to the trend of ionization energy and why it's lower. However, I want to clarify why other Group 16 elements (Sulfur, Selenium, etc.) don't have a lower ionization energy like oxygen? Or hold on, do they?

Joseph_Armani_3K

I like talking to particles, but sometimes they just wave, and it gets really annoying.

Joseph_Armani_3K

What does steric number have to do with hybridization? I know how to assign hybridizations based on steric number, but does a larger steric number mean more hybrid orbitals?

Joseph_Armani_3K

The bent molecule shapes are either AX₂E, or AX₂E₂, meaning the central atom would have either one or two lone pairs.

Joseph_Armani_3K

Hydrogen bonding happens between molecules; the slightly positive hydrogen is attracted to the slightly negative side of a polar molecule. Normal bonding happens within a molecule and binds the atoms in a molecule together

Joseph_Armani_3K

London Dispersion forces happen between every type of molecule, because it has to do with the very brief polarizability of an electron field. Dipole-dipole forces have to happen between two polar molecules, because the unequal covalent bond makes the opposite ends of each molecule attract, pulling t...

Joseph_Armani_3K

When ions interact, it's because the resulting compound would be more stable than if they were individual ions. That's why when they interact and form an ionic bond, they release energy.

Joseph_Armani_3K

I'm not sure, but I think it has to do with the d-subshell being on the same energy level (same quantum number) as 3p. The expanded octet works by using a different type of orbital.

Joseph_Armani_3K

Covalent Lewis structures are drawn how a normal Lewis structure is drawn, but ionic Lewis structures are drawn with the cation between brackets and the charge indicated, and the anion drawn the same way next to the cation structure. (E.x. [Li]+[| F |]-, I don't quite know how to type out a lewis st...

Joseph_Armani_3K

As we go across a period, the number of protons increase one by one, which would result in a progressively higher electrostatic attraction

Joseph_Armani_3K

In Dr. Lavelle's latest lecture, he gives a rough guide that electronegativity differences higher than 2 indicate ionic bonds, whereas electronegativity differences lower than 1.5 indicate covalent bonds. How about electronegativity differences between 1.5 and 2? If such bonds exist, what is the nat...

Joseph_Armani_3K

Usually the octet rule has to be kept in mind when showing a Lewis structure and when calculating formal charge, but formal charge is used to see which Lewis structure is the most stable. Also, some elements (those of level n=3) can expand their octet to make their formal charge 0. Phosphorus can fo...

Joseph_Armani_3K

In a part of Dr. Lavelle's lecture, he mentions charge separation between sulfur and oxygen atoms in sulfate. What does that mean exactly? I feel like it's kind of making sense, but it's also far from my grasp. Would anyone clarify what he meant and what this means for formal charges?

Joseph_Armani_3K

I'd just finished watching the section of Dr. Lavelle's most recent lecture, about how electrons cannot be confined to the space of the nucleus because the indeterminacy of velocity would be way too high, higher than the speed of light. What would the indeterminacy equation look like for Bohr's mode...

Joseph_Armani_3K

I was watching Dr. Lavelle's latest lecture, and his discussion of whether or not an object's De Broglie wavelength can be analyzed as a wave depending on how short it is. If they're too short, they can't be analyzed as waves (and are instead analyzed by particles, from my understanding.) Does that ...

Joseph_Armani_3K

I have just started watching the October 12th lecture about quantum mechanics, and the explanation of quantum mechanics involving discrete amounts instead of continuous ones (e.x. electrons cannot be in between two energy levels), reminded me of a principle that has to do with the activity of neuron...

Joseph_Armani_3K

I would like to know more about how salts burning in differently colored flames is related to how the electrons of an element's atoms release energy when they traverse through energy levels to the ground state. Is it that most electrons emit the energy wavelength equivalent to red when they're stimu...

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