CHEMISTRY COMMUNITY

Ivan Chen 2H

I think if you determine the oxidation states of the substances, you can compare them before and after the reaction to figure out which one is reduced and oxidized.

Ivan Chen 2H

When a reagent oxidizes another substance, it means that the reagent itself is being reduced. That means we have to compare the reduction potentials of each atom, with a higher reduction potential meaning that it is more likely to be reduced. That is why Co2+ (-0.28) is able to oxidize Cr (-0.74), b...

Ivan Chen 2H

Its the same as finding Kc, we use the concentrations of the products and divide it with the concentrations of the reactants. We are not given the other concentrations because the other substances are both solids

Ivan Chen 2H

When I balance half reactions, first I try to balance the other atoms that are not H or O. After that, if I need to add oxygen anywhere I use H2O to balance the O atoms. Finally I use H to balance out the H atoms.

Ivan Chen 2H

When you find the added electrons on each half reaction you find the lowest common factor between the two added reactions so they can cancel out and be balanced. Then you multiply each of the half reactions by the multiple required to reach that lowest common factor so that the added electrons match...

Ivan Chen 2H

That's correct, and moles are not necessary in reduction potential because reduction potential is an intensive property, meaning it does not change no matter how many times the reaction is run.

Ivan Chen 2H

In order to convert a balanced redox equation in an acidic solution into a basic solution you simply need to find the number of H+ ions in the equation and add the same number of OH- ions on both sides of the equation. Then, you convert the side with both H+ and OH- into water molecules, and then ca...

Ivan Chen 2H

You don't need to multiply by its coefficients and your answer is in joules instead of kilojoules

Ivan Chen 2H

The cathode will have the higher reduction potential.

Ivan Chen 2H

Yes, you find the reduction potential in the list of ions that is between the reduction potentials of the two reactions in the question. The idea is that the reduction potential that is higher works as the oxidizing agent.

Ivan Chen 2H

It looks like the sulfur atoms aren't balanced, which might affect the rest of the equation
Edit: Nevermind, I realize that I misread the post, do you have a picture of your work process?

Ivan Chen 2H

The standard potential for silver ions is +0.80

Ivan Chen 2H

Calculate the cell potential for the reaction as written at 25.00 °C , given that [Mg2+]=0.808 M and [Sn2+]=0.0180 M . Use the standard reduction potentials in this table. Mg(s)+Sn2+(aq)↽−−⇀ Mg2+(aq)+Sn(s) I figured out which formula you need to use, but I'm having trouble solving for Q. How come we...

Ivan Chen 2H

Shorthand notation is a simpler representation of the reaction in a electrolytic cell. You have your anode on the far left side and the cathode on the far right side. You write the phases of the reaction in the order they are in contact from the anode to cathode, separating them by a single line to ...

Ivan Chen 2H

Calculate the standard free-energy change for the reaction at 25 ∘C. Refer to the list of standard reduction potentials. 2Au3+(aq)+3Cr(s)↽−−⇀2Au(s)+3Cr2+(aq) I know you need to find the number of electrons traded and use the Faraday constant to find standard free-energy change, but I'm not too clear...

Ivan Chen 2H

Entropy tells us how many microstates a system can access

Ivan Chen 2H

The question wants you to find the change in internal energy for the neutralization reaction, so we need to find the amount of heat and work done in the reaction because deltaU = q + w. Since the calorimeter is at constant volume, and work can be calculated with w= -PdeltaV, that means that no work ...

Ivan Chen 2H

Gibb's free energy equation and deltaG = -RTlnK

Ivan Chen 2H

I don't think internal energy is related to Gibb's free energy

Ivan Chen 2H

Flipping the numbers simply switches whether its positive/negative, so either you added another sign to cancel it out, or the change was insignificant enough that Sapling just accepted it within the range of answers

Ivan Chen 2H

I'm pretty sure that Gibb's free energy and enthalpy are measured in kilojoules, and enthalpy is in joules, but if you're worried about using the correct units on the midterm you can always just check what units the answers use

Ivan Chen 2H

I'm not too sure about how refrigerators work, but I think the idea is that heat is constantly being transferred out of the system to keep the system cool, but you don't see any of that coolant leaking out of the refrigerator hopefully. This would make it a closed system. On the other hand, gasoline...

Ivan Chen 2H

NH3 has a higher molar entropy than Ne because it's amore complex molecule, and thus has more possible microstates.

Ivan Chen 2H

The molar entropy of vaporization is calculated by dividing the enthalpy of vaporization by the boiling point of the liquid in kelvin. Since the change in Gibb's free energy is zero during phase transitions, the equation deltaG = deltaH -TdeltaS can be rewritten as deltaS = (deltaH/T)

Ivan Chen 2H

It looks like you forgot to include the Final Temperature variable on the ice cube side. Using 1.54*10^4 + 195.6x for the ice cube side gets you around the 30ish range

Ivan Chen 2H

I agree with this. I found this website that says the same:
https://thefactfactor.com/facts/pure_sc ... e%20system.

Ivan Chen 2H

Use the formula q= n x CV,m x deltaT to find heat. The problem gives you all the variables you need to plug in, but you also need to know what type of gas CO2 is in order to find the right constant to multiply the gas constant with.

Ivan Chen 2H

For the first part, you are given the amount of moles and change in temperature, and you need to figure out what type of gas Xe (g) is. With this, you can use q= n x Cvm x deltaT to find heat.

Ivan Chen 2H

It looks like you understand the steps to solving this problem. First you found the amount of heat required to melt 80g of ice into liquid water. Next, you find the amount of heat required to raise 80g of water by 20 degrees. That is why instead of using the specific heat capacity for ice, you need ...

Ivan Chen 2H

The pKa value is -logKa. Ka, the acid disassociation constant, is very high for strong acids, and very weak for weak acids. What this means is, if you have a small Ka, you would have a large pKa. Since weak acids have strong conjugate bases, and larger pKa's are indicative of a weaker acid, the larg...

Ivan Chen 2H

Energy is required to break bonds, in this case being X2 into 2 Xs, making it endothermic. And since heat is being added, the system will try to lower the amount of heat by running in the direction where heat is being absorbed. I think a good model would look something like this:
heat + X2 ==> 2X

Ivan Chen 2H

An important thing to think about is that the amount of heat gained by the colder water should be equal to the amount of heat lost by the hotter water after they mix. This means that we have to find the amount of heat within each body of water based on specific heat capacity, density, and mass, as w...

Ivan Chen 2H

Yes, that's correct

Ivan Chen 2H

The inclusion for "another quantity" makes more sense for the other questions, and it does make it seem misleading. However, I couldn't find anything that claims that the "combustion of CH4" was anything different from the equation above, in burning in the presence of oxygen to p...

Ivan Chen 2H

When liquid water is vaporized, the hydrogen bonding that holds water together is not present at all in water vapor. On the other hand, in fusion the hydrogen bonding found in ice can still be seen when it melts in liquid water, but to a lesser degree.

Ivan Chen 2H

When you you a large amount of energy to break a strong bond, and the result is the formation of a weaker bond that releases fewer energy you have an endothermic reaction. When you use a fewer amount of energy to break a weak bond, and the result is the formation of a stronger bond that releases a g...

Ivan Chen 2H

The carbon double bond is completely broken and replaced with a single bond. I remember Dr. Lavelle emphasized during the lecture that the double bond isn't losing its pi bond to become a single bond, but that it's actually broken and another single bond forms in its place.

Ivan Chen 2H

I vaguely remember doing something like this in my discussion section. Basically you want to set up an ICE table for the decomposition of A into B+C, and figuring out "n" will give you the correct coefficent. The chart gives you the initial and final partial pressure at equilibrium, so you...

Ivan Chen 2H

It wants you to calculate and compare the bond enthalpies of benzene with resonance (notice there is a specific carbon-carbon bond in the chart for benzene) and without it (using only single and double bonds). A higher bond enthalpy means more energy required to break the bond, meaning a higher bond...

Ivan Chen 2H

I thought a small K value like less than 10^-3 was more of helpful indication that x might be negligible, and the 5% ionization was more of a definite indication that it was actually negligible.

Ivan Chen 2H

Looking at how you set the problem up, everything looks correct, assuming that the initial values are 2.21 mol/L NO2 and 0.435 mol/L N2O4. Have you tried finding Kc again with your new values and see if it equals 11.2 again? It might indicate something went wrong with the quadratic equation. You mig...

Ivan Chen 2H

Using cross multiplication is always allowed if you're trying to simplify an equation or figuring out a variable between two ratios. I'm interested to figure out how you used cross multiplication when one was a ratio and the other was a numerical value. Based on your given values, I would multiply {...

Ivan Chen 2H

For the salts, you have to recognize if their cations are part of strong or weak bases, and if their anions are part of strong or weak acids.
By comparing the relative strengths of these anions and cations, you can figure out if they are more acidic, basic, or neutral.

Ivan Chen 2H

If you plug in your value for x into any of the terms in the formula and the concentration comes out negative, then you know its extraneous because a negative concentration is physically impossible to occur. If I remember correctly, this means that the lower/negative value for x that you found is us...

Ivan Chen 2H

I don't think solid or liquid reactants apply to Le Chatelier's principle, but I think you bring up an excellent point. I'm inclined to believe that it wouldn't change much because the professor didn't cover such an important detail, but I could be wrong.

Ivan Chen 2H

You need to divide the mols by 3.00L in order to get the concentrations for the gases. Other than that, you're spot on.

Ivan Chen 2H

Since the amount of diatomic molecules and single atoms doesn't change after the third flask, I think it's safe to say that it means the reaction has reached equilibrium in the third flask.

edit: didn't notice your edit. oh well

Ivan Chen 2H

That's correct. The reaction quotient would temporarily be unequal to the equilibrium constant

Ivan Chen 2H

There should be two reactions that should match the given reactions, although you will have to multiply or reverse them.

Ivan Chen 2H

Did you make sure the value for c is negative? In my problem, Kp was 419 and initial pressure of PCl5 was 0.04 bar, which gave me (1) - 4((419) * (-0.04)) inside the square root, which gives me a positive number. It's sounds amazing that you got the right answer with imaginary numbers.

Ivan Chen 2H

The equilibrium concentration for hydrogen gas will be your starting point for filling out the ICE table. Since the hydrogen gas concentration at equilibrium is 0.040M, and you know the volume of the system is 50L, you can figure out how many moles of hydrogen gas was made to reach equilibrium. With...

Ivan Chen 2H

When an reversible reaction at equilibrium encounters a change in condition, the position of equilibrium moves in order to return the reversible reaction to equilibrium, favoring one side of the reaction over the other. If the concentration of one side increases, the reaction would proceed in the fo...

Ivan Chen 2H

The right gas constant R depends on the units for pressure and volume that the question uses. For example, if the question has the pressures measured in atm and the volume measured in liters, you would need to use 0.082057 L*atm*mol^-1*K^-1 for R.

Ivan Chen 2H

Yes, the s-character is quantified just as you explained it. In terms of question 2F.15, it means that bond angle will increase as s-character increases, as an sp2 orbital has 33% s-character, while an sp3 orbital has 25% s-character. Thank you for your help! I don't remember learning about this in...

Ivan Chen 2H

Yes, the s-character is quantified just as you explained it. In terms of question 2F.15, it means that bond angle will increase as s-character increases, as an sp2 orbital has 33% s-character, while an sp3 orbital has 25% s-character.

Ivan Chen 2H

The total number of nodes is always one less than the principal quantum number, n. The number of angular nodes is equal to the second quantum number, l. With these two numbers, you can find the number of radial nodes it has. As for whether or not it will be on the final, we never covered it in our h...

Ivan Chen 2H

Yes, its the number of atoms bonded to the central atoms plus the number of lone pairs the central atom has

Ivan Chen 2H

As a lewis structure it would be possible. But as a 3d structure it would be impossible to place chlorine atoms opposite to each other in a tetrahedral shape, which makes it polar.

Ivan Chen 2H

Since the chlorine atoms are closer together in structure 1, they pull electrons in the same direction in a way that's closer compared to structure 2.

Ivan Chen 2H

You could use any number as long as the molar concentration of your second solution was 12% of your first.

Ivan Chen 2H

Hi Chloe, I'm not sure how to totally describe it with words, so I drew a picture instead. I think I labeled everything correctly. Edit: all the bonds with hydrogen and between the two carbon atoms are sigma bonds. The triple bond between carbon and nitrogen has two pi bonds and one sigma bond.

Ivan Chen 2H

The conjugate acid is just the original compound with another H atom, while the conjugate base is the original compound but without an H atom. For HSO4-, the conjugate acid would be H2SO4, and the conjugate base would be SO4-2. Remember to keep track of the charges when you add and subtract hydrogen...

Ivan Chen 2H

I'm pretty sure that we only use the numerical prefixes (di-, tri-, tetra-) to describe the number of ligands, ie: what's inside the brackets. So what you're saying is correct.

Ivan Chen 2H

To add on, from what I've read it looks like hexagonal planar structures are basically unknown and can only be found in higher coordination structures like hexagonal bipyramids.

Ivan Chen 2H

Since the final questions will be from the textbook, and there are only 5 questions assigned for Naming, I assume that there won't be too many questions compared to the others. I still it would be important to remember the names of common ligands and prefixes, as well as the order you arrange them in.

Ivan Chen 2H

What the questions asks is what geometries are most common for coordination complexes with a coordination number of 6. Even though the other two are possible, they seem to be a lot rarer to find in nature.

Ivan Chen 2H

Coordination number is the number of ligands that are attached to the central metal atom, while oxidation state would be the charge of the central metal atom without its ligands and electron pairs

Ivan Chen 2H

Transition metals like iron have different names depending on its oxidation state. In Fe(CN)6-3, the iron is +3 so it's considered ferric. In Fe(CN)6-4 the iron is +2 and considered ferrous. If I remember correctly this is also the case for other metals like copper (cupric/cuprous) and lead (plumbic...

Ivan Chen 2H

Ring structures are just atoms connected to each other in a way to forms a "ring." Note in my crude drawing of benzene how the carbons are connected in this way.

Ivan Chen 2H

That would be correct if the molecule had 2 lone pairs. However, since it has three lone pairs, the lone pairs occupy the equatorial positions and forces the "x" atoms into the axial positions. This is what makes them linear.

Ivan Chen 2H

You are correct in thinking that the smallest bond angle is less than 90 degrees. The question just asks for the approximate smallest bond angle based on VSEPR theory since you would need to figure it out experimentally to get the accurate answer, so 90 degrees suffices.

Ivan Chen 2H

The type of atoms and its molecular shape help contribute to determining its polarity

Ivan Chen 2H

Basically. Just count groups of bonds and lone pairs.

Ivan Chen 2H

The overall structures of atoms don't change but their bonds (single/double/triple) can change

Ivan Chen 2H

From what I understand, lone-pair repulsion is greater than bond-pair repulsion, so in order to stay the farthest away from each other, the lone pairs take up the equatorial plane instead of the axial plane.

Ivan Chen 2H

Since the carbonate ion has three bonding pairs, they repel each other to form a trigonal plane. However, the sulfite also has a lone pair. In order to accommodate the lone pair in 3D space, the three bonding pairs are repelled downwards to form a trigonal pyramid.

Ivan Chen 2H

I don't think there is any better way to memorize the VSEPR models beyond simply memorizing the shapes of the models, but I think it might be helpful to think about how each name describes the structure of the bonding pairs and how the lone pairs contributes to each model's shape.

Ivan Chen 2H

That's right, ionic bonds doesn't require hybridizations

Ivan Chen 2H

We're supposed to look at the geometry of the individual carbon atoms. If you move the structure around you can see that it is bonded to two hydrogen atoms and two other carbon atoms. Since it does not have any lone pairs attached to it, its geometry is tetrahedral.

Ivan Chen 2H

It has 3 bonded atoms and one lone pair, so 4 hybrid orbitals are needed.

Ivan Chen 2H

You make a ring with the three carbons bonded together, with a double bond between two of them. Then attach the hydrogens wherever needed.

Ivan Chen 2H

Hydrogens bonded with carbon don't participate in hydrogen bonding because their electronegative difference isn't significant enough to form a dipole.

Ivan Chen 2H

The electronegativity difference between carbon and hydrogen isn't significant enough to create a dipole compared to something like oxygen and hydrogen.

Ivan Chen 2H

London dispersion forces are present in all molecules because the electrons are always moving around a nucleus, sometimes creating temporary dipoles when they group up on one side of the nucleus. This means that even nonpolar molecules still experience intermolecular attraction through London disper...

Ivan Chen 2H

For starters, since Cl is a lot more electronegative compared to C, it creates a dipole where electrons tend to favor the Cl side of its covalent bond with carbon. This makes Cl more negatively charged, and carbon positively charged. Therefore, the strongest intermolecular attractions would be prese...

Ivan Chen 2H

I think this post helps describe it best: viewtopic.php?f=31&t=67475

Essentially, ample bond character seems to imply that it is somewhat similar to what is observed, while overwhelming bond character would be extremely similar.

Ivan Chen 2H

Since oxygen has a oxidation number of -2 when bonded to chlorine, and the sum of oxidation numbers must equal the total charge, we find that chlorine has an oxidation number of +7, which is its formal charge. SInce there isn't a diagram with a Cl+7 ion, we just look for the next best thing, which w...

Ivan Chen 2H

Are ample/overwhelming actually scientific terms used to describe bond character or was it only used in that problem in order to differentiate between being slightly close and extremely close to the bond lengths?

Ivan Chen 2H

The nitrogen would have 5 bonds, which violates the octet rule. Second period elements always have to follow it without exceptions.

Ivan Chen 2H

Electron affinity is a measurement of energy released in attaching an electron to a neutral gas atom/molecule. This helps us determine whether or not an atom/molecule is an electron acceptor or donor

Ivan Chen 2H

It helps us determine what is the most representative Lewis structure based on how close the overall formal charge of the structure is to zero

Ivan Chen 2H

Since carbon has 4 valence electrons, it will usually share all of them with the oxygen atoms in order to fill its outer shell and avoid any formal charges. Sharing 4 electrons between the three oxygen atoms means that one of them will form a double bond with carbon with 2 of its shared electrons, a...

Ivan Chen 2H

The order goes: triple>double>single.
Since there are more electrons being shared in double bonds, there is a greater attraction between the nuclei of the bonding atoms than we would see in a single bond.

Ivan Chen 2H

They are two constants to find different things. 3.29 x 10^15 is used in Hz in order to find the frequency of a given line, while 1.0974*10^-7 m^-1 is used to find 1/wavelength

Ivan Chen 2H

Gamma rays have the highest amount of energy out of any of the EM waves because of its incredibly high frequency. Because of this, it has the shortest wavelength.

Ivan Chen 2H

You can also find the mass of a single atom by dividing its molar mass with Avogadro's constant

Ivan Chen 2H

I kept getting this problem wrong as well until I realized my unit conversions were incorrect. It's important to make sure that mass is in kg and position in meters.

Ivan Chen 2H

velocity is a lowercase v, while frequency is curved. I think it helps that in most of the equations so far, v (for velocity) deals with the movement of electrons, and v (for frequency) deals with light

Ivan Chen 2H

I think it helps you describe how precise your answer or measurement is. For example if you obtained measurements with a lot of sig figs (precise) and measurements with very few (imprecise) in an experiment, it would be safer to opt for the less precise sig figs in order to highlight the imprecision...

Ivan Chen 2H

Since atomic units are incredibly small and hard to measure, we use Avogadro's constant to convert them to moles, which are easier to physically measure

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