CHEMISTRY COMMUNITY

Alexis Webb 2B

My TA said homework is still due, you just send a photo through email.

Alexis Webb 2B

k' is the rate constant for the reverse reaction.

Alexis Webb 2B

In the textbook and solution, it says L.mol-1.s-1.

Alexis Webb 2B

Cl2-->HOCl + Cl- Cl2--> Cl- - balance the Cl and the charge (Cl2 + 2e--> 2Cl-) Cl2-->HOCl - balance the Cl (Cl2-->2HOCl) - balance the O ( 2H2O + Cl2--> 2HOCl) - balance the H and charge (2H2O + Cl2--> 2HOCl + 2H+ +2e-) Combine the two by canceling the electrons (no need to multiply either because t...

Alexis Webb 2B

We covered how rates related to the equilibrium constant, the Arrhenius equation, and ways to approach reaction mechanisms (direct computation, determine rate limiting step, steady-state, or pre-equilibrium).

Alexis Webb 2B

Which part of the question are you referring to?

Alexis Webb 2B

When there are two aqueous ions or two of the same phase. For example, Cu(s)|Cu 2+ (aq)|| Ce4+ (aq), Ce3+ (aq)| Pt (s)

Alexis Webb 2B

I think it is Ecell.

Alexis Webb 2B

It should be a negative value in the end based off the cell diagram.

Alexis Webb 2B

The hydrogen is the only element you need to worry about in this case, so the two half reactions are the same thing just flipped: H2 -> 2H+ + 2e-. The left side of the cell diagram is the anode, so that means the electrons should be on the right side of the reaction, and its the opposite for the cat...

Alexis Webb 2B

I am not sure if it is a typo, but I was wondering what answer would you get if the Cu2+/Cu is the cathode so that I can check mine.

Alexis Webb 2B

For this question, you use the equation standard delta G of the reaction= -nFE. All you do is plug in all the variables. E is given, F is a constant, and n is the number of moles of the reaction.

Alexis Webb 2B

I think it is a typo. it should be Cl- like it is in the solutions.

Alexis Webb 2B

If you are balancing out the half run from Br2->BrO3-, you have to first balance the Br, so now its Br2->2BrO3-. Then you have to balance the O, so you add 6H2O to the left side. Now you have to balance the H, so you add 12H+ + 12 OH-= 12 H20 to the right side. Since you added 12 OH- to the right, y...

Alexis Webb 2B

we discussed the nernst equation further and applications of electron transfer reactions like in electrolysis and ion-selective electrodes. We also discussed concentration cells where there is a transfer of electrons but the voltage is very low and E knot is zero.

Alexis Webb 2B

For this specific reaction, Au + acts in both the cathode and anode reaction, so you should see both in each reaction. For cathode, the half reaction is: Au+ + e- -> Au For anode, the half reaction is" Au3+ + 3e- -> Au+ Then, you should multiply the half reaction of cathode by 3 and flip the a...

Alexis Webb 2B

Since the reaction is forming a bond, it is exothermic, so if more heat is added, the reaction would favor the formation of the reactants. If the reaction was reversed, it would be breaking a bond, and that would be endothermic.

Alexis Webb 2B

I know that for irreversible and reversible there are two different equations for work. For irreversible it is w=PdeltaV, but for a free expansion there is no work, so it would be zero.

Alexis Webb 2B

Any material covered after the midterm.

Alexis Webb 2B

The equation for delta G of the reaction equals -RTlnK (standard delta G for rxn) + RTlnQ. The problem gives you K and T, and the pressures it gives you can be used to solve for Q, which equals the concentration of products over concentration of reactants at a given time. Plug in all the values you ...

Alexis Webb 2B

It depends on the units you are solving for and any other units involved in the equation by other constants, etc. Can you give a specific instance that you have a question about?

Alexis Webb 2B

A kind of brief summary is that using the Gibbs free energy equation (∆G = ∆H - T∆S) when ∆H is negative and ∆S is positive,the reaction is spontaneous and when ∆H is positive and ∆S is negative, its not.This is because -delta G means spontaneity. I'm not quite sure if thats what the bullet point is...

Alexis Webb 2B

For part 2, it is like the example in class where you set delta G equal to zero and then use the Gibbs equation to solve for T.

Alexis Webb 2B

Positional disorder is when there are more positions for a substance to fill, like if a substance spreads out into a greater volume, it will have greater positional disorder. Thermal disorder occurs when a substance heats up, and there is more disorder because there is an increase in motion in the m...

Alexis Webb 2B

Entropy should be J/K, enthalpy is kJ/mol, and I think GFE is kJ/mol but I also did notice that the solutions guide switched around, so I would assume that maybe you can leave it as kJ, but I don't think its wrong to have kJ/mol because the moles don't really cancel out I think it just means thats t...

Alexis Webb 2B

When there is no heat being transferred, so the system is adiabatic.

Alexis Webb 2B

I think so because it cannot exchange heat or work with the surroudings.

Alexis Webb 2B

A reversible reaction is where products and reactants are being formed at the same time, and once the forward and reverse reactions occur at the same rate, they reach equilibrium.

Alexis Webb 2B

I think you have to use the conversion from L atm to J. 101.325 J is one L atm.

Alexis Webb 2B

You only find enthalpy if the substance is going through a phase change I think.

Alexis Webb 2B

You have to use q=mCdeltaT for the substances they are asking you to find the final temperature for. For example, if they ask you to find the final temperatures for an ice cube in water, once you calculate the delta H for the ice cube, then you find the q for the ice and q for the water, set them eq...

Alexis Webb 2B

you have to balance the equation of the combustion of the C6H6 then find how many moles of gas you have (it should be -1.50 mil). Plug it into the equation w=-nRT.

Alexis Webb 2B

it only depends on the current state of the system not how that state was prepared.

Alexis Webb 2B

The chemical equation you want is N2+5/2O2->N2O5, so you have to cancel out the NO and the NO2.

Alexis Webb 2B

viewtopic.php?t=9345

Alexis Webb 2B

Use the equation M=n/v (molarity=moles/liter) in order to solve for number of moles.

Alexis Webb 2B

The buffering capacity is dependent on the number of moles of buffer in the solution. Since both have the same number of moles of HCN, they have the same buffering capacity.

Alexis Webb 2B

Enthalpy is an extensive property because it depends on the amount of matter that is involved. If you double the amount of matter, then you are doubling the enthalpy.

Alexis Webb 2B

To answer part of this post, at equilibrium, the forward and reverse reactions are occurring at equal rates.

Alexis Webb 2B

Catalysts can affect the rate of a chemical reaction, but I do not think that they affect the equilibrium constant.

Alexis Webb 2B

https://www.usna.edu/Users/chemistry/mo ... onal18.doc This document might help your question.

Alexis Webb 2B

The question states, "Air in a bicycle pump is compressed by pushing in the handle. The inner diameter of the pump is 3.0 cm, and the pump is depressed 20. cm with pressure of 2.00 atm. a) How much work is done to the compression?" So, work equals the -external pressure times the change in...

Alexis Webb 2B

More energy is required to turn water into steam, so when it comes into contact with skin, it transfers a greater amount of heat energy.

Alexis Webb 2B

I think it is because the bond enthalpies are calculated as averages from many different molecules, so they are not the most accurate.

Alexis Webb 2B

I think they multiplied the [OH-] over and then divided by Kw.

Alexis Webb 2B

Just reverse the fraction and you should get 1.5x10^-14.

Alexis Webb 2B

Can you post a picture of the problem or your work for reference?

Alexis Webb 2B

In the solutions, it says that it takes energy to break an X-X bond, so processes with halogens will be endothermic and increased temperatures favors the formation of products.

Alexis Webb 2B

I am confused about what Dr.Lavelle was discussing at the end of lecture. He said that if [H3O+]< 10^-7 then the solution is considered neutral because we know autoprotolysis generates 10^-7 M [H3O+]. Can someone explain what this means?

Alexis Webb 2B

Use the five percent rule that was discussed in lecture to ensure that you can use the approximation though.

Alexis Webb 2B

The question states for part c: 4NH3 (g) + 5O2 (g) <-> 4NO (g) + 6H2O (g) Since there are more moles of gas on the right, the reaction will shift to the left towards the reactants when there is compression. I think you just forgot some of the information in the problem.

Alexis Webb 2B

Also, the way I think about it is that endothermic reactions like heat because they absorb it, so more heat will help the reaction favor the products. If the reaction is exothermic, it "doesn't like heat" so it lets it go, and wouldn't want to create more products if the temperature rises.

Alexis Webb 2B

The question states, "The value of Kw for water at body temperature (37 C) is 2.1x10^-14. (a) What is the molar concentration of H3O+ ions at 37C? (b) What is the molar concentration of OH- in neutral water at 37 C?" How does the temperature affect the equation? Also, how do they get Kw=[H...

Alexis Webb 2B

It’s the same equation, but the concentrations used are during a different time in the reaction, which may or may not be at equilibrium depending on if Q is less than, equal to, or greater than K.

Alexis Webb 2B

After doing the ICE table for this problem, the equation is 3.2x10^-34=x^2/(0.22-2x^2). The book says that we can omit the 2x^2 because we can assume that x <<0.22 since K is so small. That means the denominator would just be (0.22)^2. I am not really sure how I would know to do this if I had anothe...

Alexis Webb 2B

I am confused because your equation doesn’t match the question. Can you clarify please?

Alexis Webb 2B

It talks about it in the textbook under topic 5H.3.

Alexis Webb 2B

K or Kp is used when there are gases in the chemical equation, unless stated otherwise because gases can be discussed in terms of molar concentration. Meanwhile, Kc is for concentrations in mol/L for solutes in a condensed phase.

Alexis Webb 2B

I believe that if you increase the concentration of reactants, then it will drive the reaction to the right and create more product.

Alexis Webb 2B

The strength of an acid depends on bond length or the stability of the anion, which occurs when there is an atom with a high electronegativity. So, if its just HF compared to HCl, then HCl is stronger by bond length. If its H-O-F and H-O-Cl being compared, then H-O-F is stronger due to electronegati...

Alexis Webb 2B

If they are in a coordination compound, you calculate the oxidation states based on the charges of the other elements in the compound.

Alexis Webb 2B

I don't think so because there are so many review sessions and office hours, but a UA posted some extra problems to help for review. Search the word "marshmallow".

Alexis Webb 2B

Metals form basic oxides and nonmetals form acidic oxides.

Alexis Webb 2B

The inductive effect is the ability to polarize a bond based on the electronegativity of an atom. So, if an atom has more electronegativity, there’s more induction, so the acid would be stronger. It’s pulling at the negative charge more to stabilize the anion.

Alexis Webb 2B

Ka is the concentration of the A- and H+ divided by AH. As this increases, the pKa (-logKa) decreases. A lower pKa means it’s a stronger acid, so I’m guessing that a lower pKa means a lower pH.

Alexis Webb 2B

I think the question was just telling you that they are weak. I don't think it was asking you to determine, but there is a table for strong acids and bases, so if its not included there, then its probably weak.

Alexis Webb 2B

It is asking for the hybrid orbitals for the central atoms.

Alexis Webb 2B

The instructions say to select an acid and a base for a neutralization reaction that results in the formation of a. potassium chloride, b. zinc nitrite, c. calcium cyanide, and d. potassium phosphate, and then write the balanced equation. I’m not really sure how to pick the acids and bases.

Alexis Webb 2B

The prefix before the ligand name tells you how many of that ligand there are. For example, pentaamminesulfatocobalt (III) chloride, there would be five (NH3) ligands. There is no prefix in front of the sulfate group so its just one SO4. The cobalt goes inside the brackets and in front of the ligand...

Alexis Webb 2B

When you draw out the Lewis structure, there will be a tetrahedral shape around one C atom and a linear shape on the other C atom. Then, you can determine the bond angles. For hybrid orbitals, you think about the number of bonding regions around the central atom you have. For tetrahedral, there are ...

Alexis Webb 2B

https://lavelle.chem.ucla.edu/wp-conten ... pounds.pdf

Alexis Webb 2B

The charges of ligands are found in tables from which you have to memorize. To find the oxidation state of the transition metal, you set up an equation (x+ (#of ligand multiplied by the charge of it)= the charge of the compound as a whole), and then you solve for x.

Alexis Webb 2B

Connect all the carbons in a chain and attach the hydrogens to the outsides. Thats how I usually try to attack those. The N would connect to a carbon as well.

Alexis Webb 2B

check the formal charges and also if its a hydrogen, it wouldn't have more than a single bond or if its a halogen (Group 7 elements), they usually like single bonds too, so any extra electrons would go on the central atom.

Alexis Webb 2B

Dipole moments will cancel out in order for a molecule to be non polar.

Alexis Webb 2B

halogens, like F, usually like to have 3 lone pairs and one single bond.

Alexis Webb 2B

I think you compare the sizes of the molecules if they have the same forces.

Alexis Webb 2B

All molecules have London Dispersion Forces, and the strength of the LDF depends of the size of the atoms. Hydrogen bonds occur when an H is bonded to an N, O, or F. Nonpolar molecules can have LDF. Polar covalent molecules can have dipole-dipole and LDF. Ionic compounds can have ion-ion. Try to det...

Alexis Webb 2B

A dipole to dipole interaction is between two polar molecules, and polar molecules always have dipole moments. By thinking about the molecules structures/shape, like we did in class, you can predict if it is polar or non polar. A dipole induced dipole interaction is usually between a polar molecule ...

Alexis Webb 2B

I’m not sure how they got 107 degrees for the angles of the molecule N2H4 in part d of the question. Can someone explain this?

Alexis Webb 2B

180 degrees for linear,
120 degrees for trigonal planar, 109.5 degrees for tetrahedral, 120 degrees for the trigonal bond angles and 90 and 180 degrees for the axial bond angles in a trigonal bipyramidal, 90 and 180 degrees for octahedral

Alexis Webb 2B

I am also wondering because my discussion is on Tuesday, and he said we will still be doing shape on Friday. I am not sure what will be covered Monday, so I am assuming all the intermolecular forces plus lewis structures and shape. Also, I would look out for practice problems from TAs.

Alexis Webb 2B

Induced dipole is when one molecule has an instantaneous dipole moment and since the charges in the molecule shifted, it induces the other molecule to have a dipole because opposite forces attract. Dipole to dipole interaction is when there are two polar molecules which means they constantly have a ...

Alexis Webb 2B

The smaller the cation is, the more polarizing power it has. The larger an anion is, the easier it is to distort.

Alexis Webb 2B

How can you determine when there is a london force or dipole to dipole interaction in a molecule? Why would CBr4 be only a london force, but the others are like london and dipole-dipole, etc?

Alexis Webb 2B

resonance structures should all have the same formal charge because you're not changing the number of bonds and lone pairs on each element. You are just moving those around.

Alexis Webb 2B

Its easier if you just think about it in the order you write out the configuration. 3d comes before 4s when you write out the configuration. So, you would remove the 4s1, and then one from the 3d.

Alexis Webb 2B

The lowest energy lewis structure would typically be the one where most of the elements have a formal charge of zero. If the molecule as a whole has a charge though, the formal charges of the elements should add up to that charge.

Alexis Webb 2B

When you draw lewis structures, you calculate the number of electrons you need first. For example, XeF4 would need 36 electrons. Once you give each fluorine a single bond to the Xe and fill in their lone pairs, you have 4 electrons left, so you attach them to the Xe because F cannot have more than 8...

Alexis Webb 2B

It’s typically the one with the lower ionization energy. After doing a lot of practice problems, I just noticed which atoms typically are in the center like carbon and such.

Alexis Webb 2B

Aufbaus Principle explains this. It’s like a pyramid looking diagram if you google it, and it explains which orbitals should be filled in which order.

Alexis Webb 2B

In the answer, it’s on the Cl.

Alexis Webb 2B

It says draw the Lewis structure of the reactive species chlorine monoxide, ClO. How do we know which element to leave an unpaired electron on?

Alexis Webb 2B

In the answer key, it says it’s not a radical.

Alexis Webb 2B

He said he is going to schedule a whole bunch more, and I would assume so since he liked to schedule a lot of hours for UA peer learning sessions and TA office hours.

Alexis Webb 2B

There are the 4 elements that form duplets like H,He,Li, and Be, and then also elements in period 3 and up could potentially have an expanded valence. That's what I would try to remember.

Alexis Webb 2B

That is what was listed on his email, so I am pretty sure that is it.

Alexis Webb 2B

I typically put one dot on each side first and then add another to form pairs if there are more left.

Alexis Webb 2B

Use the period table to help you write out the configurations. For a shortcut, you can use the noble gas the comes before the element and then write out the rest of the configuration. For example,Na would be [Ne] 3s1.

Alexis Webb 2B

For part B, I do not understand how that structure came about. Can someone explain and also why are the K+ ions floating around the P?

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