CHEMISTRY COMMUNITY

Searra Harding 4I

How can we tell if something is in its most stable form? I assumed diatomic molecules like O2, H2, and N2 were in their most stable state but in Lyndon's worksheet for week 4, Q1.A we plugged in bond enthalpies. This must've been explained at the time but I forgot. Does it depend on the reaction?

Searra Harding 4I

In 7E.5 we are given the diagrams for each step. How do we know which molecule is the catalyst for the reaction? Is it the intermediate or reactant in the first step?

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What is the benefit in using one over the other for a particular problem?

Searra Harding 4I

The slow step is always the rate determining step. So the rate of this step will be the overall rate.

Searra Harding 4I

So if one half reaction transfers 2 electrons and the other half reaction transfers 3 electrons, would n be 6? This way they would cancel out in the total reaction.

Searra Harding 4I

So for part a mine asks to order from neutral to second oxidation state while part b says second to neutral. The given E cells all go from second oxidization states to neutral so would it be right to use the opposite values for part a and the values given for part b?

Searra Harding 4I

If you are ordering in increasing reducing power, do you order from most negative E cell to positive or is it the other way around? And for ordering in increasing oxidation power is it the opposite of what you would put for reducing?

Searra Harding 4I

Jim Brown 14B Lec1 wrote:It is either stated explicitly or has the smaller k value

Why does the slow step have a smaller k value conceptually speaking?

Searra Harding 4I

Yes zero, first, and second order are all we need to know for this class but there are higher orders.

Searra Harding 4I

k is a rate constant and commonly seen as a proportionality constant. You can determine units by plugging in your rates to the rate expression and raising them to the respective exponent (rates are in M/s which is the same as mol/(L*s)). So if k= rate/([A]^2[B]) then k will have the units M^-2 s^-1.

Searra Harding 4I

I believe you're okay just knowing the concept and applying it but being able to derive it could give you a better understanding.

Searra Harding 4I

Maya_Peterson1C wrote:Does anyone know if it will also include entropy and previous thermodynamic concepts?

I don't think it will because those were covered on the midterm but it can't hurt to study those too.

Searra Harding 4I

You can look at the oxidation number of an atom and if that number is greater in the product then that is the oxidized substance.

Searra Harding 4I

Yes when delta G is positive it is an endergonic reaction that favors the reactants.

Searra Harding 4I

As long as you understand the concept you're good. I think that's why Dr. Lavelle purposely leaves out homework problems denoted with the calculus symbol.

Searra Harding 4I

Another thing to remember is that isolated systems don't have change in internal energy (deltaU=0), meaning q=-w.

Searra Harding 4I

Molecules that are more complex, have more possible disorder, or are larger have higher molar entropy.

Searra Harding 4I

It can be both but I've noticed that more often in our practice problems we see isothermal reversible.

Searra Harding 4I

A great way to prepare is doing all the homework problems, attending UA/TA sessions and office hours, as well as watching youtube videos to clarify anything else.

Searra Harding 4I

It asks to find the enthalpy of vaporization and gives an amount of moles and an amount of heat. Why do we divide heat by moles to get the answer? Is this derived from another equation or did I miss something? Its simplicity confuses me lol

Searra Harding 4I

You will know what to use based on the question. It will have certain given aspects that are keys to particular methods.

Searra Harding 4I

Extensive properties are dependent on matter measured, like volume and mass. Intensive properties don't depend on amount of matter, like color or density.

Searra Harding 4I

I saw this question was asked on chem community before and here was their answer: "The reaction enthalpy is the heat given off or taken up for the rxn, i.e., the enthalpy difference between the reactants and products. The enthalpy of formation of a compound is the enthalpy change between the el...

Searra Harding 4I

Enthalpy will be positive when the reaction is endothermic meaning it absorbs heat. It is negative when the reaction is exothermic meaning giving off heat.

Searra Harding 4I

Use the units given in the question. I don't think we're expected to convert. How do you convert atm to bars?

Searra Harding 4I

The 7 strong acids are HCl,HBr,HI,HNO3,HClO3,HClO4, and H2SO4. The 8 strong bases are LiOH,NaOH,KOH,RbOH,CsOH,Ca(OH)2,Sr(OH)2, and Ba(OH)2. I'd recommend memorizing them because they may be useful in the future.

Searra Harding 4I

Should we memorize the strong acids and bases so that we know if something is 100% dissociated or not? Or do you think questions will be set up in a way that we know we need to do ICE box?

Searra Harding 4I

Increasing the temperature will increase the pressure and other factors can change pressure if you consider the equation PV=nRT.

Searra Harding 4I

Plug in your initial that you are given as well as the change that you are given into ice box. Substitute what you don't know for x to start.

Searra Harding 4I

It requires energy to break a X-X bond, making it an endothermic reaction which favors formation of products.

Searra Harding 4I

I understand that the reactants are 1 because they are solid and liquid but why do only the aqueous molecules in the product stay in the answer? Is there a certain rule? I know that there is a similar rule for keeping gases when in the reactants.

Searra Harding 4I

When you know the forward reaction and are trying to find the backward reaction you can simply take the inverse of your answer.

Searra Harding 4I

If a question asks to find K, how do we know whether to make our answer Kp or Kc? I thought that if it is all gases then you use Kp but we have examples where we do the opposite.

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cisplatin is platinum in the middle with two chlorines on one side (cl) and two ammines on the other (NH3). So there should be four bonds.

Searra Harding 4I

Ethan Breaux 1J wrote:Is water then polyprotic?

No water is not a polyprotic acid.

Searra Harding 4I

Sulfur dioxide and nitrogen oxides have the biggest impacts on it.

Searra Harding 4I

Consult the table on page 723 (7th edition) named toolbox 9C.1. It has all the helpful tips.

Searra Harding 4I

Butanol has stronger interactions therefore the melting point is higher. H bonding can usually explain a higher melting point.

Searra Harding 4I

If pi bonds are weaker than sigma bonds then why are double and triple bonds stronger than single bonds? You are correct that pi bonds are weaker than sigma bonds. When considering why double and triple bonds are stronger than single bonds you should consider that all 3 types have one sigma bond. F...

Searra Harding 4I

What is the formula?

Searra Harding 4I

The name's bond...sigma bond. (hope you all get the reference)

Searra Harding 4I

"...if the atom has more than three valence electrons in its outer shell three of the electron orbitals hybridize and one of the p orbitals remains unhybridized: It is the unhybridized p orbitals that then form pi bonds for double bonding" (chem.fsu.edu). You may want to go over this link ...

Searra Harding 4I

These are to show that the atoms are in different planes. They are facing this way because the lone pair makes the molecular shape trigonal pyramidal. Think back to the 3D model Dr. Lavelle showed us in lecture.

Searra Harding 4I

What is the difference between molecular geometry vs electronicgeometry? Electronic geometry describes the shape of a molecule based on the number and arrangement of electron pairs around a central atom. Molecular geometry is describing the shape of the molecule in terms of bonds. So if a molecule ...

Searra Harding 4I

If we need to include the types of bonds and show hybridization of orbitals I'm sure it will specify on the test/final. It can't hurt to practice writing it all out on homework problems though.

Searra Harding 4I

Will molecules of the same shape always have the same bond angles? Like will all tetrahedral molecules etc have the same angles regardless of the molecule? Hypothetically, Molecules of the same shape would have the same bond angles since shape/ molecular geometry is what we use to predict the angle...

Searra Harding 4I

https://www.youtube.com/watch?v=wD004L8XlNg
This link shows a professor who explains the shape of Iodine Trichloride very well.

Searra Harding 4I

Matthew Tran 1K wrote:The other way around is true as you can use VSEPR to predict whether a molecule has a net dipole moment.

How do you apply VSEPR to predict the net dipole moment?

Searra Harding 4I

I don't think you need to memorize them but you may want to know that they are generally between 100 and 200 picometers or 1-2 angstroms.

Searra Harding 4I

If you are asked which structure has a longer bond length and both have double bonds, then check how many resonance structures each has. If one has four resonance structures and the other only has two, then you know the one with four resonance structures has longer bond lengths.

Searra Harding 4I

In addition to the above answer, triple bonds are stronger than double bonds because they have a higher pull of electrons.

Searra Harding 4I

Oops nevermind. My mistake I see that it is the week after.

Searra Harding 4I

I see that we have a test the week of Thanksgiving. My discussion is Thursday but we don't have class that day, as it is Thanksgiving. Will the test be moved to the week after or week before?

Searra Harding 4I

You would look at the electrons in the highest sub shell. Everything below the highest sub shell will fill first so any unpaired electrons will be at the top. These are your valence electrons. Remember the rule that electrons are parallel to each each other before two can fill up an orbital. You can...

Searra Harding 4I

Personally I am holding off on taking Chem 14BL, but if you love chem and have a good understanding of it then its not a bad idea to take them together. It also depends on what your schedule looks like concerning other classes. Taking both may be an overload if you have heavy course loads in your ot...

Searra Harding 4I

I would say going to step-up sessions has been super helpful to me since I haven't taken chem since sophomore year. The UA's can be a great help. Also try doing all the assessments that go along with Dr.Lavelle's videos on his website. These are great ways to test yourself and if you get a bad score...

Searra Harding 4I

When drawing electron configuration models, another thing to remember is that the electrons are parallel first. This means that there will be an upward arrow in each line drawn before you start pairing them with downward facing arrows.

Searra Harding 4I

Yes the s sub shell is closer to the nucleus than the p sub shell, therefore it has a lower energy than p. The electrons in 2p are more excited than those in 2s.

Searra Harding 4I

It's a good idea to study them anyways. Even if these questions aren't asked on Test 2, they may be asked on the midterm or final in the future. The understanding of these concepts will also benefit you when solving problems that will be on the test.

Searra Harding 4I

Why can't atoms with certain orbitals interact with each other? Dr.Lavelle mentioned the x, y, and z planes but can someone explain it again?

Searra Harding 4I

You can use both terms but indeterminacy is preferred. The word "uncertainty" implies that we have no idea so "indeterminacy" is used because we have a general idea but aren't exactly sure.

Searra Harding 4I

In lecture Dr.Lavelle said that an orbital is like a math function. Will someone explain this please?

Searra Harding 4I

Is there a way to know exactly what color light is based on its wavelength? I know that visible light falls between 700nm (red) and 400nm (violet). If something was 515nm, is there a way to define what color that is? Has each color been given a set length of nanometers that defines it? How did peopl...

Searra Harding 4I

One joule is equivalent to other units. You can use this equation: 1J = (1kg)*(m^2)*(s^-2). Once substituting joules for these units, you can often cancel certain ones out. For example, J * s is the unit for h, but it can also be written as (1kg)*(m^2)*(s^-1) because of the multiplied s.

Searra Harding 4I

How does amplitude affect frequency? And what is the relationship between the wavelength and frequency? Amplitude doesn't necessarily affect frequency. When thinking of amplitude you can think "How large?" and when thinking about frequency think "How fast?" Wavelength and freque...

Searra Harding 4I

To find the number of water molecules in 1.00 kg of water, you would have to convert the 1.00 kg of water to moles of water (using the molecular mass of water and the relevant equation - don't forget to convert kg to g when using the equation!). Then, once you have the moles of water in 1.00 kg of ...

Searra Harding 4I

If your number is very large or very small then it is safe to state it in scientific notation. Keep in mind your sig figs when answering.

Searra Harding 4I

This exercise says "Calculate the mass, in grams, of one water molecule". Then it says "Determine the number of water molecules in 1.00 kg of water." I know that for the first one I need to go from molecules to moles to grams. To go from moles to grams I can use molar mass. But h...

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