CHEMISTRY COMMUNITY

Tanya Nguyen 1B

For the equations, E=E°-(RT/nF)lnQ or E°=(RT/nF)lnK, Q and K is [products]/[reactants] and given the concentration of the anode and cathode, why is it [anode]/[cathode] and not the other way around?

Tanya Nguyen 1B

A catalyst changes the pathway to lower the activation energy. Catalysts do not affect enthalpy or the overall reaction, it is still the same reaction just at a faster rate.

Tanya Nguyen 1B

When a question is asking to state whether a reactant or product is more favorable or more stable, would it be whichever one there is more of?

Tanya Nguyen 1B

Izamary Marquez 2H wrote:
Colin Juett 2F wrote:The rate is then dependent on how quickly the catalyst can catalyze a reaction.

But if it's independent of [R] does the catalyst work the same way in the sense that it lowers the activation energy?

Yes, the role of catalysts is that it lowers the activation energy so it can speed up the reaction.

Tanya Nguyen 1B

My favorite chemistry channels are The Organic Chemistry Tutor, Professor Dave Explains, Crash Course, and Melissa Maribel! They cover a lot of the topics we learned and really clarified things for me.

Tanya Nguyen 1B

The order of a reaction is not based on the stoichiometric coefficients, there might be instances where they are the same but that is a coincidence. The order of reaction would have to be determined by looking at experiment data and adding up each order value to get the overall order of the reaction...

Tanya Nguyen 1B

Could the differential rate law also be used when time is given, like a time period/change in time because of dt?

Tanya Nguyen 1B

Changing the stoichiometric coefficients does not affect the concentration or how the rate law is written rate=k[A]ⁿ but the coefficients can affect the rate constant, k, thus affecting the reaction rate.

Tanya Nguyen 1B

Hi, for problem 6N.13 part a, it is asking us to find the value of Q. I understand the steps to find it but when I check the solution my answer is different, I got approximately 3x10 6 by doing e 15 . I don't know if the solution manual might be wrong or I am doing something else wrong but this is w...

Tanya Nguyen 1B

To add on, something I found useful while reading chapter 7A.3, they mentioned that the ideal gas law PV=nRT can be rewritten as n/V=P/RT. Meaning the concentration in mol/L is proportional to pressure, so pressure can be used as a measure of concentration.

Tanya Nguyen 1B

E° is when the cell potential is under standard conditions 1atm, 25°C/298K, and 1 M. E is when the cell potential is not under standard conditions. If you are given a value of E or E° that is not at equilibrium, you would use the equation E = E° - (RT)/(nF) lnQ. But when the cell potential is at equ...

Tanya Nguyen 1B

Cr is in its natural state, so it would have an oxidation number 0. To calculate how many electron Cr is losing, calculate the oxidation numbers of CrO 4 2- , oxygen has an oxidation number of 2-(4)=8-, the overall charge of that molecule is 2-, so Cr would have to be 6+. Cr in the reactant side is ...

Tanya Nguyen 1B

The cathode reaction is incorrect and unbalanced. The product side should have 2Ag, not AgCl. 2AgCl(s) + 2e- ---> 2Ag(s) + 2Cl-

Tanya Nguyen 1B

The statement above is correct. To determine the △G° you would use the equation E° = (RT/nF)lnK, for K>1 you would get a positive value but for K<1 you would get a negative value. Using the value of E° you can find △G° by using ΔG° = -nFE°, since this equation has a negative, the value of △G° would ...

Tanya Nguyen 1B

Since this is a basic solution, the first step is to write the half-reactions. Then balance the oxygens by adding H2O to whichever side it is needed. Then balance the hydrogens by adding H2O, one for each hydrogen that is needed (if you have 2H20 then add 4H2O on the opposite side). Once the hydroge...

Tanya Nguyen 1B

What exactly is the work that a coloumb is doing on the galvanic cell?

Tanya Nguyen 1B

In Friday's lecture, Dr. Lavelle said that that day's lecture material revolves around E knot Cell, meaning that the cell is in standard conditions (pressure 1 atm, temperature at 298K (I would assume)). Next lecture we will be talking about E cell, not in standard conditions. Yes, cells in standar...

Tanya Nguyen 1B

Where does the equation △U=3/2nRT come from and when do we need to use it? This was used in a workshop problem

Tanya Nguyen 1B

A reversible work is when there is an infinitely small change in a variable, which could be external pressure, you would use the equation w = nRTln(v2/v1). Irreversible work is when a variable does not go through infinitely small changes, so you would use the equation w = -P△V.

Tanya Nguyen 1B

In addition to what was previously said, a similar equation could be used for entropy where the reaction is an isothermal reversible expansion, △S = nRln(v2/v1)

Tanya Nguyen 1B

From outline 3 its only 4A, 4b, 4C right? And all of outline 4?

Tanya Nguyen 1B

K is for when a system is at equilibrium and Q is for when it is not. You would have to use the correct equation that corresponds to whether the system is at equilibrium or not. Also, note that K is used to find △G° while Q is used to find △G.

Tanya Nguyen 1B

Is there a time where it won't be at constant pressure? If so how would we calculate $\Delta H$ ?

Tanya Nguyen 1B

In addition, Cp and Cv also relate to monatomic and diatomic ideal gases.

Tanya Nguyen 1B

Just to clarify, is an isothermal reaction and reversible reaction the same thing, or is an isothermal reaction classified as a reversible reaction?

Tanya Nguyen 1B

In addition, I understand that work is the integral from v2 to v1 (-p(delta v)), but how does it also equal -nRTln(v2/v1)?

Tanya Nguyen 1B

Just to clarify, delta U=delta H when pressure and volume are constant and no work is being done? yeah if we have constant volume, delta U is equal to qv and when we have constant pressure delta U is equal to qp. As a result we have delta U = delta H - PdeltaV. However, if P and V are constant then...

Tanya Nguyen 1B

Is an irreversible reaction only when pressure is constant or can it also be related to temperature?

Tanya Nguyen 1B

Steam/gas/vapors have higher energy than liquid and solids. When steam touches an object it undergoes a phase change from gas to liquid (condensation), going from a gas to a liquid is an exothermic process, so energy will be released, thus, burning your skin.

Tanya Nguyen 1B

You would use the initial volume (4.35) in the ideal gas, then use the volume it expands to (7.58) for the w=-nRTln(v2/v1) equation.

Tanya Nguyen 1B

You would use the equation q=mC $\Delta T$ . Remember that $\Delta T$ is the change in temperature so you would subtract the final temperature with the initial temperature. Then plug in values, mass*specific heat*(final temp - initial temp) and solve for the final temperature.

Tanya Nguyen 1B

It would be easier to think of heat as a reactant or a product in addition to the actual reactants and products. For exothermic reactions, heat would be a product, so if temperature is increased more reactants would form and more product if temperature is decreased. While for an endothermic reaction...

Tanya Nguyen 1B

It's good to remember that C2 (graphite) is a solid, Br2 is a liquid, and I2 is a solid. Other diatomic molecules like H2, N2, O2, etc. would be gases.

Tanya Nguyen 1B

For problem 15 the delta Hc was given, whereas in this problem we are told to use the appendix, so we would have to find the standard enthalpy formation of each molecule. For pure elements or elements in the most stable form their enthalpy is zero.

Tanya Nguyen 1B

Solid air fresheners are also an example of sublimation.

Tanya Nguyen 1B

The phase change diagram shown in the lecture went from solid to liquid to gas, with a positive slope in each phase and a slope of 0 when it is changing phases. Sublimation is a direct change of solid to gas, the diagram for sublimation is a positive slope at solid, a slope of 0 at solid-gas, then a...

Tanya Nguyen 1B

Work (w) and heat (q) depend on the path taken, so it is not a state property (state property: not dependent on the path taken to obtain that state). But heat can also be a state property if it is a constant pressure (which is enthalpy). Work and heat correlate because energy is being transferred in...

Tanya Nguyen 1B

Your answer is correct because the reaction will respond to the disturbance to go back to equilibrium as stated in Le Chatalier's principle. If there was an increase in product then reactants will increase, vice versa.

Tanya Nguyen 1B

It is a weak acid and the Ka value is small (less than 10^-4) is the x value would not change the values too much so we could approximate by omitting it. To check, if x is less than 5% of the initial concentration, then the approximation is okay.

Tanya Nguyen 1B

NH3 is a product so for the change it is gaining, that is why its 0.2+x, not 0.2-x, and we leave out the NH4HS because it is a solid, we only use gases and aqueous for equilibrium.

Tanya Nguyen 1B

Yes, the same would go for Kb and pKb. The higher the K is for Ka/Kb means there is more acid/base, so for high values of K, since pK is the -log(K) you would get smaller values for pK. Hope this helps.

Tanya Nguyen 1B

pKa and pH are not the same things but they are related. pH is -log[H30+] while pKa is -log[H3O+][Conjugate Base]/[Acid]. If you know one value you can use the Henderson-Hasselbalch equation pH = pKa + log ([conjugate base]/[weak acid]) to find the other value. You can find more information on the s...

Tanya Nguyen 1B

A dilute solution is a solution that the concentration is decreased, water is typically used to dilute solutions otherwise it would be stated.

Tanya Nguyen 1B

We can use the reverse reaction! Since we are starting with only product, we can flip the equation around so that PCl5 is a reactant (and the other two compounds are products). The Kp value of this reverse reaction would be 1/Kp (where Kp is the Kp of the forward reaction). Then proceed as normal, ...

Tanya Nguyen 1B

As stated in the previous responses, you would divide moles by the volume to find the molar concentration. The molar concentration is usually written with a capital M, which is the same as mole/liter (mol.L -1 ). If the moles of the solute is grams you would need to convert it to moles, and the volu...

Tanya Nguyen 1B

Is Kc not the equilibrium constant using concentrations? Kc is the equilibrium constant of concentration whereas K is the general term of an equilibrium constant. In a reaction with all gases, K is the value of partial pressure, so K=Kp. To find the value of K given Kc or vice versa you can use the...

Tanya Nguyen 1B

For Kc you would use the concentration, Kp uses partial pressure. On another note, if K is not specified as Kc or Kp and all of the molecules are gases then you would solve for Kp.

Tanya Nguyen 1B

Going off of the previous reply, Kc is small when it is 10^-3 or less and Kc is big when it is 10³ or more. When Kc is between 10^-3 and 10³ neither reactants or products are favored, this was mentioned in today's (1/06) lecture.

Tanya Nguyen 1B

a) they switched the placements of the reactants/products so you would just take the inverse of K, so K in this problem would be 1/41 b) the given equation is the given equation in the problem but the coefficients are just divided by 2 so you would take the square root of 41 as your answer (~6.4). ...

Tanya Nguyen 1B

The answer would be A because the equilibrium constant is the ratio of the concentration of products to the concentration of reactants, thus it gives the relative concentration.

Tanya Nguyen 1B

Taha 1D wrote:You can tell it is basic because the cation is Na and that is a specatator ion. the proton transfer is just the anion pulling a hydrogen from water and leaving OH-

What is a spectator ion and how are we supposed to identify it? Was it ever mentioned in one of the lectures?

Tanya Nguyen 1B

Memorizing them is a good way to go but if it is too difficult to remember all 7 acids, a good way is to remember the phrase "Sorry I Brought No Clean Clothese" where each of the underlined correlates to one of the strong acids.

Tanya Nguyen 1B

Lewis acids and bases deal with electrons:
Lewis acid - accept electrons
Lewis base - donates electrons

Bronsted acids and bases deal with protons:
Bronsted acids - donates protons
Bronsted bases - accepts protons

It can be easier to remember that Bronsted is the opposite of Lewis.

Tanya Nguyen 1B

I would try and memorize the strong Bronsted acids and bases, anything that is not those are weak acids or bases. The strong Bronsted acids are H2SO4, HI, HBr, HNO3, HCl, HClO3, HClO4, another way to quickly memorize this is to remember the phrase " So rry I Br ought No Cl ean Clo thes". F...

Tanya Nguyen 1B

For this problem, you'll need to write an equation for the given acids and bases with the product of salt and water (acid+base->salt+water). So for (a) potassium hydroxide is K(OH) (base) and acetic acid is CH3COOH (acid). The equation for this reaction should be K(OH) + CH3COOH -> CH3OOK + H2O. The...

Tanya Nguyen 1B

Bases feel soapy because they react with the fatty acids and oils on our skin. I am not sure as to what soft salts are exactly, maybe it has to do with the facts that acids and bases are salts and they can be either 'soft' or 'hard' (polarizable or nonpolarizable).

Tanya Nguyen 1B

Just as the previous post stated, it is good to know what equilibrium means and how it can be used, but we will not need to know how to calculate it in this course.

Tanya Nguyen 1B

What is (en)? Is it just a symbol for a bidentate ligand or is it a specific ligand?

Tanya Nguyen 1B

The metal atom would come first then the ligands, the cation ligand comes before the anion ligand then the neutral ligands. For more information you can check out https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Modules_and_Websites_(Inorganic_Chemistry)/Coordination_Chemistry/Structure_a...

Tanya Nguyen 1B

You would separate it with a space and sometimes the charge of the atom would separate what is outside of the bracket if it comes after.

Tanya Nguyen 1B

Bound atoms are atoms that are bonded to each other. Sigma bonds are single bonds that allow the bonded atoms to rotate whereas pi bonds don't allow atoms to rotate/move once they are bonded.

Tanya Nguyen 1B

They are perpendicular to each other because it needs to be arranged in a way that is evenly spaced from each other. And yes the carbon would have a 2sp hybridization because of the double bond and a 2p orbital.

Tanya Nguyen 1B

You could determine it by the number of lone pairs and bond pairs or you could determine it by the number of atoms it is bonded to and the number of lone pairs. I find the second way better because you wouldn't confuse it by counting the actual number of bonds (for a double/triple bond you wouldn't ...

Tanya Nguyen 1B

Either way is correct, it depends on your personal preference. I personally like to write spd as it in on order of energy levels.

Tanya Nguyen 1B

The three carbon atoms have two pi bonds because there is an even number of bonds/odd number of atoms the bonds would have to be perpendicular to each other. This image helped me visualized it

Tanya Nguyen 1B

To find the charge of the molecule, you would add up all of the formal charges from atom and that should give you the ion's charge.

Tanya Nguyen 1B

A dipole-dipole interaction is between 2 dipoles, both will have a polar charge where the positive and negative are attracted to each other. A dipole-induced dipole is an interaction between a dipole and a neutral/nonpolar atom, the dipole will induce the neutral atom to be a dipole where the opposi...

Tanya Nguyen 1B

Electron structure can either be the Lewis structure or the electrons grouped around the nucleus drawn as an electron shell. Whereas the molecular structure is the structure of a molecule consisting of multiple atoms and where there are bonded together.

Tanya Nguyen 1B

I believe that transition metals can only have 2 valence electrons is because the s-block has higher energy than the d-block and "s" can only hold 2 electrons, so all transition metals only have 2 valence electrons.

Tanya Nguyen 1B

Sana Nagori 2J wrote:Similar to what someone said I remember CATions as being PAWsitive :))

A friend told me the same thing, and I thought it was funny so I still remember it to this day and it helps a lot!

Tanya Nguyen 1B

More electronegative atoms should have negative charges, and phosphorus less electronegative charge than oxygen. Overall it is best to avoid any charges on the central atom when possible and for a compound with three atoms, the most stable structure would be where the negative formal charge is at th...

Tanya Nguyen 1B

You would need to find the oxidation number for each atom and it should equal the charge of the compound. The oxidation number for oxygen is -2 and there are four oxygens (-2*4). The compound has a -1 charge so x+(-2*4)=-1, x would be the charge of chlorine.

Tanya Nguyen 1B

Yes! Listening to Dr. Lavelle's music at the beginning of class gets me excited for class. And I'm pretty sure there are enough people listening that most of us would know some songs so we could also make the playlist ourselves.

Tanya Nguyen 1B

Oxidation numbers tell you of electrons are lost or gained. The chart posted above is a good reference. For neutral compounds (no charge) all the oxidation numbers should add up to 0. For ions, all the oxidation numbers should add up to the charge of the ion. Then for free elements its oxidation num...

Tanya Nguyen 1B

How do you determine which structure contributes the most or least to the overall structure?

Tanya Nguyen 1B

The charge of the overall molecule goes outside of the Lewis structure which is in a square bracket. You could also write the charge of each individual atom, Dr. Lavelle recommends underlining the formal charge of the individual atom to make it easier to distinguish.

Tanya Nguyen 1B

Formal charge is used to determine whether a molecule is stable or not, a formal charge with 0 is the most stable. Since it is assumed that all electrons are shared equally there are some that break/is an exception to the octet rule.

Tanya Nguyen 1B

Bond character is determined by the difference in electronegativity of the atoms involved. It should either be ionic or covalent. I am not sure what you mean by ample or overwhelming, but I hope this helps a little.

Tanya Nguyen 1B

I think that that answer is not correct. Fluorine should fill its octet and the molecule must have 28 electrons, so fluorine should have another lone pair. Bromine can have an extra lone pair because its principal quantum number is n=4 so it has a d shell that can accommodate extra electrons. I agr...

Tanya Nguyen 1B

The Greek letter that represents the slightly negative/positive atom is the lowercase delta sign. It is written like an s but you connect the end so it's almost like an 8. The delta sign means that the more electronegative atom will pull the shared electrons towards it (delta negative) while the low...

Tanya Nguyen 1B

An element enters their excited state when an electron temporarily occupies an energy level greater than its ground state. This occurs when the outer electrons observe energy and jump to a higher orbital. Eventually it can release this energy and fall back to a lower state. During this process, the...

Tanya Nguyen 1B

How I visualize it is that the shell is the outer layer (n=1,2,3,4,etc.) that contains the subshells (s,p,d,f), inside the subshells are the orbitals (each orbital holds up to 2 electrons that spins up or down). Hope this helps.

Tanya Nguyen 1B

Should we specifiy 2pxpypx or 2p^3 for electron configurations? How should we write it for tests? does this apply to the d or f subshell? what letters are used for those larger subshells I believe it would apply to the d and f orbitals as well. Since p has 3 orbitals there is px, py, pz. There is a...

Tanya Nguyen 1B

l could be 4, but Dr. Lavelle says that in this class we will only use up to l=3 since the subshell for l=3 is f, which is the highest orbital we'll use.

Tanya Nguyen 1B

Yes I agree with the previous post, you should base your sig figs off of the wavelength/frequency given in the question since electron shells can only have whole numbers.

Tanya Nguyen 1B

Yes, I would try to memorize as much of the EM spectrum as you can. My TA told me that it will not be provided on the test, so it would be good to memorize it.

Tanya Nguyen 1B

It would be false because each photon/electron has a certain amount of energy, increasing the intensity just means that you are increasing the number of photons which increases the number of electrons with the same amount of energy.

Tanya Nguyen 1B

It would usually be final - initial, but I heard that some people switch it up. Just be sure that if you do, remember where things are and possibly have to switch the sign of your answer. There is also another way to write the equation and it is the equation given on the equation sheet linked on the...

Tanya Nguyen 1B

Not necessarily. There are 7 diatomic molecules that you will have to memorize: H2, N2, F2, O2, I2, Cl2, and Br2. Other molecules would not need 2 atoms per molecule when you only have one element in a molecule. They are pretty common though, like O2 for combustion reactions. What are diatomic mole...

Tanya Nguyen 1B

The limiting reactant will affect how much product can be formed. It helps to calculate the theoretical yield to find the amount that could be produced, and there will side reactions so the actual yield will be less than the theoretical yield.

Tanya Nguyen 1B

Work is the threshold energy which is the minimum amount of energy needed to eject an electron from a metal. The work/threshold energy will usually be written as the Greek letter phi Φ. You will need to use the work when asked to find the energy of a photon or the kinetic energy. The energy of the p...

Tanya Nguyen 1B

VincentLe mentioned it before, e and 10 has different values, whereas E is referring to 10 to the power of_. Just be sure to check your calculator so you don't confuse the two, but I am pretty sure most calculators will note it with a capital E.

Tanya Nguyen 1B

Folowing the chart that was posted eariler, SI units are always usually always in factors of 3 (with the exception of die and centi). If your answer does not fit into one of the following SI units you would have to rewrite/convert it in a way that it would. An example would be 5.51x10^-7, since ther...

Tanya Nguyen 1B

Usually, I start by balancing the element that occurs least then working my way to the element that occurs most. It's best if you use whole numbers for the coefficient because it will make future calculations easier. If you end up with a mixed number, there should be a number you can multiply it by ...

Tanya Nguyen 1B

When calculating I try to use as many decimal places as I can (usually four to five decimal places) to get the most accurate answer. For the answer, I would round it to however many sig figs was given in the question.

Tanya Nguyen 1B

Do we need to memorize these unit lengths and how to write them out? Or will there be a guide/chart of some sort to help us when calculating?

Tanya Nguyen 1B

I was confused with this question at first too. All of the reactants and products are in a gas state, so the question is asking for the moles of all of the chemical compounds. To find the net number of moles produced, you would take the total number of moles of the products and subtract with the tot...

Tanya Nguyen 1B

Will the Periodic Table we receive on tests and activities have the electronegativity and other more specific details about certain elements? I believe we will be receiving a standard periodic table for the test so it will most likely not have the electronegativity or specific details about certain...

Tanya Nguyen 1B

When I am calculating I like to use the most amount of numbers given (usually around four to five significant figures) so that I can get the most accurate answer. Then I would round the answers to the smallest amount of significant figures, if not I would usually keep it around four to five figures,...

Tanya Nguyen 1B

If your equation has a common factor and it can be simplified it is best to do so. In the lecture, Professor Lavelle says the coefficient must be the lowest whole number. It would also make it easier to do calculations later.

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