CHEMISTRY COMMUNITY

Ryan Danis 1J

Yes, this affects molecules in the gas phase.

Ryan Danis 1J

Nope, it only depends on the concentration/partial pressure.

Ryan Danis 1J

No, because an inert gas is not a part of the chemical equation used to find K, so K does not change when an inert gas is added.

Ryan Danis 1J

How do we know if work is reversible or irreversible?

Ryan Danis 1J

I believe so, because at constant volume work is zero so heat is equal to delta U (internal energy)

Ryan Danis 1J

Since it appeared in homework but it isn’t on the formula sheet, you probably need to memorize it if you don’t know how to derive it from the form of the Arrhenius equation given on the constants and equations sheet. (Assuming the constants and equations sheet on the class website will be the same a...

Ryan Danis 1J

Is nitrogen gas an ideal gas?

Ryan Danis 1J

Dear Dr. Lavelle, Thankyou for being such a great professor who truly cares about his students. I appreciate the time and effort put into the vast resources available. I learned so much chemistry in a short amount of time and feel excited going into the rest of the chem series.

Thankyou, Ryan Danis

Ryan Danis 1J

These questions were very helpful for my understanding of electrochem especially. Thankyou!

Ryan Danis 1J

I find that when I read the textbook and take notes on the material I understand the concepts better. Also, there is occasionally a bit of information in the book that isn’t always covered in class (for instance, reducing and oxidizing power in electrochem) and this info can show up on tests. It tak...

Ryan Danis 1J

For the midterm, Prof Lavelle said there would be no cubic equations or approximations in the equilibrium problems. Will this be the case for the final as well?

Ryan Danis 1J

For what type of question would I need to use the pre-equilibrium approach? I did not encounter any book problems where I had to use it.

Ryan Danis 1J

These problems were very helpful for studying thermo, thanks!

Ryan Danis 1J

It comes from the Arrhenius equation in the form of ln kr + ln A - (Ea/RT). When we are given two different temperatures, we can find the activation energy by using the Arrhenius equation for each temperature.: At temperature T1: ln kr1 = lnA - (Ea/RT1) At temperature T2: ln kr2 = lnA - (Ea/RT2) The...

Ryan Danis 1J

What is meant by an inert gas and why doesn't it cause a shift towards reactants or products?

Ryan Danis 1J

Rank the following species in order of increasing oxidation power going from their third oxidation state to neutral: U3+, Cr3+, Al3+ The standard reduction potentials for each species are: U3+/U = -1.79V, Cr3+/Cr = -0.74V, Al3+/Al = -1.66 In the book it says that the more positive the cell potential...

Ryan Danis 1J

I believe it would be spontaneous because combustion is an exothermic process, so delta H would be negative. Because delta G = delta H - T delta S, and delta H is negative, delta G should be negative. When delta G is negative, the reaction is spontaneous.

Ryan Danis 1J

When and why do we add platinum to a cell diagram?

Ryan Danis 1J

I believe that in a galvanic cell the overall Ecell is positive so that would mean the larger Ecell is on the right (cathode).

Ryan Danis 1J

Sometimes in a cell diagram, H+ and/or H20 are next to an element in a cell diagram separate by a comma. For example, from test 6: Balanced Equation: 2NO3-(aq) + 4H+ (aq) + Co (s) -> NO3- (aq) + 2H20 (l) + 2CO^3+ (aq) Co(s) I Co^2+ (aq) II NO31 (aq), H+ I NO2(g) I pt (s) How come H+ is added to the ...

Ryan Danis 1J

In 7th edition chapter 6.O, the exercises tell use to base our answers off of the potentials in the appendix with the exception of the reduction/oxidation of water at pH=7: 2H2O(l) + 2e- -> H2(g) + 2OH-(aq). E = -0.42V at pH=7 O2(g) + 4H+(aq) + 4e- -> 2H2O(l). E = +0.82 at pH=7 Which potential of wa...

Ryan Danis 1J

Is n just the number of electrons that appear on either side of each half reaction (ie: amount of electrons added to the oxidation side, that are then transferred from anode to cathode?)

Ryan Danis 1J

I understand how to find/use cell potential using the equations, but I am struggling to conceptualize what potential difference actually is. Can someone describe what potential difference is conceptually?

Ryan Danis 1J

This question asks to balance the following redox reaction:

Reaction of Chlorine in water
Cl2(g) -> HClO(aq) + Cl2(g)

I am confused because it appears that Cl is being oxidized from 0 (in CL2) to +1 (in HCLO), but I cannot find what is being reduced.

Ryan Danis 1J

What is the difference between expansion work and non-expansion work?

Ryan Danis 1J

Gibbs free energy is the energy of a system that is free to do work at constant pressure and temperature. As entropy increases, spotenaity increase. Because G=H-TS, as S increases, G decreases, so as G decreases spontaneity increases.

Ryan Danis 1J

I faced the same problem and was confused why I could get neither the equation in the solutions manual via manipulating other equations nor the answer in the book. Must be an error in the 7th edition solutions and solution manual unless anybody else has an explanation.

Ryan Danis 1J

Can someone explain to me why heat is not a state function even though enthalpy is a state function?

Ryan Danis 1J

So the answer is 28J! The back of the book said the answer was 8J so it must be a typo, no wonder I was so confused. Thanks for your explanation!

Ryan Danis 1J

How do I calculate the change in internal energy of a system if the amount of heat transferred is not given? (7th edition 4A.3 part c)

Ryan Danis 1J

I was having some trouble with this problem as well and the above replies have helped (I wasn’t squaring r or converting to liters). However I have one question. How come the work here is negative since it appears to be work done on the system instead of the system doing work? Is the system here the...

Ryan Danis 1J

Usually delta H is given and you can tell by its sign. If delta H positive it’s endothermic, if delta H is negative it’s exothermic.

Ryan Danis 1J

This question asks whether reactants or products will be favored by an increase in pressure (resulting from compression) on the equilibria. b. H2O(g)+C(s) <-> H2(g)+CO(g) I understood parts a,c,d,e because when pressure increases, the side with the fewer number of gas molecules is favored because it...

Ryan Danis 1J

This question says ‘Use the information in table 5G.2 to determine the value of K at 300 K for the reaction 2BrCl(g)+H2(g) <-> Br2(g)+2HCl(g).

I am confused about how to combine reactions in table 5G2 to determine the value of K. Thanks! I

Ryan Danis 1J

Problem 5G.5 shows a series of flasks containing the diatomic molecule, X2, with each flask showing it's dissociation over time. The first flask shows 11 X2 molecules. In the third flask, when the dissociation of X2 has reached equilibrium, there are 5 X2 molecules and 12 X atoms. Thus, 54.5% of the...

Ryan Danis 1J

One example of the significance of polyprotic acids and bases is how the oceans help maintain a constant concentration of carbon dioxide in the atmosphere. Because carbonic is a polyprotic acid, it can successively donate protons, so when it reacts with water, it donates H+ to water reducing acidity.

Ryan Danis 1J

Can someone explain why electronegativity has an effect on the strength of acids? Thanks!

Ryan Danis 1J

When reading this question (which is the stronger base, the hypobromite ion or morphine) I was confused because the sections we were supposed to read (6C.3 - 6C.4) only talked about the strength of acids in terms of trends. However, the answer uses the value of pKb to say that BrO- is the stronger b...

Ryan Danis 1J

Cosplatin forms a coordination compound with DNA (bonds to guanine) stopping cell division.

Ryan Danis 1J

On question 38, how come the LDF’s are the determining factor instead of dipole-dipole in determining the boiling point?

Ryan Danis 1J

Amphoteric substances can function as either acids or bases. Amphiprotic substances can accept or donate H+.

Ryan Danis 1J

If the dipole moments cancel out, the molecule is non polar.

Ryan Danis 1J

BaO is basic since it's a metal oxide (Ba is in group 2).

Ryan Danis 1J

Do we need to know how to tell if a compound is amphoteric, or do we just need to memorize the amphoteric oxides?

Ryan Danis 1J

Question J. 9 part b in the 7th edition asks us to identify the salt produced from the acid-base neutralization reaction between ammonia and phosphoric acid. I was able to identify the salt produced, but not in the right quantity. I first wrote out the balanced equation as NH3 (aq) + H3PO4 (aq) -> N...

Ryan Danis 1J

I was just about to ask why in parts b and d, the cobalt was simply stated as cobalt and not cobaltate in part c. Now I know that’s it’s because we only use the ate ending if the ion is negative. Thanks!

Ryan Danis 1J

On question 1a, the name of the coordination compound of [Fe(CN)6]4- is hexacyanoferrate (II) ion. How come the CN is denoted as cyano instead of cyanido in the name of the compound? Thanks!

Ryan Danis 1J

Question 3 says to identify the types of IMF’s between molecules of the following substances. Part d gives the molecule SO2. The answer says that only hydrogen bonding and dipole-dipole forces may arise. How come London forces do not apply here? Thanks!

Ryan Danis 1J

If there is a molecule with let’s say dsp3 hybridization does it matter if we put the d first? Or can we say sp3d?

Ryan Danis 1J

For Lewis structures, it is best to consider resonance (resonance can help us determine bond angles). For the VSEPR model, resonance does not matter because each resonance structure has the same amount of regions of electron density. Moreover, double and triple bonds act the same as a single bond in...

Ryan Danis 1J

Your explanation makes a lot of sense. So the lone pairs actually do affect the molecular shape by influencing the arrangement of the atoms, while only the atoms are used to then name the shape. The way the book explained it tripped me up. Thankyou!!!

Ryan Danis 1J

I am a bit confused about how/why the lone pairs on a central atom affect (or don’t affect) the VSEPR model. The book says that if lone pairs are present, only the electron arrangement is affected, but not the shape. Does this mean that a Lewis structure be an example of an electron arrangement of a...

Ryan Danis 1J

Question 2A.1 c. asks for the amount of valence electrons in Mn.

I am confused about how to find the amount of valence electrons for elements in the d-block. Can someone explain this and how I would apply it to finding the number of valence e- in Mn? Thanks!

Ryan Danis 1J

In ionic bonds, metals and non metals either gain or lose electrons to achieve the electron configuration of the nearest noble gas. Thus, the transfer of electrons leads to an octet of electrons (although there is an exception for H, He, Li, and Be). Main group metals form cations. They lose s and p...

Ryan Danis 1J

I am confused about the filling of d-orbitals in electron configurations. How does silver have a 4d10 5s1 electron configuration when it is in period 11 of the periodic table? Why isn't it 4p9 5s2?

Ryan Danis 1J

Yes. Also remember that using the fact that s has 0 nodal planes, p has 1 nodal plane, and d has 2 nodal planes, we can predict that f orbitals have 3 nodal planes.

Ryan Danis 1J

n, l, and ml are always integers. Keep in mind that n can never be 0, l can never be negative but can be 0 and positive, and ml can be negative, 0, and positive.

Ryan Danis 1J

Question 1D.23 asks, "How many orbitals can have the following quantum numbers in an atom?" a. n=2, l=1 b. n=4, l=2, ml=-2 c. n=2 d. n=3, l=2, ml=+1 I understand that (a.) corresponds to a p subshell which has 3 orbitals, and that (c.) both p and s orbitals can have the quantum number 2 wh...

Ryan Danis 1J

So the book says that nodal planes separate the two lobes of a p-orbital where the wave function is 0. How come s orbitals do not have a nodal plane?

Ryan Danis 1J

m subscript l is the third quantum number known as the magnetic quantum number. It distinguishes the the individual orbitals within a subshell (tells us the number of orbitals and their orientation. It can have the values l, l-1, ... , -l.

Ryan Danis 1J

The back of the textbook has a table labeled "RELATIONS BETWEEN UNITS"

It shows the relationship between 1 eV = 1.60218x10^-19

Keep in mind that 1 keV = 1,000 eV when converting!

Ryan Danis 1J

First I converted keV to Joules using the table in the constants in the back of the book. From there I found the frequency using E=hv. Then I used c=lambda(v) to find the wavelength.

Ryan Danis 1J

I am stuck on question 1A.15. It asks "In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line." So the first thing I did ...

Ryan Danis 1J

First you have to use the molar mass of NH4ClO4 to convert 1.325 kg NH4ClO4 into moles of NH4ClO4 (keep in mind you have that you have to convert kg to g). From there you multiply the moles of NH4ClO4 by the molar ratio of Al:NH4ClO4. You find the molar ratio by looking at the coefficients of the ba...

Ryan Danis 1J

Question G 17 asks: a. Determine the mass of anhydrous copper(II) sulfate that must be used to prepare 250 mL of 0.20 M CuS04 (aq). b. Determine the mass of CuSO4 x 5(H20) that must be used to prepare 250mL of 0.20 M CuSO4 (aq0. I was able to solve part a by finding the amount of moles of CuSO4 and ...

Ryan Danis 1J

Significant figures only need to be applied in the final answer. In your example with the number of given sig figs as 2, but the molar mass having 4 sig figs, I recommend keeping the 4 molar mass sig figs throughout the calculation, and then giving your answer with 2 sig figs. Keeping all sig figs t...

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