CHEMISTRY COMMUNITY

Joanna Pham - 2D

Could someone possibly explain the collision theory to me please?

Joanna Pham - 2D

They don’t affect the oxidation numbers, but it affects the charge of the molecule and thus, the number of electrons needed to balance the charges on both sides

Joanna Pham - 2D

I like to think of spontaneity as the ability of a reaction to occur on its own, meaning that the reaction does not require additional energy in order for the reaction to take place

Joanna Pham - 2D

I believe sig figs will be important on the exam. I believe TAs had checked for sig figs in the midterm, so I assume it’ll be the same for the final as well

Joanna Pham - 2D

does anyone happen to understand why the slow step determines the rate?

Joanna Pham - 2D

the units vary depending on the order. rate has the units of mol/(L*s), and concentration has units of mol/L. Thus, to find the units of k, you need to first determine the order of the reaction. For example, if you had A + A -> Product, the rate = k[A]^2. To get the right side of the equal side equa...

Joanna Pham - 2D

You can use the equation PV = nRT. Find the value of n (units = moles) then divide it by the volume (units = L) to find concentration

Joanna Pham - 2D

I would recommend knowing how he derived in case there are conceptual questions about it. I would also be familiar with the graphs, such as which order has a linear graph, etc.

Joanna Pham - 2D

For Q1 part c on the midterm, the question asked us to comment on the relative stability of the reactants and products, and the equilibrium constant (Kp) given was 3 x 10^4. The solutions said the formation of SO3- was more stable because Kp is a large number, but I don’t really understand why. Coul...

Joanna Pham - 2D

This problem asked us to determine if a pH = 7 is acidic or basic when the temperature went from 25 Celsius to 10 C. Standard enthalpy was 58 kJ/mol and Kw at 25 Celsius = 10^-14, and the equation was 2H_{2}O (aq) \leftrightharpoons H3O^{+} (aq) + OH^{-} (aq) Does anyone happ...

Joanna Pham - 2D

On test 2, one of the questions asked us to place the following in order of increasing oxidation power going from their second oxidation state to neutral: Ti2+, Sn2+, Mg2+

I'm a bit confused how to rank them based on their oxidation power. Can someone explain please?

Joanna Pham - 2D

Would we be expected to know how to write the intermediate steps for a certain compound/molecule?

Joanna Pham - 2D

Will the final mainly be on the materials we learned after the Midterm and/or Test 2?

Joanna Pham - 2D

It honestly depends on how you prefer to study. If you like going going through problems and solving them step by step, then the STEP UP sessions would be beneficial. However if you’re like me, where you’re confused about certain topics and would rather do problems on your own then ask questions, th...

Joanna Pham - 2D

It’s essentially the coefficient in front of the reactant or product and it’s raised to the concentration of that reactant or product. For example, if given 2NO2 -> 2NO + O2, and asked to find the rate of consumption of NO2, it’ll be rate = k[NO2]^2.

Joanna Pham - 2D

When given a reaction, how would we determine if a reactant or product is a zero order reactant or some other order reaction? For example, in the book, they said for 2NH3 -> N2 + 3H2 the rate of consumption of NH3 is a zero order reaction, so the rate is equal to k. How would we have known from the ...

Joanna Pham - 2D

An UA told me you don't need it when you have a metal present on both sides of the salt bridge. However, if one or both sides lacked a metal, then you would insert Pt (s) on the side(s) without a metal

Joanna Pham - 2D

When you switch the reaction, the standard potential sign is reversed. However, it is important to note that if you multiply an entire chemical equation by a number, you DO NOT multiple the standard potential by that number. You only that for standard gibb free energy of the reaction. For example if...

Joanna Pham - 2D

One of the UAs told me that in order to figure out if O3 is being oxidized or reduced, you would need to know if the other element in the equation is being reduced or oxidized. For instance, if you had O3 + Br- -> O2 + BrO3-, Br- is being oxidized. Thus, if Br- is oxidized, that means O3 must be red...

Joanna Pham - 2D

Does anyone happen to know how to write the half reactions for 14 b and c? I'm stuck 14.24) Predict the standard cell potential and calculate the standard reaction Gibbs free energy for galvanic cells having the following cell reactions: b) 2 H2(g) + O2(g) -> 2 H2O(l) in acidic solution c) 2 H2(g) +...

Joanna Pham - 2D

For 14.11 part d, the question asks us to write the half reactions and the balance redox reaction for the following galvanic cell: Pt(s) | O2 (g) | H+ (aq) || OH- (aq) | O2 (g) | Pt (g) I understand that the side to the left of the salt bridge represents oxidation and the side to the right represent...

Joanna Pham - 2D

everything from gibbs energy to the end of friday's lecture, which is section 14.6 in the 6th edition of the textbook

Joanna Pham - 2D

Faradays constant = 96485 C/mol.

It's given on the formula sheet so you don't have to memorize it

Joanna Pham - 2D

I do not believe so since I don't recall Professor Lavelle going over that during lecture yet

Joanna Pham - 2D

For the example Professor Lavelle did in lecture Wednesday, 2/20/19, he said the oxidation state of MnO4- was +7. Can someone please explain why the oxidation number +7 please? I am confused how to find the oxidation state for metals in the d-block.

Joanna Pham - 2D

What is the best way to determine if a compound or reaction is stable or unstable?

For example, for 9.65, the question asks us to determine which of the compounds is less stable when temperature is raised: PCl5, HCN, NO, and SO2. How w ould I determine the stability of the compounds?

Joanna Pham - 2D

What exactly is potential? Dr. Lavelle mentioned potential and potential difference today in lecture, but I'm unsure what it is exactly.

Joanna Pham - 2D

How would we figure put the oxidation number for the transition metals or the ones in the d-block, such as Mn for example? Will it be given to us on the exam?

Joanna Pham - 2D

Is molar Gibbs free energy the same thing as the standard Gibbs free energy?

Joanna Pham - 2D

Could someone please explain why exothermic reactions are mostly spontaneous?

Joanna Pham - 2D

I know for sure that Gibbs free energy itself is a state function. I’m not too sure about the change in G though.

Joanna Pham - 2D

I believe you would need to convert it since U is supposed to be in terms of J or kJ. Like someone said, the formula to covert it is on the formula sheet so I would think that you need to convert it. I’m not sure if the TAs will take off points if you leave it in L•atm, but I would just convert it t...

Joanna Pham - 2D

Could someone possibly explain residual energy? I’m still having a hard time understanding what it is exactly...

Joanna Pham - 2D

In lecture yesterday for one of the review problems that asked to calculate deltaS of an isothermal reaction, Lavelle mentioned that U = (3/2)nRT. Thus, If there’s no change in temperature, since n, R, and T are all constant, that means there’s no change in internal energy.

Joanna Pham - 2D

Can someone please explain what an extensive and intensive property is?

Joanna Pham - 2D

For part a, the questions asks us to find the reaction enthalpy for 3C2H2 (g) -> C6H6 (g). In the solutions manual, it says 6 moles of the C-C bonds are formed in the reaction. Where did they get 6 moles from? When I drew out the Lewis structure of C6H6, which came out to be a carbon ring with 6 hyd...

Joanna Pham - 2D

Hello! I wasn't able to stay for the entire lecture today (2/8/19) since I had a meeting, so I was wondering if one of you guys could possibly send me photos of the lecture notes.

Thanks!

Joanna Pham - 2D

How do you know to calculate for specific or molar capacity if it's not specified in the question? For instance, for 8.31, the question asks for us to "calculate the heat released by 5.025 g of Kr(g) at 0.400 atm as it cools from 97.6 C to 25.0 C at (a) constant pressure and (b) constant volu...

Joanna Pham - 2D

Entropy has the units energy over temperature, or joules per kelvin. You are correct that you need to add them together. However, you need to find the individual entropies by dividing the joules by their temperature in kelvin. Then add those values like the book to find entropy. hope this helps. Oh...

Joanna Pham - 2D

The question asks us to calculate the change in entropy when the pressure of 1.50 mol Ne(g) is decreased isothermally from 15.0 atm to 0.500 atm while assuming ideal behavior. When I used the equation from the book \Delta S = nR\ln (P1/P2) , I got -42.416. However, in the back, the answer sa...

Joanna Pham - 2D

The questions asks to find the TOTAL entropy change of a process in which 40 kJ of energy is transferred as heat from a large reservoir at 800 k to one at 200 k. I thought I had to just add them, but the solutions manual did it differently. They did -40000 J / 800 K and 40000 J / 200 K then added th...

Joanna Pham - 2D

qv is heat at constant volume, while qp is heat at constant pressure, as denoted by the subscripts. The question would typically ask you which one to solve for or would typically state which one is constant. Hope this helps! just wondering, if a question asked us to solve for Qv or Qp, how would we...

Joanna Pham - 2D

Today in lecture, Professor Lavelle talked about residual energy. Could someone please explain what it is? I'm still a bit confused.

He also mentioned that CH4 had no residual energy, but CH3Cl had residual energy. Could someone explain how to determine if a molecule has residual energy please?

Joanna Pham - 2D

Today Professor Lavelle talked about dengenracy. I was wondering if someone could explain what degeneracy actually is. I’m having a hard time thinking about it conceptually? Is it just the number of possible outcomes?

Joanna Pham - 2D

For the lecture Wednesday, 1/30/19, Professor Lavelle started off with thermodynamics. Does anyone happen to know if this is still part of CH8 of the 6th edition (7th edition: CH4) or another chapter?

Joanna Pham - 2D

For this question, we are asked to find the enthalpy of vaporization of methane, given that the vaporization of .579 moles of CH4 (l) requires 4.76 kJ of heat? My friend told me that to find the answer, I need to divide heat by the moles (4.76 / .579), but I don't understand why. Can someone please ...

Joanna Pham - 2D

Could someone please explain what the difference between heat capacity and enthalpy is? I’m still a bit confused.

Thanks!

Joanna Pham - 2D

Professor Lavelle gave example of a hot/cold pack during lecture one day, and I thought it was helpful. Endothermic reactions require heat to obtain the products (delta H = positive) while exothermic reactions release heat during reactions (delta H = negative). Given that, with a hot pack, when you ...

Joanna Pham - 2D

Yes, I believe we will be getting them back during discussion this week since our midterm is coming up. If not, then latest by next week or so.

Joanna Pham - 2D

According to some TAs and UAs, Professor Lavelle should be providing the values for Ka, Kb, pKa, and pKb on the exam

Joanna Pham - 2D

Strong Acid: Large Ka, small pKa; also means the conjugate base will be weak Weak Acid: Small Ka, large pKa; also means the conjugate base will be strong Strong Base: Large Kb, small pKb; also means the conjugate acid will be weak Weak: Small Kb, large pKb; also means the conjugate acid will be strong

Joanna Pham - 2D

To remember which direction the reaction will favor if the reaction is endothermic or exothermic, I like to have a visual in mind. If the reaction is endothermic, that means the reaction requires heat to form its products. So in the chemical equation, on the side of the reactants, heat should be add...

Joanna Pham - 2D

The question asks us to arrange the bases in order of increasing strength based on the pKa values of their conjugate acids (given in paraentheses): ammonia (9.26), methylamine (10.56), ethylamine (10.81), aniline (4.63) Does anyone happen to know how to solve this? Would I need to convert the pKa va...

Joanna Pham - 2D

Does anyone happen to know if points will be taken off if we don't include the phases of the molecules when writing the chemical equations?

Joanna Pham - 2D

Yes that is correct! I would not worry about significant figures too much for this class though. According to the TAs, they will not pay too much attention to significant figures this quarter, meaning they won't take off points if you use an incorrect number of sig figs. Unless the question specific...

Joanna Pham - 2D

Adding on to what Andre said, if Q < K, then it means there's a greater concentration of reactants, which means the reaction will favor and produce more products (reaction goes to the right) since it'll want to balance out the equation. However, if Q > K, then it means there's a greater amount of pr...

Joanna Pham - 2D

I believe the test will cover everything from the first lecture to friday's lecture, which starts from chemical equilibrium to some of acids and bases (i think my TA said the professor might go over salts on friday)

Joanna Pham - 2D

For this question, it says to use tables 12.1 and 12.2 to place the bases in order of increasing strength: F-, NH3, CH3CO2-, and C5H5N.

Only C5H5N is present on the tables. How do I determine which base is stronger and weaker (F-, NH3, and CH3CO2-)?

Joanna Pham - 2D

For the sixth edition, CH12 #39, it says use tables 12.1 and 12.2 to place the following acids in order of increasing strength: HNO2, HCLO2, +NH3OH, and (CH3)2NH2+ +NH3OH and (CH3)2NH2+ aren’t included on the two tables. How do I figure out which is the stronger acid? Is there a way to figure this o...

Joanna Pham - 2D

I haven't taken Chem 14A in a long time, so I don't remember how to figure out if an acid/base is strong or weak. Can someone please explain how you could determine if an acid or base is strong or weak without being given the chemical equation? Also, in class,the Professor did an example where we ha...

Joanna Pham - 2D

I would recommend you look at the values you're given in the problem first to determine if you solve for Kc or Kp. In the problem, if you're given values for the reactants and products and they're in units of bars, then that means you'll be solving for Kp since pressure is measured in bars. However,...

Joanna Pham - 2D

For this question, we are asked to find the reaction quotient Q. For part b, the equation is P_4S_10(s)+16H_2O(l)\rightleftharpoons 4H_3PO_4(aq)+10H_2S(aq) and the answer is [H3PO4]^4[H2S]^1^0 . I am confused why we still need to take aqueous solutions into account. I...

Joanna Pham - 2D

For this question, we are asked to balance then write the equilibrium expression Kc for the reactions For part b, the equation is I_2 (g) + F_2 (g) -> IF_5 . I balanced the equation and got I_2 (g) + 5F_2 (g) -> 2IF_5 . Then I used the equation in the book, K = (R...

Joanna Pham - 2D

I believe Professor Lavelle will give us the concentrations on the exams.

Joanna Pham - 2D

i think all you need to know is that elements in period 3 and below can have expanded octets, and that H, Li, Be, and He don't have full octets

Joanna Pham - 2D

It would help to know the charges on the ligands. There's a chart on page 742 that gives you all the common ligands and their charges. Once you know the overall charge on the ligand, to find the oxidation number of the transition metal, then you would need to see what number added to the ligand char...

Joanna Pham - 2D

I'm not too sure which ones exactly, but I was told to look at the chart on pg. 742 in the textbook

Joanna Pham - 2D

For this problem, we are being asked to state if the following oxides are acidic, basic, or amphoteric of BaO, SO3, As2O3, and Bi2O3.

How do you determine if it’s acidic, basic, or amphoteic if we’re just given the molecule? Do we just draw out the Lewis structure and see from there?

Joanna Pham - 2D

Yes, I believe it does. My TA said coordination number is not equal to the number of ligands, but it's equal to the number of LIGAND ATTACHMENTS (or bonds) to the central atom.

Joanna Pham - 2D

Could someone please explain how you know if a molecule is polydentate or not? I’m still confused on this. For example, in 17.33, we’re asked if the given molecules are polydenatate or not, and if they are, how many places can it bind simultaneously? Two of the molecules given were (b) CO3 -2 And (c...

Joanna Pham - 2D

In class, we had this example I believe: [Fe(CN)6] I know the coordination number is 6 since there are 6 ligand attachments to the central atom, but I believe Professor Lavelle said the oxidation state of Fe was +1. How is it +1? I know the charge on the CN ion is -1, but since Fe is attached to 6 l...

Joanna Pham - 2D

Oxidation number is the same as formal charge except bonding pairs are not split equally. They are both assigned to the more electronegative atom. Oxidation number = V - LPE - (BE shared with less electronegative atoms) Will we be expected to remember the charges of common polyatomic compounds for ...

Joanna Pham - 2D

Yes, a sigma bond is stronger than a pi bond. This is because the length of a sigma bond is shorter than a pi bond, and it takes more energy to break a sigma bond. Wait but aren't sigma bonds single bonds? Wouldn't sigma bonds be weaker since single bonds are weaker than double bonds (which is what...

Joanna Pham - 2D

The first figure can have a lone pair because based on what Professor Lavelle said in the lecture the other day, if the central atom has two other atoms surrounding it, it shuld be linear, such as the figure shown in b. However, in a, the molecule has a bent shape. That means the molecule must have ...

Joanna Pham - 2D

Yes he was only referring to the valence electrons of carbon. And I believe my TA told me that there was a hybridization question on one of the past finals, so there’s a chance we will see it on our final. I think the only type of question that we’d be asked is what the hybridization of the orbitals...

Joanna Pham - 2D

When it's asking for stability, you need to consider if all atoms in the molecule have a full octet and if it has a low formal charge. For the way you did it with C having a pair of lone e- and having it be double bonded to O, which has two lone pair e-, O would have a full octet but C would not. C ...

Joanna Pham - 2D

The best way to approach these questions is to first write the electron configuration of Bi. The electron configuration for Bi is [Xe]4f14 5d10 6s2 6p3. But because the question is asking for the elec. config. of Bi 3+, that means you must remove 3 e- from the outermost shell or the highest e- level...

Joanna Pham - 2D

I believe the formula for perchlorate for given to us in a chart/diagram in Fundamentals Section D

Joanna Pham - 2D

I was told you should at least know or understand what a Lewis acid and base is for the test

Joanna Pham - 2D

Yes, we started Chapter 6 on Friday, but it was only a brief section on hydrogen bonds.

Joanna Pham - 2D

The easiest way to approach these problems is to write out the normal electron configuration for the element first. The electron configuration for Sb is [Kr]4d1055s25p3. To find the configuration of Sb+3, you need to remove the e- from the highest energy level, which is the 5p subshell, so the confi...

Joanna Pham - 2D

I believe there are some topics in Chapter 3 that we didn't touch upon, so I would say the test encompasses everything Professor Lavelle talked about during lecture (Lewis structures, bond strenth, etc.)

Joanna Pham - 2D

For part b, we are asked to draw the Lewis structure of CH3OH. I drew it differently (see image below) from the book, but I still got a formal charge of 0 for each atom. Is the way I drew it still right or no?

: Diagram for 3.41b

Joanna Pham - 2D

Wait, where are you guys getting ionization energy from? I thought the central atom has to be the element that was the least electronegative, which is why C is the central atom since it has the electronegativity

Joanna Pham - 2D

I still don't understand letters b and d. For the explanation for letter d, what do you mean by "only one orbital can exist in that location in space"? If l=2 aren't there 5 orbitals (ml)? And doesn't n=3 and l=2 refer to row 3 in the d block? Thank you and sorry if the questions are conf...

Joanna Pham - 2D

I'm positive my TA told us last week that points will be docked off for having an incorrect number of significant figures.

Joanna Pham - 2D

I think it also depends on the question, so be sure to read the question carefully! I believe if the question asks for the FULL electron configuration, you would need to write out all the subshells. But if the question just asks for the ground state, I believe you could use the noble gas abbreviatio...

Joanna Pham - 2D

For ground state electron, you need to order the subshells from lowest to highest energy first, so the electron configuration of Sn would be [Kr] 4d^10 5s^2 5p^2. When it's written this way, it's easier to see which subshell, at least for me, the electrons are removed from, which is outermost shell ...

Joanna Pham - 2D

Will we need to be able to explain the existence of orbitals using the Heisenberg Uncertainity Principle or anything about the uncertainty principle for that matter? We will need to know how to do problems concerning the uncertainty principle, but I am not too sure about using it to explain the exi...

Joanna Pham - 2D

Also, could someone please explain to me why for part e, tungsten is [Xe]4f^14 5d^4 6s^2? If you follow the logic stated in some of the previous replies of how 4d^5 and 4^10 are more stable than 4d^9, then shouldn’t the ground state electron configuration of tungsten be [Xe]4f^14 5d^5 6s^1 instead o...

Joanna Pham - 2D

So how do we know when the element’s a “special case”? Do we only write, for example, 4d^10 5s^1 instead of 4d^9 5^2 when the element is near 4d^5 or 4d^10?

Joanna Pham - 2D

For further explanation for the whole question, (a, Carbon) shows 2 electrons in one p orbital when there are empty p orbitals, so it is in an excited state because ground state electrons want to be in separate orbitals. For (b, Nitrogen), one electron has opposite spin compared to the other two, b...

Joanna Pham - 2D

If an atom undergoes a transition from say 1s to 2p, does the energy of the electron also increase? I know the energy state increases for sure since it’s going from the s-orbital to the p-orbital, but does that also mean the energy of th ELECTRON also increases? Can someone please explain why or why...

Joanna Pham - 2D

I’m confused as to why 4g can’t exist. Can someone explain this to me please?

Joanna Pham - 2D

Could someone explain part a and b please? I’m confused why the answer for a is 6 and 2 for part b. The question’s asking “how many electrons can have the following numbers in an atom.” For part a, we’re given that n=2 and l=1, so it’s referring to the 2p shell. I know that the p shell can hold a ma...

Joanna Pham - 2D

I was wondering if someone could clarify my confusion about the magnetic quantum number (ml). I understand ml goes from l to -l. So if for example, ml = -2, -1, 0, 1, and 2, do each of the numbers correspond to an orbital? For instance, is -2 referencing to the d-orbitals along the negative x, y, z ...

Joanna Pham - 2D

Could someone please explain what the difference between a shell, subshell, and orbital is? I don’t really see the difference between them.

Joanna Pham - 2D

I am curious,why exactly does 3d have a lower energy level than 4s?

Joanna Pham - 2D

Is there a difference between the electron configuration and the ground state configuration? Is ground state config. just another term for electorn config.?

Joanna Pham - 2D

I was confused about this too. I don't understand the exact reason why 3d comes before 4s when writing the electron configuration.

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