CHEMISTRY COMMUNITY

Jasmine 2C

Kw is the equilibrium constant for water, and it is always equal to 1 * 10^-14. This can only be applied for conjugate acid-base pairs because the concentration of H+ and OH- the two produces are tied together. If one goes up, the other goes down, thus the conjugate seesaw.

Jasmine 2C

While I may not share the same love for Athena as you do, I love Greek mythology so thank you for sharing this special piece.
Thank you for everything Dr Lavelle! I hope these past two quarters have been worth your time. Please take care, stay safe, and have a good break!

Jasmine 2C

Does anyone remember what was the mnemonic Lyndon taught us for the state functions PDTVHUGS?

Jasmine 2C

KeyaV1C wrote:I don’t think it is. I saw the Thursday one floating around here but not the Tuesday one. Did you have any specific questions on the Tuesday test?

I wanted to know the answer for Question 4

Jasmine 2C

Does anyone know if the answer key for the test 2 given during Tuesday discussion sessions are posted anywhere?

Jasmine 2C

(a) What is the overall reaction for the following mechanism? ClO- + H2O ⇌ HClO + OH- (fast equil) HClO + I- ⇌ HIO + Cl- (very slow) HIO + OH- ⇌ IO- + H2O (fast equil) (b) Write the rate law based on this mechanism. (c) How will the reaction rate depend on the pH of the solution? (d) How would the r...

Jasmine 2C

Hiba Alnajjar_2C wrote:
Chem_Mod wrote:Test 2 answer key

Will the answer key for Tuesday's test be posted as well? Thank you!

Wondering the same thing!

Jasmine 2C

The presence of a catalyst provides a reaction pathway in which the activation energy of a certain reaction is reduced from 125 kJ/mol−1 to 75 kJ/mol−1. (a) By what factor does the rate of the reaction increase at 298 K, all other factors being equal? (b) By what factor would the rate change if the ...

Jasmine 2C

How does a catalyst affect (a) the rate of the reverse reaction; (b) the value of ∆Hr° for the reaction?

Can someone explain the answer for part B?

Jasmine 2C

This is from Outline 6: Understand the difference between activation energy and free energy of activation.
Can someone explain their differences?

Jasmine 2C

What's the difference between activated complex and transition state in the transition-state theory?

Jasmine 2C

MingdaH 3B wrote:I think we do need to understand it since I remember Lavelle talking about it in lecture.

He did? Along with its equation??

Jasmine 2C

Do we need to know what collision frequency is for collision theory?

Jasmine 2C

Since there's a post for saying thank you to Dr Lavelle, I felt like there needs to be a post dedicated to Lyndon and the other UAs. Due to the sudden cancellation of all in-person classes and gatherings, it seems like we can't properly express our gratuity to Lyndon (and of course the other UAs as ...

Jasmine 2C

To Dr Lavelle, Due to the unexpected circumstances, it seems that we cannot properly say goodbye to you tomorrow. But I really want to take this time to say a big THANK YOU for the past two quarters. Chemistry has always been a subject that I've dreaded (due to bad prior experiences)-- and honestly,...

Jasmine 2C

In lecture today, the slide mentioned something about how the rate law and integrated considers the reactant only and that "therefore the product must be in a different phase or remove product". What does that mean?

Jasmine 2C

I know Dr Lavelle explained this a bit in lecture but I don't remember all too much about it. How does a catalyst/enzyme cause the reaction rate to be independent of the initial concentration of the reactant?

Jasmine 2C

Am I the only one being utterly confused about the homework problems? The examples in class and in the textbook for section 6L doesn't even compare to the exercise problems. It's like what we learn from lecture and the textbook have a huge difference in the homework problems we are asked to solve an...

Jasmine 2C

So if we start off with an equation: 2KMnO4 + 8FeCl2 --> 2KCl + 2MnCl2 + 8FeO + 5Cl2. Through this equation you would see that your potassium value doesn't change, its charge is still +1. You also notice that the charge of Cl doesn't change and that it is still -1. That means MnO4 and Fe are your c...

Jasmine 2C

Cd(OH)2(s)+2e- →Cd(s)+2OH^-(aq) E°(anode)=-0.81V Ni(OH)3(s)+e-→ Ni(OH)2(s)+OH^-(aq) E°(cathode)=+0.49V Reversing the anode rxn and multiplying the cathode rxn by 2 yields Cd(s)+2OH^-(aq)→Cd(OH)2(s)+2e- 2Ni(OH)3+2e-→2Ni(OH)2(s)+2OH^-(aq) then, upon addition, 2Ni(OH)2(s)+Cd(s)→Cd(OH)2(s)+2Ni(OH)2(s) ...

Jasmine 2C

For Part B "Ce4+(aq) + I-(aq) -> I2(s) + Ce3+(aq)", why is there a Pt(s) on the side of the anode as well? Isn't only the electrode on the cathode side made of platinum? In the solutions manual, it says an inert electrode is needed when both oxidized and reducing species are in the same so...

Jasmine 2C

Do we not input stoichiometric coefficients in cell diagrams?

Jasmine 2C

For Part D "(d) Pt(s)|O2(g)|H1(aq)||OH2(aq)|O2(g)|Pt(s)", the balanced equation for the cell reaction is H20(l) -> H+(aq) + OH-(aq) and Ecell°= -0.83V. Can someone explain why the solution manual says "Note: This balanced equation corresponds to the cell notation given. The spontaneou...

Jasmine 2C

The right side of the electrode is for reduction and the left side of the electrode is for oxidation so the half reactions are Oxidation (at anode): 2H2O —> O2 + 4H^(+) + 4e- Reduction (at cathode): O2 + 2H2O + 4e- —> 4OH- How do we know the oxidation reaction is H20 oxidizing to O2 and 4H+ when on...

Jasmine 2C

Can someone explain where the Cl- came from in Step 1 and where the H+ came from in Step 2? Aren't cell diagrams supposed to depict all reactants and products in the reaction?

Jasmine 2C

(a) Reaction of thiosulfate ion with chlorine gas: Cl2(g) + (S2O3)^2- (aq) -> Cl2(aq) + (SO4)2- (aq) Can someone explain how the balanced oxidation reaction (S2O3)^2- (aq) + 5H20 (l) -> 2(SO4)2- (aq) + 10H+ (aq) + 8e- shows the change of oxidation number of sulfur that corresponds to the 8e-? I'm tr...

Jasmine 2C

I understand that the oxidation number/state is the charge of an element. But what I don't understand is how certain elements can have so many different oxidation numbers, i.e. carbon, while others have so less, i.e. oxygen and hydrogen? For example, homework problem 6K1 "The following redox re...

Jasmine 2C

Are all redox reactions either an acid reaction or base reaction? If not, what are some examples of redox reactions that aren't acid/base reactions?

Jasmine 2C

Can someone explain why the two hydrogens have a +1 charge each? Don't hydrogens have a neutral charge unless it's a H+ proton?

Jasmine 2C

Understand why reaction free energy depends on pressure and the equilibrium constant.
Can someone explain why G depends on pressure?

Jasmine 2C

I know that if ∆G° is negative, that means the reaction is spontaneous (since K>1 and products are favored at equilibrium) and if ∆G° is positive, the reaction is not spontaneous. Does this apply for ∆G as well?

Jasmine 2C

For questions like 5G.15, (a) Calculate the reaction Gibbs free energy of N2(g) + 3 H2(g) -> 2 NH3(g) when the partial pressures of N2, H2, and NH3 are 4.2 bar, 1.8 bar, and 21 bar, respectively, and the temperature is 400. K. For this reaction, K = 41 at 400. K. (b) Indicate whether this reaction m...

Jasmine 2C

Hi,
Would someone please be kind enough to share their notes from Monday's lecture? I had to leave early so I missed like the last two slides of notes :(

Jasmine 2C

This is probably one of the easiest redox questions but I don't understand redox overall (with the balancing, half-rxns, etc) :( can someone explain how to do this? The following redox reaction is used in acidic solution in the Breathalyzer test to determine the level of alcohol in blood: H1 (aq) + ...

Jasmine 2C

In lecture, there was a slide about half-reactions having no conducting solids and the reaction was 2Fe^3+(aq) + Cu(s) -> Cu^2+(aq) + 2Fe^2+(aq).
What does it mean there are no conducting solids? Is the Cu(s) not a conducting solid?

Jasmine 2C

In lecutre, Professor Lavelle said, when we use the Van't Hoff equation to calculate K at two different temperatures, the ∆H and ∆S don't have any subscripts because enthalpy and entropy aren't temperature dependent. How do we know they aren't temperature dependent? What is the reasoning behind that...

Jasmine 2C

Does anyone know if the midterm/final/course overall is curved?

Jasmine 2C

I don't know about 14C but I'm taking 14BL currently with 14B and the workload of 14BL seems decent at the moment. I don't think there should be a problem taking 14C and 14BL. You will just need to retain mainly acid-base concepts for 14BL because it focuses on that a lot.

Jasmine 2C

Calculate the standard reaction entropy, enthalpy, and Gibbs free energy for each of the following reactions from data in Appendix 2A: (a) the decomposition of hydrogen peroxide: 2 H2O2(l) -> 2 H2O(l) + O2(g) (b) the preparation of hydrofluoric acid from fluorine and water: 2 F2(g) + 2 H2O(l) -> 4 H...

Jasmine 2C

Do higher bond enthalpies indicate higher stability?

Jasmine 2C

Can someone explain the difference between all these notations: ΔH, ΔH°, ΔH(rxn)°, and ΔH(f)°? I feel like some questions refer to ΔH°as the same as ΔH(rxn)°but some don't so I'm utterly confused. It would also help if you explain this with the units correlating to each because I know some has "...

Jasmine 2C

Why does the solution manual (6th edition) put "The reaction we want is N2 (g) + 5/2 O2 (g) -> N2O5 (g)" when there's no N2 in the reactions given? Shouldn't we create a reaction that does include the reactants and products of the 2 reactions given, which will be 2NO (g) + 3/2 O2 (g) -> N2...

Jasmine 2C

When we talk about enthalpy in any aspect (standard rxn enthalpy, standard enthalpy formation, change in enthalpy, etc), is it always defined as the amount of heat released or absorbed at constant pressure?

Jasmine 2C

Emma Popescu 1L wrote:For this question, why do we use the specific heat capacity of liquid water instead of ice?

we use the specific heat capacity of liquid water for ice because we're calculating the heat after it has been melted from solid to liquid

Jasmine 2C

for parts a and b, you would use similar processes. for part a, you would use the equation q=nCpdeltaT, and for part b, the equation q=nCvdeltaT. These are pretty much the same equations, just one is for constant pressure, whereas the other one is for constant volume. Plug in the values in each equ...

Jasmine 2C

Calculate the final temperature and the change in enthalpy when 765 J of energy is transferred as heat to 0.820 mol Kr(g) at 298 K and 1.00 atm (a) at constant pressure; (b) at constant volume. Treat the gas as ideal.

Can someone run through the steps on how to solve this problem?

Jasmine 2C

In lecture, we went over 3 methods to calculate enthalpy as well as ΔH = H(products) - H(reactants). In the textbook, they have the formula ΔH = ΔU + PΔV. Are we not allowed to use this formula (alongside ΔU = q + w) to calculate the change in enthalpy?

Jasmine 2C

Celena Kim 2I wrote:If you search up "worksheet," you can find a few! I believe Hannah just posted one recently from her session.

I tried searching but I don't find anything?

Jasmine 2C

Do we need to know the concepts in Topic 4B3? I don't remember Dr. Lavelle mentioning any of those terms in lecture.

Jasmine 2C

I know that the purpose of this image is to show that internal energy is a state function because the internal energy of both are the same, just that the path taken is different. However, what I'm wondering is how the volume of b expanded if there's no work done and no heat input.

Jasmine 2C

A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solu- tion in the calorimeter (q 5 23.50 kJ), resulting in a temperature rise of 7.32 8C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 m KOH(aq) wer...

Jasmine 2C

For part a of this problem: (a) Calculate the heat that must be supplied to a copper kettle of mass 400.0 g containing 300.0 g of water to raise its tem- perature from 20.0 8C to the boiling point of water, 100.0 8C. (b) What percentage of the heat is used to raise the temperature of the water? why ...

Jasmine 2C

Can someone give a dumb downed explanation of how reversible processes generate maximum work?

Jasmine 2C

q equals delta H when pressure is constant

Jasmine 2C

Does anyone know up to which outline the midterm will be covering?

Jasmine 2C

Bomb calorimeter is just a specific type of calorimeter. It works best when trying to keep volume and moles of the gas constant bc it's perfectly sealed and isolated.

Jasmine 2C

I believe Dr Lavelle gave a list of gases that are in the purest form (O2, N2, etc). I think there should be a list in the textbook.

Jasmine 2C

Can someone explain how and when the three methods should be the used?

Jasmine 2C

Wouldn't that be the work integral equation? Dr Lavelle didn't go through how to solve problems with it but he did show the equation

Jasmine 2C

I don't have my notebook with me currently but if I remember correctly, Method 2 was adding the bond energies of every bond in the molecule before and after the reaction and subtracted them from each other. And whether the result is positive or negative, it would indicate that the reaction is endoth...

Jasmine 2C

To change something from one phase to another, say, solid to liquid, heat is needed. This can be easily seen in any real-life example (ice becoming water due to heat). What the slide means from "temperature staying constant" means that the process of adding heat is slow so the temperature ...

Jasmine 2C

a small percentage indicates that a very very minute amount of reactant had donated a proton; a very very minute amount could mean 0.00000001, and from ICE boxes, subtracting that very small value by, say, 0.1, would make essentially no difference. So approximating 0.1-x to 0.1 is perfectly fine

Jasmine 2C

it basically means the delta H values can be added together (even if it's a negative number, which will just make the addition into a subtraction)

Jasmine 2C

:o we can pick up our exam?

Jasmine 2C

If I'm not wrong, in the scopes of our class, solvents tend to be H2O (l) and will probably only be water.

Jasmine 2C

I wondered the same thing. I just thought the solutions manual to be wrong and wrote the equation as HClO2 + H2O ⇌ ClO2 + H3O+ After this, I calculated the concentration of H3O+ from the pH value. Now I'm trying to solve for the Ka but I was wondering, is 0.10 M of HClO the equilibrium concentration...

Jasmine 2C

If NH3 + H20 -> NH4+ + OH- has a certain kb value that is related to the concentration of OH- in the solution, is the ka of that reaction related to the concentration of H3O+ in that same solution? If so, wouldn't that make ka and kb the same as pH and pOH, especially since ka * kb = kw and pH + pOH...

Jasmine 2C

Does anyone know if there are any practice worksheets from UAs, TAs, etc for Chem 14B? I remember for Chem 14A last quarter, some UAs had worksheets posted on here so I'm just wondering if there is any for this course.

Jasmine 2C

Please correct my understanding if I'm wrong: in, say, a weak base reaction like NH3 + H20 ⇌ NH4+ + OH-, there are still H30 molecules in the reaction (to maintain autoprotolysis equilibrium Kw), but H30 is just not explicitly written. Am I correct? Reasoning: we can always calculate the pH from the...

Jasmine 2C

Yes, Na2O (s) + H2O (l) ⇌ 2Na+ (aq) + 2OH- (aq) is the correct reaction If I broke that reaction into two composite ones, would they be 1) Na2O (s) + H2O (l) -> 2NaOH (aq) and 2) 2NaOH (aq) -> 2Na+ (aq) + 2OH- (aq) ? If so, why doesn't the 2nd reaction not have H20 in the reaction? I tried to write...

Jasmine 2C

Hello, Can someone write out the reaction equation for this problem? I just want to make sure I'm understanding it. "A student added solid Na2O to a volumetric flask of volume 200.0 mL, which was then filled with water, resulting in 200.0 mL of NaOH solution. Then 5.00 mL of the solution was tr...

Jasmine 2C

Are all reactions exothermic or endothermic, whether slightly or strongly exo/endothermic? And on this topic, are all reactions with a positive delta H going to be endothermic and all reactions with a negative delta H going to be exothermic, despite forming or breaking bonds during the reaction?

Jasmine 2C

How come changing temperature permanently changes K and not just Q, like the effect of other (adding reactant/products, etc) changes? Since K, the equilibrium constant, is a constant, wouldn't temperature just affect Q like the others?

Jasmine 2C

I struggled to understand acids and bases a lot for Chem 14A so can anyone give me a small run-down of what they are, how to tell which is which, and how to understand salt reactions? Also, how much about acids and bases in general do we need to know in order to do pH, pOH, Kw, Ka, and Kb calculatio...

Jasmine 2C

Karina Kong 2H wrote:Could someone explain how autoprotolysis of water leads to Kw?

need help on this too; also, does anyone know how much we need to know about the topic of autoprotolysis for the test?

Jasmine 2C

I agree with the last user's post in that it is best to round to the number of given sig figs at the very end. When dealing with pH however, the sig figs are typically calculated differently (calculated in the way of a logarithm) which I believe is 3 sig figs usually. For pH, the sig figs in the gi...

Jasmine 2C

I know that Dr Lavelle always ask us to try and keep as many digits as possible when doing multi-step problems but do we do the same for equilibrium questions (with ICE box and such)? For example, after calculating x (through quadratic or whatever necessary algebra), should we round to proper sig fi...

Jasmine 2C

Can anyone in Dis Sec 2A, 2C, 2J share their notes from Week 1's discussion section?

Jasmine 2C

For question like Module 4 Q17: Determine the shift in equilibrium, if any, which will occur for the following reactions when the temperature is increased a) Photosynthesis: 6 CO2 (g) + 6 H2O (l) ⇌ C6H12O6(s) + 6 O2 (g) delta H° = +2802 kJ.mol-1 b) The hydrolysis of ATP: ATP (aq) + H2O (l) ⇌ ADP + P...

Jasmine 2C

The photosynthesis reaction, 6 CO2(g) + 6 H2O(l) ⇌ C6H12O6(aq) + 6 O2(g), is endothermic. What effect will the following changes have on the equilibrium composition. a) Water is added. b) The partial pressure of CO2 is decreased. A. a) Decrease [C6H12O6] and [O2], b) Decrease [O2] B. a) Decrease [C6...

Jasmine 2C

Ronak Naik wrote:I attached a picture of my notes.

You're awesome! Do you by chance have notes from the Week 1 discussion?

Jasmine 2C

State whether the equilibrium shifts towards products, reactants, or neither when the given change occurs. 2 HI(g) + Cl2(g) ⇌ 2 HCl(g) + I2(s) delta H° = -238.0 kJ.mol-1 i. The volume of the system is compressed. ii. The temperature of the system is decreased. For part i, using the quick way, we kno...

Jasmine 2C

Hello!
To anyone in Discussion Sec 2A, 2C, or 2J, can you share the notes from Week 1 discussion?
I greatly appreciate your help!

Jasmine 2C

For question 5I.19 "A reaction mixture that consisted of 0.400 mol H2 and 1.60 mol I2 was introduced into a flask of volume 3.00 L and heated. At equilibrium, 60.0% of the hydrogen gas had reacted. What is the equilibrium constant K for the reaction H2(g) 1 I2(g) ⇌ 2 HI(g) at this temperature?&...

Jasmine 2C

V is also divided by PRT :) it's just typed (n/V)RT for it be easily seen as concentration * RT. (nRT)/V means the same thing

Jasmine 2C

I don't know why they were rounded before plugging in. But the general rule for tests, midterm, and final is to keep as many digits as possible (in multi-step problems) for each calculation and at the end when you have a final answer, go according to the least number of sig figs in the problem.

Jasmine 2C

K changes with temperature because there are endothermic or exothermic reactions. These reactions are affected by temperature changes (increase heat or decrease heat) and the concentrations of the reactants or products (depending on which one is affected) are permanently changed, thus the K value ch...

Jasmine 2C

First off, what do you mean by "regular equilibrium conventrations"? And second, I think ICE boxes can be used for any equilibrium question if there is a change in the equilibrium concentration (from an initial amount to a final amount). ICE boxes make those kind of questions more organize...

Jasmine 2C

The two are just different units of measurement. Depending on what unit is given and what unit they want in the final answer, you will need to use dimensional analysis to convert between the two. To convert between them, you need to know that 1 bar = 100 kPa (obtained from online) and 1 atm = 101.32...

Jasmine 2C

If the initial amounts of CO and H2O were both 0.100 M, what will be the amounts of each reactant and product at equilibrium for the following reaction? Keq = 23.2 at 600K. CO (g) + H2O (g) ⇌ CO2 (g) + H2 (g) Can someone show the step-by-step on how to solve this? I got to the part where I have 0 = ...

Jasmine 2C

Can someone explain why there are 2 OH-?

Jasmine 2C

Why is there a [HCL]0 on the denominator? Isn't the new molarity just going to be 0.12 x [HCL]0 since the molar concentration is reduced to 12% of the initial value?

Jasmine 2C

Looking at question J.7, for neutralization equations in general, since they are balanced, are all of the reactants (and products) going to contain a neutral charge?
And applying this to a broader spectrum, do all chemical equations have reactants and products that have a neutral charge?

Jasmine 2C

How do you know the acid and base needed to create zinc nitrite in part C of the question: "Select an acid and a base for a neutralization reaction that results in the formation of (a) potassium bromide; (b) zinc nitrite; (c) calcium cyanide, Ca(CN)2; (d) potassium phosphate. Write the balanced...

Jasmine 2C

Acids and bases, is there a reason why these compounds want to accept/donate a proton? Doing so causes their molecule to be less stable so why do it? Why gain a positive or negative charge when you can remain stable at net charge = 0? This question kind of came up from me trying to understand why KO...

Jasmine 2C

Rather than memorizing strong acids and bases (and thus knowing which are weak acids and bases), is there a way to tell from the molecule's structure? Like lone pairs, charges, etc?

Jasmine 2C

Does anyone know where the list of strong acids and strong bases that we need to know is located?

Jasmine 2C

Q2A: "Hydrogen bonding is important for nucleic acids. Draw how two separate nucleic acids below (guanine (G) and cytosine (C)) will interact via H-bonding to form a GC pair." - can someone explain where the H-bonds are and how they're formed? Q2.B: "There are two different base pair...

Jasmine 2C

Can someone give a hierarchy of the electronegativities of main elements we should know about? Like I know F is the most electronegative and then O (I think?). And then there's C and S that are very similar? I would try to search up periodic tables of them but most give varying values. And I underst...

Jasmine 2C

Oxalate is bidentate because only two of the oxygens have a minus 1 charge that they use to form a bond with the central metal atom. The other two oxygens form a double bond with the carbon so they have a neutral formal charge. Does it matter if they have a negative bond or not? For molecules like ...

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