CHEMISTRY COMMUNITY

Xuan Kuang 2L

There is no change in enthalpy for part b since it is under constant volume, not pressure. You would use 765 J= qv

Xuan Kuang 2L

For this problem, you solve for Ecell, using this formula for the Nernst equation: Ecell=Eocell-(0.025693V/n)lnQ. Then substitute that value in for deltaG= -nFEcell.

Xuan Kuang 2L

The easiest way to figure out n is to split the the reaction into its reducing and oxidizing half-reactions, and then balance out those reactions os they both have the same number of e- in each rxn. For part b), we know to put the 14H+ for Cr because we see that its product has an O in it, meaning t...

Xuan Kuang 2L

Could someone please help me on part a? Thanks!

For the first-order reaction A-->3B + C when [A]0=0.015 mol.L^-1, the concentration of B increases to 0.018 mol.L^-1 in 3.0 min
a) What is the rate constant for the reaction expressed at the rate of loss of A?

Xuan Kuang 2L

Yes, I believe the final is cumulative, so chemical equilibria will probably be on the exam.
It is under the file titled "Important Final Exam Information" on the 14B website I think :)

Xuan Kuang 2L

Could someone help to explain this question to me?

Q:The half-life of A in a second-order reaction is 50.5s when [A]0= 0.84 mol. L^-1. Calculate the time needed for the concentration of A to decrease to
a) one-sixteenth
b) one-fourth
c) one-fifth

Thank you!

Xuan Kuang 2L

A student was given a standard Cu(s)|Cu2+ (aq) half-cell and another half-cell containing an unknown metal M in 1.00 M M(NO3)2(aq) and formed the cell M(s)|M+(aq)||Cu2+ (aq)|Cu(s). The cell potential was found to be -0.689 V. What is the value of E(M2+/M)? From the cell diagram, I though Cu/Cu2+ was...

Xuan Kuang 2L

a) Write balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron(II) chloride. b) Write the balanced equation for the cell reaction and devise a galvanic cell to study the reaction (write its cell diagram) For this reaction, how do you determine whi...

Xuan Kuang 2L

Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions:
a) AgBr(s)--> Ag+ (aq) + Br-(aq), a solubility equilibrium

Could someone explain to me how to approach this problem? Thanks!

Xuan Kuang 2L

Essentially, the methods are the same as the acidic reaction up until the part when you have to cancel out electrons. From that point, you add an additional step where you add the same amount of OH- ions on both sides so that the number of H+ ions will completely react with the OH- ions to create H2...

Xuan Kuang 2L

If one side of the diagram yields no solid metal, do we automatically know that we should write Pt(s) on that side? Is there a way to know which alternative metal we use, if we don't use Pt(s)?

Xuan Kuang 2L

Just for clarification from Friday's lecture, why does the E of a reduction/oxidation reaction not change whenever you alter a reaction by multiplying the coefficients? Thanks in advance!

Xuan Kuang 2L

In this case, we consider Le Chatelier's Principle. If the partial pressure of O2 were to increase, there would be more O2 molecules present, which results in the equilibrium ratio having a higher partial pressure of O2 than initially (Qp>Kp). To minimize this effect, the reaction will shift to the ...

Xuan Kuang 2L

Do all elements in their most stable form have standard Gibbs Free Energy of formation of zero? If so, could someone conceptually explain to me why this is so?

Xuan Kuang 2L

For those particular problems, you need to solve for a total change in entropy caused by both temperature and volume. I believe in those cases we are generally considering a reversible reaction, so we use two separate equations, one for temperature change (S=nCln(T2/T1)) and another for volume (S=nR...

Xuan Kuang 2L

Could someone re-explain for me why entropy is a maximum at equilibrium? More specifically, could someone explain why at equilibrium, all possible states have been reached?

Xuan Kuang 2L

Yes, I believe that is the case because they're converting it to atm I think.

Xuan Kuang 2L

COF2 would have a higher molar entropy than BF3. When you take a look at the molecular structures, BF3 is a trigonal planar with the same B-F bond on each end. This means that is it very ordered, compared to COF2, which has two F's and an O at the ends. This means that for some molecules, it could p...

Xuan Kuang 2L

SO2 would be the limiting reactant because if you had 0.030 mol of O2, then by the molar ratio given to us by the coefficients of the reaction (2 mol SO2 for every 1 mol of O2), then you'd need 0.060 mol of SO2 to fully react. However, in the question, we are given only 0.030 mol of SO2, half the nu...

Xuan Kuang 2L

I believe average kinetic energy is calculated using the formula 3/2RT

Xuan Kuang 2L

Bond enthalpy is the least accurate because it represents the average of a series of different bonds from different molecules, so it represents an approximation of a bond rather than a more precise measurement like formation.

Hope that helps!

Xuan Kuang 2L

To approach this problem, you'd first have to recognize that you're using the formula qp=nCp,mdeltaT. You would then substitute given values, with 765 J being qp, 0.820 mol for n, and 298 K for initial temperature. However, in this problem, you'd also have to recognize the rotational contribution of...

Xuan Kuang 2L

On Friday's Lecture, there was an example for Method 2 which considered the bond enthalpies regarding CH2=CH2 + H-Br --> CH3-CH2Br Could someone reiterate why we utilized the value of the C=C bond on the reactants' side, and why we considered using the bond enthalpy of C-C on the products' side? I g...

Xuan Kuang 2L

Hello, I hope these answers help! a) The change in internal energy would only be zero if q+w=0. Since we've established no energy is transferred as heat (q=0) we can then say that this statement is only true when w=0, or if no work is done b) This is always true because the question stated that ther...

Xuan Kuang 2L

6B.9 a) Complete the following table [H3O+] [OH-] pH pOH i) 1.50 mol.L-1 ii) 1.50 mol.L-1 iii) 0.75 iv) 0.75 b) Rank the four solutions in order of increasing acidity (I understand iii) and iv), but I am not sure why I keep getting i) and ii) wrong. When I calculate for i), I get [OH-]= 6.67x10^-15 ...

Xuan Kuang 2L

Both sides of the reaction contain the same number of moles (2:2), so the reaction doesn't favor any particular side.

Xuan Kuang 2L

Hey there! I believe we could use this method with Kc as well, if we needed it.

Xuan Kuang 2L

Hello there, not sure if anyone asked this already, but could someone explain to me how we know that Group I/II and some of the halogens (Cl-, Br-. I-) have no effect on the pH when it dissociates in water?

Xuan Kuang 2L

I believe that this is always the case. There is an equation relating the temperature to K that may help you understand why, and you can see the full derivation of it in the textbook (For me, it is in 5H, pg 413, not sure about the 6th edition)

Hop this helps

Xuan Kuang 2L

Hey there! I believe it has to do with the coefficient of the reactant, which has a 2 on it, I assume (Sorry, I'm not too sure about this because I don't think I have the same edition as you) If there's a 2 as a coefficient, we have to consider this when forming the ICE Box. In this case, if the pro...

Xuan Kuang 2L

Not sure if you wanted all of the answers, but I provided them all down below with some explanations. Hope it helps! a) When you add NO, Q>K, so more reactants are formed. This means more products are used up, so the amount of H2O, which we assume is constant and hasn't changed in concentration, dec...

CHEMISTRY COMMUNITY

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