CHEMISTRY COMMUNITY

Joseph Saba

On the final, there was a problem where it asked you to calc the deltaG/deltaH/deltaS of ionization of water of a specific temp. How would you have approached this problem?

Joseph Saba

Sine it says pi comes from ATP, the two concentrations cancels and K depends on [ADP] only. Maybe I am wrong about how I interpreted this problem, but I assumed that since all the Pi came from ATP, I assumed it meant that it only came from ATP that was broken into ADP...so Pi = ADP concentration......

Joseph Saba

IM pretty sure it stays constant

Joseph Saba

One way is to see if the slow step rate law matches the overall rate law. Remember that no matter the substitutions u may have to make for intermediates, the rate law will have the same order no matter what.

Joseph Saba

Yes this is the concept of a pseudo rate law

Joseph Saba

First, you would wanna figure out how much H+ there is in solution. You do this by setting up an ice table and solve for H+ (remember is 2H+ in the equation). Then you have the amount of H+ in solution, and in order to neutralize it, you need the same amount of OH- to balance this out. You then use ...

Joseph Saba

So the rate law would be based off of if each reactant is a first, second, or zero order reactant. Based from the info, you can infer that both reactants are first order because as you increase their concentration by a constant, the rate also increases by the same amount. therefore it would be k[CH3...

Joseph Saba

He's referencing deltaG overall. He used this equation to see which side (reactants or products) will be favored given the conditions. Since deltaG is positive, it isn't spontaneous but that's for the forward reaction, the reverse reaction will be spontaneous in this case.

Joseph Saba

Even with the current situation, Lavelle has been a really great professor for both my 14a and 14b careers. I truly thank him for making my chemistry “good chemistry” :)

Joseph Saba

Does anyone know any book problem with a situation that we need to use this? The example in the book is the example we did in class. I also dont understand how to do number 14 on the "endgame" worksheet pertaining to this.

Joseph Saba

Will there also still be TA Office Hours?

Joseph Saba

Ok thank you!

Joseph Saba

How do we know, when drawing this reaction profile, where the energies of the products of the first reactants lie energy-wise in relation to the whole profile? I know the whole reaction must be exothermic but where should the middle products/reactants lie? The answer implies they are both the same e...

Joseph Saba

How should we think of the rate of decomposition vs rate of formation in this type of scenario? Will we have to do this one a test?

Joseph Saba

Lavelle states on a worksheet on his website that "2N2O(g) → 2NO(g) + O2(g) • Write the overall rate expression for this first-order reaction. rate= k[N2O] *Note that the exponent does not match the coefficient in front of N2O. By just looking at the overall balanced equation, you cannot tell t...

Joseph Saba

I keep getting 1.12x10^8 M/s =k2 regardless of the order of the equation, but that's incorrect according to the book which has 2.5x10^9M/s as the answer.

Joseph Saba

What does the A stand for in the Ae^(-Ea/RT) equation? I haven't seen this equation directly tested/used on the homework

Joseph Saba

Why is it when you plot the half-life against [A] for a reaction that is zero order, that the plot is linear?
Also, why is the initial rate of a 1st order rxn vs [A] linear?

Joseph Saba

Well, when we derived the equation in class, the equation so happened to yield a negative number in front of k resulting in a negative slope. Remember, zero-order reactants don't affect the rate, so it doesn't mean much to the reaction rate, it just speaks to the relationship between [A] vs time.

Joseph Saba

I found an equation in book which helped. Ea(with catalyst)-Ea(w/o catalyst)/RT= a number. That number you then add a negative sign to and raise it to the e^power. Basically, its putting k2/k1 with the Arrhenius equations both on the top and bottom, respectively. so for part a i got 75000-125000/(8....

Joseph Saba

7.31 The rate constant of the reaction O2(g) + N2(g) --> NO(g) + N(g), which takes place in the stratosphere, is 9.7 x 10^10 M/s at 800 degree C. The activation energy of the reaction is 315 kJ/mol. What is the rate constant at 700 degrees C? I used the equation ln(k2/k1)=Ea/R(1/T2-1/T1) but im gett...

Joseph Saba

Half-life of A in a second-order reaction is 50.5 sec when [A]intial=.84 M. Calc the time needed for the conc of A to decrease to (a) one-sixteenth, (b)one-fourth, (c)one-fifth its original value. Can someone explain their thought process and method of doing this problem? I thought all you had to do...

Joseph Saba

Thank you!

Joseph Saba

c) 2 A --> B + C, given that [A]intial= 0.153 M and that after 115 s the
concentration of B rises to .034 M.
How would I set up this problem? I dont understand how i should use the conc of B since the problem also gave us the initial conc of A.

Joseph Saba

7E.5 The hydrolysis of an organic nitrile, a compound containing a OCqN group, in basic solution, is proposed to proceed by the following mechanism. Write a complete balanced equation for the overall reaction, list any intermediates, and identify the catalyst in this reaction. Why is the catalyst fo...

Joseph Saba

7D.7 For the reversible, one-step reaction A + a <—>C + D the forward rate constant for the formation B is 265 L/molmin and the rate constant for the reverse reaction is 392 L?mol ?h . The activation energy of the forward reaction was found to be 39.7 kJ?mol21 and 25.4.0 kJ?mol21 for the reverse rea...

Joseph Saba

Step 1 NO + Br2 --> NOBr2 slow
Step 2 NOBr2 + NO --> NOBr + NOBr fast
Write the rate law for the formation of NOBr implied by this
mechanism.
I got rate= k[NO2]^2[Br2], but the book has rate= k[NO2][Br2], why is that?

Joseph Saba

"The potential supplied to an electrolytic cell must be at least as great as that of the cell reaction to be reversed. If there is more than one reducible species in solution, the species with the greater potential for reduction is preferentially reduced. The same principle applies to oxidation...

Joseph Saba

6.43 Indicate for each of the following statements whether it applies to Ecell8, to Ecell, to both, or to neither: (a) decreases as the cell reaction progresses; (b) changes with temperature; (c) doubles when the coefficients of the equation are doubled; (d) can be cal- culated from K; (e) is a meas...

Joseph Saba

In a neuron (a nerve cell), the concentration of K+ ions inside the cell is about 20–30 times as great as that outside. What potential difference between the inside and the outside of the cell would you expect to measure if the difference is due only to the imbalance of potassium ions? Do we conside...

Joseph Saba

Reactant B is second order. Since you know reactant C is zero order, you can focus on two reactions where reactant A is constant and reactant B is doubling and look at what it does to the rate constant. Hope this helps

Joseph Saba

How do I know if a metal will dissolve in a certain solution? Should it be in a spontaneous way, where the metal will be oxidized by the molecules in the solution?

Joseph Saba

When will Final Review Sessions start? i need to go to all of them lol

Joseph Saba

I wouldn't think of it like that just to be sure, I would just make sure I know how to balance them

Joseph Saba

^^^^^

Joseph Saba

You can use the general equation for Gibbs free energy of formation (products-reactants=rxn total) and then set that equal to deltaG=-RTlnK. For part b its a regular ice table problem.

Joseph Saba

I would also suggest reading lesson 7A in the book as a good overview as well. Make sure to understand initial versus average rates

Joseph Saba

When a pH meter was calibrated with a boric acid–borate buffer with a pH of 9.40, the cell potential was +0.060 V. When the buffer was replaced with a solution of unknown hydronium ion concentration, the cell potential was +0.22 V. What is the pH of the solution? How would i begin this problem? I do...

Joseph Saba

The Outline for EChem mentions the electrochemical series, what should we know about this? It seems like its just a ranking of the most likely to get oxidized metal to the most likely to get reduced metal. Am i missing something else?

Joseph Saba

Thermo outline 4: Understand why reaction free energy depends on pressure and the equilibrium constant
I understand the equations that go along with this statement, but what else should we know about this?

Joseph Saba

6.57 Use the data in Appendix 2B and the fact that, for the half- reaction F2(g) + 2 H+(aq) + 2 e- ---> 2 HF(aq), E(knot)= +3.03 V, to calculate the value of Ka for HF.
How would I do this problem?

Joseph Saba

Oh yes, my bad.

Joseph Saba

Calculate the potential of a cell constructed with two nickel electrodes. The electrolyte in one compartment is 1.0 m Ni(NO3)2(aq).In the other compartment, NaOH has been added to a Ni(NO3)2 solution until the pH was 11.0 at 298 K. Ksp=6.5x10^-18 How would I start this problem? I got the concentrati...

Joseph Saba

This question asks for a concentration of one of the species given the cell potential in the problem. However, they give us partial pressures for the other species in the reaction. Do we have to factor this into our Q equation or not at all? How would this work exactly?

Joseph Saba

Are we still able to pick up 14A finals? I definitely forgot until now.

Joseph Saba

6L.7 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) + Br2(aq), a solubility equilibrium (b) H+(aq) + OH-(aq)--> H2O(l) How would i write the half reactions for these and the cell diagrams? Its confusing to ...

Joseph Saba

The difference between the two is that delta G naught is at standard conditions. The reason Professor Lavelle emphasized it is because delta G naught is always the same because it is referring to when the reactants/products are at standard temperature/pressure. As the rxn goes towards equilibrium, ...

Joseph Saba

6L.9 (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). Are we supposed to know that the Fe...

Joseph Saba

How would you write the half-reactions given the cell is :
Pt(s) I O2 (g) I H+(aq) I OH-(aq) I O2 (g) I Pt(s)

Joseph Saba

Most likely on tests im pretty sure lavelle would give us the charges. If not, just know some common ones like phosphate, sulfate, etc.

Joseph Saba

The way i start this problem is by balancing the solution in acidic solution and then, at the end, adding OH- to both sides so the H+'s cancel out. The OH- + H+ turns into neutral H2O molecules (which may or may not cancel out. Therefore, Oxidation: 8OH- +P4 --> H2PO2-+4e- Reduction: 12e-+ 12H2O+ P4...

Joseph Saba

Could you fix the formatting of this question?

Joseph Saba

Your logic is correct. Using the equation delta G = delta H - (T)(delta S), it is apparent that the value of delta G will be close to that of delta H when you have a value of delta S close to or equal to 0. Therefore, the answer with the smallest change in entropy, as you mentioned, would be the co...

Joseph Saba

Q3B Why is the answer for the question 50ml of 2M HCl and 50ml of 2 M NaOH?
Q3D: How are we supposed to determine the net charge of acetic acid given its at a pH of 6 with pKa = 4.75?

Joseph Saba

Reaction of chlorine in water:
Cl2(g) --> HClO(aq) + Cl2(g)
Can someone help me balance this in an acidic solution?

Joseph Saba

Make sure that the amount of electrons transferred are all accounted for on the other side of the equation

Joseph Saba

If you find yourself with a cubic function you can probably approximate.

Joseph Saba

Cell potential is also equivalent to the max amount of work that the battery can do.

Joseph Saba

https://www.relatably.com/m/img/light-memes/thumb.jpeg
You won't regret seeing this even though its a Chem14A joke

Joseph Saba

I would only do the calculation for irreversible reactions if the problem says specifically.

Joseph Saba

805317518 wrote:Conceptually speaking, would an adiabatic system always be an isolated system? Or is there a more specific definition?

It would be an isolated system usually because there is no heat transfer

Joseph Saba

I would look at complexity first. The more orientation it has, the higher the entropy will be. Ne may be heavier but can occupy fewer orientations then NH3.

Joseph Saba

Calorimeters measure the temperature difference in a reaction. Bomb calorimeter means that the volume is constant. I would review what it means for a system to be isolated, closed, or open.

Joseph Saba

In an adiabatic process, deltaH is equal to 0, so deltaU is equal to work.

Joseph Saba

It does more work then an irreversible reaction due to that fact.

Joseph Saba

I think about it like this, if you and your friend go on a hike and there are two paths, one more difficult and one easier. You take the easier way while your friend goes the long way. Remember, work = pdeltav but also work= force x distance. If your friend goes a farther distance then you but you b...

Joseph Saba

You're given pKb so you can find Kb. However, in the reaction given you need Ka because HF is an acid. Solve for Ka by using Ka*Kb=Kw, K =1*10^-14. Ka is now your equilibrium constant.Then use the given initial concentration of hydrogen fluoride, 0.12M, and complete an ice table using the Ka consta...

Joseph Saba

Because when work is being done into the surroundings, the system loses energy and thus the work is negative. If work is being done on the system then there is a positive sign.

Joseph Saba

It's also easier to think about the amount of work as synonymous with energy or the amount of effort it would take to do something like that.

Joseph Saba

Hi, can someone explain how they got the answer on test 1 for #5? For reference, "The pkb of fluoride is 10.8. A .12 M solution of hydrogen fluoride was made for silicon water processing. What is the pOH of this solution at equilibrium? HF + H2O -> F- + H3O+"

Joseph Saba

Can someone explain the difference between intensive vs extensive properties?

Joseph Saba

They have the ability to form naturally with very little energy required but a lot of energy released when formed (thus why it is so stable).

Joseph Saba

I believe part a is correct, treat heat as a product and apply le chatlier.

Joseph Saba

The way I understand it is from treating heat as a reactant/product and therefore apply le chatliers principle to it.

Joseph Saba

I would just remove an H from the polyprotic acid and give it the conjugate base a negative charge.

Joseph Saba

Will we be given equations on test 1 or will we have to infer whether the molecule acts as an acid or a base?

Joseph Saba

Probably, keep it in mind while doing calculations. Look for the Ka/b value that is lower then 10^-3. If you are unsure you can always calculate it and see that the x is insignificant at the end.

Joseph Saba

I would just know how to look for a change in pressure in terms of moles on each side to make it easier, but also make sure to understand how the changes in pressure affect the molecules themselves,

Joseph Saba

I would suggest to just look at it in terms of concentration, activity seems like an advanced topic for gen chem.

Joseph Saba

I think its a physical change. But I also think you should see someone about this nightmare.

Joseph Saba

Water is usually implied to be H20(liquid), therefore when do we put it into the Kc equation? Some problems include H20 while others leave it out. Any help would be appreciated

Joseph Saba

Concentration of gases would be one of the only reasons we would use the ideal gas law at this point of the class.

Joseph Saba

It could be disturbed by either taking away/adding products/reactants to the reaction momentarily.

Joseph Saba

When you increase the concentration of a reactant, the reaction must shift left in order to balance out the change in the reaction.

Joseph Saba

Q is also calculated the same exact way as the K value would be calculated. The only difference is that it's not at equilibrium.

Joseph Saba

I don't think that would work, gases are usual in concentrations relating to the gaseous form, so making the assumption that it's in the liquid form would be incorrect. I think gaseous products/reactants are most likely always going to be in the Kp form.

Joseph Saba

Gibbs free energy is energy that is able to do work

Joseph Saba

Determine it by the intermolecular forces of the molecules as compared with another.

Joseph Saba

Yea that works

Joseph Saba

Identify the acid or oxyacid and then determine if it has an electron pair to donate to a proton and therefore maybe also amphoteric.

Joseph Saba

SGonzales_3L wrote:One thing to know that Dr. Lavelle mentioned in class is that if a pKa value is given it is highly likely that that acid is a weak acid. Strong acids strongly favor the products and, thus, have an astronomically large pKa.

Does that mean strong acids have a high conc of H+?

Joseph Saba

i believe it was 11 hydrogen bonding sites if I remember correctly. Count up the number of lone pairs and the number of hydrogens that are bonded to NOF to and add them together to get the number of hbonding sites

Joseph Saba

An acid will be stronger if it can easily lose hydrogen to a base. The CH3 in acetic acid donates electrons which makes the O-H bond stronger due to electronegativity therefore the H is harder to remove, which isn't what we want. This makes formic acid the stronger acid. Basically CH3 is electron d...

Joseph Saba

Resonance generally makes a molecule stable, therefore it would be less likely to react if put into water. So I would say in general, resonance doesn't correlate with how strong an acid is.

Joseph Saba

Remember when a polyprotic acid gives up a proton (H+), the resulting conjugate base is also able to dissociate more but at a much lower pKa value and is generally not considered a strong acid anymore.

Joseph Saba

Im pretty sure it always acts a bidentate.

Joseph Saba

I am also confused about this. In my notes I have that "pH>Pka: the solution is more alkaline and the acid will give off H+ to form A- and is negatively charged." I'm not completely sure what the application of this means though.

Joseph Saba

You can use multiple tests. First, check whether each acid/base is a known strong acid or base. For bases, it would be alkaline oxide/hydroxides and for acids, it would be any halogen bonded with hydrogen or an inorganic anion bonded with hydrogen (HNO3). If this isn't the case, I would try to ident...

Joseph Saba

Jorge Ramirez_4H wrote:Wait, I thought that it was one bonding site. Why do the lone pairs count I thought it explicitly needed to show H bonding to F,O, or N.

Lone pairs count because the resulting shape (trigonal pyramidal, tetrahedral, etc.) may not cancel out the enlarged lone pair thus leaving a delta negative charge

Joseph Saba

Always balance the charges using the outside potassium and not the chromate.

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