DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

General non-science questions and class announcements.

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Karyn Nguyen 1K
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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Karyn Nguyen 1K » Tue Feb 12, 2019 10:22 pm

Celine Hoh 2L wrote:
Karyn Nguyen 1K wrote:For worksheet 4, is the answer for 6a wrong? I did (3/2)(31.9 mol)(8.314 J/Kmol)(311.15 K) = 124 kJ. When I didn't convert the temperature from C to K I got 15.1 kJ which is the answer given in the key.


We don’t have to convert it to kelvin as it is change in temperature (38-0)
Last edited by Karyn Nguyen 1K on Tue Feb 12, 2019 10:25 pm, edited 1 time in total.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Karyn Nguyen 1K » Tue Feb 12, 2019 10:24 pm

Celine Hoh 2L wrote:
Karyn Nguyen 1K wrote:For worksheet 4, is the answer for 6a wrong? I did (3/2)(31.9 mol)(8.314 J/Kmol)(311.15 K) = 124 kJ. When I didn't convert the temperature from C to K I got 15.1 kJ which is the answer given in the key.


We don’t have to convert it to kelvin as it is change in temperature (38-0)


Don't we need to convert it to K to cancel out the units and end up with J?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby ariana_apopei1K » Wed Feb 13, 2019 12:13 am

Celine Hoh 2L wrote:Quick question for Worksheet 1 ques8:

When I2 is added, neither products nor reactants is favored as I2 is a solid.
What happens when I2 is removed, does the reaction not shift too?

Yeah, since it is a solid it doesn't affect it either way

Jane Burgan 1C
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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Jane Burgan 1C » Wed Feb 13, 2019 1:48 pm

Karyn Nguyen 1K wrote:
Celine Hoh 2L wrote:
Karyn Nguyen 1K wrote:For worksheet 4, is the answer for 6a wrong? I did (3/2)(31.9 mol)(8.314 J/Kmol)(311.15 K) = 124 kJ. When I didn't convert the temperature from C to K I got 15.1 kJ which is the answer given in the key.


We don’t have to convert it to kelvin as it is change in temperature (38-0)


Don't we need to convert it to K to cancel out the units and end up with J?


We don't need to convert to K because the temperature difference in terms of celsius and in terms of kelvin are the same value.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Anjali_Kumar1F » Wed Feb 13, 2019 1:51 pm

Is there answer where it shows the work for these worksheets.

Karyn Nguyen 1K
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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Karyn Nguyen 1K » Wed Feb 13, 2019 3:36 pm

Anjali_Kumar1F wrote:Is there answer where it shows the work for these worksheets.


No, she only posts the answer key online, but during her workshop, she goes over how to do the problems!

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Emily Huang 1E » Thu Feb 14, 2019 3:40 pm

Why is for delta H combustion, the equation is the the delta h combustion of reactants minus delta h combustion products whereas for delta h of formation it is the opposite?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Thu Feb 14, 2019 11:21 pm

Hi students, there will be no workshop on Sunday because of the long weekend. Sessions will resume 2/24.

Enjoy the weekend after your midterm!

-K

Julia Lee
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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Julia Lee » Sat Feb 16, 2019 9:35 am

So is there no worksheet for this week?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Sat Feb 16, 2019 5:45 pm

Julia Lee wrote:So is there no worksheet for this week?


No worksheet this week! The next session will cover all topics on Test 2.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Karina Jiayu Xu 4E » Thu Feb 21, 2019 1:15 am

This is so helpful. Are the attachments basically study guides?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Fri Feb 22, 2019 6:05 pm

This week we will go over Gibbs free energy and most of electrochemistry (everything your test will cover). This is two sessions worth of material so please bear with me, see you there!
Attachments
Worksheet 7 - Electrochemistry .pdf
(90.9 KiB) Downloaded 338 times
Worksheet 6 - Free Energy.pdf
(111.27 KiB) Downloaded 314 times

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Kobe_Wright » Sun Feb 24, 2019 11:00 pm

Thanks for the worksheet it helped a lot!

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Mon Feb 25, 2019 12:55 am

Here are the keys to the Gibbs free and electrochem worksheets. As promised, for electrochem, I tried including as much detail as I can to follow through since there was not enough time to go over it.

NOTE:
For Gibbs free energy worksheet #3a, I made a mistake today in session saying that the conditions are at equilibrium. That is INCORRECT - the conditions are at standard conditions but not equilibrium. This follows through such that delta G at equilibrium is 0 and shouldn't be shifting to any side of the reaction. In 3a, it just so happens that P is 1, because 1/1^2 is 1, but P does not equal K (which is based on concentrations). So instead of writing RTlnK, I should've wrote RTlnP. Sorry for confusion.

If there are any other further confusions/mistakes, please let me know! I am still in the process of editing and perfecting these worksheets.
Attachments
electrochem worksheet W19.pdf
(1.13 MiB) Downloaded 376 times
Worksheet 6 KEY - Free Energy.pdf
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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Julia Lee » Mon Feb 25, 2019 5:18 pm

Can someone please explain #4 on the electrochem worksheet? I don't understand why the answer is Ag+ not Fe2+

Karyn Nguyen 1K
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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Karyn Nguyen 1K » Mon Feb 25, 2019 5:56 pm

For the worksheet 7 (electrochem) question 2, I don't get why the E value would cause C to be false. Can someone explain this to me please?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Karyn Nguyen 1K » Mon Feb 25, 2019 8:34 pm

When we balance the equations on worksheet 7, how do we know which side of the reaction to add H2O to?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Vincent Li 4L » Mon Feb 25, 2019 10:12 pm

Julia Lee wrote:Can someone please explain #4 on the electrochem worksheet? I don't understand why the answer is Ag+ not Fe2+


Since you want copper to spontaneously reduce, then you need to check the oxidation values of elements/options given. In order to have a spontaneous reaction with copper reducing, the cell potential must be positive, so the oxidation potential of the substance must be positive, or the reduction potential of the substance must be negative. Fe2+ and Al3+ both work since they fulfill this criterion. I think the #4 answer just has an error.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Madison Hurst » Tue Feb 26, 2019 12:45 am

On #1 of the Gibbs to find the standard enthalpy and entropy of formation you have to do the sum of products minus the sum of the reactants using the numbers given right? For some reason I am not getting the same answer.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Madison Hurst » Tue Feb 26, 2019 1:00 am

In the Gibbs WS #4 how do you find T? or can you just assume its at 25 C?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Tue Feb 26, 2019 12:35 pm

Vincent Li 4L wrote:
Julia Lee wrote:Can someone please explain #4 on the electrochem worksheet? I don't understand why the answer is Ag+ not Fe2+


Since you want copper to spontaneously reduce, then you need to check the oxidation values of elements/options given. In order to have a spontaneous reaction with copper reducing, the cell potential must be positive, so the oxidation potential of the substance must be positive, or the reduction potential of the substance must be negative. Fe2+ and Al3+ both work since they fulfill this criterion. I think the #4 answer just has an error.


Actually, when something says plain "copper" or "iron" use the actual solid and not the ion form (Cu2+, Fe3+, etc). With that said, because the question is asking for what can copper reduce, copper is acting as a reducing AGENT, which means it is oxidized, so we will use -0.52V for its oxidation potential. For reduction potentials, we leave as is on the chart. For Ag+, it is 0.80V. Total potential = reduction potential + oxidation potential, so 0.80 + (-0.52) leaves you with a positive potential value, which is what we want in order for a reaction to be spontaneous because delta G = -nFE. The values for the other ions, all have an absolute value less than 0.52 which would cause the total E to be negative, which is NON-spontaneous.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Tue Feb 26, 2019 12:37 pm

Karyn Nguyen 1K wrote:For the worksheet 7 (electrochem) question 2, I don't get why the E value would cause C to be false. Can someone explain this to me please?


In order for a spontaneous reaction to occur, total E must be a positive value and when you add up the values for answer choice c, it is negative.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Tue Feb 26, 2019 12:38 pm

Karyn Nguyen 1K wrote:When we balance the equations on worksheet 7, how do we know which side of the reaction to add H2O to?


Usually add H2O to the opposite side you added H+ or OH- in order to balance the number of O and H atoms

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Shivangi_2J » Tue Feb 26, 2019 3:30 pm

on electrochem worksheet #8d, does it matter if on the cell diagram NO is listed first or NO3 is listed first? Or can the order of these two be reversed and the diagram still denotes the same reaction

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Angela Grant 1D » Tue Feb 26, 2019 5:47 pm

Madison Hurst wrote:In the Gibbs WS #4 how do you find T? or can you just assume its at 25 C?


yeah you just assume 25 C, so 298 K

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Angela Grant 1D » Tue Feb 26, 2019 5:50 pm

Madison Hurst wrote:On #1 of the Gibbs to find the standard enthalpy and entropy of formation you have to do the sum of products minus the sum of the reactants using the numbers given right? For some reason I am not getting the same answer.


the values are given per mole, are you multiplying them by the respective moles for each compound?
so delta H for example would be [-657.0 + 2(-110.5)] - [-910.0 + 2(0) + 2(0)] = 32 kJ/mol

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Angela Grant 1D » Tue Feb 26, 2019 5:52 pm

for #4 on gibbs free energy, does it matter that the standard delta G is given in kJ instead of kJ/mol? i thought we'd have to divide by 2 to get the delta G per mole of NH3, but that didn't give me the right answer so i'm a little confused because plugging in the given value does give me the right answer even though it's not technically per mole

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby 005199302 » Tue Feb 26, 2019 7:19 pm

For #4 on the Gibbs worksheet, I keep getting -42.2 kj/mol and I can't figure out what I'm doing wrong

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby 005199302 » Tue Feb 26, 2019 7:34 pm

For #6 on the Gibbs free energy worksheet, how do we know that delta G is zero? Also, if delta G is zero and delta S of system is zero, why isn't delta S of surroundings also 0?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Samantha Ito 2E » Tue Feb 26, 2019 9:24 pm

Can someone please explain #4 on the Gibbs Free Energy worksheet?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Josephine Lu 4L » Wed Feb 27, 2019 12:40 am

could someone please explain #8 part a on the electrochemistry worksheet? How do we know that S2O8 2- is reduced and NO is oxidized?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby 905084274 » Wed Feb 27, 2019 9:45 am

Did Karen post her most recent handout answer key that we weren't able to go over in session?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby AhYeon_Kwon_2H » Wed Feb 27, 2019 2:07 pm

Could someone explain #3 on Worksheet 6? How would we find K without using partial pressure? Thanks!

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby AhYeon_Kwon_2H » Wed Feb 27, 2019 2:18 pm

Samantha Ito 2E wrote:Can someone please explain #4 on the Gibbs Free Energy worksheet?


I used deltaG = deltaGo + RTlnQ. I found Q with the pressure values that were given and assumed temperature to be 25oC, or 298K.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby melissa_dis4K » Wed Feb 27, 2019 5:52 pm

Can someone pls explain how to calculate the equilibrium constant for Gibbs Free Energy wkst #1d? Thank you!

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby melissa_dis4K » Wed Feb 27, 2019 6:32 pm

Can someone pls explain how to do #3 from the Gibbs Free Energy worksheet.Thanks!

Fionna Shue 4L
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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Fionna Shue 4L » Thu Feb 28, 2019 2:21 pm

For Worksheet 7 #8d, why is OH-(aq) not included in the cell diagram?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby ariana_apopei1K » Thu Feb 28, 2019 5:43 pm

Josephine Lu 4L wrote:could someone please explain #8 part a on the electrochemistry worksheet? How do we know that S2O8 2- is reduced and NO is oxidized?

I also have this question

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Fri Mar 01, 2019 3:21 pm

ariana_apopei1K wrote:
Josephine Lu 4L wrote:could someone please explain #8 part a on the electrochemistry worksheet? How do we know that S2O8 2- is reduced and NO is oxidized?

I also have this question


You look at the chart of reduction potentials. The one with the higher reduction potential will be reduced. For the other half reaction, it will become oxidized and all you need to do at that point is change the sign of the reduction potential for the half reaction that will become oxidized.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Fri Mar 01, 2019 3:47 pm

Here is this week's worksheet focusing on reaction rates specifically differential rate law.
Attachments
Worksheet 8 - Kinetics Pt 1.pdf
(166.79 KiB) Downloaded 234 times

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Mon Mar 04, 2019 10:48 am

Key for differential rate laws.
Attachments
Worksheet 8 KEY - Kinetics Pt 1 .pdf
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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Julia Lee » Sat Mar 09, 2019 6:49 am

Does anyone know if Karen posted worksheet 9 yet?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby ariana_apopei1K » Sat Mar 09, 2019 2:48 pm

Julia Lee wrote:Does anyone know if Karen posted worksheet 9 yet?

no it would have been posted here, week 8 is the most recent

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Sun Mar 10, 2019 11:48 am

Sorry for the delay in this week's worksheet! Didn't realize my last post didn't go through. This week we are reviewing integrated rate laws and if time permits, I will introduce reaction mechanisms. On Wednesday I will post a last worksheet for reaction mechanisms since I won't be seeing you next week due to your final on Sunday.

See you all tonight!
Attachments
Worksheet 9 - Kinetics Pt 2.pdf
(182.97 KiB) Downloaded 259 times

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Chem_Mod » Wed Mar 13, 2019 12:56 pm

Here is the key for last Sunday's worksheet and another worksheet focusing on reaction mechanisms. Full solutions are also given.

Good luck on your final!!!!!! It has been a great quarter!

Best,
K
Attachments
14B Mechanisms Worksheet Key.pdf
(2.09 MiB) Downloaded 242 times
Worksheet 10 - Mechanisms.pdf
(166.58 KiB) Downloaded 202 times
Worksheet 9 KEY - Kinetics Pt 2.pdf
(194.53 KiB) Downloaded 199 times

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby CHEM 14B Lover » Wed Mar 13, 2019 9:24 pm

Thank you :)

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby annabel 2A » Wed Mar 13, 2019 11:04 pm

For the integrated rate law worksheet #5a, I found the answer using
1/((7.0*10^9 M*s)*(120 sec) + 1/0.086M)
= 1/ (8.4*10^11 M*s^2 + 11.63 M^-1)
and I got the right answer but I'm confused by the units. How do the units work out to be M? And how do you add 8.4*10^11 M*s^2 with 11.63 M^-1?

Josephine Lu 4L
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writing rate laws: "rate"or "d[A]/dt?"

Postby Josephine Lu 4L » Wed Mar 13, 2019 11:46 pm

when we write the rate laws, do we write it as "rate=..." or ""d[A]/dt=..."? Specifically in question #3 of the Reaction Mechanisms worksheet, could we replace "d[F]/dt" with "rate"?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby sonalivij » Thu Mar 14, 2019 12:30 am

For worksheet 8 #4d I am getting 144 M/s instead of 140 M/s. Am I doing something wrong?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby sonalivij » Thu Mar 14, 2019 12:56 am

How do you do #8 on worksheet 9? I tried to do .99[A]=.5^n[A] and solving for n by ln(.99)/ln(.5)=n, but this didn't work.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Semi Yoon » Thu Mar 14, 2019 9:08 pm

On Worksheet 9, how would you solve for #7?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby sonalivij » Thu Mar 14, 2019 11:46 pm

Semi Yoon wrote:On Worksheet 9, how would you solve for #7?

For a first order reaction, you can use the equation (1/2)^n=whatever fraction of A is left because the half life is constant throughout the reaction. For this problem, use (1/2)^n=1/8 which means n is 3 (n is the number of half lives). We know the length of each half life is 355 seconds so the total time taken is 3x355=1065 s

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Re: writing rate laws: "rate"or "d[A]/dt?"

Postby sonalivij » Thu Mar 14, 2019 11:47 pm

Josephine Lu 4L wrote:when we write the rate laws, do we write it as "rate=..." or ""d[A]/dt=..."? Specifically in question #3 of the Reaction Mechanisms worksheet, could we replace "d[F]/dt" with "rate"?

Yes they are synonymous. Writing it as d[A]/dt is just better because it specifies which species we are referring to.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Vincent Li 4L » Thu Mar 14, 2019 11:54 pm

Why is it that in #3 in the reaction mechanisms worksheet we're able to use the pre-equilibrium assumption to substitute and replace [C]? Wouldn't the approximation fail since the first and second steps are both fast, so there's no bottleneck to stop [C] form being consumed instead of forming A and B again?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby sonalivij » Fri Mar 15, 2019 1:36 am

Celine Hoh 2L wrote:Quick question for Worksheet 1 ques8:

When I2 is added, neither products nor reactants is favored as I2 is a solid.
What happens when I2 is removed, does the reaction not shift too?


Yes! Because it is a solid it is not included in the equilibrium equation so any change in concentration would not affect the reaction.

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Emily Tam 1k » Fri Mar 15, 2019 2:11 am

for number 5 of karen's 9th worksheet (kinetics), it says that the rate constant is 7.0x10^0 M.s. Does M stand for molarity or for minutes?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Emily Tam 1k » Fri Mar 15, 2019 2:18 am

for number 6 of karen's 8th worksheet (kinetics pt 1),

why does k not depend on the order of the reaction? wouldn't the reaction order depend on the value of K?
If there is a higher order then wouldn't the k value be higher?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Emily Tam 1k » Fri Mar 15, 2019 2:26 am

how do you solve 5a on worksheet number 9?
I know the second order equation is 1/[A]=kt+1/[A]0. If I were to use this equation, wouldn't I just plug the values given into the equation?
The answer that i got was 7.14x10^-11, which is different from the answer. pls help thxxxx

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Emily Tam 1k » Fri Mar 15, 2019 2:38 am

how do you solve for worksheet 9 number 6?

I used the half-life equation for a first-order reaction and solved for k when the half-life was 6 days.
my k value was 0.1155.
In order to find the percent of Hg(II) left in the body, would I have to find the k value for the 30-day half-life and divide the two k's?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Katie_Duong_1D » Fri Mar 15, 2019 2:57 am

can someone please explain how to get the equilibrium constant for 1d in Gibbs free energy/worksheet 6? I keep getting 1.014.

Katie_Duong_1D
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Postby Katie_Duong_1D » Fri Mar 15, 2019 3:02 am

Katie_Duong_1D wrote:can someone please explain how to get the equilibrium constant for 1d in Gibbs free energy/worksheet 6? I keep getting 1.014.

I forgot to convert delta G from kj/mol to j/mol to match units. Now I get the correct answer 1.663 x 10^6.

sonalivij
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Postby sonalivij » Fri Mar 15, 2019 1:08 pm

Emily Tam 1k wrote:for number 5 of karen's 9th worksheet (kinetics), it says that the rate constant is 7.0x10^0 M.s. Does M stand for molarity or for minutes?

M stands for molarity, or mol/L

sonalivij
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Postby sonalivij » Fri Mar 15, 2019 1:11 pm

Emily Tam 1k wrote:how do you solve for worksheet 9 number 6?

I used the half-life equation for a first-order reaction and solved for k when the half-life was 6 days.
my k value was 0.1155.
In order to find the percent of Hg(II) left in the body, would I have to find the k value for the 30-day half-life and divide the two k's?


For first order reactions you can use the equation (1/2)^n=whatever fraction of A is remaining, with n being the number of half lives, since the half life is constant throughout the reaction. In this case we know 5 half lives would have passed (30/6=5), so we do 1/2^5 which yields 1/32 (3.1%) which means 3.1% of A is left after 30 days.

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Postby Shally Li 2C » Fri Mar 15, 2019 7:08 pm

sonalivij wrote:For worksheet 8 #4d I am getting 144 M/s instead of 140 M/s. Am I doing something wrong?

She rounded to 140 because you need to have two sig figs.

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Postby Jane Burgan 1C » Fri Mar 15, 2019 9:54 pm

how would you solve for worksheet 10 number 2 part c and d?

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Postby riddhiduggal » Fri Mar 15, 2019 10:47 pm

Amy Dinh 1A wrote:On #4a Worksheet 2, I keep getting pH=4.40, while the answer key says 4.30, when both using the quadratic formula and the shortcut way. I don't understand how to get the answer to


The pH is 4.40

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Postby abbydouglas1K » Sat Mar 16, 2019 12:14 pm

005199302 wrote:
ariana_apopei1K wrote:
005199302 wrote:For the first law worksheet, how do you do #2?

First you have to do stoichiometry to find how many moles of Pb is made from 49.7 g PbO. You multiply the number of moles of product times the enthalpy value given, which gives you the q to plug into your regular q=mCs(Tf-Ti). Once you solve for mass you should get the right answer


Which value should Cs be?

it should be the specific heat capacity for water but you must convert it to kilojoules

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Postby abbydouglas1K » Sat Mar 16, 2019 12:39 pm

Karyn Nguyen 1K wrote:
Celine Hoh 2L wrote:
Karyn Nguyen 1K wrote:For worksheet 4, is the answer for 6a wrong? I did (3/2)(31.9 mol)(8.314 J/Kmol)(311.15 K) = 124 kJ. When I didn't convert the temperature from C to K I got 15.1 kJ which is the answer given in the key.


We don’t have to convert it to kelvin as it is change in temperature (38-0)

Why do we use that equation for the change in internal energy and not q+w

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Postby Carissa Young 1K » Sat Mar 16, 2019 12:44 pm

How do you solve #8 on worksheet 9? How do you find the half-life given that 99% of the reactant decomposes in 137 min?

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Postby Ashley P 4I » Sat Mar 16, 2019 12:55 pm

Is there any worksheets for kinetics?

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Postby Ashley P 4I » Sat Mar 16, 2019 1:05 pm

Ashley P 4I wrote:Is there any worksheets for kinetics?

Nevemind I just found them, thank you for your help! Do you by chance have a final practice test? Or does anyone else have one?

rkang00
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Postby rkang00 » Sat Mar 16, 2019 6:24 pm

For the electrochem worksheet 8d, why don't we include the OH- in the cell diagram?

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Postby BenJohnson1H » Sat Mar 16, 2019 8:52 pm

Yes, it is further up in this thread and there is a key as well. There's also two parts!

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Postby abbydouglas1K » Sat Mar 16, 2019 10:53 pm

Chem_Mod wrote:
ariana_apopei1K wrote:
Josephine Lu 4L wrote:could someone please explain #8 part a on the electrochemistry worksheet? How do we know that S2O8 2- is reduced and NO is oxidized?

I also have this question


You look at the chart of reduction potentials. The one with the higher reduction potential will be reduced. For the other half reaction, it will become oxidized and all you need to do at that point is change the sign of the reduction potential for the half reaction that will become oxidized.

Thank you !!!

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Lisa Werner 2F » Sat Mar 16, 2019 11:07 pm

in worksheet 5 problem 6, how do we know that work is 0?

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Postby Lisa Werner 2F » Sat Mar 16, 2019 11:08 pm

thank you so much karen! these worksheets were so helpful!

Madison Hurst
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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Madison Hurst » Sun Mar 17, 2019 12:39 am

For kinetics ws pt 1 number 5 why isn't C included in the rate law? Is it an intermediate? if so, how can you tell?

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Postby Claudia Luong 4K » Sun Mar 17, 2019 10:21 am

For worksheet 4 #6, I get a different value for the amount of work done. I get 12.4 kJ instead of 10.1kJ. Is there a mistake in the solutions?

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby AhYeon_Kwon_2H » Sun Mar 17, 2019 10:24 am

Sorry, can someone explain worksheet 4 number 5 to me? Thank you!

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Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Postby Simmi Diwanji 2B » Mon Mar 18, 2019 12:38 pm

Thank you!


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