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Quiz 2 Winter 2017

Posted: Thu Feb 16, 2017 12:31 pm
by Chem_Mod
Quiz 2 covers only Kinetics up to the end of page 73 in the course reader.

Re: Quiz 2 Winter 2017

Posted: Thu Feb 16, 2017 1:16 pm
by Derek Lee 2K
Does quiz 2 just cover up to the end of kinetics? Is it cumulative?

Re: Quiz 2 Winter 2017

Posted: Thu Feb 16, 2017 1:30 pm
by Maya Kandah 3M
From the quiz 2 preparation in the course reader, it seems that it will just cover kinetics.

Re: Quiz 2 Winter 2017

Posted: Thu Feb 16, 2017 1:53 pm
by Melanie Martinez 1K
How many questions will be on quiz 2?

Re: Quiz 2 Winter 2017

Posted: Thu Feb 16, 2017 2:00 pm
by Chem_Mod
We are still working on quiz 2 (and working our tails off as the midterm was last night, and answering questions on Chemistry Community, etc., got home long after midnight).

Re: Quiz 2 Winter 2017

Posted: Fri Feb 17, 2017 9:44 am
by Chem_Mod
Quiz 2 has 6 questions.

Re: Quiz 2 Winter 2017

Posted: Fri Feb 17, 2017 11:18 am
by Sarai_Ferrer_3C
Hey guys, so does that mean that the concepts generally covered on the quiz include ad follows: 1st order, second order, third order, and 1/2 life? Thanks in advance for the clarification.

Re: Quiz 2 Winter 2017

Posted: Fri Feb 17, 2017 7:31 pm
by Winnie Liu 1M
Yup! That's what is outlined in the coursereader :D

Re: Quiz 2 Winter 2017

Posted: Sat Feb 18, 2017 9:04 am
by 704709603
Would it be possible to get the answers to the practice quiz please?

Re: Quiz 2 Winter 2017

Posted: Sat Feb 18, 2017 12:52 pm
by Kaitlin_Ryan_ 3K
Will answers to the practice Quiz 2 in the back of the course reader be posted to Chemistry Community as the answers to practice Quiz 1 were?

Re: Quiz 2 Winter 2017

Posted: Sat Feb 18, 2017 4:18 pm
by Nikhita_Jaaswal_2H
Will Quiz 2 also cover materials from before the midterm (in between Quiz 1 and midterm)?

Re: Quiz 2 Winter 2017

Posted: Sat Feb 18, 2017 4:29 pm
by Katie McCombs 3G
Nikhita_Jaaswal_2H wrote:Will Quiz 2 also cover materials from before the midterm (in between Quiz 1 and midterm)?


No quiz 2 will only cover kinetics

Re: Quiz 2 Winter 2017

Posted: Sat Feb 18, 2017 5:46 pm
by Chem_Mod
Quiz 2 Answers

1. 2 N2O5(g) → 4 NO2(g) + O2(g)
5.78 (mol NO2)⋅L–1⋅s–1

2. False

3. 2 N2O(g) → 2N2(g) + O2(g)
120 sec

4. first-order
2.00 s–1

5. has a rate that does not change much with temperature.

6. 0.30 M

7. 9.88×10−3 min−1 or 1.65 ×10−4 s−1

8. 6.06 min

9. D

10. false

11. 100 min−1

Re: Quiz 2 Winter 2017

Posted: Sat Feb 18, 2017 7:48 pm
by Brian Huynh 3D
How is question one done from quiz 2?

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 7:50 am
by 704709603
Can some one explain question 1 and 5 please? Also, can we do calculations with any unit of time?
Thank you!

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 10:46 am
by Diwana Lucero 3K
Brian Huynh 3G wrote:How is question one done from quiz 2?

When you balance the reaction, you get 2 mol N2O5, so you multiply the rate of decomposition of N2O5, 2.89, by 2 to get the rate of formation of NO2. So, this would be 2(2.89)= 5.78 (mol NO2)⋅L–1⋅s–1

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 1:03 pm
by nicoleclarke_lec1M
Do we need to know how to do #9 and #11 from Quiz 2 Prep?

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 2:43 pm
by Annie Tagvoryan 3A
I know the quiz covers material up to page 73 in the course reader, but does that correspond to up to 15.11 in our textbook?

Thanks.

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 3:54 pm
by Ariana de Souza 4C
for number 8, is it okay if we express it in seconds, since the question gave the rate constant in seconds?
Additionally, do we need to know how to do numbers 5, 9, and 11 ? They all have to do with enzymes and the arrhenius equation, and i thought we didn't have to know that

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 4:02 pm
by Leo_Navejas_3B
For rxn mechanisms will we have to infer the intermediate for a rxn or will it be given to us?

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 4:04 pm
by Ariana de Souza 4C
Leo_Navejas_3B wrote:For rxn mechanisms will we have to infer the intermediate for a rxn or will it be given to us?


Pretty sure the mechanism will be given to us. The intermediate will be the compound that is in the products of the first reaction and in the reactants of the second, and so will be canceled out -- it should be clear what it is

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 4:45 pm
by Diana_Anum1G
I know that quiz 2 covers up to page 73 in the course reader, but where does it cover up to in the homework problems? Is it up to 15.55 because 61 starts talking about activation energy?

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 5:25 pm
by Madison_Moore_1I
Could someone explain to me how to do #6?

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 5:38 pm
by Ariana de Souza 4C
Madison_Moore_1I wrote:Could someone explain to me how to do #6?



So this one you need to split into two problems. The first step will be to determine what k is.
1) you have your initial concentration (0.95 M) and your final concentration (0.44 M) and the time it takes (11 minutes)
you use your equation 1/(At) - 1/(A0) = k*t, and from there, find k.

2) now you know k. You now need your final concentration. You have your initial concentration (still 0.95 M) and your k and your time (21 minutes). So you plug everything into that same second order integrated equation, and you find At.
Hope that helps! :)

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 5:39 pm
by Chem_Mod
nlc_lec1 wrote:Do we need to know how to do #9 and #11 from Quiz 2 Prep?


9 yes
11 no

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 5:41 pm
by Chem_Mod
Ariana de Souza 4C wrote:for number 8, is it okay if we express it in seconds, since the question gave the rate constant in seconds?
Additionally, do we need to know how to do numbers 5, 9, and 11 ? They all have to do with enzymes and the arrhenius equation, and i thought we didn't have to know that


8 okay to give answer in seconds

5 no
9 yes (see comments on zero order reactions)
11 no

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 5:51 pm
by Mannat Sukhija 1E
Does anyone know on the dates of the first and last lecture that will be covered on Quiz 2?

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 6:46 pm
by Abigail_Low_1A
Diana_Anum1G wrote:I know that quiz 2 covers up to page 73 in the course reader, but where does it cover up to in the homework problems? Is it up to 15.55 because 61 starts talking about activation energy?


Yes, I think so. That's where I stopped.

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 6:52 pm
by Morgan_McMasters_3A
For #1, I used the unique rates with stoichiometric coefficients and set it up as -(1/a)(deltaA/deltat)=(1/c)(deltaC/deltat) and got -(1/2)(2.98)=(1/4)(x) would this be incorrect? I got -5.78mol NO2/L/s and I noticed the answer is +5.78.

Quiz 2

Posted: Sun Feb 19, 2017 8:23 pm
by Calderon_Humberto_3E
What will the quiz cover? Is it the content of the midterm till now or is it cummalative since day one?

Re: Quiz 2

Posted: Sun Feb 19, 2017 8:31 pm
by Melanie Martinez 1K
Calderon_Humberto_3E wrote:What will the quiz cover? Is it the content of the midterm till now or is it cummalative since day one?


The quiz only covers Kinetics, which up to the end of page 73 in the course reader.

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 9:23 pm
by Chem_Mod
Morgan_McMasters_3A wrote:For #1, I used the unique rates with stoichiometric coefficients and set it up as -(1/a)(deltaA/deltat)=(1/c)(deltaC/deltat) and got -(1/2)(2.98)=(1/4)(x) would this be incorrect? I got -5.78mol NO2/L/s and I noticed the answer is +5.78.


Rates are always positive values.

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 10:02 pm
by 204177206
Will Quiz 2 be 40 minutes as well, and of similar format as Quiz 1?

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 10:10 pm
by Madeline Fox 2B
Will we have to derive equations for quiz 2?

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 10:20 pm
by Jaret Nishikawa
Will it ask us to use specifically to use pre-equilibrium approach for reaction mechanisms or can we use either pre-equilibrium or steady state? Thanks

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 11:33 pm
by 104781135
Hi everyone and sorry, this might be a dumb question, but will we need to know page 65 in the course reader? I don't want to be surprised if radioactivity shows up. Thank you so much!

Re: Quiz 2 Winter 2017

Posted: Sun Feb 19, 2017 11:37 pm
by Jerry_Dar_3C
Will we be quizzed on any reactions past second order? Or do we only need to know up to second?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 12:58 am
by nicoleclarke_lec1M
Chem_Mod wrote:
nlc_lec1 wrote:Do we need to know how to do #9 and #11 from Quiz 2 Prep?


9 yes
11 no


could you please explain #9? It has to do with enzymes and I don't really know anything about them.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 10:19 am
by 904621096
What is the unique rate of reaction?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 11:26 am
by Yasmine Choroomi 2C
Hi! I know you said we need to know number 9, but it has to do with enzymes and I thought we didn't need to know that?

Also are there any examples of using the equilibrium approach problems in the book?

Thanks :)

Re: Quiz 2 Winter 2017. Help on Quiz 2 Prep please!

Posted: Mon Feb 20, 2017 11:53 am
by Kira_Maszewski_1B
It is important to distinguish between the reaction and the rate constant. The units of rate constant are always M * s^-1. True or False.

I think the answer is True, however I'm not sure about this question. Could someone please explain?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 12:37 pm
by Arshia_Sabir_3E
Can someone please help me with #3? I used the integrated rate law for first order and I got t=205 seconds

Re: Quiz 2 Winter 2017. Help on Quiz 2 Prep please!

Posted: Mon Feb 20, 2017 12:56 pm
by Christian Hardoy 3F
Kira_Maszewski_1B wrote:It is important to distinguish between the reaction and the rate constant. The units of rate constant are always M * s^-1. True or False.

I think the answer is True, however I'm not sure about this question. Could someone please explain?


The rate constant can be M * s^-1 for zero order, s^-1 for first order, and M^-1 * s^-1 for 2nd order. The units of the rate are constant; it will be M * s^-1 for zero order, first order, and second order. Because the units of the rate are constant, k must change units when the reaction is a different order because there is another term in a 2nd order rate as compared to a 1st order rate. 1st order: Rate = k*[A], 2nd order: Rate=k*[A]^2. If the 2nd order rate is in M/s and the 1st order rate is in M/s, then k must be different because the 2nd order rate has an additional [A], which is in M.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 1:16 pm
by Sarah_Kremer_1A
Arshia_Sabir_3E wrote:Can someone please help me with #3? I used the integrated rate law for first order and I got t=205 seconds



For #3, it is a first order reaction, so you use the corresponding equation
ln[A] = -kt + ln[A0]
so, ln(.33) = -(.0068)t + ln(.75)
ln(.33/.75) = -.0068t
t = ln(.33/.75)/-.0068
t = 120 sec

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 2:27 pm
by Morgan_McMasters_3A
What parts of chapter 15 will be covered in the quiz? Only until 15.10 or..?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 2:58 pm
by ChristineCastanon_1B
Sarah_Kremer_1A wrote:
Arshia_Sabir_3E wrote:Can someone please help me with #3? I used the integrated rate law for first order and I got t=205 seconds



For #3, it is a first order reaction, so you use the corresponding equation
ln[A] = -kt + ln[A0]
so, ln(.33) = -(.0068)t + ln(.75)
ln(.33/.75) = -.0068t
t = ln(.33/.75)/-.0068
t = 120 sec


Thank you! I had the same question

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 3:38 pm
by eric_beraut_2B
Mannat Sukhija 1E wrote:Does anyone know on the dates of the first and last lecture that will be covered on Quiz 2?

Quiz two covers the lectures from Monday 2/6/17 up to the lecture on Friday 2/17/17

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 3:55 pm
by BrianaBarr2A
204177206 wrote:Will Quiz 2 be 40 minutes as well, and of similar format as Quiz 1?


Yes this is correct, Dr. Lavelle formats all his quizzes this way.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 4:23 pm
by Andrea Medina 1A
Can someone explain the graphing part of question 4 on the practice quiz?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 4:34 pm
by danny_nguyen_3C
If the answer to #2 if false, what other possible units can be used to signify rate constant?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 4:46 pm
by Ariana de Souza 4C
Andrea Medina 1A wrote:Can someone explain the graphing part of question 4 on the practice quiz?


It tells you that you have a graph where you're plotting the natural log of NOBr against time, and you get a straight line. on page 63 in the course reader, you can see that that's basically how you know that the reaction is first order. You can also check this with the equation
ln (A) = -kt + ln(A)
from here you can see the formula of a line, where -k is the slope and ln(A) is the y intercept. Therefore, ln(A) must be what you plot against t.

The other part asks that if you have a slope of -2, what k must be. Since the slope of the graph would be -k, and -k = -2 /s you can see that k=2/s

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 4:48 pm
by Ariana de Souza 4C
danny_nguyen_3C wrote:If the answer to #2 if false, what other possible units can be used to signify rate constant?

It depends on what order the reaction is. you can just check this with the rate equations.

ZERO ORDER:
Rate=k
the units of the rate are M/s
so k must be M/s too for zero order reactions

FIRST ORDER:
Rate = k[A]
M/s = ? (M)
so k must be /s

SECOND ORDER:
Rate = k[A]^2
M/S = ? * (M^2)
so k must be 1/s*M

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 4:51 pm
by ChristineCastanon_1B
Could anybody briefly explain how you did number 11?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 5:00 pm
by Ann Zhang_1M
how many questions are included in quiz2?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 5:01 pm
by Madeline Fox 2B
Can someone explain why question 10 is false? I thought half-lives are always the same.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 5:02 pm
by Chem_Mod
Ann Zhang_1M wrote:how many questions are included in quiz2?

See above answer.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 5:04 pm
by Chem_Mod
204177206 wrote:Will Quiz 2 be 40 minutes as well, and of similar format as Quiz 1?

All quizzes are 40 minutes. See Syllabus.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 5:06 pm
by Chem_Mod
Madeline Fox 2B wrote:Will we have to derive equations for quiz 2?

Derivations are not asked on quizzes.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 5:09 pm
by Chem_Mod
Jaret Nishikawa wrote:Will it ask us to use specifically to use pre-equilibrium approach for reaction mechanisms or can we use either pre-equilibrium or steady state? Thanks


You can use either approach to solve a reaction mechanism problem.
However, as I discussed in class you are only expected to know the pre-equilibrium approach.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 5:12 pm
by Chem_Mod
104781135 wrote:Hi everyone and sorry, this might be a dumb question, but will we need to know page 65 in the course reader? I don't want to be surprised if radioactivity shows up. Thank you so much!


Page 65 will not be asked. Since you are Life Science majors I include it for students to see the biological relevance.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 5:16 pm
by Chem_Mod
Jerry_Dar_3C wrote:Will we be quizzed on any reactions past second order? Or do we only need to know up to second?


That would be super mean and 'bad' chemistry if I were to ask students topics we have not covered.
In class we covered: zero, first, and second order reactions

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 5:34 pm
by Flamingos 3L
Up to what chapter in the textbook are advised to study up to for this quiz? I see that the Arrhenius equation shows up during 15.11 so are we advised to just study the chapters before that?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 6:07 pm
by Chem_Mod
Flamingos 3L wrote:Up to what chapter in the textbook are advised to study up to for this quiz? I see that the Arrhenius equation shows up during 15.11 so are we advised to just study the chapters before that?


All of kinetics except the Arrhenius equation and catalysis.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 7:14 pm
by Ashley Van Belle 2B
What problems out of the textbook given in the course reader would be sufficient in covering kinetics? Because some of the problems begin to cover activation energies, which we are not being tested on in this quiz. Would it be up until 5.55?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 7:44 pm
by Jonathan Orozco 1A
Can anyone help me with number 6 from Quiz two preparation? I don't understand how the answer is 0.30 M
I used the second order integrated Rate law, and my answer for K was 0.11092 i was wondering if i am going in the right direction and if so can you help me finish peals and thank you very much.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 7:45 pm
by Chem_Mod
Monday night of the holiday weekend and I don't have the textbook on me.
Just omit any questions related to the Arrhenius equation and catalysis.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 8:48 pm
by Imani Johnson 1H
Do we have to know how to use the pre-equilibrium approach since that is where we left off or no?

Thanks.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 9:30 pm
by Shelby Slaughter 3D
Will we need to know the details of radioactive decay?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 10:02 pm
by Henry_Shin_3B
Shelby Slaughter 3D wrote:Will we need to know the details of radioactive decay?


No, I do not believe so. I think the radioactive decay thing was just an example to show what real-life scenarios the concept can be applied.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 10:10 pm
by Chem_Mod
Imani Johnson 1H wrote:Do we have to know how to use the pre-equilibrium approach since that is where we left off or no?

Thanks.


Yes you do. See previous Q&A on this.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 10:47 pm
by Natalie Hunt 1E
Jonathan Orozco 1A wrote:Can anyone help me with number 6 from Quiz two preparation? I don't understand how the answer is 0.30 M
I used the second order integrated Rate law, and my answer for K was 0.11092 i was wondering if i am going in the right direction and if so can you help me finish peals and thank you very much.


Yes, you are going in the right direction! To finish the problem, you use the second order integrated rate law again with [Ao] = 0.95 M, k=0.11092 (which is what you just found), and t = 21 minutes. You then solve for [At] to get 0.30 M.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 10:49 pm
by Natalie Hunt 1E
Henry_Shin_3B wrote:
Shelby Slaughter 3D wrote:Will we need to know the details of radioactive decay?


No, I do not believe so. I think the radioactive decay thing was just an example to show what real-life scenarios the concept can be applied.


No, we do not need to know that information. As Dr. Lavelle said in an earlier post, "Page 65 will not be asked. Since you are Life Science majors I include it for students to see the biological relevance."

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 10:55 pm
by Chem_Mod
Thank you Natalie. Introduce yourself at the end of class.

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 11:04 pm
by ben maryamian
which homework problems will the quiz cover?

Re: Quiz 2 Winter 2017

Posted: Mon Feb 20, 2017 11:50 pm
by Simone Seliger 1C
Madeline Fox 2B wrote:Can someone explain why question 10 is false? I thought half-lives are always the same.


I am also confused by this question. I know that the equation is second-order, but do not understand why the decomposition would take different amounts of time.

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 12:20 am
by rebecca_handler_1B
Madeline Fox 2B wrote:Can someone explain why question 10 is false? I thought half-lives are always the same.


You know this one is a second order reaction because rate=[A]^2, and if you set up two equations using the 2nd order integrated rate law (one for 1.0 M and 0.5 M and the other for 0.5 M and 0.25 M), you can solve for t knowing k is constant. Once you solve, you can see that t will change values.

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 1:00 am
by Terry1A
Simone Seliger 1C wrote:
Madeline Fox 2B wrote:Can someone explain why question 10 is false? I thought half-lives are always the same.


I am also confused by this question. I know that the equation is second-order, but do not understand why the decomposition would take different amounts of time.


For number 10 you use the integrated rate law for the second order reaction which is 1/[R]=kt+1/[R]0. You can then manipulate the equation to solve for time, so t=(1/[R]-1/[R]0)/k. The k constant will be the same whether the concentration is decreasing from 1 M to 0.5 M or 0.5 M to 0.25 M. If you plug in the concentrations, you'll get t=1/k for 1 M --> 0.5 M, and t=2/k for 0.5 M --> 0.25 M. This means that the time it takes for the concentrations to decrease are both different, therefore the statement is false.

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 1:01 am
by danny_nguyen_3C
nlc_lec1 wrote:
Chem_Mod wrote:
nlc_lec1 wrote:Do we need to know how to do #9 and #11 from Quiz 2 Prep?


9 yes
11 no


could you please explain #9? It has to do with enzymes and I don't really know anything about them.



It is not possible to explain everything about enzymes, but I will try to explain why the answer is D. First of all, enzymes are catalysts, meaning they increase the reaction rates of chemical reactions. A and B speak about the concentration of substrate. What is important to know is that the rate of reaction of the enzyme-catalyzed reaction depends on the amount of substrate (reactants) you are given. This means that as you are given more substrate, enzymes become "active" in order to breakdown more of the substrate. On the other hand, if you are given less substrate, the enzymes aren't required to catalyze as many reactions than if there were large amount of substrates. I cannot explain C just because you need to know that all enzymes are proteins, but not necessarily the other way around (just like how a square is a rectangle, but a rectangle is not a square). Therefore, the answer is D.

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 1:02 am
by Aditya Mamtora 2C
ChristineCastanon_1B wrote:Could anybody briefly explain how you did number 11?


We do not need to know how do do #11 for Quiz #2

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 1:24 am
by Angela To 2B
Madeline Fox 2B wrote:Can someone explain why question 10 is false? I thought half-lives are always the same.

I think half-lives are the same for only 1st order reactions

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 2:01 am
by Veronica_Giap_1C
Angela To 2B wrote:
Madeline Fox 2B wrote:Can someone explain why question 10 is false? I thought half-lives are always the same.

I think half-lives are the same for only 1st order reactions

To expand on this, if you look at the half reactions formulas, you will see how both the 0th order rxn and the 2nd order rxn are dependent on the initial reactant concentration. So when the quiz problem gives you two ranges of concentrations [1.0,0.50] and [0.50,0.25], it is in a way giving you a "new" initial concentration for the 2nd equation and because the initial concentrations are different, your half life values will be too: t1/2=1/k[R]0

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 2:06 am
by Katelyn_Nakamura_1B
Jonathan Orozco 1A wrote:Can anyone help me with number 6 from Quiz two preparation? I don't understand how the answer is 0.30 M
I used the second order integrated Rate law, and my answer for K was 0.11092 i was wondering if i am going in the right direction and if so can you help me finish peals and thank you very much.



So this problem you need to split into two parts. You use the same equation but with diff #s

First part of the question you need to find k. With what you're given you know that it is a 2nd order and you have time involved (that is not in regards to half life) so you know to use the integrated rate law. You plug in all the numbers known to get k which you found was correct.

With k known you can use the same equation and plug in the new numbers given ([A]initial is known because that does not change). The final answer is rounded to .30M using the sig fig rules.

I hope this helped :)

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 5:36 am
by Jennifer_Lam_1A
Can someone please explain #5 on the practice quiz? I thought the answer would be A because you have to take into account temperature when finding the activation energy.

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 9:18 am
by 704709603
For the pre-equilibrium approach: What if there are more than two steps in the mechanism? Also, how did you go from rate = k1 [CHBr3] ((k2[Br2])/k' 2) to rate = k [CHBr3][Br2]?

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 10:21 am
by Jordan Pace 2B
For #11:
I'm not 100% sure this is how to approach this problem, but this is what a friend and I did to solve it!

ln k2/k1= Ea/8.314 [1/T1 - 1/T2]

k2=35 min^-1
k1=25 min^-1
T1=298
T2=350

Solve for Ea

0.336= 0.000498Ea/8.314

Ea=5617.3

Now find rate constant at 770K

ln x/25= 5617.3/8.314 [1/298 - 1/770]

ln x/25 = 1.3898

x=25e^1.38, so x=99.37 min^-1 or 100 min^-1

Hope this helps! If this isn't the correct way to solve this problem, please feel free to correct it!

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 12:11 pm
by ariana_cruz_1C
Hi, can someone show me how they did #7, I know you use the first order integrated rate law, but when I work it out I am not getting the answer that is posted.

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 12:17 pm
by Chem_Mod
Veronica_Giap_1C wrote:
Angela To 2B wrote:
Madeline Fox 2B wrote:Can someone explain why question 10 is false? I thought half-lives are always the same.

I think half-lives are the same for only 1st order reactions

To expand on this, if you look at the half reactions formulas, you will see how both the 0th order rxn and the 2nd order rxn are dependent on the initial reactant concentration. So when the quiz problem gives you two ranges of concentrations [1.0,0.50] and [0.50,0.25], it is in a way giving you a "new" initial concentration for the 2nd equation and because the initial concentrations are different, your half life values will be too: t1/2=1/k[R]0


Correct. Half-life formulas with [A]o depend on the initial concentration (as discussed in class). See pages 64, 66, and 67 in the lecture notes.

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 1:07 pm
by ariana_cruz_1C
ariana_cruz_1C wrote:Hi, can someone show me how they did #7, I know you use the first order integrated rate law, but when I work it out I am not getting the answer that is posted.



nevermind!

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 1:18 pm
by Diana Catapusan 1N
ariana_cruz_1C wrote:Hi, can someone show me how they did #7, I know you use the first order integrated rate law, but when I work it out I am not getting the answer that is posted.


First, you need to rearrange the first order integrated rate law and isolate k. (k=ln(A/A0)/t) After, plug in each value. k=ln(0.622M/0.773M)/22.0 min, which should give you 9.88x10-3min-1. Hope this helps, I'm sorry I couldn't figure out how to upload a picture!

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 2:00 pm
by Tiffany Wee 2D
This might be dumb question, but could someone quickly explain the difference between the reaction rate and the rate constant?

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 2:27 pm
by AnnaTong1E
Is there any place that all of the course reader quiz 2 answers (written out, long, and explanatory) are compiled in one place? I know there are the answers on this site.

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 2:50 pm
by Melanie_Wong_1K
Diwana Lucero 3K wrote:
Brian Huynh 3G wrote:How is question one done from quiz 2?

When you balance the reaction, you get 2 mol N2O5, so you multiply the rate of decomposition of N2O5, 2.89, by 2 to get the rate of formation of NO2. So, this would be 2(2.89)= 5.78 (mol NO2)⋅L–1⋅s–1


Does this mean the coefficient in front of the reactants doesn't matter for this question?

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 5:53 pm
by Mizuno_Mikaela_1D
Simone Seliger 1C wrote:
Madeline Fox 2B wrote:Can someone explain why question 10 is false? I thought half-lives are always the same.


I am also confused by this question. I know that the equation is second-order, but do not understand why the decomposition would take different amounts of time.


Since it is second order, the equation for t1/2 is t1/2 = 1/([A]0 *k) which means it depends on [A]0 . Since in #10, the half lives you are comparing have different initial concentrations, the half life is different. Initial concentration also affects goes a zero order reaction but not a first order.

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 7:44 pm
by SarahTian3k
Could someone please explain number 7? I keep getting 7.46x10-3 min-1

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 8:27 pm
by Hirmand_Sarafian_2N
Can somebody explain to me why 10 on the quiz 2 prep is false?

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 8:33 pm
by 604735966
Can someone please explain number 7! I know it's a straight forward problem, but I must be missing a step because I can't seem to get the correct answer.

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 8:38 pm
by 604735966
As for number 7, when do we know to use the rearranged integrated rate law and when to use the differential rate law?

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 8:41 pm
by Amy_Hoang_1E
604735966 wrote:Can someone please explain number 7! I know it's a straight forward problem, but I must be missing a step because I can't seem to get the correct answer.


So for number 7, you can use the 1st order integrated rate law, which is ln[A] = -kt + ln [A]initial and then isolate k, since you're solving for k
ln [A] is 0.622M
ln [A] initial is 0.773 M
t is 22 mins
and you're solving for k

all plugged in, it should be ln 0.622= -k (22) + ln 0.773
so, - (ln 0.622 - ln 0.773)/ 22 = k
then it should be straight algebra after that. The answer I got is 0.009877, which is the same as 9.88 x 10^-3

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 9:20 pm
by christy_zambrano_2E
ChristineCastanon_1B wrote:
Sarah_Kremer_1A wrote:
Arshia_Sabir_3E wrote:Can someone please help me with #3? I used the integrated rate law for first order and I got t=205 seconds



For #3, it is a first order reaction, so you use the corresponding equation
ln[A] = -kt + ln[A0]
so, ln(.33) = -(.0068)t + ln(.75)
ln(.33/.75) = -.0068t
t = ln(.33/.75)/-.0068
t = 120 sec


Thank you! I had the same question


the answer I got was 120.73... are we not suppose to round to three sig figs? So wouldn't it be 121 sec?

Re: Quiz 2 Winter 2017

Posted: Tue Feb 21, 2017 9:27 pm
by chris2E
Is there a reason why number six's answer has three significant figures despite the given concentration 0.35M having two significant figures? Do we not bother with sig figs when ln is involved?