CHEMISTRY COMMUNITY

Karyn Nguyen 1K

Nevermind I understand now, thanks!

Karyn Nguyen 1K

Sorry I'm still a little confused. How did you get rid of k1?

Karyn Nguyen 1K

A reaction rate increases by a factor of 1000. in the presence of a catalyst at 25 'C. The activation energy of the original pathway is 98 kJ!mol!1. What is the activation energy of the new pathway, all other factors being equal? In practice, the new pathway also has a different pre-exponential fact...

Karyn Nguyen 1K

Madelyn Cearlock wrote:is the second equation necessary to use? would the first equation produce the same answer?

Yes, they produce the same answer. These two equations are the same thing, just in different formats.

Karyn Nguyen 1K

I'm getting stuck on this question too. I was looking at the solution and I was wondering where 0.59 came from. This is the solution: ln(k'/k) = (38 kJ/mol)/(0.08314 kJ/molK) ln(\frac{k'}{k}) = \frac{38 kJ/mol}{0.08314 kJ/molK}(\frac{1}{298 K}-\frac{1}{310 K}) - 0.59 \frac{k'...

Karyn Nguyen 1K

How do we determine which one is K1 and which one is K2?

Karyn Nguyen 1K

I'm getting stuck on this question too. I was looking at the solution and I was wondering where 0.59 came from.

Karyn Nguyen 1K

Don't we add water to basic solutions too?

Karyn Nguyen 1K

When do we know when to add H2O on both sides?

Karyn Nguyen 1K

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

Karyn Nguyen 1K

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?

Karyn Nguyen 1K

Just to make sure, the most stable form is the substance that has a delta G formation that is less positive right?

Karyn Nguyen 1K

For question 9.57 in the 6th edition, I don't get how to calculate \Delta H^{\circ}_{r} . In the solution manual, it says \Delta H^{\circ}_{r} = 2 \Delta H^{\circ}_{f} (H2O, aq) - 2 \Delta H^{\circ}_{f} (H2O2,l). Where did H2O,aq come from? Also, what is the general formula for \Delta H^{\circ}_{r}...

Karyn Nguyen 1K

Which of the following compounds become less stable with respect to the elements as the temperature is raised: (a) PCl5(g); (b) HCN(g); (c) NO(g); (d) SO2(g)? How do we know which substances to use when writing the balanced equation? For instance, in (b) why do we use C(s), graphite instead of C(g) ...

Karyn Nguyen 1K

For question 9.57 in the 6th edition, I don't get how to calculate \Delta H^{\circ}_{r} . In the solution manual, it says \Delta H^{\circ}_{r} = 2 \Delta H^{\circ}_{f} (H2O, aq) - 2 \Delta H^{\circ}_{f} (H2O2,l). Where did H2O,aq come from? Also, what is the general formula for \Delta H^{\circ}_{r} ?

Karyn Nguyen 1K

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!

Karyn Nguyen 1K

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 con...

Karyn Nguyen 1K

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)

Karyn Nguyen 1K

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.

Karyn Nguyen 1K

Water expands when it freezes. How much work does 100. g of water do when it freezes at 0.0 C and pushes back the metal wall of a pipe that exerts an opposing pressure of 1070 atm? The densities of water and ice at 0.0C are 1.00 gcm3 and 0.92 gcm3, respectively. I'm a little confused on how to...

Karyn Nguyen 1K

How do we know if the external pressure is constant in order to use $w=P_{ex}\Delta v$ ?

Karyn Nguyen 1K

Where did you get 0.38 J/gC?

Karyn Nguyen 1K

Do we have to convert C to K or can we just leave it as C?

Karyn Nguyen 1K

Calculate \Delta H^{\circ}_{rxn} using bond dissociation energy of: H_{2} + Cl_{2}\rightarrow 2 HCl H-H = 432 kJ/mol Cl-Cl = 239 kJ/mol H-Cl = 427 kJ/mol Why do we divide the equation by 2 and use \frac{1}{2}H_{2} + \frac{1}{2}Cl_{2} \rightarrow 1HCl to get the right answer which is -91.5 kJ/mol?

Karyn Nguyen 1K

For 4b on worksheet 2, I keep getting 4.73x10^(-8) for the concentration of CO3. Can someone explain what I'm doing wrong? I got 3.99x10^(-5) for the concentration of H2CO3.

Karyn Nguyen 1K

Also, are we expected to be know how to write the chemical reaction?

Karyn Nguyen 1K

I have the same question too! I looked at Tables 12.1 and 12.2 but I didn't see the K value for it.

Karyn Nguyen 1K

For (b) in this question, I was wondering why we don't balance the equation first and then give K?

Write the equilibrium expression K for each of the following reactions:
(a) 2C2H4(g) + O2(g) + 4HCl(g) = 2C2H4Cl2(g) + 2H2O(g)
(b) 4NH3(g) + 6NO(g) = 7N2(g) + 6H2O(g)

Karyn Nguyen 1K

Cienna Henry 1J wrote:
Karyn Nguyen 1K wrote:What acids and bases (strong and weak) would be helpful to memorize?

Memorize all strong acids and bases (there aren't that many). Then you will know that all other acids/bases are weak.

Thanks! If anyone is wondering, in the 6th edition of the textbook, Table J.1 lists strong acids and bases.

Karyn Nguyen 1K

$N_{2} + 3H_{2} \rightleftharpoons 2NH_{3}$

What happens if we increase $N_{2}$ ? Increase $NH_{3}$ ? Decrease $H_{2}$ ?

This was explained during lecture, but I'm still a little confused. Can someone explain this to me again?

Karyn Nguyen 1K

Will we be tested on concepts (like multiple choice or short answers) or will it just be math problems?

Karyn Nguyen 1K

Test 1 covers Equilibrium and Acid & Base Equilibria so it'll be outlines 1 and 2

Karyn Nguyen 1K

What acids and bases (strong and weak) would be helpful to memorize?

Karyn Nguyen 1K

Also, since Le Chatelier's principle is only used at equilibrium what do we use if it's not at equilibrium?

Karyn Nguyen 1K

Can someone explain why changing the concentration doesn't change K but changing the temperature does?

Karyn Nguyen 1K

Why do we multiply K instead of adding it?

Karyn Nguyen 1K

What's the difference between the formula for the equilibrium constant K and the formula for the reaction quotient Q?

Karyn Nguyen 1K

Can someone explain what exactly Q is? I know that it is the reactant quotient but I don't get why Q and K wouldn't always equal each other if they have the same formula [P]/[R]?

Karyn Nguyen 1K

How would we solve the problem if we didn't assume ADP and P are 0?

Karyn Nguyen 1K

When will the "TA Office Hours & Discussion Sections Lecture 4" page be updated? As of right now, it's displaying information for lecture 2.

Karyn Nguyen 1K

I'm just a little confused because this doesn't apply when comparing MgCl2 and CaCl2 because CaCl2 has a greater ionic character.

Karyn Nguyen 1K

I thought the greater difference in electronegativity corresponds with a greater ionic character? NaBr has a lower difference in electronegativity than NaI doesn't it?

Karyn Nguyen 1K

Which ligands and their charges do we have to memorize for the final?

Karyn Nguyen 1K

How do we find out the charge for the ligand?

Karyn Nguyen 1K

I'm in the same situation. How are we supposed to know which one is an acid or base by looking at it?

Karyn Nguyen 1K

How do we know which bond coordinates to the metal? I know the atoms with lone pairs have the potential to coordinate, but which ones actually do?

Karyn Nguyen 1K

When ranking compounds in order of acidity or basicity, do we just look at the bond length and the corresponding strength of the bond? Also, do we convert the compound to its conjugate acid for bases in order to rank them?

Karyn Nguyen 1K

What exactly are optical isomers and how do we draw them?

Karyn Nguyen 1K

why does NaBr have a greater ionic character than NaI?

Karyn Nguyen 1K

Are there going to be set ups and workshops during finals week?

Karyn Nguyen 1K

vivianndo_1L wrote:If the two resonance structures have the same formal charge, would they be considered equal in rank?

Resonance structures are supposed to have the same formal charge, but they can differ in rank.

Karyn Nguyen 1K

Is lewis acids and bases on test 3?

Karyn Nguyen 1K

Just to clarify, something has greater covalent character if its electronegativity is lower and has a bigger atomic radius?

Karyn Nguyen 1K

How do we rank resonance structures in order of importance to the overall structure?

Karyn Nguyen 1K

Oh okay thank you!

Karyn Nguyen 1K

I'm a little confused on what else we're supposed to know about chapter 3 other than being able to draw lewis structures?

Karyn Nguyen 1K · Chapter 6 Did we start chapter 6 on Monday 5/21/18?

Did we start chapter 6 on Monday 5/21/18?

Karyn Nguyen 1K

Will midterms be handed out during discussion if we can't get it after class on Wednesday?

Karyn Nguyen 1K

I'm a little confused on how we're supposed to know KCl --> K+ + Cl- . Also for CaCl2 --> Ca2+ + 2Cl-

Karyn Nguyen 1K

Are the solutions for the tests going to be posted or would we have to go to office hours?

Karyn Nguyen 1K

Update: she never responded

Karyn Nguyen 1K

If we don't have to apply this equation in the class, would we be expected to explain the experiment and how they derived the equation on the midterm?

Karyn Nguyen 1K

Which workshop or step up is the best one to go to for a test review?

Karyn Nguyen 1K

Are there going to be that many questions on test 2? Because the last test was already a time crunch...

Karyn Nguyen 1K

Thanks Phil for the offer, but it's okay I worked it out!

Karyn Nguyen 1K

1-1:50 on Fridays!

Karyn Nguyen 1K

I have the same question and emailed my TA about this a day ago. When she replies, I'll post it here, but if anyone else knows that would be helpful!

Karyn Nguyen 1K

I like to look at the syllabus for the homework since it's all compiled together which makes it easier to keep track of. For week 2, I'm pretty sure we do problems under "Review of Chemical & Physical Principles" and "The Quantum World."

Karyn Nguyen 1K

Here on this website :)

Karyn Nguyen 1K

Nevermind, I found the answer to this question under the section empirical and molecular formulas.

Karyn Nguyen 1K

Some of the homework problems ask us to write the name of the compound in the question. Which ones should we memorize or are we expected to know how to identify any compound?

Karyn Nguyen 1K

Hey is anyone in dis 1L willing to switch with me into dis 1K. I would greatly appreciate it!

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