CHEMISTRY COMMUNITY

Sara Sasaki 1K

You want to control the concentration of the reactant you are determining the order of, so you would compare the two experiments in which only that reactant's concentration differs. Hope this helps! (-:

Sara Sasaki 1K

I believe this is in our notes, but it states that H20, H30+, and OH- can be present in the rate law if they are part of the reaction mechanism (although we end to omit water because it's concentration is so much higher). I don't think it's an intermediate because it has a fixed, long-term presence ...

Sara Sasaki 1K

Catalysts don't show up when writing the overall reaction, and aren't included in the rate law either. However, they indirectly change the k value of the rate law by lowering the activation energy of the reaction.

Sara Sasaki 1K

There's a recent post that discusses the Arrhenius equation as well. Here's the link

viewtopic.php?f=151&t=29213

Sara Sasaki 1K

I believe dimerization is just when 2 molecules of the same composition react with each other! so an example of this would be something like A + A → A2

Sara Sasaki 1K

I believe it's 2 because looking at the graph, there are two lower points in between each step of the reaction. Page 652 in the textbook shows this on the graphs in the top left corner

Sara Sasaki 1K

You can use the Arrhenius equation to show the effect a change of temperature has on the rate constant (and thus the reaction as well). Hope this helps!

Sara Sasaki 1K

Joshua is right! 15.69 shouldn't be on our test this week, and I don't believe we've covered it in any lectures yet, so I wouldn't really worry about this until we cover it in class

Sara Sasaki 1K

you might also find this helpful for additional info!
https://chem.libretexts.org/Core/Physic ... _Reactions

Sara Sasaki 1K

the other post about test 3 recommended going up to #43, so just to be safe I would include those for extra practice!

Sara Sasaki 1K

I believe that's right as well; it's probably more commonly written as Cl2(g)|Cl-(g) because it makes a little more sense in conveying the reaction occurring, but it doesn't really matter as long as they're both on the anode side

Sara Sasaki 1K

I agree! I believe it's a solution manual error, so I wouldn't worry about it too much.

Sara Sasaki 1K

Yeah, I believe this test will follow a similar format where you should understand both concepts and applications

Sara Sasaki 1K

it matters; the question is focusing on the copper cube, so the copper cube is the system and would be the positive q. it also depends on the direction the energy is flowing, so since the surroundings are losing energy to the copper cube (which is absorbing energy), q for surroundings would be negat...

Sara Sasaki 1K

there's a possibility it could show up on the test so I'd know/understand it just in case!

Sara Sasaki 1K

I believe we'll be supplied with all the equations we'll need for the midterm! I also heard we won't need to do any derivations, however it'd still be really helpful to understand them and know when to use them. I don't think the Van't Hoff equation is included on the sheet, but that one is pretty s...

Sara Sasaki 1K

Is this for problem 9.19? I believe you do so because the problem is asking for the entropy when the vaporized water is 85 degrees celsius (as the final temperature), therefore you have to cool the water after you change its state by vaporization. Hope that makes sense!

Sara Sasaki 1K

Additionally, electrons always flow out of the anode and into the cathode

Sara Sasaki 1K

Was it a typo that you said 83 degrees? I agree with Tanaisha; you'll have to change the state of the water by heating it up, then you bring the temperature back down to the desired temp in the problem!

Sara Sasaki 1K

I agree! If polarity does play any roles in determining bond enthalpy, I'm pretty sure it's a negligible effect.

Sara Sasaki 1K

You add delta H fusion/vaporization because the enthalpy of the objects are different values when they are in different states, so you have to include that specific change in energy when calculating the total, if that makes sense! (for example, if you look at it in terms of water's heat curve, you c...

Sara Sasaki 1K

I agree. For the majority of his tests, a majority of points come from calculations/problem-solving, however it will definitely require an understanding of the concepts, so it would definitely be helpful to study both!

Sara Sasaki 1K

I believe so! Since there is no transfer of heat or mass, the contents of the vacuum would be isolated.

Sara Sasaki 1K

I think it's best to keep your answer in Kelvin since it's the standard unit for Gibbs Free Energy! I'm not entirely sure if the reason is so that it's a positive value, but it makes sense to me. Hopefully someone can clarify that part

Sara Sasaki 1K

how similar are the homework questions to lavelle's test questions? Dr. Lavelle usually includes a homework problem or one that is very similar to the homework in his tests, so it can be pretty similar. In general I find it really helpful to do the homework! If anything, sometimes the homework can ...

Sara Sasaki 1K

Warda Sahib 2E wrote:Does Dr. Lavelle only test on things he's talked about?

For the most part, Dr. Lavelle covers everything we should know for the test conceptually with some examples, but it's definitely recommended to prepare by doing the homework while also reviewing notes!

Sara Sasaki 1K

Can you please clarify which concept this is from? Your reasoning sounds correct, but I'm not sure which equation/concept you are referring to about the cooling and I couldn't find it in my notes. Thanks!

Sara Sasaki 1K

Payton Schwesinger 1J wrote:I also think that if the system is doing work on the surroundings, then energy is being released and therefore the work has a negative value... am I thinking about this right?

Yes, that's also right!

Sara Sasaki 1K

I believe it is because there are 2 moles of C6H6, and so in order to find the change in enthalpy you must multiply by 2. I think the book explains this a little more at the top of page 289 if that helps!

Sara Sasaki 1K

Sara Sasaki 1K

Sara Sasaki 1K

I agree with Juanyi! These problems ask for the exact equation, so even though it might make more sense or be easier to use whole numbers, you have to convert it according to the given equation

Sara Sasaki 1K

I don't think it really matters since it's the same quantity, but to be safe I would put it in the units given in the problem, which is moles for #37. Hopefully someone else can clarify as well!

Sara Sasaki 1K

We can consider x negligible if it if the value of Kc is less than 10^-7. In this case, you can omit the "-x" but still leave it in the product (ex. Kc=(2x)/(1-x)(4-x) could be rewritten as (2x)/(1)(4) if Kc is less than 10^-7). You can also note that if there's ever a cubic situation, you...

Sara Sasaki 1K

At least for the practice final, K referred to Kc, so I think unless otherwise stated it will be Kc. Hopefully someone else can confirm

Sara Sasaki 1K

I could be mistaken but I think it's the opposite actually: the two sp hybridized carbon atoms are in a more constrained position since it's in a six-figure chain (at 120 degree angle), instead of the arrangement it would normally have, which is linear (with a 180 degree angle). Therefore, it's more...

Sara Sasaki 1K

Yes I believe so, since Test 4 is supposed to cover Ch. 4, 17, and Ch. 11.1 to the end of 11.8, and coordination compounds are covered all in Ch. 17.

Hope this helps!

Sara Sasaki 1K

Just for clarification, on the syllabus it says that "only at the end of the class when the class average score (out of 500 points) is known are final grades assigned."

So does this mean that the class is curved at the end of the quarter?

Sara Sasaki 1K

Yeah, it has to do with electron repulsion! Since there are 2 lone pairs on Iodine in ICl3, the electron repulsions balance each other out so the shape remains T-shaped, as opposed to how Sulfur in SOCl2 has a single lone pair that repels the bonded electron pairs.

Sara Sasaki 1K

There are 3 different ways to draw the Lewis structure for N2O: 1. N with 3 lone pr, 1 bonding pr to N with 3 bonding pr to O with 1 lone pr 2. N with 2 lone pr, 2 bonding pr to N with 2 bonding pr to O with 2 lone pr 3. N with 1 lone pr, 3 bonding pr to N with 1 bonding pr to O with 3 lone pr The t...

Sara Sasaki 1K

Hi everyone, I am confused on understanding the electron configuration of certain elements in the d-block. I had thought the only exceptions were Cu, Cr, and Ag, and everything else continued with the trend of filling the s-block then d-block. But, for example, Ruthenium has the configuration [Kr] 4...

Sara Sasaki 1K

Additionally from a previous Chemistry Community post: "As the occupied energy levels increase in principal quantum number, the energies get closer and closer together to the point that their energy DEPENDS on how many electrons in that level. This does not happen until the transition metals, w...

Sara Sasaki 1K

https://www.youtube.com/watch?v=6OxRB9ShoHw
This is a video with a general description of ions.

https://www.youtube.com/watch?v=zTUnjPALX_U
This is another video that goes more in-depth with ions.

Hopefully these are helpful in determining the difference between the two!

Sara Sasaki 1K

Hi everyone, I don't think I am understanding the concept of En=-(hR)/(n^2). In the homework set problem 1.15, I started by solving for the frequency using the given wavelength (102.6 nm), then using the frequency to solve for the energy, and now I'm stuck. I'm comparing my work to the solutions man...

Sara Sasaki 1K

My book said that the electrical field corresponds to the amplitude of the wavelength, so when the frequency is decreased the waves flatten out, thus decreasing the slope (extent of change) of the wave too. Hope this helps!

Sara Sasaki 1K

I think it's a typo. I solved the problem as wavelength = (c/v) = ((2.998E8 m/s)/(2.0E18 Hz)) and also got 150 pm.

Sara Sasaki 1K

Technically you only need to round to 2 sig figs at the end since that's how many are given in the problem, but when you're converting from moles to grams or vice versa or doing other calculations you should use the full numbers given to you on the periodic table. I'm sure someone else can confirm f...

Sara Sasaki 1K

You can still use the Molarity = mol/vol equation, the question is just worded in an unusual way. I could be wrong, but in summary I think the problem was just stating that 55.1g of KCl is added to 125 mL of water.

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