CHEMISTRY COMMUNITY

LexyDenaburg_3A

Hi, can someone explain how to solve for this question, I've been struggling. Dinitrogen pentoxide, N2O5, decomposes by first‑order kinetics with a rate constant of 3.7×10−5 s−1 at 298 K. What is the half‑life, in hours, of N2O5 at 298 K? If [N2O5]0=0.0512 mol⋅L−1, what will be the concentration of ...

LexyDenaburg_3A

For #7 on Sapling, I'm still struggling with this question.

Write the rate law for the reaction where k is the rate constant.

How do we find the rate law?

LexyDenaburg_3A

Hi, I've been having trouble with this question on Sapling, can anyone help? The presence of a catalyst provides a reaction pathway in which the activation energy of a reaction is reduced by 44.00 kJ⋅mol−1 . Uncatalyzed: A⟶B Ea=116.00 kJ⋅mol−1 Catalyzed: A⟶B Ea=72.00 kJ⋅mol−1 Determine the factor by...

LexyDenaburg_3A

How many points is the final worth?

LexyDenaburg_3A

I'm also thinking about pre-med. It's a long road and a lot of hard work but that will make it so much more worth it. I believe it's definitely do-able if you put all your effort and hard work into it and keep trying. Not easy though!

LexyDenaburg_3A

Goodluck on the final everyone!! Trust all the hard work

LexyDenaburg_3A

When are chem community points due?

LexyDenaburg_3A

The textbook problems are very helpful for me!!

LexyDenaburg_3A

Goodluck on the final!!!

LexyDenaburg_3A

I'm probably going to spend it studying but try not to stress too much! We got this !!

LexyDenaburg_3A

I would say confirm with your TA just to be sure!!

LexyDenaburg_3A

These are great tips, thank you!!

LexyDenaburg_3A

Will we use chemistry community for 14C?

LexyDenaburg_3A

I don't think he will be teaching for 14C, super sad about it :(

LexyDenaburg_3A

Chem Equilibrium for me!!

LexyDenaburg_3A

I was having trouble with this but thank you for these instructions!! Super helpful

LexyDenaburg_3A

I was struggling with #17 as well but this is super helpful, thank you!!

LexyDenaburg_3A

Calculate the cell potential for the reaction as written at 25.00 °C , given that [Zn2+]=0.790 M and [Ni2+]=0.0110 M . Use the standard reduction potentials in this table.

Zn(s)+Ni2+(aq)↽−−⇀ Zn2+(aq)+Ni(s)

Can someone explain how to start this question?

LexyDenaburg_3A

Calculate the standard free-energy change for the reaction at 25 ∘C.

Refer to the list of standard reduction potentials.

2Au3+(aq)+3Zn(s)↽−−⇀2Au(s)+3Zn2+(aq)

How is delta G calculated in this question?

LexyDenaburg_3A

Hi, what are the steps to starting this question?
Separate this redox reaction into its balanced component half‑reactions. Use the symbol e− for an electron.

Cl2+2Li⟶2LiCl

LexyDenaburg_3A

Does anyone know when midterm 2 grades will be up?

LexyDenaburg_3A

I believe that the 14C lectures will be recorded and able to watch at a different time

LexyDenaburg_3A

How many posts should we have by the end of week 7?

LexyDenaburg_3A

Good luck to everyone still taking midterms!! Glad we got through this second one in chem !

LexyDenaburg_3A

Hi, can someone walk me through how to solve this question from the textbook? I'm a little confused (a) Calculate the heat that must be supplied to a copper kettle of mass 400.0 g containing 300.0 g of water to raise its temperature from 20.0°C to the boiling point of water, 100.0°C. (b) What percen...

LexyDenaburg_3A

This is all super helpful thank you everyone!!!

LexyDenaburg_3A

I've been struggling a lot with the topics we've been doing lately as well. These tips are super helpful thanks everyone!

LexyDenaburg_3A

can anyone walk me through how to start this equation?
Given the information

A+BC⟶2D⟶DΔH∘ΔH∘=710.6 kJΔS∘=323.0 J/K=514.0 kJΔS∘=−226.0 J/K

calculate ΔG∘ at 298 K for the reaction

A+B⟶2C

LexyDenaburg_3A

Hi a question on sapling says The molar heat capacity for carbon monoxide at constant volume is CV, m=20.17 J/(K·mol) . A 10.00 -L fixed-volume flask contains CO(g) at a pressure of 6.00 kPa and a temperature of 25.0 °C. Assuming that carbon monoxide acts as an ideal gas and that its heat capacity i...

LexyDenaburg_3A

When given a positive or negative sign for delta H or delta S, how do we know what the phase change should be? If delta H is positive and delta S is positive, how can we tell if the phase change is from liquid to gas, solid to gas, liquid to gas, etc.?

LexyDenaburg_3A

A question on sapling asks,
A heat source generates heat at a rate of 81.0 W (1 W=1 J/s) . How much entropy does this produce per hour in the surroundings at 25.3 ∘C ? Assume the heat transfer is reversible.
How do we start to solve this question?

LexyDenaburg_3A

Definitely the Bucc's!!

LexyDenaburg_3A

Yeah including 14A we should have 75 posts by tonight!!

LexyDenaburg_3A

I would agree. The UA sessions are super helpful. I didn't do great on this midterm either though so don't worry!!

LexyDenaburg_3A

I can definitely relate to this. I would say just double, triple check your work and try to take your time and go through slowly.

LexyDenaburg_3A

I'm struggling too. These topics are pretty hard so thanks for the tips! I'm definitely going to have to get to some step up sessions

LexyDenaburg_3A

Going to step up sessions really helped me last quarter!! And also doing the practice problems in the textbook.

LexyDenaburg_3A

Honestly, I do find it tough not to rush through problems but we just have to take our time and analyze the situation!! Double checking my work also helps me

LexyDenaburg_3A

When should we get our midterm grades back?

LexyDenaburg_3A

This week's homework on #13 says "At constant pressure, which of these systems do work on the surroundings?", and then gives some chemical formula's. I'm just wondering how are we supposed to tell which systems do work on the surroundings?

LexyDenaburg_3A

A hot lump of 30.3 g of aluminum at an initial temperature of 60.3 °C is placed in 50.0 mL H2O initially at 25.0 °C and allowed to reach thermal equilibrium. What is the final temperature of the aluminum and water, given that the specific heat of aluminum is 0.903 J/(g·°C)? Assume no heat is lost to...

LexyDenaburg_3A

When there are phase changes, like when something goes from a solid to a liquid, how can we tell if the reaction is endothermic or exothermic?

LexyDenaburg_3A

I'm a little confused on this question. It says "H3 is a weak base ( Kb=1.8×10−5 ) and so the salt NH4Cl acts as a weak acid. What is the pH of a solution that is 0.019 M in NH4Cl at 25 °C?"
Can anyone walk me through how to solve for this problem?

LexyDenaburg_3A

I'm still a little confused on #7 as well. After we do this and convert Ka to Kb, what do we do after this step?

LexyDenaburg_3A

For this question to get the Kb I did 1.0x10^-14/Ka(given) and then I used the quadratic formula to solve. I'm not sure if I set up the ICE table wrong but my equation came out to x^2/.033-x=2.5x10^-6 but when I solve for x I keep getting the wrong answer. Can anyone explain how they did this questi...

LexyDenaburg_3A

Hi so on the week 2 homework on #4, I ended up solving it using the quadratic formula and still got the correct answer eventually. When I solved after the quadratic formula, I got the answer 0.0015. After this though, how do I know which number is the pH and which is pOH? Because after I did -log(1....

LexyDenaburg_3A

In friday's lecture of week 3, professor talks about the overall (net) enthalpy change. When he does the second example for using method 2, where is he getting the numbers in kJ.mol^-1 for the bonds? He gets the numbers 612 kJ.mol^-1, 366 kJ.mol^-1, -348 kJ.mol^-1, -412 kJ.mol^-1, -276 kJ.mol^-1 and...

LexyDenaburg_3A

Will a lecture be posted tomorrow even though we have classes off?

LexyDenaburg_3A

In this question, how did you set up Kc?

LexyDenaburg_3A

At a certain temperature, 0.680 mol SO3 is placed in a 3.50 L container.

2SO3(g)↽−−⇀2SO2(g)+O2(g)

At equilibrium, 0.130 mol O2 is present. Calculate Kc.

I'm pretty confused on how to start this question. Can anyone help?

LexyDenaburg_3A

I'm still a little confused on how the ice box works. So does the change concentration for PCl5 have a negative change in X, and then PCl3 and PCl2 have positive change in X? And then how do you find the initial concentration?

LexyDenaburg_3A

In the monday lecture of week 2 in the very first example professor uses, how does he get the change in concentration to be -2X, -X, and +2X?

LexyDenaburg_3A

thank you for clearing this up!! I wasn't sure how they were structured either

LexyDenaburg_3A

this was super super helpful!! I'm always in need of good study tips so thank you!

LexyDenaburg_3A

Does much of 14A material carry over to 14B?

LexyDenaburg_3A

Will the midterm and final format be the same as 14A format with lockdown browser on zoom?

LexyDenaburg_3A

Does anyone know where we find the link for step up/workshop sessions?

LexyDenaburg_3A

I struggle with memorizing this too, so thank you for these tips!!

LexyDenaburg_3A

Thank you Dr. Lavelle!!! You make learning chemistry so much fun and you're doing such an amazing job teaching the material. Thanks for a great quarter and excited for the next one with you!!

LexyDenaburg_3A

When one physicist asks another, "What's new?" what's the typical response?

C over lamba

LexyDenaburg_3A

Yeah I think the 50% is just for passing but the rest of the scales for A/A- still apply

LexyDenaburg_3A

Yeah I believe a 50% overall on assignments is a passing grade!!

LexyDenaburg_3A

When should we know final grades?

LexyDenaburg_3A

why are ligands important/what are they?

LexyDenaburg_3A

Do we have to draw the lewis structures every time when trying to find coordination numbers?

LexyDenaburg_3A

Do we need to memorize the prefixes for finding coordination numbers?

LexyDenaburg_3A

Is the final cummulative?

LexyDenaburg_3A

Will what we've learned in 14A carry over a lot into what we will start learning in 14B?

LexyDenaburg_3A

How do I determine the negative pole on molecules?

LexyDenaburg_3A

How do you determine the number of sigma and pi bonds in a molecule given the lewis structure?

LexyDenaburg_3A

Can someone explain how to find hybridization? I'm pretty confused on this question

LexyDenaburg_3A

Given the lewis structure, how do we find the polarity of the bond and then the overall molecule? For example, H20 and BeCl2

LexyDenaburg_3A

When given a 2D representation of a molecule that doesn't necessarily show the 3D shape of the model, how do we use VSEPR to predict the smallest bond angle?

LexyDenaburg_3A

Given the lewis structure of CO2, is it polar?

LexyDenaburg_3A

How can we determine which molecules are linear given the chemical formula?

LexyDenaburg_3A

A question on sapling says
"How many outer atoms and lone pairs are present in a molecule with a square pyramidal shape?"

How are we supposed to determine the lone pairs from this shape?

LexyDenaburg_3A

Does anyone know if final grades are curved?

LexyDenaburg_3A

Why did the white bear dissolve in water?

Because it was polar!

LexyDenaburg_3A

Will we need to know what the shape of a molecule is from it's name on the final?

LexyDenaburg_3A

Will we need to calculate dipole moments on midterm 2?

LexyDenaburg_3A

Does midterm 2 have a review session?

LexyDenaburg_3A

What's the show cesium and Iodine love watching?

CSI

LexyDenaburg_3A

One of the questions on Sapling says: "Urea is an organic compound widely used as a fertilizer. Its solubility in water allows it to be made into aqueous fertilizer solutions and applied to crops in a spray. What is the maximum theoretical number of water molecules that one urea molecule can hy...

LexyDenaburg_3A

When given molecules, how do I tell which ones only exhibit London Forces?

LexyDenaburg_3A

How can we tell what the oxidation number is when given a resonance structure? Why are oxidation numbers important?

LexyDenaburg_3A

When it comes to bond length, is a single bond shorter than a triple bond? I'm kind of confused on how to order lengths of bonds.

LexyDenaburg_3A

When given different resonance structures, how does formal charge tell us which structure is most plausible?

LexyDenaburg_3A

How are we supposed to tell if a molecule is an acid or a base? I know that if it donates electrons then it's a base and if it accepts electrons then it's an acid but is there a more in depth explanation?

LexyDenaburg_3A

There is a question on sapling that says: "The formulas of the bromate ion, BrO−3, and chlorate ion, ClO−3, are very similar. However, the formulas of the nitrate ion and phosphate ion contain different numbers of oxygen atoms. This is also true for the formulas of the nitrite ion and phosphite...

LexyDenaburg_3A

When drawing Lewis structures, how can we tell if it's okay that a molecule doesn't have an octet? For example, Boron on BF3 (lecture example)? How do we know that it's correct if Boron doesn't form an octet?

LexyDenaburg_3A

Can someone explain how the sizes of the atomic/ionic radius works? I'm struggling with remembering how big/small a radius is according to where the element is on the periodic table.

LexyDenaburg_3A

Can someone explain the main difference between ionic and covalent bonds?

LexyDenaburg_3A

Are these the only exceptions to the rule in the whole periodic table? Not just the ones we will be working with?

LexyDenaburg_3A

Thank you for this clarification!! I was wondering the same thing. Just to be sure, any post counts as points for that week correct?

LexyDenaburg_3A

How do we tell how many quantum numbers specifies a subshell?

LexyDenaburg_3A

What is a cation afraid of?

A dogion

LexyDenaburg_3A

I've mostly heard that Schrodinger on the MT will be more conceptual from UA's and TA's!!

LexyDenaburg_3A

I'm pretty confused still on the uncertainty problems. Can someone explain how to start this problem?
A proton is accelerated in a cyclotron to a very high speed that is known to within 3.0 × 10^2 km⋅s^−1. What is the minimum uncertainty in its position?

LexyDenaburg_3A

Thank you guys this helped a ton!!

LexyDenaburg_3A

Hi, there is a problem from the textbook that says
"The work function of zinc is 3.63 eV. What is the longest wavelength of electromagnetic radiation that could eject electrons from zinc?"

Can anyone walk me through how to start this problem?

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