CHEMISTRY COMMUNITY

Jared Khoo 1G

Usually, aren't E* values by default given for reduction?

Jared Khoo 1G

Will the final still account for the 180 points on the syllabus or will it be worth less?

Jared Khoo 1G

The review is canceled but I imagine they will post solutions in the near future.

Jared Khoo 1G

Dear Dr. Lavelle,

Thank you for being a great chemistry professor and an even better person. All the resources you put into this class have really helped all of us students and helping us through this stressful time will never be underappreciated!

Jared Khoo 1G

Are we expected to know how to use the steady-state approximation?

Jared Khoo 1G

Does anyone know how we will get our tests 2s back as classes are cancelled.

Jared Khoo 1G

Use negatives when looking at reactants as their concentrations decrease over time.

Jared Khoo 1G

For hypothetical equation, A + B <-> C + D, K = [C][D]/[A][B]. We know that the rate of the forward reaction is k [A][B], and the rate of the reverse is k'[C][D]. At equilibrium (so we can use K), the forward rate is equal to the reverse rate. So, k [A][B] = k'[C][D]. If you divide [A][B] from both ...

Jared Khoo 1G

Yeah you would get 1*10^4 if 2 electrons were transferred but that is not the case here. The answer should be 107

Jared Khoo 1G

Does anyone know which elements are considered conductive enough that platinum is not used to transfer electrons? I remember seeing liquid mercury as something that can transfer electrons but I forgot whether that was true or not.

Jared Khoo 1G

I'm don't really understand your question. The oxidation would be Au+ going to Au3+ with 2 electrons being on the products side, signifying oxidation.

Jared Khoo 1G

Is the Van't Hoff Equation on the equation sheet?

Jared Khoo 1G

Albert was a chemist. Albert is no more.
What he thought was H₂O. Was H₂SO₄

Jared Khoo 1G

In the absence of a salt bridge, the anode will keep losing electrons and hence get more positive. A salt bridge would pump anions to the anode making it less positive.

Jared Khoo 1G

Salt bridges ensure neutrality on both the cathode and the anode. As the cathode gets more negative over time and the anode gets more positive over time, salt bridges pump anions to the anode and cations to the cathode.

Jared Khoo 1G

Honestly just doing all the homework problems will probably give you the best grasp of what will be expected from you on the test.

Jared Khoo 1G

A diamond is thermodynamically unstable as it has a negative delta G value indicating that the reaction from diamond to graphite is favorable. however, it is kinetically stable as the reaction barrier is very high, so the reaction takes place at a very slow rate.
A diamond is not forever.

Jared Khoo 1G

What was oxidation again? My science is a bit rusty.

Jared Khoo 1G

I would highly recommend doing all A-D first as some upper-division science classes require C or D as prerequisites. For example, LS 107 requires C as a prerequisite and it is a part of many life science majors, so getting BL and CL done is not that important right now.

Jared Khoo 1G

I've heard BL is a LOT of work so keep that in mind as there will probably be a good amount of studying needed for 14C.

Jared Khoo 1G

I believe we are covering kinetics next week which will NOT be on test 2.

Jared Khoo 1G

Tests aren't curved but I am also interested to see if he will adjust grades at the end in order to meet a specific distribution.

Jared Khoo 1G

Water molecule: Hey oil wanna hang out?
Oil molecule: I can't mix with you guys
Water molecule 2: You're such a hydrophobe!

Jared Khoo 1G

Why is STP at 273.15 K (0 Celcius) and not 298 K like many constants are given at. Is there a separate constants list for values at STP?

Jared Khoo 1G

Clara Cho 2K wrote:I feel like I'm doing #6 correctly , but I'm not getting the correct answer. Can someone explain how I calculate the work of expansion for the step with the reversible, isothermal expansion?

W_by = nRT (ln V₂/V₁), and -W_by = W_on which is the component of dU = q + w.

Jared Khoo 1G

Hiba Alnajjar_2C wrote:Could someone explain when to use Cp or Cv? Is Cp used when the pressure is constant, while Cv is used when the volume is constant? Thank you!

You got it, also remember how to calculate it when presented with an ideal gas, although it is on the formula sheet.

Jared Khoo 1G

Can anyone give me examples of when the answer requested should be left as kJ or as kJ/mol. Some of the homework questions asked for standard reaction enthalpies and proceeded to answer in kJ.

Jared Khoo 1G

U is the same as E_th I believe, which is the thermal energy an object has. Therefore, U is also determined by temperature and is equal to the average kinetic energy per mole multiplied by the number of moles (n).

Jared Khoo 1G

Everything is given but you would have to know what each symbol/letter means.

Jared Khoo 1G

When converting celcius to kelvin, you added 273. For a more accurate conversion, add 273.15 as mentioned on Dr. Lavelle's formula sheet. Also, the textbook probably used R = 8.3145 as the gas constant. This should get the right answer.

Jared Khoo 1G

I think at least for the scope of this class acids and bases will be present in aqueous form.

Jared Khoo 1G

Delta U is equivalent to 3/2 NK_B(Delta T), so if T is constant then Delta U is constant as well.

Jared Khoo 1G

In a perfect system with no energy lost or gained, q lost/gained by system = q gained/lost by surroundings.

Jared Khoo 1G

I believe that if it there is negative heat then the reaction is exothermic, so the surroundings increase in temperature and the system in question is releasing heat.

Jared Khoo 1G

In physics classes the first law of thermodynamics was $\Delta Eth = Q+W$ . However, in this class the equation is $\Delta U = Q+W$ . I just want to make sure that U and Eth are the same so it doesn't get confusing.

Jared Khoo 1G

What atoms make up aspirin?
As P Ir In

Jared Khoo 1G

The standard formula for the first law of thermodynamics is $\Delta U = Q + W, or \Delta H + W$ . Here, W is equivalent to P $\Delta V$ , which by the ideal gas law is the same as nR $\Delta T$ , which is where this equation came from.

Jared Khoo 1G

As the latent heat of vaporization is very high, the amount of energy released when steam is condensed is much higher than the amount of energy released when boiling water is cooled, therefore the burn will be much more significant.

Jared Khoo 1G

The standard enthalpies of formation are usually given at STP therefore it would be different under nonstandard conditions.

Jared Khoo 1G

Pressure has a direct relationship with enthalpy which is why it is usually easier to calculate enthalpies at STP, using 1 atm as standard.

Jared Khoo 1G

Freezing would be considered exothermic because it is converting particles from a less ordered state to a more ordered state, which would make the value of mass*latent heat of fusion, negative, hence exothermic.

Jared Khoo 1G

State functions are functions where only the final state and the initial state matter when doing calculations and all intermediate states are effectively immaterial. For example, when calculating energy for a gas at two different temperatures, the fact that it is at any other value besides the start...

Jared Khoo 1G

What is the difference between the 5% rule and the rule saying that you can disregard x in the denominator if K < 10^-3, or are they the same thing. Also, is this mentioned in the textbook and if so, where?

Jared Khoo 1G

Use the R constant that uses the appropriate unit of pressure.

Jared Khoo 1G

Which element is the coldest?

Brrryllium

Jared Khoo 1G

A lot of times when using ice tables, the equilibrium concentration equation will end up looking like x 2 /number-x = constant. Therefore, when you cross multiply by (number-x) and move it over to have one side of the equation equal to zero, you will end up with a quadratic equation, which can be so...

Jared Khoo 1G

Yes, acids and bases are at equilibrium which can allow calculation of K_A and K_B

Jared Khoo 1G

Did you hear about the man who got cooled to absolute zero?
He's 0 K now.

Jared Khoo 1G

The textbook seems to not specify the K value, by this I mean K_c or K_p. The K values should all be the same though, it is just convention to use partial pressure when dealing with only gasses and concentration in other circumstances.

Jared Khoo 1G

There is no such thing as a negative concentration, therefore this value should be disregarded and only the positive value should be used.

Jared Khoo 1G

By using brackets you are denoting a value that is concentration, therefore you should plug in concentrations with the units molL^-1, which will get you K_c.

Jared Khoo 1G

I think it is because their concentrations do not change throughout the reaction and do not affect the concentrations at equilibrium. As the density of a pure solid or liquid remains the same no matter what volume, the concentration is also the same.

Jared Khoo 1G

Lauren Haight 1E wrote:for mini marshmallow 2b, why is the coordination number for Dihydroxoyoxolatocobalt (III) 4?

Oxalate is BIdentate, so it will form 2 coordinate covalent bonds. Add this to the two bonds made to hydroxide and the coordination number is 4.

Jared Khoo 1G

Joanne Kang 3I wrote:min marshmallows 1c... why isn't it neutral?

ammonium is a conjugate acid of a weak base, so it will lower pH by giving a proton (H+) to water to form hydronium.

Jared Khoo 1G

For mini marshmallows 2c, why is it cupperate instead of copper? Isn't it a +1 oxidation state? The coordination complex has a 1- charge, so it is cuprate. This is shown because it forms an ionic bond with potassium which has a +1 charge, so you know the coordination complex must have a -1 charge. ...

Jared Khoo 1G

For e, Al has a strong charge (+3) so it can take away protons. Remember that small highly charged metals act as acids. As Cl - is a conjugate base of a strong acid, it does not affect pH. For f, Cu again is a metal that has a strong charge (+2, which is kind of borderline). I think that Copper can ...

Jared Khoo 1G

I'm kind of lost so I'll just walk through the problem. Ok to start we have 1.94 *10 -18 J for the change in energy by converting 102.557 nm to Energy which you have done. Then this value is equivalent to E final - E initial . However, as you are subtracting a negative (the E initial ), it becomes E...

Jared Khoo 1G

The unit for energy is Joules, which is equivalent to a Newton*meter. Planck's constant h is in the units of m 2 kgs -1 and the unit for v frequency v is s -1 . Multiplying these together you would get m 2 kgs -2 . As a newton is in the units of kgms -2 , you can see that this equation indeed does f...

Jared Khoo 1G

It is a negative ion, so you must add -ate to the end of the transition metal name. For reference Dr. Lavelle has the naming guide and it should be there.

Jared Khoo 1G

What would be the total number of hydrogen bonding sites in Uric Acid?

Jared Khoo 1G

I think if you haven't gotten them already you will get them next week in discussion.

Jared Khoo 1G

Technically it is the concentration of Hydronium as the H⁺ will attach to a water molecule. However, it is easier to write H⁺ concentration which is why it is common.

Jared Khoo 1G

I think there will be a good balance between the two as it should probably follow the format of the midterms.

Jared Khoo 1G

Most of the substances that we will work with, if not all, will have pH values between 0 and 14 corresponding to Hydronium ion concentrations that range from 1 * 10⁰ M*L^-1 to 1* 10^-14 M*L^-1

Jared Khoo 1G

Does anyone remember what specific nucleotide Cisplatin attaches to?

Jared Khoo 1G

Why is working with ammonia easy?
Because its quite basic.

Jared Khoo 1G

I believe it goes up to 2F.1.

Jared Khoo 1G

Thank you Dr. Lavelle for putting the Cation in education.

Jared Khoo 1G

How often do I tell chemistry jokes?
Periodically.

Jared Khoo 1G

Aman Sankineni 3E wrote:The questions on the syllabus from 3F, 2E, and anything that covers sigma and pi bonds, so 2F.1 will cover topics on the test.

Thank you.

Jared Khoo 1G

Probably up to "Explain how hybridization arises from atomic orbitals"

Jared Khoo 1G

Just with N, O, or F.

Jared Khoo 1G

All molecules have London Dispersion forces.
Molecules with uneven sharing of electrons (think polar/non-polar) will have dipole-dipole.
Molecules with Hydrogen bonded to a N, O, or F will have Hydrogen bonding.

Jared Khoo 1G

SO₂ is polar, hence the dipole-dipole interactions.

Jared Khoo 1G

As CH₄ and CCl₄ are symmetrical (and tetrahedral) they are nonpolar and dipole dipole interactions will not be that important. However, they still have London dispersion forces despite being nonpolar.

Jared Khoo 1G

Ozone is polar as it is bent, therefore it has a net dipole.

Jared Khoo 1G

To finish off this problem,

C. CHI3 will have a higher melting point because iodine is bigger than chlorine with more electrons and therefore higher IMFs.
D. Methanol will have a higher melting point because of the presence of Hydrogen bonds.

Jared Khoo 1G

Amy Luu 3I wrote:How do you determine that buthanol has h-bonds? How come diethyl ether doesn't have h bonds?

H bonds form when H is bonded to N, O or F.

Jared Khoo 1G

Yeah, doesn't ether also have H bonds? They're bonded to the carbon just as in Butanol, so what's the difference? Is it because unlike in Ether, theres a carbon bonded to an Oxygen? If so, why is this important?? I don't think so because the Hydrogen is not bonded to N, O, or F, therefore there are...

Jared Khoo 1G

Victor James 4I wrote:how does this relate to orbitals?

I believe that valid solutions of Schrodinger's equation, psi, correspond to orbitals.

Jared Khoo 1G

ayushibanerjee06 wrote:For 6b., I am confused about why GarBreadium has the longer deBroglie wavelength. Shouldn't it be He because it weighs more?

As mass is on the denominator for deBroglie wavelength calculations, a lower mass atom will have a longer wavelength as it is inversely proportional.

Jared Khoo 1G

I believe he said in class it will include up to Focus 2D.

Jared Khoo 1G

OMG did you hear Oxygen and Magnesium were a couple?

Jared Khoo 1G

Don't throw sodium chloride around. It's a salt.

Jared Khoo 1G

Me: Hey Siri, can you give me the formula for Nitric Acid?
Siri: NO
Me: ...

Jared Khoo 1G

Fundamentals, Quantum World, and Chemical Bonds up to Section 2D

Jared Khoo 1G

I think you may have looked at the answer key incorrectly, mine says the right answer. Anyways, the thing that really matters is the l value, as it determines the orientation of the different orbitals. An l of 1 corresponds to a p orbital, which can be oriented 3 ways. When the m l is given, then th...

Jared Khoo 1G

Hopefully this helps. Also there is a chemistry stackexchange post on this topic with helpful images. If electrons share the value n, it is part of a shell. If electrons share n and l, it is part of the same sub-shell. If electrons share n, l and ml then it is in the same orbital. https://chemistry....

Jared Khoo 1G

l can go up to n-1, but in this class, we are only required to know up to the f orbital. Most likely we won't even see f orbitals as it doesn't really apply to living systems.

Jared Khoo 1G

With some exceptions where the s orbital is lower energy, since the d orbital is in a different shell you order that first. Eg. 4d then 5s.

Jared Khoo 1G

If electrons share the value n, it is part of a shell.
If electrons share n and l, it is part of the same sub-shell.
If electrons share n, l and m_l then it is in the same orbital.

Jared Khoo 1G

Yes theoretically speaking there is nothing that can exceed the speed of light so if you calculate the velocity of an election exceeding the speed of light that is not possible.

Jared Khoo 1G

Given he provides 2.99792 × 10^8 m/s on the formula sheet pdf, I would use that, although I'm sure he would specify/be fine with either on homework.

Jared Khoo 1G

I don't believe so, which is why there are discrete absorption/emission line spectra for each element. If an element were to absorb all frequencies and therefore all energies of light, then there would be no black spots in the emission spectrum. If you google hydrogen emission spectrum you'll see on...

Jared Khoo 1G

DesireBrown3K wrote:If someone was able to complete the Angstrom question, can you please explain to me (step by step) how to solve the problem?

An angstrom is 10^-10m, so there are .1 angstrom in a nanometer and 100 angstroms in a picometer.

Jared Khoo 1G

As you are given 1 mol of photons, and the energy per photon is calculated in part A, you take the energy (part A) in J/photon multiplied by 6.022 photons/mol which would yield the units J/mol, which is what the answer is looking for. You multiply this my 1 mol, and get the answer.

Jared Khoo 1G

In class, we learned it as Delta P* Delta X >= h/4pi, but in the solutions manual it states that it is greater than or equal to (1/2)h. Can someone please clarify which one is the correct formula? Thanks.

Jared Khoo 1G

Planck's constant relates the energy in one photon of electromagnetic radiation to the frequency of that radiation. m²*kg/s is the same as Joule*second, as a joule is a kg *m²*s^-2, so this multiplied by frequency in Hz (or s^-1) would yield energy.

Jared Khoo 1G

You would want to take 32W * 2 seconds and divide it by your result from the energy released by each photon. You then should take the photons you have and divide by 6.022 *10^23 photons/mol, leaving you with moles of photons.

Jared Khoo 1G

As Romina said, the Lyman series refers to UV light, which has more energy than the visible light spectrum which is why it corresponds to going from n=1 to n=3, for example. The further away an electron is from the nucleus, less energy is required to jump to the next level, so lower energy light wil...

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