CHEMISTRY COMMUNITY

AhYeon_Kwon_2H

Sorry, can someone explain worksheet 4 number 5 to me? Thank you!

AhYeon_Kwon_2H

Thank you Dr. Lavelle for a great two quarters!

AhYeon_Kwon_2H

Oops, I put in the wrong numbers for that problem. But regardless, can there be a negative k value?

AhYeon_Kwon_2H

For 7B.9 part a in the 7th edition, I got that k is -0.17, but the answer key gives it without the negative. Does k always have to be positive, and if so, do I just drop the negative sign and keep the numerical value the same?

AhYeon_Kwon_2H

k' is the rate constant for the reverse reaction. It'll probably be used with the equation K=k/k', where equilibrium constant is the ratio of k_forward over k_reverse.

AhYeon_Kwon_2H

So then unless it's specified otherwise, do we just assume that the initial product concentrations are 0 and the amount we end up with after time passes is how much the reactant concentration decreased by?

AhYeon_Kwon_2H

It should pop up when you type "PORK RAMEN" into the search bar! :)

AhYeon_Kwon_2H

Oh ok, so is the answer key just wrong then? (They calculated it in terms of moles but wrote it down as mmol)

AhYeon_Kwon_2H

Is it because we're dealing with rates that the negative isn't present?

AhYeon_Kwon_2H

Samantha Ito 2E wrote:Can someone please explain #4 on the Gibbs Free Energy worksheet?

I used deltaG = deltaG^o + RTlnQ. I found Q with the pressure values that were given and assumed temperature to be 25^oC, or 298K.

AhYeon_Kwon_2H

Could someone explain #3 on Worksheet 6? How would we find K without using partial pressure? Thanks!

AhYeon_Kwon_2H

State function is a property that depends only on the current state of the system and is independent of how that state was prepared. In other words, it doesn't matter how much or how many times the enthalpy value changed. All that matters is the net result (the sea level example that Dr. Lavelle gav...

AhYeon_Kwon_2H

Calculate the pH, pOH, and percentage protonation of solute in each of the following aqueous solutions: (a) 0.057M NH₃(aq); etc.

How do we find the OH- concentration without the K_b given?

AhYeon_Kwon_2H

Percentage deprotonation is the percentage of acid molecules deprotonated.
Percentage protonation is different, since it's the percentage of base molecules protonated.

AhYeon_Kwon_2H

A reaction mixture that consisted of 0.400 mol H 2 and 1.60 mol I 2 was introduced into a flask of volume 3.00 L and heated. At equilibrium, 60.0% of the hydrogen gas had reacted. What is the equilibrium constant K for the reaction H 2 (g) + I 2 (g) <--> 2HI(g) at this temperature? ------------- Sho...

AhYeon_Kwon_2H

Think of it like K will determine how pressure/concentration changes (because K is constant, pressure and concentration must increase or decrease to have [product]/[reactant] equal K), while temperature is what determines K.

AhYeon_Kwon_2H

Will we be assuming that pK_w is always 14 for this unit? If we change the temperature to something other than 25 degrees C so that pK_w is not 14, won't that mess up the pH and pOH scale?

AhYeon_Kwon_2H

I don't think any of the textbook questions cover cubic equations, so we'll probably only have to worry about quadratic equations. Not entirely sure though

AhYeon_Kwon_2H

Cool, so when in doubt, just check the formal charge. Got it, thank you so much!

AhYeon_Kwon_2H

Why does sulfur in SO₂ have a normal octet, but sulfate (SO₄^2-) have an expanded octet? Shouldn't it be consistent?

AhYeon_Kwon_2H

Can the transition metal cation ever be outside the brackets of the chemical formula of a coordination compound?

AhYeon_Kwon_2H

Hope this helps a little!

AhYeon_Kwon_2H

Since boiling point is contingent upon bond strength, which in turn is measured by dissociation energy (energy required to separate bonds completely), the double bonded molecule will have a higher boiling point.

AhYeon_Kwon_2H

Yup, molecules with a single lone electron rather than a lone electron pair are radicals. Because of this, radicals tend to be highly reactive and can even damage DNA.

AhYeon_Kwon_2H

The way I thought of it was SO₃ can combine with water to form H₂SO₄, but I'm not sure of the actual reason either. Sorry, hope this helped a little though!

AhYeon_Kwon_2H

Thank you so much! :)

AhYeon_Kwon_2H

Dear Dr. Lavelle:
Thank you so much for organizing multiple study sessions to help us out every single week. Chemistry hasn't been the chore I expected it to be, thanks to you! :)

AhYeon_Kwon_2H

Hi, I came in late to lecture on Wednesday, can someone upload their notes? Sorry, thanks!

AhYeon_Kwon_2H

I think so, since the key concept is that strong acids lose H + easily, and weaker bonds lead to more acidity. Electronegativity seems to be more relevant for other examples, like hypochlorous acid vs. hypoiodous acid, where Cl's higher electronegativity stabilizes oxygen and makes hypochlorous acid...

AhYeon_Kwon_2H

Do we have to draw the trigonal planar diagram with the shaded-in triangle and lined triangle, or would it be fine to just draw a regular Lewis structure with normal lines?

AhYeon_Kwon_2H

If an acid is more acidic the longer its bond length is, does that mean the converse holds true for bases (the shorter the bond length, the more basic the molecule)?

AhYeon_Kwon_2H

Hmm, I don't think it should change anything? I haven't seen any other compound written like this before.

AhYeon_Kwon_2H

If a molecule has a dipole moment, would that make it more easily dissolvable in water or less? What about melting/boiling temperature?

AhYeon_Kwon_2H

8 questions, some with multiple parts to them! :)

AhYeon_Kwon_2H

Think of uncertainty like a range: if the velocity given is 373.23 plus or minus .34 m/s, the velocity will be something between 372.89 m/s and 373.57 m/s. We know it must fall between these two values but we're not sure what the exact velocity will be, so the uncertainty is 373.57-372.89 = 0.68. Lo...

AhYeon_Kwon_2H

Unless the problem were specific about what element it is looking for or how many electrons are in the outmost subshell (ex: 3d 2 ), it would probably be too vague to give a clear answer. Perhaps you could give a range of how many electrons there could potentially be? For example, if the only inform...

AhYeon_Kwon_2H

Since there is no actual electron exchange taking place (whether by the sharing of electrons in covalent bonds or the transfer of electrons in ionic bonds), hydrogen bonds are much weaker, as they only rely electromagnetic attraction.

AhYeon_Kwon_2H

When there is a high effective nuclear charge, more energy is released when the electrons are attached; this accounts for the high electron affinity in the top right of the periodic table. Electronegativity is tangentially related to this, in that it increases when the effective nuclear charge incre...

AhYeon_Kwon_2H

I don't think we'll be using it in this course, but if there were to be a problem that makes use of this equation, it'll probably provide the kinetic energy and potential energy and using the hamiltonian found from those two values, you'd be able to calculate the wavefunction and the energy. Because...

AhYeon_Kwon_2H

When we're determining the empirical formula from the mass percentage composition, would the molar ratio be the the ratio found when we divide all the moles by the smallest mole, or the ratio with the whole numbers? Or does it even matter? Ex: Is molar ratio 1.00 : 1.33 : 1.00 or 3 : 4 : 3? Thank yo...

AhYeon_Kwon_2H

Oh okay! That was helpful, thank you! :)

AhYeon_Kwon_2H

The best way of approaching this is to try to multiply the decimals by the smallest number possible. For example, we can either multiply based on the 0.13 or the 2.23. 0.13 is close to 0.10, so we would theoretically multiply all the numbers by 10. 2.23 is close to 2.25, so we would theoretically mu...

AhYeon_Kwon_2H

Atoms, molecules, and formula units all fall under the same category of actual tangible units. There physically exist atoms, molecules, and formula units (which are basically ionic compounds). However, mole is a hypothetical unit that exists to help us compare the mass of various elements. For each ...

AhYeon_Kwon_2H

The molar mass of the metal hydroxide M(OH)₂ is 74.10 g/mol. What is the molar mass of the sulfide of this metal?

Please help! :( I'm not sure where the sulfide is coming from. I don't quite remember what metal hydroxide has to do with sulfide.

Thank you! :)

AhYeon_Kwon_2H

Oh, okay! Thank you! :)

AhYeon_Kwon_2H

Yes, it does include that part. The answer given in the back of the book is $1.38*10^{23}$ atoms of oxygen, which you get when you assume that there are 11 oxygen atoms in the compound (4 in the sulfate, 7 in the heptahydrate).

AhYeon_Kwon_2H

You can use however many significant figures you want for the molar mass and whatever other numbers are needed in the calculation, but eventually, your final answer has to have the same number of significant figures as the numbers provided in the problem.

AhYeon_Kwon_2H

I don't know what I did wrong for one of the study module questions for "Molarity and Dilution of a Solution": 5.00 g of KMnO 4 is dissolved in a 150.00 mL flask of water. If 20.00 mL of this solution is removed and placed in a new 2nd 250.00 mL flask and filled with water, what is the con...

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