CHEMISTRY COMMUNITY

Sydney Wu 2M

Can someone help me with #3 I don't understand how both of them are nucleophiles? The line diagram has multiple double bonds which are made up of a pi bond. These pi bonds serve as areas of high electronegativity due to their being so many localized electrons at each pi bond. This make it attracted...

Sydney Wu 2M

Entropy is a measure of disorder, so if you make delta S less positive, you decrease entropy (more order), and if you make delta S less negative, you increase entropy (more disorder), correct? In lecture, we were told that catalysts and enzymes speed a reaction by putting reactants in the correct or...

Sydney Wu 2M

"In the reaction of Her with the reactive intermediate CH 3 CH=CHCH 2 + , at low temperatures the predominant product is CH3CHBrCH=CH2, but at high temperatures, the predominant product is CH 3 CH=CHCH 2 Br. (a) Which product is formed by the pathway with the larger activation energy? (b) Does ...

Sydney Wu 2M

Page 60 of the course reader says that the reaction rate is -(1/a)*(dR/dt) = k[R]ⁿ. Is there any specific derivation to come to this conclusion, or is this just the definition of a reaction rate?

Sydney Wu 2M

The textbook gives us: 2 H2(g) + O2(g) --> 2 H2O(l) Ecell = +1.23V at pH = 7 2 H2O(l) --> 2 H2(g) + O2(g) Ecell = -1.23V at pH = 7 O2(g) + 4 H+ (aq) + 4e- --> 2 H2O(l) E = +0.82V at pH = 7 How do we know when to use these equations as an anode or cathode reaction, and how do we determine which one t...

Sydney Wu 2M

"Arrange the following metals in order of increasing strength as reducing agents for species in aqueous solution: (a) Cu, Zn, Cr, Fe (b) . . . " When looking up the standard reduction potentials in Appendix 2B, there are multiple values for some of the metals (i.e. Cu has E* values for Cu ...

Sydney Wu 2M

When calculating delta G* using -nFE*, units cancel nicely to yield a result in units J. However, in previous exercises, delta G* has had units kJ.mol^-1. I know you can convert J to kJ, but what are the correct units for delta G*?

Sydney Wu 2M

On page 41 of the course reader, it says delta G* is positive when K<1 and that delta G* is negative when K>1. Does that mean the forward reaction is not spontaneous when K<1 and is when K>1? I understand the arithmetic but I don't understand because if K<1, the reaction will want to go forward (spo...

Sydney Wu 2M

Does a negative delta G* mean stability in addition to spontaneity? Why?

Sydney Wu 2M

a) For Part (a), why was -w rev substituted in for q rev in the SSM? Also, will delta S tot always = 0 for reversible reactions? b) Part (b) asks to calculate delta S tot , delta S sys , and delta S surr for an isothermal, irreversible free expansion of an ideal gas beginning at 323K, 1.67L, and 4.9...

Sydney Wu 2M

"The enthalpy of formation of TNT is -67 kJ.mol -1 , and the density of TNT is 1.65 g.cm -3 ...Explore its potential as a rocket fuel by calculating its enthalpy density (enthalpy released per liter) for the reaction 4C 7 H 5 N 3 O 6 (s) + 21 O 2 (g) --> 28 CO 2 (g) + 10 H 2 O(g) + 6 N 2 (g) I ...

Sydney Wu 2M

Appendix 2A tells that delta h_f^* for K₂S(aq) is -471.5. The answer in the textbook and SSM uses -417.5. Which is the correct delta h_f^* value?

Sydney Wu 2M

Thank you! :)

Sydney Wu 2M

Why are fractional coefficients required when balancing the equation? Don't whole numbers make everything cleaner?

Sydney Wu 2M

"Calculate the pH at the stoichiometric point for the titration of 15.00mL of 0.100M HCOOH (K a = 1.8 x 10 -4 ) with 0.150M NaOH." Can someone please explain how to start this? I'm looking at the answer key and lecture notes, but I am completely lost on the logic of how to start and procee...

Sydney Wu 2M

Are pH=pKa and pOH=pKb? I am unsuccessfully trying to figure out why the answers the 12.57 are what they are. Part (a) gives tells that the pH of .10M HClO₂ was measured to be 1.2 and asks us to to determine Ka and pKa. Isn't 1.2 the same as pKa?

Sydney Wu 2M

Question 12.9c asks if the reaction CH₃COOH(aq) + NH₃(aq) ---> CH₃CONH₂ (aq) + H₂O (l) can be classified as reaction between Bronsted acids and bases and to identify the acid and base if it as an acid-base reaction. Can someone please explain how no proton is transferred?

Sydney Wu 2M

Alright, thanks!

Sydney Wu 2M

Should we memorize the strong/weak acids and bases listed on pages 163-64 in the course reader?

Sydney Wu 2M

Ok, thanks!

Sydney Wu 2M

"0.020 mol NO 2 was introduced into a 1.00-L flask and the reaction 2 NO 2 (g) <--> N 2 O 4 (g) was allowed to come to equilibrium at 298 K. (a) Using information in Table 11.2, calculate the equilibrium concentrations of the two gases. (b) The volume of the flask is reduced to half its origina...

Sydney Wu 2M

Should we always use atm (unless specified in the question to use bar)? For instance, Q8 on p. 43 of the quiz workbook asks us to calculate the equilibrium partial pressures but does not specify which units to use. Q10 on the following page requires you to convert from molar concentration to partial...

Sydney Wu 2M

Great, thank you!

Sydney Wu 2M

Got it, thank you!

Sydney Wu 2M

Is this the type of question where it gives you too much information (are K and the molar concentrations necessary)? Do you even need to use an ICE box?

Sydney Wu 2M

My answer and the answer key do not match at all, but I don't know where I went wrong! Can someone please explain how to find K if 8.15% of the reactant remains at equilibrium? Thank you!

Sydney Wu 2M

Liquids and solids are pure substances, and pure substances are not included in the calculation.

Sydney Wu 2M

If NH₃ is amine, how come there are only 2 Hs for each amine in en and dien?

Sydney Wu 2M

The SSM uses the initial pressure value for both the numerator and denominator; how? Should we assume that the pressure is constant?

Sydney Wu 2M

I notice that when water is a ligand (looking at #31), the SSM writes its formula as H₂O for one exercise and OH₂ for another one. I know the order of the atoms matter, so which one is correct? Why?

Sydney Wu 2M

Finding the oxidation number of metals is generally pretty straightforward as you would just subtract the overall charge of the compound by any negatively charged ligands located between the brackets (for the iron compound, there are 6 CN - molecules so subtract that from -4 gives a 2+ charge for t...

Sydney Wu 2M

So, generally speaking, ionization energy and electronegativity are directly related (IE and EN increase across a period), but oxygen is an exception since it has one e- over a half-filled orbital?

Sydney Wu 2M

Oh wait, I understand now, thank you!

Sydney Wu 2M

So are pi bonds always not hybridized?

Sydney Wu 2M

For double bonding, why are the overlapping orbitals that form a pi bond not hybridized?

Sydney Wu 2M

Are we expected to know what wavelength values each atomic spectra region includes?

Sydney Wu 2M

The midterm covers only up to the end of hybridization, so there is no MO Theory.

Sydney Wu 2M

When you have a heteronuclear diatomic molecule with one Z > 8 and the other Z < 8, how do you know when the pi bonding orbital comes before the sigma bonding orbital, and vice versa? i.e. CO

Sydney Wu 2M

How is oxygen more electronegative than nitrogen if it has a lower ionization energy?

Sydney Wu 2M

That's right, thank you!

Sydney Wu 2M

Why is N the central atom for N₂O? Doesn't O have the lower ionization energy?

Sydney Wu 2M

I understand now, thank you!

Sydney Wu 2M

Great, thank you!

Sydney Wu 2M

How can you determine whether or not an element is a Lewis acid or base? For instance, for AlCl₃, is Al donating e-s to Cl so that Cl has a full octet, therefore making it a Lewis base?

Sydney Wu 2M

I do not understand how hybrid combinations are derived. For instance, the 4 hybrid orbitals of sp³ are:

h₁ = s + p_x + p_y + p_z
h₂ = s - p_x - p_y + p_z
h₃ = s - p_x + p_y - p_z
h₄ = s + p_x - p_y - p_z

Are these fundamental? Will we be expected to know these for the midterm?

Sydney Wu 2M

How is possible for elements in Group 18 to form bonds (don't they already have a filled octet)?

Sydney Wu 2M

Can someone please explain why P is the central atom of the Lewis structure? It makes sense on paper because it looks nice, but doesn't K have the lower ionization energy?

Sydney Wu 2M

I am very confused on the concept on n, l, and m l ... 1) Can the relationship between n, l, and m be described as shell, sub-shell, and orbital within a sub-shell, respectively? 2) Does the l-value tell you the highest possible sub-shell of that particular energy level? (i.e. n=3; l=0, 1, & 2 -...

Sydney Wu 2M

I too, at first, converted the cm into m and got a different answer from the SSM. I re-read the problem, and it is says that it's "common to express energy in terms of v/c with units cm -1 " (for this particular kind of spectroscopy). So literally all you have to do is set up v/c = some va...

Sydney Wu 2M

In the Atomic Spectra and The Bohr Frequency Condition module, we derived an equation that resulted in $-R[\frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}}]$ . In the book and SSM, R is positive, not negative. Which equation is correct?

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