CHEMISTRY COMMUNITY

Michael_Johanis_2K

Do we need to draw the wedges and the dashed lines for SN2 mechanisms (When I say "dashed," I am not referring to what is being broken/formed)? Is it fine if we draw all bonds as lines (except for the broken/formed ones, which in the TS I will draw as dashed)?

Michael_Johanis_2K

For electrophilic addition, 2-methyl-1-butene + HBr -----> 2-bromo-2-methylbutane OR 1-bromo-2-methylbutane. Does it matter which one we write? Should we write both? Do we have to know the distinction between minor product and major product? I think I remember hearing that Chem 14C covers where we a...

Michael_Johanis_2K

On the final, if we need to draw a mechanism with the transition step(s), do I have to put the electronegativity of each atom? For example, in electrophilic addition, propene + HBr ---> 2-bromopropane. For the first step, do I need to put partial positive next to H, and partial negative next to Br? ...

Michael_Johanis_2K

Is there a rule (at least for Chem 14B) that tells me when I need to put Z or E in front of a compound? I know how to determine whether I should use Z or E, but I am not quite sure when I should even have one of these letters in front of my compound's name.

Michael_Johanis_2K

Can someone explain why K = k/krev? In lecture, did Dr. Lavelle cover how to derive or infer this?

Michael_Johanis_2K

Is it true that every electrophilic addition reaction will have two steps and therefore two transition states?

Michael_Johanis_2K

Page 144 of "Introduction to Organic Chemistry" states that nucleophiles are "often negatively charged, although they can also be neutral." The text then states that H2O, NH3, and NH2CH3 are examples of nucleophiles. What makes H2O, NH3, and NH2CH3, by definition "electron-r...

Michael_Johanis_2K

C2H2+3O2--->2CO2+2H2O The unique rate of combustion is .44 M/s. Find the rate at which oxygen reacts. I solved this by using: -1/3 * d[O2]/dt = .44 M/s d[O2]/dt = -1.32 M/s However, the answer is (positive) 1.32 M/s. Why is my answer wrong? Am I incorrectly using the unique reaction rate rule, which...

Michael_Johanis_2K

I am confused by Chem_Mod's answer. I have been under the impression that we need to use BOTH DeltaS = nClnT2/T1 AND DeltaS = nRlnV2/V1 if both the temperature and volume change. For example, if initial temperature = 10 K, initial volume = 5 L, final temperature = 20 K, and final volume = 40 L, then...

Michael_Johanis_2K

Suppose that 50 g of H2O(l) at 20 degrees C is mixed with 65 g of H2O(l) at 50 degrees C at a constant pressure in a thermally insulated vessel. Calculate delta S and delta S total for the process. I understand that we find the sum of two entropies, one for each water sample. We use ChangeEntropy = ...

Michael_Johanis_2K

2I- (aq) + 2Ce4+ (aq) ----> I2 (s) + 2Ce3+ (aq)

I thought the cell diagram should be:
I2(s)| I- (aq) || Ce4+ (aq), Ce3+ (aq) | Pt(s)

However, it is:
Pt(s)| I- (aq) | I2 (s) || Ce4+ (aq), Ce3+ (aq) | Pt(s).

Why is Pt the solid on the left side even though we already have I2 (s)?

Michael_Johanis_2K

"A pressure cooker containing 100.0 g of liquid water at 25 C is placed on the stove until all water becomes superheated steam at 121 C. Assume no steam escapes the pressure cooker. a) Find q from 25C to 100C b) Find q during boiling c) Find any other heat gained or lot by the water as it goes ...

Michael_Johanis_2K

I believe that we will be given w = -(Pex)(DeltaV), though this is a very easy equation to memorize.

We can easily find the other equations by simply substituting some values.

We know that PV = nRT. Therefore, by applying a change in one value to each side, P(DeltaV) = (DeltaN)RT = nR(DeltaT).

Michael_Johanis_2K

Hi. This question is for TA Jack, who read my email and said he would answer this: When we use bond enthalpy, reactant - product, and Hess's Law, assuming that we have exact numbers of moles (from the equation), the significant figures in the answer are ONLY limited by addition, right? For instance:...

Michael_Johanis_2K

For HW 9.25, to calculate the residual entropy of SO2F2, we need to draw out all the arrangements of the Lewis structure. I found that there are 6 different arrangements. After find the degeneracy, I used to S = Kb lnW. Is there a method to be sure that I have drawn out every possible Lewis structur...

Michael_Johanis_2K

One reservoir loses heat (q is negative), while the other reservoir gains the heat (q is positive).

Michael_Johanis_2K

If T = 0, there is no thermal entropy, correct?

If T = 0, is there residual (positional) entropy? I think that if W > 1, then there is residual entropy, even if T = 0, correct?

Michael_Johanis_2K

For 8.93, we have to write the combustion reaction for C6H6 (l). The solutions manual says: C6H6 (l) + 7.5 O2 (l) ----> 6CO2 (g) + 3H2O (l) 1) Why is 3H2O a liquid? Shouldn't all the products in combustion reactions be gases? 2) Why is 7.5 the coefficient for O2? Shouldn't everything be in whole num...

Michael_Johanis_2K

Thank you! But what if q = -501 kJ and w = 500 kJ (compression)?

Delta U = -1 kJ

PV = nRT
The temperature decreases since DeltaU = negative. The volume decreased since this is compression.
If T goes down, V goes down, n is constant, and R is constant, what happens to P?

Michael_Johanis_2K

In 8.93, we need to write the combustion reaction for C6H6 (l).

Are the products for all combustion reactions always in the gas phase (H2O gas + CO2 gas)?

Michael_Johanis_2K

The enthalpy of formation of trinitrotoluene (TNT) is -67 kJ·mol^-1, and the density of TNT is 1.65 g·cm^-3. In principle, it could be used as a rocket fuel, with the gases resulting from its decomposition streaming out of the rocket to give the required thrust. In practice, of course, it would b...

Michael_Johanis_2K

Do we need to memorize the specific heats of H2O in the solid, liquid, and vapor states?

For example, in the equation q = m * C * DeltaT for H2O (l), do I have to memorize that 4.184 J/(g C) is the specific heat capacity?

Michael_Johanis_2K

Are DeltaU and q not important? Does it only matter that w is negative (gas expands)?

Michael_Johanis_2K

I have a question regarding significant figures. "Air in a bicycle pump is compressed by pushing in the handle. If the inner diameter of the pump is 3.0 cm and the pump is depressed 20. cm with a pressure of 2.00 atm, (a) how much work is done in the compression? (b) Is the work positive or neg...

Michael_Johanis_2K

From 2007 Midterm: Given that a a gas sample expands, doing 536 kJ of work, while 214 kJ of heat is added to the gas: a) Calculate DeltaU b) Will the pressure of the gas be higher or lower when these changes are completed? I understand Part A: a) DeltaU = q + w. q is +214 kJ since the heat is ADDED ...

Michael_Johanis_2K

#3. "If 2.00 mol of an ideal gas at 300. K and 3.00 atm expands isothermally and reversibly from 6.00 L to 18.00 L and has a final pressure of 1.20 atm, what is q,w, and DeltaU?" Can anyone clarify what I am doing wrong? w = -nRT ln (V2/V1) OR w = -nRT ln (P1/P2) ln(V2/V1) and ln(P1/P2) ha...

CHEMISTRY COMMUNITY

Search found 26 matches

Do we need to draw the Wedges for this class?

Major Product vs Minor Product

Partial Charge [ENDORSED]

When to Use Z and E?

Why is K = kfor/krev?

Always 2 Transition States for Electrophilic Addition?

Nucleophiles that are Neutral?

15.5 Positive vs Negative

Re: Changes in both volume and temp [ENDORSED]

9.43 - Where do we get Cp of H2O (l) = 75.3 J/Kmol?

Why Pt(s) when we already have I2 (s)? HW 14.13

Specific Heat Capacity vs Cv(Vap) vs Cp(vap) [ENDORSED]

Re: equations

Significant Figures

Rule that Guarantees all Re-Arranged Lewis Structures?

Re: HW 9.5

If T = 0, can residual entropy still exist?

Combustion Reaction - Writing and Balancing

Re: Given q and w, will a gas's pressure increase or decrease? [ENDORSED]

Combustion Products - Physical States

8.51 Sig Figs, Sign [ENDORSED]

Values Given on Exams?

Re: Given q and w, will a gas's pressure increase or decrease? [ENDORSED]

Significant Figures Question [ENDORSED]

Given q and w, will a gas's pressure increase or decrease? [ENDORSED]

Quiz 1 Preparation: Question #3 - Conflicting Information? [ENDORSED]