## Search found 26 matches

- Sat Mar 18, 2017 8:12 pm
- Forum: *Nucleophilic Substitution
- Topic: Do we need to draw the Wedges for this class?
- Replies:
**1** - Views:
**686**

### Do we need to draw the Wedges for this class?

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)?

- Sat Mar 18, 2017 8:04 pm
- Forum: *Electrophilic Addition
- Topic: Major Product vs Minor Product
- Replies:
**2** - Views:
**835**

### Major Product vs Minor Product

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...

- Fri Mar 17, 2017 10:42 pm
- Forum: *Organic Reaction Mechanisms in General
- Topic: Partial Charge [ENDORSED]
- Replies:
**1** - Views:
**759**

### Partial Charge [ENDORSED]

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? ...

- Mon Mar 13, 2017 1:51 pm
- Forum: *Constitutional and Geometric Isomers (cis, Z and trans, E)
- Topic: When to Use Z and E?
- Replies:
**4** - Views:
**568**

### When to Use Z and E?

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.

- Tue Mar 07, 2017 8:51 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Why is K = kfor/krev?
- Replies:
**3** - Views:
**725**

### Why is K = kfor/krev?

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

- Fri Mar 03, 2017 10:47 pm
- Forum: *Electrophilic Addition
- Topic: Always 2 Transition States for Electrophilic Addition?
- Replies:
**1** - Views:
**608**

### Always 2 Transition States for Electrophilic Addition?

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

- Mon Feb 27, 2017 1:02 pm
- Forum: *Nucleophiles
- Topic: Nucleophiles that are Neutral?
- Replies:
**2** - Views:
**470**

### Nucleophiles that are Neutral?

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...

- Fri Feb 24, 2017 4:48 pm
- Forum: General Rate Laws
- Topic: 15.5 Positive vs Negative
- Replies:
**2** - Views:
**410**

### 15.5 Positive vs Negative

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...

- Tue Feb 14, 2017 5:52 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Changes in both volume and temp [ENDORSED]
- Replies:
**5** - Views:
**811**

### Re: Changes in both volume and temp [ENDORSED]

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...

- Tue Feb 14, 2017 4:46 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 9.43 - Where do we get Cp of H2O (l) = 75.3 J/Kmol?
- Replies:
**1** - Views:
**907**

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

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 = ...

- Mon Feb 13, 2017 1:49 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Why Pt(s) when we already have I2 (s)? HW 14.13
- Replies:
**2** - Views:
**376**

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

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)?

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)?

- Sat Feb 11, 2017 9:15 pm
- Forum: Phase Changes & Related Calculations
- Topic: Specific Heat Capacity vs Cv(Vap) vs Cp(vap) [ENDORSED]
- Replies:
**1** - Views:
**509**

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

"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 ...

- Thu Feb 09, 2017 4:38 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: equations
- Replies:
**1** - Views:
**308**

### Re: equations

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).

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).

- Wed Feb 01, 2017 5:56 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Significant Figures
- Replies:
**1** - Views:
**407**

### Significant Figures

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:...

- Tue Jan 31, 2017 4:17 pm
- Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
- Topic: Rule that Guarantees all Re-Arranged Lewis Structures?
- Replies:
**1** - Views:
**300**

### Rule that Guarantees all Re-Arranged Lewis Structures?

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...

- Thu Jan 26, 2017 9:06 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: HW 9.5
- Replies:
**1** - Views:
**318**

### Re: HW 9.5

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

- Tue Jan 24, 2017 8:56 pm
- Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
- Topic: If T = 0, can residual entropy still exist?
- Replies:
**1** - Views:
**292**

### If T = 0, can residual entropy still exist?

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?

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

- Sun Jan 22, 2017 12:52 am
- Forum: Calculating Work of Expansion
- Topic: Combustion Reaction - Writing and Balancing
- Replies:
**2** - Views:
**401**

### Combustion Reaction - Writing and Balancing

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...

- Sun Jan 22, 2017 12:39 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Given q and w, will a gas's pressure increase or decrease? [ENDORSED]
- Replies:
**4** - Views:
**541**

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

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?

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?

- Sun Jan 22, 2017 12:33 am
- Forum: Calculating Work of Expansion
- Topic: Combustion Products - Physical States
- Replies:
**1** - Views:
**273**

### Combustion Products - Physical States

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)?

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

- Thu Jan 19, 2017 11:06 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.51 Sig Figs, Sign [ENDORSED]
- Replies:
**3** - Views:
**433**

### 8.51 Sig Figs, Sign [ENDORSED]

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...

- Tue Jan 17, 2017 1:46 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Values Given on Exams?
- Replies:
**2** - Views:
**393**

### Values Given on Exams?

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?

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?

- Tue Jan 17, 2017 1:43 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Given q and w, will a gas's pressure increase or decrease? [ENDORSED]
- Replies:
**4** - Views:
**541**

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

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

- Tue Jan 17, 2017 1:40 pm
- Forum: Calculating Work of Expansion
- Topic: Significant Figures Question [ENDORSED]
- Replies:
**1** - Views:
**360**

### Significant Figures Question [ENDORSED]

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...

- Tue Jan 17, 2017 9:57 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Given q and w, will a gas's pressure increase or decrease? [ENDORSED]
- Replies:
**4** - Views:
**541**

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

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 ...

- Mon Jan 09, 2017 11:46 pm
- Forum: Calculating Work of Expansion
- Topic: Quiz 1 Preparation: Question #3 - Conflicting Information? [ENDORSED]
- Replies:
**4** - Views:
**596**

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

#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...