## Search found 32 matches

Mon Mar 13, 2017 11:49 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: Conformation Determining
Replies: 2
Views: 789

### Re: Conformation Determining

You cannot. However, if they give you a formula, they could ask you to draw its Newman Projection in the gauche conformation or in the eclipsed conformation.
Mon Mar 13, 2017 11:48 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: General for Confirmations
Replies: 1
Views: 260

### Re: General for Confirmations

The only calculation in this section has been to determine the ratio of molecules in two different conformations. For example if we are trying to determine the ratio of anti to gauche conformations (gauche \leftrightarrow anti), we must use the equation \Delta G = -RT lnK where K = anti/gauche. In t...
Mon Mar 13, 2017 11:32 pm
Forum: Balancing Redox Reactions
Topic: Final 2013 Q3A
Replies: 3
Views: 571

### Re: Final 2013 Q3A

Correct! Step 1: Write and balance the two half reactions individually Step 2: Make sure each half reaction has the same number of electrons. If not, multiply one or both reactions so that the number of electrons cancel. Step 3: Add the two half reactions. *If the half reactions were balanced correc...
Mon Mar 06, 2017 11:52 pm
Forum: *Alkenes
Topic: question 1.11
Replies: 1
Views: 345

### Re: question 1.11

Double and triple bonds get priority over substituents. So you want to make sure your triple bond gets the lowest number possible. The molecule below has only 7 carbons, what you named 5-diethyl-3-hexyne indicates two ethyl groups (CH2CH3) and a six carbon chain so a total of 10 atoms. Try drawing o...
Mon Mar 06, 2017 11:41 pm
Forum: *Nucleophiles
Topic: Self Test 4.1B
Replies: 1
Views: 732

### Re: Self Test 4.1B

Answers to all Self-Test questions are in the back of the book. 4.1B is found on page 207 But to answer your question about how it reacts: cyanide acts a nucleophile in the reaction. If you look at the formal charge it's actually - CN where the carbon has the negative formal charge. Therefore while ...
Sat Mar 04, 2017 9:45 pm
Forum: *Nucleophiles
Topic: H2O [ENDORSED]
Replies: 4
Views: 625

### Re: H2O[ENDORSED]

When you draw out the Lewis structure for water, you have two lone pairs on the water creating a bent shape. The lone pairs are regions of electron density. These lone pairs are attracted to positively charged atoms. They are "nucleous loving" and thus water is a nucleophile. As a generali...
Mon Feb 27, 2017 10:06 pm
Topic: Electrophilic addition reaction (p. 84 CR)
Replies: 1
Views: 361

### Re: Electrophilic addition reaction (p. 84 CR)

The pi bond acts as the nucleophile. A nucleophile is attracted to positively charged species (electrophiles). In H-Br, the hydrogen has the delta positive charge. Therefore, the pi electrons are attracted to the H. Once the H is bonded, you now have a carbocation (a C without a full octet). This Br...
Fri Feb 24, 2017 9:26 pm
Forum: *Nucleophiles
Replies: 2
Views: 484

### Re: Course reader p. 82

I think the best way to think about it is that the pi bond is the "nucleophilic region" in ethene. It is the pi electrons that are involved in "attacking" the delta positive Bromine electrophile. Whatever is attacking the electrophile, we can consider the nucleophile.
Fri Feb 24, 2017 9:13 pm
Forum: *Organic Reaction Mechanisms in General
Topic: Reaction Mechanism Energy Trends
Replies: 1
Views: 334

### Re: Reaction Mechanism Energy Trends

What you need to remember is that breaking bonds require energy, while forming bonds release energy. (Bonds are formed because the two atoms are more stable and have a lower energy when they are bonded together, rather than as individual atoms.) Think about what it means to "require" energ...
Mon Feb 13, 2017 11:59 pm
Forum: Balancing Redox Reactions
Topic: 2015 Midterm Question #7
Replies: 2
Views: 426

### Re: 2015 Midterm Question #7

Cell potential means calculate voltage. When everything is under standard conditions, cell potential means E o . However, in this particular question, we are dealing with a concentration cell. When we have a concentration cell, we no longer have 1.0 M solutions, therefore we must use the Nernst equa...
Mon Feb 13, 2017 11:55 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 2014 midterm #8
Replies: 4
Views: 488

### Re: 2014 midterm #8

This question is asking to calculate the K a for HF. If we write the dissociation equation for HF, we get HF \leftrightharpoons H + + F - . This tells us we want HF as a reactant and H + and F - as products. In order for us to match the overall equation, we must flip the first half reaction. When we...
Mon Feb 06, 2017 9:16 pm
Forum: Balancing Redox Reactions
Topic: Chapter 14 Question 1
Replies: 2
Views: 467

### Re: Chapter 14 Question 1

Let's break it down. H: as both H+ and H 2 O, the hydrogen has an oxidation state of +1. Cr: in Cr 2 O 7 -2 , each oxygen has a -2 charge so (-2)(7) = -14; with a overall -2 charge, we are left with two Cr atoms to split the +12 charge. Thus Cr as a reactant has an oxidation state of +6. As a produc...
Mon Feb 06, 2017 9:06 pm
Forum: Balancing Redox Reactions
Topic: Basic vs. Acidic Redox Reactions
Replies: 1
Views: 406

### Re: Basic vs. Acidic Redox Reactions

The reducing agent is the compound undergoing oxidation (it helps reduce the other compound). The oxidizing agent is the compound undergoing reduction (it oxidizes the other compound). In writing a half reaction under acidic conditions, we are able to add both H+ ions and H 2 O molecules. When writi...
Tue Jan 31, 2017 1:27 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cell Diagram Contents [ENDORSED]
Replies: 1
Views: 337

### Re: Galvanic Cell Diagram Contents[ENDORSED]

In the anode, we have the solid zinc electrode. The solution that was used in class consisted of Zn +2 cations and Cl- anions. As electrons move from the anode to the cathode, some of the zinc electrode dissolves and becomes Zn +2 cations in solution. The Cl- anions are what went through the salt br...
Thu Jan 26, 2017 10:13 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: +DeltaG
Replies: 1
Views: 320

### Re: +DeltaG

Using the example in the course reader of Br 2 liquid \rightarrow Br 2 gas, we determined that the boiling point was 333K. If T < 333 K, then the reaction is non spontaneous. This means that if you have a beaker of liquid bromine and you walk into a room that is at 300K, it will stay as liquid bromi...
Thu Jan 26, 2017 10:05 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy
Replies: 1
Views: 329

### Re: Gibbs free energy

There are actually 3 ways that we can calculate Gibbs free energy. Depending on what information/chart of values is provided will help us determine which of the three methods we use to solve for \Delta G . 1. \Delta G formation: \Sigma G products - \Sigma G reactants 2. Hess's Law approach: this is ...
Sun Jan 22, 2017 8:36 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework: Chapter 8, #67
Replies: 2
Views: 374

### Re: Homework: Chapter 8, #67

You are correct! They are equal and opposite values. The amount of heat it takes to go from a solid to a liquid is the same amount of heat released when going from a liquid to a solid. So if for a specific element s\rightarrow l = +10 kJ/mol (it is positive because it is absorbing heat), then for th...
Mon Jan 16, 2017 10:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Methods
Replies: 1
Views: 238

### Re: Methods

To calculate enthalpy, there are three methods. For Hess's Law, the equations will have a delta H value with it. For bond enthalpy, you will be given a bond enthalpy chart. Remember that this chart only gives positive values, so if you we are looking at bonds being broken (the reactants) we keep the...
Thu Jan 12, 2017 10:54 pm
Forum: Phase Changes & Related Calculations
Replies: 1
Views: 352

### Re: Question about Molar Enthalpy

Both the enthalpy of fusion (solid to liquid) and enthalpy of vaporization (liquid to gas) are constants. They are experimentally determined, they are not calculated by an equation. For water, the enthalpy of fusion is 6.01 kJ/mol while the enthalpy of vaporization is 40.7 kJ/mol. However, you shoul...
Thu Jan 12, 2017 10:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Rounding in Hess's Law
Replies: 1
Views: 342

### Re: Rounding in Hess's Law

For any calculation, whether it is for delta H or heat or anything else, we only round in our final step of the calculation. What we round to depends on the sig figs of the problem. Remember that when we multiply or divide, our final answer uses the smallest amount of sig figs of the given values in...
Tue Nov 29, 2016 10:09 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Assuming X is small
Replies: 5
Views: 1947

### Re: Assuming X is small

You only do the assumption that X is small when your equilibrium constant, K is less than 10 -4 . Weak acids and weak bases have a K value because they do not fully dissociate. Strong acids and strong bases fully dissociate (hence the single sided arrow rather than the equilibrium arrow). Therefore,...
Mon Nov 21, 2016 2:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp and Kc
Replies: 4
Views: 598

### Re: Kp and Kc

Anything with a "K" means equilibrium constant. We have learned multiple K expressions: K c - used for concentration K p - used for partial pressure K a - used for weak acids K b - used for weak bases K w - used for water [H 3 O + ][OH - ] = 1.0 x 10 -14 All of these equilibrium constants ...
Mon Nov 21, 2016 2:33 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strong/weak acids
Replies: 6
Views: 1942

### Re: Strong/weak acids

That is correct! Strong acids and strong bases completely dissociate in water. Therefore, there is no equilibrium constant. K only exists for weak acids and weak bases. For weak acids and weak bases, the incomplete dissociation means that in order to solve for say pH, we must use an ICE box. For str...
Wed Nov 16, 2016 3:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc vs Kp vs Q [ENDORSED]
Replies: 1
Views: 3355

### Re: Kc vs Kp vs Q[ENDORSED]

K c is the equilibrium constant when dealing with concentration (molarity). Sometimes gases are given in partial pressures rather than a concentration. When this is the case and all values are given in pressures, we use K p , which is the equilibrium constant for pressure. So K c for Concentration a...
Wed Nov 09, 2016 2:29 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Z
Replies: 2
Views: 426

### Re: Z

When doing molecular orbitals and there are two diagrams, Z < 8 and Z \geq 8, all this is saying is that if your molecule has one or both atoms with an atomic number less than 8 (anything before oxygen), then you use the Z < 8 diagram. If both of your molecules have an atomic number greater than or ...
Wed Nov 09, 2016 2:26 pm
Forum: Naming
Topic: Charge on Compounds
Replies: 2
Views: 424

### Re: Charge on Compounds

On the chart in the course reader, any unfamiliar compounds such as oxalato (ox) show the charges of these ligands by showing any atom that has a formal charge. You just count up the formal charges to get the overall charge. Thus, oxalato has two oxygen atoms, each with a -1 formal charge. Therefore...
Fri Nov 04, 2016 9:09 am
Forum: Hybridization
Topic: Polar vs Non polar
Replies: 5
Views: 1232

### Re: Polar vs Non polar

For molecules that do not have lone pairs on the central atom (AX 2 - linear, AX 3 - trigonal planar, AX 4 - tetrahedral, AX 5 - trigonal bipyramid, AX 6 - octahedral), if all the attached atoms, "X" are the same, then the molecule is nonpolar because all of the dipole moments will cancel ...
Thu Oct 27, 2016 12:49 pm
Forum: Hybridization
Topic: Sigma Bonds vs Pi Bonds
Replies: 2
Views: 1564

### Re: Sigma Bonds vs Pi Bonds

In a sigma bond, the electrons are in orbitals between the nuclei of the bonding atoms (in the plane of electron density), where electron density is greatest. The end-to-end axial overlap of electrons attracts the nuclei to form a strong bond. In a pi bond, the p-orbitals overlap side-to-side above ...
Sat Oct 22, 2016 12:16 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Molecular Shape
Replies: 1
Views: 351

### Re: Molecular Shape

To answer your question, no, bond type does not affect molecular shape but rather bond length only. For example, NH 4 + 's tetrahedral shape is determined by the four single Nitrogen-Hydrogen bonds surrounding the Nitrogen atom, forming an average bond # of 1. In SO 4 -2 , the Sulfur atom is surroun...
Thu Oct 13, 2016 7:12 pm
Forum: Quantum Numbers and The H-Atom
Topic: Electron Spin
Replies: 2
Views: 404

### Re: Electron Spin

When drawing out the Aufbau diagram and filling in the "orbitals" with the electrons, we want to make sure we follow both Hund's rule (electrons in the same subshell with occupy different orbitals) and Pauli Exclusion Principle (no more than two electrons per orbital). For example, when we...
Tue Oct 04, 2016 11:36 pm
Forum: Properties of Light
Topic: Textbook Example 1.5 Analyzing the Photoelectric Effect [ENDORSED]
Replies: 1
Views: 411

### Re: Textbook Example 1.5 Analyzing the Photoelectric Effect[ENDORSED]

When solving problems regarding the Photoelectric Effect or any energy question in general, the SI units for energy is Joules (J). An electron-volt (eV) is also an energy term and is used a lot in physics. However, in this course, we will stick with the SI unit of Joules. The 1.602 x 10 -19 J/1eV is...
Fri Sep 30, 2016 9:47 am
Forum: Properties of Electrons
Topic: Kinetic Energy of Electrons [ENDORSED]
Replies: 4
Views: 7697

### Re: Kinetic Energy of Electrons[ENDORSED]

When dealing with the photoelectric effect, it is a 1:1 ratio of photon:electron. For each photon of light that comes into contact with the metal, one electron gets removed from the metal surface. Therefore, we calculate the kinetic energy using the equation E(photon) = E(threshold) + KE. Then, we c...