## Search found 50 matches

Tue Mar 13, 2018 10:34 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.99
Replies: 1
Views: 136

### Re: 15.99

The different ordered reactions have different axes to plot to show them as linear. Linear plots for a zero-order reaction would be seen by plotting the concentration against time. For a first-order reaction, it would be the natural log of the concentration against time. For a second-order reaction,...
Mon Mar 12, 2018 8:09 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: reaction profile
Replies: 3
Views: 238

### Re: reaction profile

They are only ever equivalent when the reaction is in equilibrium
Fri Mar 09, 2018 4:51 pm
Forum: *Nucleophiles
Topic: Nucleophiles on the final?
Replies: 3
Views: 593

### Re: Nucleophiles on the final?

Professor Lavelle used the SN2 organic reaction in class as an example for a substitution reaction. I would probably say that anything discussed in lecture is fair game for the final. But that would mean we would only need to know this as a conceptual example, nothing too intensive, because that is ...
Fri Mar 09, 2018 4:47 pm
Forum: First Order Reactions
Topic: The integrated rate laws
Replies: 3
Views: 328

### Re: The integrated rate laws

The only real reason you see the basic integrated rate laws look so many different ways is because they are being manipulated to answer specific values that the problem gives. All of the variations of the integrated rate laws all have the same basic structure. The typical way of writing the integrat...
Wed Mar 07, 2018 3:11 pm
Forum: Administrative Questions and Class Announcements
Topic: Formulas on test?
Replies: 3
Views: 308

### Re: Formulas on test?

No, you won't have to memorize the equations. The constants and equations sheet has all of the necessary 1st order and 2nd order formulas and the half-life formulas that you will need on the test. However, they are not labeled as 0, 1st, or 2nd order, so you will have to recognize which equation app...
Tue Mar 06, 2018 8:49 pm
Forum: General Rate Laws
Topic: Units in 15.17 vs. 15.19
Replies: 2
Views: 166

### Re: Units in 15.17 vs. 15.19

The proper units for molar concentrations are mol*L^-1. It would be safe to always convert the given concentrations into these units and then work out the equation like the question asks. The only difference I see is that the initial rate for 15.17 is given with respect to the product G, while the i...
Sun Mar 04, 2018 12:07 pm
Forum: Second Order Reactions
Topic: 15.35 homework
Replies: 2
Views: 197

### Re: 15.35 homework

You cannot use the ratio alone to solve for the half-lives of a second order reaction, because the half life of a second order reaction is not dependent only on the rate constant, but also on initial concentration ([A]0). 15.27 deals with the half life of a first order reaction, so it is only depend...
Sun Mar 04, 2018 11:58 am
Forum: First Order Reactions
Topic: half life
Replies: 3
Views: 258

### Re: half life

"n" half lives just refers to how many half lives have occurred at any stage of the reaction in question. A half life occurs at the specific time when the current value of the concentration of reactants is halved. For example, after 2 half lives (n=2), the concentration of the reactants wo...
Sun Mar 04, 2018 11:49 am
Forum: First Order Reactions
Topic: First Order- Half life
Replies: 1
Views: 150

### Re: First Order- Half life

The half life for a first-order reaction is derived from the integrated rate law for first order reactions. And when manipulating this integrated rate law into a half life equation, the concentration of the reactant [A]t is changed to 1/2[A]0, which allows the initial concentration ([A]0]) to cancel...
Wed Feb 21, 2018 4:09 pm
Forum: Balancing Redox Reactions
Topic: 14.5 a, balancing redox O3 to O2?
Replies: 1
Views: 347

### Re: 14.5 a, balancing redox O3 to O2?

The way I worked out the problem, saw that the Bromine ion was oxidized, so it only followed that the oxygen had to be reduced. And any half reaction for reduction has the electrons added to the left side. You can come to this same answer of the electrons being on the left, because when you take the...
Wed Feb 21, 2018 4:00 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: TEXTBOOK 14.57
Replies: 1
Views: 136

### Re: TEXTBOOK 14.57

Before the questions in the electrolysis section chapter 14, there is a statement saying to use the potentials listed in the standard potentials chart, except for the reduction and oxidation of water at pH=7. Then they say that the equation with water as a reactant (being reduced) has a potential of...
Wed Feb 21, 2018 3:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: #29.c
Replies: 1
Views: 95

### Re: #29.c

In these electrical cell diagrams, the reactant of a half reaction is usually found on the left, with the product being found on the right. I do not think that the fact that the two irons being in the same state changes this. So, the Fe2+ should be put to the left of the Fe3+.
Tue Feb 13, 2018 4:48 pm
Forum: Calculating Work of Expansion
Topic: When to use w= -P∆V
Replies: 1
Views: 180

### Re: When to use w= -P∆V

For the equation w = -P∆V to work properly, it just has to be under constant external pressure. Temperature does not affect this part of the equation at all, because it deals with work. But if you are trying to calculate the change in internal energy, you have to make sure that you add the heat appl...
Tue Feb 13, 2018 4:39 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.83 standard deltaG
Replies: 1
Views: 128

### Re: 11.83 standard deltaG

Yes, you can use the deltaG(rxn) = deltaG(products) - deltaG(reactants) equation for the first part of the question because it is at 25 degrees Celsius. I think the only reason the book does it a different way is because it is more convenient when finding k at two different temperatures. They use th...
Tue Feb 13, 2018 4:20 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy equation
Replies: 2
Views: 201

### Re: Entropy equation

When it says "C" without any subscript, it signifies heat capacity, as an extensive property. This is not as common in application; an intensive property is more applicable as it can be applied to any amount of a substance. So we either divide it by the mass or moles of a sample to get spe...
Wed Feb 07, 2018 4:11 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13
Replies: 1
Views: 165

### Re: 9.13

The book says that the equation nRln(V2/V1) applies to both reversible and irreversible gas expansions given that it expands between the same two states and is at a constant temperature. But ultimately, this equation can be used in the problem because entropy is a state function. Because entropy is ...
Wed Feb 07, 2018 3:57 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Self-Test 9.7A
Replies: 2
Views: 280

### Re: Self-Test 9.7A

Trouton's law says that the standard entropy of vaporization are commonly 85 J/(K*mol). It talks about entropy, not enthalpy. The question, on the other hand, asks you to solve for the enthalpy of vaporization of bromine liquid. The question asks you to apply the assumption that the entropy of vapor...
Wed Feb 07, 2018 3:32 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: HW 9.19
Replies: 2
Views: 249

### Re: HW 9.19

The only way this problem can be solved in a way that has been taught to us is if we add the sum of the change in entropy for the reversible reactions of heating the water, vaporizing the water, and cooling the water to the desired temperature. The water vapor can exist at lower temperatures as long...
Sun Feb 04, 2018 10:05 pm
Forum: Calculating Work of Expansion
Topic: Reversible Expansion Homework Questions
Replies: 1
Views: 120

### Re: Reversible Expansion Homework Questions

In chapter 8, dealing with the first law, there are problems dealing with reversible reactions of gas. Part (b) in the questions 8.11-8.12 deal with this topic. Neither one of these seem to be too intense, but the concept and the use of the equation is present. There are not many other problems in t...
Sun Feb 04, 2018 9:59 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Standard Entropy of Vaporization for Mercury
Replies: 1
Views: 134

### Standard Entropy of Vaporization for Mercury

Why is the standard entropy of vaporization for mercury so high considering that it appears stable since it does not participate in hydrogen bonding?
Sun Feb 04, 2018 9:52 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: Trouton's Law
Replies: 1
Views: 147

### Re: Trouton's Law

While it is mentioned in the book, Professor Lavelle did not strictly emphasize it during lecture. It is probably best to know the law since it is quite simple, yet it most likely will not appear as an exam question.
Sun Jan 28, 2018 5:06 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp and Cv Values
Replies: 2
Views: 505

### Re: Cp and Cv Values

In regards to the two types of molar heat capacities of an ideal gas (Cp and Cv), both are related by the equation Cp= Cv + R. This relationship is derived from the equation deltaH = deltaU +nRdeltaT , as shown on page 280 in the textbook. Because the molar heat capacity at a constant volume (Cv) fo...
Sun Jan 28, 2018 4:07 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy based on initial temp
Replies: 3
Views: 161

### Re: Entropy based on initial temp

It is expected for the change of entropy to be greater when the temperature is low rather than high, because the energy that is brought into the system stirs up the molecules of the colder system much more than that of the warmer system. The molecules of the lower temperature gas initially has littl...
Sun Jan 28, 2018 3:53 pm
Forum: Calculating Work of Expansion
Topic: irreversible system
Replies: 2
Views: 137

### Re: irreversible system

To find the change in entropy of an irreversible expansion at a constant temperature, you could use the equation deltaS=nRln(V2/V1). This change in entropy equation can be used for both reversible and irreversible expansions, because entropy is a state function and is independent of the path taken t...
Sun Jan 21, 2018 5:21 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hesss Law
Replies: 6
Views: 312

### Re: Hesss Law

You will most likely need to know it. The lecture outline that has all of the chapter 8 material we need to know states: "Define enthalpy and explain how Hess's law depends on the fact that enthalpy is a state property."
Sun Jan 21, 2018 5:11 pm
Forum: Phase Changes & Related Calculations
Topic: Heating curve slope
Replies: 1
Views: 142

### Re: Heating curve slope

On a heating curve, the x-axis is the heat supplied and the y-axis is the temperature. This means that the slope of the heating curve is (temperature)/(heat supplied). And since the equation for heat capacity is (heat supplied)/(temperature rise produced), it is essentially the reverse of the slope ...
Sun Jan 21, 2018 3:39 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat vs. Thermal Energy
Replies: 3
Views: 178

### Heat vs. Thermal Energy

It says in the textbook to be careful not to confuse the terms "heat" and "thermal energy." But even the description of what makes them different sounds very similar. I am not sure if I would be able to tell if the energy described in a problem is due to heat or thermal energy un...
Sun Jan 21, 2018 3:29 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.115
Replies: 2
Views: 186

### Re: 8.115

I believe they do initial minus final because the question asks for how many moles were burned. Moles can only exist in a positive quantity; you cannot have negative moles of any substance. So conceptually, to see how much hydrogen is left in the tank, a positive value would result from doing initia...
Sun Jan 14, 2018 10:56 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Intrinsic Property
Replies: 1
Views: 202

### Intrinsic Property

Why is it that when one extrinsic property is divided by another it becomes an intrinsic property?
Sun Jan 14, 2018 10:53 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Closed Versus Isolated System
Replies: 3
Views: 230

### Closed Versus Isolated System

In which case would a closed system be more applicable than an isolated system? Why?
Sat Dec 09, 2017 10:27 pm
Forum: Hybridization
Topic: how to determine hybridization
Replies: 4
Views: 380

### Re: how to determine hybridization

In the case mentioned above where a central atom is bonded to two other atoms via double bonds, the hybridization of the central atom would be sp. This is because hybridization relies on the regions of electron density, not on the actual number of bonds present.
Sat Dec 09, 2017 10:20 pm
Forum: Photoelectric Effect
Topic: nm to m
Replies: 4
Views: 360

### Re: nm to m

nm is just the size of the measurement used. A nanometer is equal to 1*10^-9 meters. So to get nm to m, just multiply by 1*10^-9.
Sun Dec 03, 2017 6:05 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Why is Kw value typically used at 25 degrees C [ENDORSED]
Replies: 6
Views: 849

### Re: Why is Kw value typically used at 25 degrees C[ENDORSED]

Because kW is the equilibrium constant, it only changes with temperature. This is because the dissociation of water molecules is an endothermic process, a process that is affected by temperature. The higher the temperature, the further the equilibrium moves to the right, which affects the kW value.
Sun Dec 03, 2017 5:59 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH and pOH
Replies: 10
Views: 750

### Re: pH and pOH

If the pH is 7, the pOH has to be 7, and so they would be neutral. Neither the pH or the pOH would be favored in hydrogen ion concentration, so it would be no more acidic than it is basic.
Sun Nov 26, 2017 6:59 pm
Forum: Naming
Topic: CH 17 #31
Replies: 1
Views: 160

### Re: CH 17 #31

I think the reason that OH2 comes before C2O4 is because of the charge of the ligand. OH2 is neutral, so it comes before the negatively charged C2O4. When the ligands have the same charge, they should be put into alphabetical order.
Sun Nov 26, 2017 6:49 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle
Replies: 2
Views: 160

### Re: Bond Angle

Because the actual bond angles of molecules not fixed by symmetry are found experimentally and differ depending on the atoms involved, the approximations of the bond angles should be more than sufficient. You would need to employ spectroscopy, most likely, if you you wanted to find the true bond ang...
Sun Nov 19, 2017 11:39 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Number of Ligands
Replies: 2
Views: 225

### Re: Number of Ligands

The number of ligands are determined by how many ions or molecules are attached to the central metal atom in a coordination complex.

For example, in Ni(CO)4, the Ni is the central atom and the CO molecules are the ligands. So in this coordination complex, there are four ligands.
Sun Nov 19, 2017 11:28 pm
Forum: Sigma & Pi Bonds
Topic: Exceptions to double bond rule
Replies: 1
Views: 430

### Exceptions to double bond rule

It is said that there are exceptions to the rule that a double bond forms one sigma and one pi bond. What are these exceptions, and why do they happen? Why, in these cases, are both bonds of the double bond pi?
Sun Nov 12, 2017 1:01 pm
Forum: Lewis Structures
Topic: Expanded Valence Shell
Replies: 2
Views: 193

### Expanded Valence Shell

Since a valence shell beyond period three can be expanded to accommodate upwards of 12 electrons, what is the largest practical expanded valence shell that can be found in a Lewis structure?
Sun Nov 12, 2017 12:41 pm
Forum: Dipole Moments
Topic: When do dipole moments occur?
Replies: 3
Views: 517

### Re: When do dipole moments occur?

As far as I know, an electric dipole exists between any two atoms in a polar covalent bond. And since a dipole moment is just how the size of an electric dipole is reported, any atoms with bonds in between ionic and covalent would have some kind of dipole moment. Enough electronegativity to cause a ...
Fri Nov 03, 2017 11:55 pm
Forum: Lewis Structures
Topic: 3.67(b)
Replies: 2
Views: 228

### Re: 3.67(b)

The molecule sticks to single bonds because if its Lewis structure was oriented any differently, the total formal charge would deviate from 0. And since the molecule has no charge, this would not be possible. If one double bond is used, the total formal charge would be +2 (this has resonance, but th...
Fri Nov 03, 2017 11:31 pm
Forum: Lewis Structures
Topic: Extra electrons
Replies: 1
Views: 159

### Re: Extra electrons

You know that the Lewis structure looks the way it does for the Iodine Dichloride anion (2 bonding pairs and 2 lone pairs on I) not only because it is the configuration in which the most atoms have a formal charge of 0 (both Cl atoms have formal charge of 0), but also because if any double bonds are...
Sun Oct 29, 2017 1:49 pm
Forum: Quantum Numbers and The H-Atom
Topic: Spin magnetic quantum number
Replies: 1
Views: 150

### Re: Spin magnetic quantum number

As expressed by the Pauli exclusion principle: No two electrons in an atom can have the same set of four quantum numbers. Electron configuration simply does not allow for two electrons in the same orbital to have the same spin. When two electrons occupy one orbital, their spins must be paired. In pr...
Sun Oct 29, 2017 1:36 pm
Forum: Trends in The Periodic Table
Topic: Ionization Energy [ENDORSED]
Replies: 2
Views: 299

### Re: Ionization Energy[ENDORSED]

Oxygen doesn't follow this trend due to repulsion between electrons of the same orbital. In this case, you can see that nitrogen (the element directly to the left of oxygen in the periodic table) has one electron in each of its p-orbitals, while oxygen has a paired electron within one of its p-orbit...
Mon Oct 23, 2017 12:26 am
Forum: *Shrodinger Equation
Topic: Double derivative [ENDORSED]
Replies: 3
Views: 351

### Re: Double derivative[ENDORSED]

A double derivative would be the derivative of the derivative of a function. So, it's basically telling you the rate of change that something is changing. For example, for a function of displacement, velocity would be its derivative (change of displacement over time), and acceleration would be its d...
Mon Oct 23, 2017 12:18 am
Forum: DeBroglie Equation
Topic: De Broglie Equation [ENDORSED]
Replies: 4
Views: 463

### Re: De Broglie Equation[ENDORSED]

The De Broglie equation is used to describe the wave properties of matter. That means that in order for it to work, your object must have some mass (which can be seen in the equation of the wavelength being equal to Planck's constant over momentum) . I don't believe photons have a mass, so this woul...
Sun Oct 15, 2017 11:59 pm
Forum: Properties of Electrons
Topic: Excited electrons returning to initial energy level [ENDORSED]
Replies: 1
Views: 201

### Excited electrons returning to initial energy level[ENDORSED]

It is understandable that when an electron is excited, due to its absorption of a photon, it jumps up to a specific energy level. Something is acting both specifically and directly on that electron, so it moves up in energy level. But it has also been said that, eventually, the electron moves back t...
Sun Oct 15, 2017 11:41 pm
Forum: Empirical & Molecular Formulas
Topic: Theoretical yield [ENDORSED]
Replies: 1
Views: 242

### Re: Theoretical yield[ENDORSED]

In order to find the theoretical yield all you need to do is find the moles of the products, and then turn those moles into grams using the molecule's molecular weight. You can't use this to find the actual yield, however. The actual yield is something that must be given, as it is the result of a pr...
Thu Oct 05, 2017 7:39 pm
Forum: Molarity, Solutions, Dilutions
Topic: Homework Problem G23
Replies: 2
Views: 669

### Re: Homework Problem G23

To start, you want to find out how many moles of each molecule (NaCl, KCl) exist within the solution. So, for each, you divide the amount of grams present by the molecule's molar mass. Now you can multiply the moles of NaCl by the volume of the solution, then multiply the moles of KCl by the volume ...
Thu Oct 05, 2017 7:24 pm
Forum: Molarity, Solutions, Dilutions
Topic: Homework E3
Replies: 2
Views: 263

### Re: Homework E3

Since the question only asks you to find out how many atoms of astatine would be needed to equal the mass of the given gallium atoms, you don't technically have to convert anything. Referring to the diagram below the problem, there are 9 gallium atoms of molar mass 70 g/mol. And since astatine's mol...