## Search found 50 matches

Mon Mar 12, 2018 8:23 am
Forum: Zero Order Reactions
Topic: Half life
Replies: 7
Views: 734

### Re: Half life

Also, be sure to use the appropriate half life equation based on the order!
Mon Mar 12, 2018 8:22 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-equilibrium Condition
Replies: 3
Views: 280

### Re: Pre-equilibrium Condition

In order to solve a problem with this situation, make sure to follow the procedure Dr. Lavelle lined out in lecture.
Mon Mar 12, 2018 8:19 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Kinetic Energy vs Potential Energy
Replies: 2
Views: 187

### Re: Kinetic Energy vs Potential Energy

I believe that the axis for the reaction profile references the total energy of the substances graphed. When the book explains it that way they are just clarifying what components of the total energy for the R and P change as the reaction goes on.
Mon Mar 05, 2018 8:37 am
Forum: Second Order Reactions
Topic: Rate of consumption vs concentration
Replies: 2
Views: 278

### Re: Rate of consumption vs concentration

I believe it would be sloping downwards I a curve, but it would be a less dramatic decrease with a more gradual decrease than an exponential decay curve.
Mon Mar 05, 2018 8:36 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: When to use pre-equilibrium approach?
Replies: 2
Views: 180

### Re: When to use pre-equilibrium approach?

From my understanding, you are correct.
Mon Mar 05, 2018 8:35 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: rate order vs contribution to overall rate
Replies: 3
Views: 237

### Re: rate order vs contribution to overall rate

The order indicates the mechanism more than just the speed of reaction, as the rate constant indicates the speed of the reaction. It is my understanding that the order itself does not indicate anything explicitly about the speed of a reaction, it merely demonstrates how many particles/molecules of t...
Tue Feb 27, 2018 9:07 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19
Replies: 3
Views: 244

### Re: 15.19

You do need to find the order for reactant C. Use Experiments 3 and 4 to find the order of reactant C.
Tue Feb 27, 2018 9:05 am
Forum: First Order Reactions
Topic: First Order Reaction Equations
Replies: 3
Views: 230

### Re: First Order Reaction Equations

I believe that both those equations are equivalent. I'm not sure where you got the equation with ln( [A]o / [A]t ) and a positive +kt, but they seem to be the same thing. Use them to find the k reaction constant value or t time it takes to get to a certain concentration from a given initial concentr...
Tue Feb 27, 2018 9:03 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Midterm 6A (Multiple Choice)
Replies: 4
Views: 427

### Re: Midterm 6A (Multiple Choice)

In terms of entropy, the phase is always more deterministic of entropy than molecule size. Since CH4 is a gas, its phase already makes it have higher entropy than any sized liquid molecule.
Tue Feb 20, 2018 9:05 am
Forum: Balancing Redox Reactions
Topic: calculating oxidation states
Replies: 2
Views: 248

### Re: calculating oxidation states

Look for atoms within the molecule that have a consistent oxidation state. For example, if you have MnO4-, you know that oxygen atoms tend to have a 2- charge, thus Mn must be of 7+ charge to have an overall charge of 1-. You can also try and attain the oxidation state of an atom based on the charge...
Tue Feb 20, 2018 9:02 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt
Replies: 1
Views: 109

### Re: Pt

Use platinum (Pt) if the half reaction for one (or both) sides of the cell do not have a conducting metal in them. If there is no conducting metal, use Pt on the outermost section of the cell diagram to show that you are using a platinum electrode because there are no conducting metals present natur...
Tue Feb 20, 2018 9:00 am
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Ion-selective electrode
Replies: 2
Views: 260

### Re: Ion-selective electrode

Ion-selective electrodes are just electrodes that measure specific ion concentrations in a solution. Examples include pH meters, K+ meters, Na+ meters, etc.
Mon Feb 12, 2018 8:22 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Delta S total
Replies: 1
Views: 876

### Re: Delta S total

When a process/reaction is at equilibrium or it is a reversible reaction, delta S total = 0. Thus, at these conditions, delta S sure = - delta S sys. The concept behind this is that in a reversible reaction or a reaction at equilibrium, any changes in entropy of the system or surroundings will be op...
Mon Feb 12, 2018 8:20 am
Forum: Balancing Redox Reactions
Topic: midterm W18
Replies: 1
Views: 125

### Re: midterm W18

No, electrochemistry will not be on the midterm. On Lavelle's site it says will only be tested on Thermodynamics and Thermochemistry (the first two outlines provided on his site / chapters 8,9, part of 11).
Mon Feb 12, 2018 8:19 am
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: W
Replies: 2
Views: 229

### Re: W

Either the question will tell you how many possible states there are, or it will be a simple enough molecule for us to draw out the Lewis structure and determine for ourselves how many possible states there are.
Tue Feb 06, 2018 9:24 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: molar entropy
Replies: 3
Views: 193

### Re: molar entropy

First try to look at the overall mass of the molecule; the molecule with more atoms will likely have more entropy. Then, if they have the same number, look at the variety of atoms; different types of atoms allow or different positions to be made (positional disorder increases --> entropy increases)....
Tue Feb 06, 2018 9:21 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: salt bridge
Replies: 3
Views: 140

### Re: salt bridge

In addition, the salt bridge is used to connect two separate electrode compartments and complete the circuit between them; the ion flow back into the compartment with the anode through the salt bridge completes the electrical circuit.
Tue Feb 06, 2018 9:19 am
Forum: Phase Changes & Related Calculations
Topic: Units for Internal Energy
Replies: 5
Views: 321

### Re: Units for Internal Energy

I believe that internal energy is usually represented in units of kJ.
Mon Jan 29, 2018 8:24 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy [ENDORSED]
Replies: 1
Views: 104

### Re: Entropy[ENDORSED]

In lecture we've been looking at entropy in a less general, "disorderly" way and more as a number we can find to represent entropy. Thus, we've kind of been looking at statistical entropy (entropy calculated from the Boltzmann formula). Positional/residual entropy is based more in calculat...
Mon Jan 29, 2018 8:19 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible an Irreversible [ENDORSED]
Replies: 4
Views: 381

### Re: Reversible an Irreversible[ENDORSED]

A reversible pathway tends to take longer because the differences in temperature or pressure between the system and its surroundings are so small that the change only occurs in small, slow increments (which is why we derived the equations used for reversible functions from an integral). Since the ch...
Mon Jan 29, 2018 8:14 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Lecture [ENDORSED]
Replies: 1
Views: 132

### Re: Lecture[ENDORSED]

Yes, exactly! Since we assume/approximate that the systems we see in thermodynamics are reversible, we can use the q(rev)=-w and deltaS=q(rev)/T equations in our problems.
Mon Jan 22, 2018 9:33 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond enthalpies
Replies: 4
Views: 292

### Re: Bond enthalpies

If the bond enthalpies are given and/or the question asks for us to calculate the reaction enthalpy by using the given table/values, I would use them and solve the problem that way. I think Dr. Lavelle told us that bond enthalpies are the least accurate way just as a note and maybe for conceptual qu...
Mon Jan 22, 2018 9:27 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Internal Energy
Replies: 3
Views: 264

### Re: Internal Energy

Internal energy is a state function because it merely measure the energy difference that the system holds from one time to another; since internal energy is not affected by how it gets from one state to another, it is a state function.
Mon Jan 22, 2018 9:26 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Difference between U and H? [ENDORSED]
Replies: 3
Views: 1621

### Re: Difference between U and H?[ENDORSED]

U is the internal energy, which is the amount of energy a system holds in both kinetic and potential energy. H is the enthalpy, which is the amount of heat released or absorbed by a system at constant pressure. Thus, U is the total energy held by a system while H is specifically the energy that is t...
Mon Jan 15, 2018 8:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 3 Methods
Replies: 4
Views: 250

### Re: 3 Methods

For Hess's Law the enthalpy of the reactants is subtracted from the products due to the general form of the change in enthalpy for the reaction being, simply, the final enthalpy of the reaction minus the initial enthalpy of the reaction. For bond energies it's the opposite because of how energy flow...
Mon Jan 15, 2018 8:47 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy vs Heat
Replies: 2
Views: 194

### Re: Enthalpy vs Heat

Heat is energy transferred as a result of a temperature difference while enthalpy is the amount of heat released by a system at a constant pressure.
Mon Jan 15, 2018 8:45 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework Problem 8.23
Replies: 1
Views: 108

### Re: Homework Problem 8.23

Hi! So you don't need to know the mass because you just need to use the definition of heat capacity.

Since C=q/deltaT you can plug in the given q value and temperatures to find the heat capacity. Hope that helps!
Tue Jan 09, 2018 8:30 pm
Forum: Phase Changes & Related Calculations
Topic: reversible process
Replies: 3
Views: 438

### Re: reversible process

Hi! So the jist of it is that a reversible process is one so sensitive (and most likely heavily controlled in the lab) that even an incredibly small change to a variable (such as pressure) would reverse the reaction. On the other hand, an irreversible process, an infinitely small change in the varia...
Tue Jan 09, 2018 8:25 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Paths and Changes of State
Replies: 3
Views: 323

### Re: Paths and Changes of State

Hi! So based on the topics covered in this unit's outline on Dr. Lavelle's website, we do not need to know how to draw out the path of change of state nor do we have to know how to describe the change of state. This is merely an educated guess, I would try asking a TA or Lavelle himself as we learn ...
Tue Jan 09, 2018 8:16 pm
Forum: Administrative Questions and Class Announcements
Replies: 2
Views: 249

### Re: Reading for Chapter 8

Based on what he discussed in lecture on Monday, I can only assume he meant to begin where the textbook discusses enthalpy. That is section 8.8 on page 278; although (disclaimer) I am not entirely sure if that's what he meant.
Mon Dec 04, 2017 8:34 am
Forum: Bronsted Acids & Bases
Topic: Question 12.53
Replies: 1
Views: 2044

### Re: Question 12.53

The key thing to remember for this problem is that for acids is that if they have more electronegative atoms attached, they will be stronger acids. And if there are more oxygens attached, they will be stronger.
Mon Dec 04, 2017 8:30 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Using The Equilibrium Arrow
Replies: 5
Views: 1279

### Re: Using The Equilibrium Arrow

I believe you use the equilibrium arrows if it is not a strong acid or base because strong acids and bases are 100% ionized in solution, while weak acids and bases are not; hence the equilibrium arrows because the reaction will continue to go back and forth without the reaction fully being completed...
Mon Nov 27, 2017 9:51 am
Forum: Naming
Topic: coordination compounds
Replies: 1
Views: 150

### Re: coordination compounds

The rules are all outlined on page 741 in the textbook, in Toolbox 17.1. Here is the outline, hope this helps!
Mon Nov 27, 2017 9:49 am
Forum: Naming
Topic: prefixes
Replies: 2
Views: 183

### Re: prefixes

The rules for naming coordination compounds are on page 741 Toolbox 17.1.

For ligands, the prefixes are based on how many molecules/atoms of that ligand are present in the compound.
Mon Nov 20, 2017 9:24 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Determining Polydentate
Replies: 1
Views: 141

### Re: Determining Polydentate

You have to look at the molecule and see if it has any atoms that can serve as part of a Lewis base. To know if it's polydentate you need to kind of have the Lewis structure of the molecule in mind to see if there is more than 1 lone pair that can be bonded to the same central metal ion. I try to dr...
Mon Nov 20, 2017 9:22 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent vs. Angular
Replies: 5
Views: 530

### Re: Bent vs. Angular

Hi! I believe in lecture Dr. Lavelle said that they are synonymous so I don't think you need to know of any differences between bent and angular.

Hope that helps!
Tue Nov 14, 2017 9:35 pm
Forum: Determining Molecular Shape (VSEPR)
Replies: 4
Views: 387

### Re: Radicals and Their Shape

Hi! So to answer your question about lone, unpaired electrons on radicals: I believe that Lavelle might have said this quickly or in passing, but it is my understanding that unpaired electrons on radicals are considered a region of electron density. Although, because there is only 1 electron and not...
Tue Nov 14, 2017 9:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 13.a)
Replies: 3
Views: 274

### Re: 13.a)

Hi! So this is kind of confusing, given how we haven't really gone over these more difficult situations. I have attached a graphic I found on the internet for this example. I think it ends up being linear because the 3 lone pairs on the Iodine repel each other and push against each other from both d...
Mon Nov 06, 2017 12:11 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Oxidation States: How to derive [ENDORSED]
Replies: 3
Views: 408

### Re: Oxidation States: How to derive[ENDORSED]

The maximum oxidation numbers can be found by figuring out how many electrons the element would need to lose or gain to end up with a filled valence shell. So, for Chlorine, the maximum positive oxidation number would be +7 because it would have to lose 7 electrons to have the complete valence shell...
Mon Nov 06, 2017 12:09 pm
Forum: Lewis Structures
Topic: Exceptions to octet rule?
Replies: 6
Views: 603

### Re: Exceptions to octet rule?

Hi! So my understanding is that most p-block elements from Period 3 and on are capable of having expanded octets and thus have more than 8 electrons in their valence shell for Lewis structures and this is because they have unfilled d-orbitals that can hold electrons above the octet. The book mention...
Wed Nov 01, 2017 9:49 am
Forum: Trends in The Periodic Table
Topic: Chapter 2, #93
Replies: 3
Views: 247

### Re: Chapter 2, #93

Yes, as David said, the Na+ ion (and all cations) becomes smaller because it loses an electron, which means there is less electron repulsion, and the electrons left are more attracted to the nucleus which results in a smaller atom. On the other hand, the Cl- ion (and all anions) becomes larger than ...
Wed Nov 01, 2017 8:44 am
Forum: Properties of Electrons
Topic: Ground State
Replies: 5
Views: 411

### Re: Ground State

In the ground state, the electrons follow the Hunds Rule and Pauli Exclusion Principle. So, the electrons must have one electron in each orbital to start off, then begin pairing electrons. When there are only one electron in each/most of the orbitals of the valence shell, they should all have parall...
Wed Oct 25, 2017 10:08 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Actual Electron Configuration
Replies: 1
Views: 304

### Re: Actual Electron Configuration

Hi! So the wave function is a mathematical expression and it represents a solution to the Schrodinger wave equation. When that solution (the wave function) is accurate, it describes the atomic orbitals of a certain atom. Thus, each wave function is the mathematical expression of an orbital. The 3 qu...
Wed Oct 25, 2017 9:55 am
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 1
Views: 173

### Re: Electron Affinity

Hi! So electron affinity is the energy released when an electron is added to an atom in the gas phase. A positive election affinity means that energy is released when an electron attaches to an atom, and this occurs if the atom has many electrons in its valence shell and thus prefers to gain electro...
Wed Oct 18, 2017 12:28 pm
Forum: Properties of Electrons
Topic: Experiments
Replies: 2
Views: 275

### Re: Experiments

I believe that as long as you understand the concepts behind the experiments and the discoveries they led to, you should be okay. Here are a couple of key points: - Photoelectric experiment = shine light on a metal surface to measure how much energy (and thus, the wavelength and frequency) of light ...
Wed Oct 18, 2017 12:16 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Homework #1.11
Replies: 2
Views: 234

### Re: Homework #1.11

Yes, as stated above, the groupings for the atomic spectra series are based on the lowest energy level involved in an electron's jump to a higher energy level or fall down to a lower energy level. Something key to remember is that when a question asks which series the wavelength of light that caused...
Wed Oct 11, 2017 12:10 pm
Forum: Properties of Light
Topic: Chapter 1 #3
Replies: 9
Views: 556

### Re: Chapter 1 #3

To answer your question Alissa, the energy would increase if the frequency increased because in the equation E=hv, h is a constant. Thus, the only thing that has an effect on the energy is the frequency. So, if the frequency increases and is multiplied by a constant, the energy will increase. If the...
Wed Oct 11, 2017 12:05 pm
Forum: Properties of Light
Topic: 1.13
Replies: 2
Views: 291

### Re: 1.13

I believe that 4 is n2 and 2 is n1 because the formula is looking at the energy levels n1 and n2 in reference to the actual formation of the electron levels. So, n1 is always the lower energy level and n2 is greater. Think about the sketch that Dr. Lavelle drew on the board in lecture, as well as in...
Wed Oct 04, 2017 5:27 pm
Forum: Molarity, Solutions, Dilutions
Topic: Calculating moles of only one element in a compound
Replies: 2
Views: 853

### Re: Calculating moles of only one element in a compound

Never mind. I figured it out, im just not sure if my reasoning is correct. Is it 0.0134 mol of cu2+ because there is one mole of cu in the compound? (1:2 ratio in CuBr2) Yes, you've pretty much got it. Since the question is only asking for the amount of Cu^2+ ions in 0.0134 moles of CuBr2, there is...
Wed Oct 04, 2017 5:10 pm
Forum: Molarity, Solutions, Dilutions
Topic: L7 Help
Replies: 4
Views: 634

### Re: L7 Help

Hi! So you're using the 454 grams of fat in part (b) because the question asks "What mass of oxygen is needed to oxidize this amount of tristearin?" and the fat mentioned in the solutions manual is the fat introduced in the intro of the question as tristearin. So the question is actually a...