## Search found 51 matches

Tue Mar 13, 2018 7:02 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow and Fast Steps
Replies: 2
Views: 176

### Slow and Fast Steps

Will we ever be required to write and derive each step on our own? Because I am a bit lost on how to create these equations in order to solve what the intermediate is and use the pre-equilibrium approach.
Tue Mar 13, 2018 6:56 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: question 15.47
Replies: 4
Views: 186

### Re: question 15.47

Because it is on either side of the equations, it is labeled as an intermediate and we want to avoid including them in the rate law. Therefore, it is not written in the rate law.
Tue Mar 13, 2018 6:54 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Mechanism Steps
Replies: 4
Views: 183

### Re: Reaction Mechanism Steps

We don't necessarily need to label it as a slow or fast step, but rather use only that equation in order to solve the rate law.
Tue Mar 13, 2018 6:53 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Relationship between K and k
Replies: 2
Views: 245

### Re: Relationship between K and k

Big K represents the equilbrium constant of an equation. Little k represents the rate constant of an equation. When you derive the equations for each, they contain concentrations of the same elements. Therefore, with substitution, you can conclude that the ratio of the forward and reverse rate const...
Tue Mar 13, 2018 6:51 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.89
Replies: 2
Views: 137

### Re: 15.89

I don't believe that we will ever have to determine which is the fastest, we most likely will be given information for that type of problem. If they give you multiple reactions, then we most likely will only have to determine the rate laws and compare it to the one given to us.
Tue Mar 13, 2018 6:49 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate-Determining Step
Replies: 4
Views: 213

### Re: Rate-Determining Step

If the first step is the slow step, then it is significantly easier to solve and determine the rate law as no intermediates appear. However, if the fast step precedes the slow step, then we use the pre-equilibrium approach, which has a more complex effect on the overall reaction as we have to find a...
Sun Mar 04, 2018 5:06 pm
Forum: Zero Order Reactions
Topic: slope
Replies: 9
Views: 481

### Re: slope

You can plot the concentration values and examine the straight (it should be straight if it's an order reaction I believe) line to see what the value of the slope is. In addition, you can derive the integrated rate laws and use the equation y = mx + b to look at the sign. For example, for the zero o...
Sun Mar 04, 2018 5:01 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Example 15.2
Replies: 1
Views: 144

### Example 15.2

Can someone please explain the explanations on page 622 for me? I understand the definitions and the rate laws of each reaction order, but I don't know how to determine the order if given a table of concentration values.
Sun Mar 04, 2018 4:57 pm
Forum: General Rate Laws
Topic: Rate Law and Initial concentration of Reactant
Replies: 5
Views: 222

### Re: Rate Law and Initial concentration of Reactant

It can't be in terms of products because if you evaluate the course of the reaction later on, you won't be able to evaluate the presence of products that well because they are constantly changing. Therefore, we examine the reactants at the beginning of the reaction because it's much easier to look a...
Thu Feb 22, 2018 9:50 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: double lines between anode and cathode
Replies: 3
Views: 194

### Re: double lines between anode and cathode

It is always used to separate the cathode and anode. It represents the salt bridge.
Thu Feb 22, 2018 9:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13c
Replies: 4
Views: 171

### Re: 14.13c

So does the fact that aqueuous elements are closer than the gases to the salt bridge trump the fact that the reactants should be listed first, then the products?
Thu Feb 22, 2018 9:43 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Metals in Cell Diagrams
Replies: 3
Views: 189

### Re: Metals in Cell Diagrams

yes, an inert electrode always has to be a solid. We normally use Pt(s) for the cell diagrams we've been doing. An inert electrode is necessary were both oxidized and reduced species are in the same solution.
Thu Feb 22, 2018 9:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Homework 14.11 part d
Replies: 1
Views: 128

### Re: Homework 14.11 part d

If they give you a cell diagram, you should first identify the cathode (right) and the anode (left). Then, you can either create the half reactions yourself, or you can easily look at the Appendix of the Electrochemical series and search for those elements in the list of the reactions given. All of ...
Mon Feb 19, 2018 12:19 pm
Forum: Balancing Redox Reactions
Topic: Basic and Acidic conditions [ENDORSED]
Replies: 11
Views: 3459

### Re: Basic and Acidic conditions[ENDORSED]

for an ACIDIC solution:
- balance the O by using H20
- balance the H by using H+ (you can also use H30+ but it's easier to do H+)

for a BASIC solution:
- balance O by using H2O
- balance H by adding H2O to the side of each half reaction that needs H & add OH- to the other side
Mon Feb 19, 2018 12:16 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test Equations Sheet
Replies: 2
Views: 120

### Re: Test Equations Sheet

Yes, they won't require you to memorize anything. If anything, it will be on a separate sheet or given with the question.
Mon Feb 19, 2018 12:15 pm
Forum: Balancing Redox Reactions
Topic: Standard Reduction Potential
Replies: 3
Views: 165

### Re: Standard Reduction Potential

Even when you multiply the half reactions by a factor in order to balance the number of electrons, the overall change of E does not change, while the value of delta G does.
Sun Feb 11, 2018 11:42 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Equation for Entropy
Replies: 1
Views: 114

### Equation for Entropy

In the textbook, section 9.10 (The Overall Change In Entropy), they explain that a process produces maximum work if it takes reversibly, which we learned in Chapter 8. However, I don't understand their explanations for this statement. They said that: w rev is more negative than w irrev and q rev is ...
Sun Feb 11, 2018 11:37 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Standard Molar Entropies
Replies: 1
Views: 128

### Standard Molar Entropies

In the textbook, section 9.7, can someone please explain the formula they give us? I don't recognize it in the lectures and maybe it's a more conceptual formula.

S(T) = S(0) + deltaS(heating from 0 to T) = deltaS(heating from 0 to T)

Thank you!
Sun Feb 11, 2018 11:33 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Non-spontaneous
Replies: 4
Views: 181

### Re: Non-spontaneous

To the posts above, why does it mean that the forward reactions are favored? What does it have to do with forward vs reverse reactions?
Fri Feb 02, 2018 4:51 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Van Hoff Equation
Replies: 3
Views: 149

### Re: Van Hoff Equation

I don't think so, I think Lavelle just wanted to show us how we arrived at that equation, and we'll only have to use it for mathematical questions in the future.
Fri Feb 02, 2018 4:49 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 3
Views: 156

### Re: Gibbs Free Energy

It measures the energy that is freely available to do work.
Fri Feb 02, 2018 4:48 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: When to use Q versus K [ENDORSED]
Replies: 6
Views: 599

### Re: When to use Q versus K[ENDORSED]

^ Yes, when the Gibb's free energy of the reactants is not equal to the Gibb's free energy of the products, you would use Q because it is not at equilibrium.

You would use K when the reaction is at equilibrium because it is a standard energy change of a reaction.
Mon Jan 29, 2018 1:20 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy vs. Degeneracy [ENDORSED]
Replies: 5
Views: 239

### Re: Entropy vs. Degeneracy[ENDORSED]

Entropy is the probability that the system will be in 1 particular state, while degeneracy is the number of ways you can achieve that energy state.
Mon Jan 29, 2018 12:19 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Lecture Diagram
Replies: 2
Views: 120

### Lecture Diagram

Can someone please explain the diagram from Wednesday's lecture? It consisted of a vacuum, work being done, external pressure, and heat. Is this a container with a gas? I'm mostly confused as to what's happening and in what system. Thanks!
Sun Jan 28, 2018 11:58 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy [ENDORSED]
Replies: 1
Views: 81

### Entropy[ENDORSED]

What is the difference between the entropy we have been discussing in class and positional (residual) entropy? Lavelle briefly mentioned the latter in the first lecture of week 3 and was unsure if we should place any importance on it. Thanks!
Sun Jan 21, 2018 7:12 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: isolated sytems
Replies: 4
Views: 191

### Re: isolated sytems

Another example besides a bomb calorimeter is coffee or any other drink in a high quality thermos bottle.
Sun Jan 21, 2018 4:36 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 1
Replies: 3
Views: 251

### Re: Test 1

Maybe if we are given the values of delta H and delta U, then we would be expected to solve for the rest of the problem, but not for those values particularly. In addition, I'm pretty sure we won't have to worry about which equations to use since they will be provided to us on his worksheet
Sun Jan 21, 2018 4:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 3 Test Topic is endorsed
Replies: 37
Views: 2062

### Re: Week 3 Test Topic is endorsed

I would focus more on the concepts of work and internal energy as well as calculating enthalpy and heat. This includes: the different methods of solving for enthalpy, calorimeter calculations. Don't worry about the equations that you need to calculate the actual work and internal energy. Hope this h...
Sun Jan 14, 2018 12:25 pm
Forum: Phase Changes & Related Calculations
Topic: Endo and Exothermic Ways to Remember
Replies: 28
Views: 3541

### Re: Endo and Exothermic Ways to Remember

You can use prefixes!

ENdo = heat ENtering --> Because heat is coming in, then the outside will be colder.

EXo = heat EXiting --> Because heat is going out, then the outside will be warmer.
Sun Jan 14, 2018 12:15 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Extensive vs Intensive Property
Replies: 3
Views: 129

### Re: Extensive vs Intensive Property

An extensive property is something you can scale with system size, while an intensive property is something you cannot scale with quantity.

Also, extensive/extensive = intensive. For example: kJ/mol
Sun Jan 14, 2018 12:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law: Method 1
Replies: 3
Views: 198

### Hess's Law: Method 1

Can someone please explain how we calculated delta H in the first method we discussed in class? I don't understand how we arrived at the net reaction of the NO2 formation. Thanks!
Sat Dec 09, 2017 11:17 pm
Forum: DeBroglie Equation
Topic: Measurable Values
Replies: 1
Views: 147

### Measurable Values

What are the measurable values for velocity in the DeBroglie equation? Because in lecture, it was said that it must be LESS than the speed of light, but then in the modules, there was a question where it was 10^5 and the answer was "NO, as it is significantly slower than c". What constitut...
Sat Dec 09, 2017 10:29 pm
Forum: Quantum Numbers and The H-Atom
Topic: Spin Quantum Number: Test 3
Replies: 3
Views: 236

### Spin Quantum Number: Test 3

For Test #3 question #8, why are the possible quantum numbers both positive and negative 1/2? I put only positive 1/2 and got it wrong. I thought that unpaired electrons start off with positive 1/2 and then after the orbitals are half filled, then the electrons are spin down. Is this completely wron...
Sat Dec 02, 2017 3:42 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Ionization and Acids/Bases [ENDORSED]
Replies: 1
Views: 130

### Ionization and Acids/Bases[ENDORSED]

What is the conceptual explanation behind ionization determining the strength of an acid/base? For example, why is it that an acid is weak because of incomplete ionization?
Sat Dec 02, 2017 3:35 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Comparing molecules and their acidity/basic character [ENDORSED]
Replies: 1
Views: 131

### Comparing molecules and their acidity/basic character[ENDORSED]

If we were given 2 or more molecules and were asked which one is the strongest/weakest acid or base, what are the steps to determining that? How can you tell which one is more basic or acidic?
Sun Nov 26, 2017 12:18 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 2
Views: 184

### Re: Bond Angles

Regions of electron density does have to do with bond angles. Some are easier to solve, like linear is 360 divided by 2 regions = 180 and tetrahedral is 360 divided by 3 regions = 120. However, others are not as easy like 109.5 (tetrahedral) and 106 (trigonal pyramidal). These angles differ because ...
Sun Nov 26, 2017 12:12 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape Memorization
Replies: 6
Views: 337

### Re: Molecular Shape Memorization

Well, you can memorize them, but I find it very helpful to look at visuals of molecules. Knowing why certain atoms are lower and closer together and understanding the effects of lone pairs on the shape can help if you look at examples. You can also make a chart of the number of regions of electron d...
Sun Nov 19, 2017 3:52 pm
Forum: Naming
Topic: writing chemical formula based on name
Replies: 4
Views: 177

### Re: writing chemical formula based on name

If it is a LIGAND , then you put the ligand names in alphabetical order + transition mental cation + roman numeral (indicating the oxidation state/charge) If it is an ANION , then anion name + -o ending + hydrate + -ate ending to the metal (if the complex has negative charge) If there is a CATION an...
Sun Nov 19, 2017 3:42 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chelates
Replies: 3
Views: 200

### Re: Chelates

They are important because chelating ligands can bind cations tightly. An example of one is EDTA with a 4- charge, which is used to remove metals from solution.
Sat Nov 11, 2017 12:14 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Electron Density [ENDORSED]
Replies: 1
Views: 115

### Re: Determining Electron Density[ENDORSED]

Lone-lone pair interactions are stronger because the electrons are closer together so they will repel the most. That's why when we're drawing Lewis structures, we want to put the lone pairs as far away from each other as possible because we want the least amount of repulsion. This causes the molecul...
Sat Nov 11, 2017 12:09 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles [ENDORSED]
Replies: 3
Views: 178

### Re: Bond Angles[ENDORSED]

I believe that some molecules have 1 bond angle because the regions of electron density are symmetric around the central atom, while other molecules have different bond angles in order to maximize the distance between the number of spheres.
Sat Nov 04, 2017 12:08 am
Forum: Lewis Structures
Topic: Bases and Acids
Replies: 3
Views: 188

### Re: Bases and Acids

A Lewis Acid is a molecule that accepts an electron pair.
A Lewis Base is a molecule that donates an electron pair.

Acids and bases can be considered in certain reactions to see how they form coordinate covalent bonds.
Sat Nov 04, 2017 12:02 am
Forum: Ionic & Covalent Bonds
Topic: Ionic or Covalent?
Replies: 4
Views: 239

### Re: Ionic or Covalent?

You can tell if a bond is ionic and covalent by calculating their electronegativity. - A bond is ionic if the electronegativity difference is > 2 - A bond is covalent if the electronegativity is < 1.5 - If the electronegativity difference is between 1.5 and 2, then it will vary what the bond is. You...
Sun Oct 29, 2017 4:23 pm
Forum: Resonance Structures
Topic: Delocalized
Replies: 7
Views: 468

### Re: Delocalized

If a resonance structure is delocalized, it means that the electrons involved in these structures are involved in multiple bonds in different locations.
Sun Oct 29, 2017 4:18 pm
Forum: Ionic & Covalent Bonds
Topic: Test 3 preparation and date [ENDORSED]
Replies: 5
Views: 357

### Re: Test 3 preparation and date[ENDORSED]

Although it says on the syllabus that the test covers material up to October 27, Test 3 will only focus on the remainder of Chapter 1 (1.6 to the end) and all of chapter 2. You can review the Heisenberg Uncertainty Principle on his online modules. The post-assignment module questions are very helpfu...
Fri Oct 20, 2017 8:18 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Electrostatic (Coulomb) Potential Energy Equation
Replies: 1
Views: 156

### Re: Electrostatic (Coulomb) Potential Energy Equation

this equation tells us factors that have an impact on energy in multi electron atoms. It describes the relationships between charge, distance between charges, and how much the electron will attract. Because the distance is in the denominator, the farther away the electrons are, the less potential en...
Fri Oct 20, 2017 8:14 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: p-orbital [ENDORSED]
Replies: 2
Views: 205

### Re: p-orbital[ENDORSED]

Well we write the x y z to indicate the orientation of the element. Writing 2p^1pp is technically correct but I'm assuming we write the x y and z to be more precise and tell us what axis it's on.
Sat Oct 14, 2017 12:25 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: lines in electromagnetic spectrum
Replies: 3
Views: 233

### Re: lines in electromagnetic spectrum

The lines in the EM spectrum correspond to the Balmer series (visible light) and the Lymann series (UV light). If there is a drop in the energy level within a spectrum, think about the chain of electromagnetic radiation and whether energy/frequency/wavelength are increasing or decreasing.
Sat Oct 14, 2017 12:22 am
Forum: Properties of Light
Topic: De Broehli [ENDORSED]
Replies: 2
Views: 275

### De Broehli[ENDORSED]

I have a question that relates to De Broeli. In chapter 1, for #33, why can't I combine and manipulate the equations for KE, E, and c in order to derive the wavelength? What's the difference between solving for the wavelength of light that ejects electrons and solving for the wavelength of the elect...
Thu Oct 05, 2017 11:27 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E7 [ENDORSED]
Replies: 9
Views: 550

### Re: E7[ENDORSED]

How many sig figs is usually ideal for an answer? Should we truncate it to 3 digits or however many there are in the numbers given in the problem?
Thu Oct 05, 2017 11:22 pm
Forum: SI Units, Unit Conversions
Topic: Exercise F11
Replies: 4
Views: 285

### Re: Exercise F11

Yes! When it is roughly a number. 8 or 9, you can round up to the next whole number. In other cases, you wouldn't round up/down if you have a number that can turn into a fraction, such as 1.33 moles. You can convert that number into a fraction: 1 1/3 = 4/3. Because this coefficient isn't a whole num...