## Search found 50 matches

Thu Mar 12, 2020 1:56 pm
Forum: First Order Reactions
Topic: equation derivations
Replies: 9
Views: 138

### Re: equation derivations

The derivations for integrated rate law will be useful to know, as well as the equations to find the rate constant or activation energy at different temperatures. We can just look in our notes for the last two lectures for the important derivations.
Thu Mar 12, 2020 1:46 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 7.23 part b
Replies: 1
Views: 39

### Re: 7.23 part b

I believe what you are asking is how to remove the intermediate from the analysis - the way to do this is by assuming that first step is at equilibrium, so the rate of production of the intermediate in the first step can be ignored. Thus, the slow step determines the rate law.
Thu Mar 12, 2020 1:37 pm
Forum: First Order Reactions
Topic: Half Life Equations
Replies: 10
Views: 95

### Re: Half Life Equations

As the final is open-book, this shouldn't be a concern anymore, but the homework question (7A.7 I believe) that discusses the units of the rate constant for different rate orders is good to review on this topic.
Thu Mar 12, 2020 1:22 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Frequency Factor
Replies: 6
Views: 114

### Re: Frequency Factor

To consolidate the important points of the other posts, the frequency factor is the frequency that molecules of the reactants collide with each other to react. This frequency is dependent on the temperature. We use it in conjunction with the rate constant, k, and the activation energy of the reactio...
Thu Mar 12, 2020 1:19 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate of the reverse reaction
Replies: 3
Views: 60

### Re: Rate of the reverse reaction

We can only evaluate one reaction's rate at a time, so the rate k [r1][r2] gives us the rate of the forward reaction. The rate of the reverse reaction can be found experimentally as well, but because of constant production of products, we focus on the forward reaction in our kinetics analysis.
Sat Mar 07, 2020 1:20 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Proposing Reaction Mechanisms
Replies: 3
Views: 51

### Re: Proposing Reaction Mechanisms

Most likely no, as finding an experimental rate law to compare to a mechanism's rate-determining step would require actual work in the lab. Maybe if we were given different mechanisms and the rates associated with their slow steps, as well as the experimental rate law, then we could decide which mec...
Sat Mar 07, 2020 1:18 pm
Forum: General Rate Laws
Topic: 7A. 7 Homework Problem
Replies: 2
Views: 60

### Re: 7A. 7 Homework Problem

Instead of memorizing another formula, which is not given on the constants and equations sheet, you can think of it this way: As the reaction goes from reactants (A) to products, A is reacting at [A]/time, which is the rate of the reaction. The general rate law is : kr[A]^r, where r is the order of ...
Sat Mar 07, 2020 1:07 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Potential
Replies: 3
Views: 97

### Re: Potential

To answer the second part of your question, wmax is the greatest work done, which would be the standard Gibbs free energy of the reaction at constant temperature and pressure. The equation that relates wmax to standard cell potential is wmax=standard delta G=-nFEcell.
Sat Mar 07, 2020 12:58 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate-Limiting Step
Replies: 5
Views: 89

### Re: Rate-Limiting Step

It may not be given in the problem which step is the slow step. As the other posters said, the slow step is the rate-determining step, so whichever step in the reaction has the slowest rate will be the slow step, or whichever step matches the experimental rate law will be the slow step. On the exam,...
Sat Mar 07, 2020 12:55 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Determining Steps in a series of Elementary Steps
Replies: 2
Views: 55

### Re: Rate Determining Steps in a series of Elementary Steps

In my notes, I have: - pre-equilibrium: reaction before the rate-limiting step is at equilibrium, use its equilibrium constant, K A--> B B--> C (SLOW STEP) - if B--> C is the bottleneck (slow step), then there is a buildup of B in A--> B, so we can treat A-->B as A--><-- B (at equilibrium) What this...
Wed Feb 26, 2020 7:14 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Work
Replies: 4
Views: 76

### Re: Work

The formula you are looking for is delta G standard = -RTlnK = -nFEcell. The Gibbs free energy gives the maximum non-expansion work, as the previous response mentioned.
Wed Feb 26, 2020 6:43 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Diamond Reaction
Replies: 4
Views: 94

### Re: Diamond Reaction

The speed of a reaction depends on kinetics, which means that the magnitude of activation energy determines the speed of the reaction. This is why catalysts like enzymes, that lower the activation energy, increase the speed of the reaction. In terms of the diamond reaction, which has high activation...
Wed Feb 26, 2020 6:36 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Products and Reactants
Replies: 5
Views: 100

### Re: Products and Reactants

Yes, the final combined reaction (after the electrons have been cancelled) is the reaction you use to find Q. K is usually given in the problem, or when equilibrium concentrations for the species in the final combined reaction are given, you can solve for K. The formula is [products]/[reactants] for...
Wed Feb 26, 2020 6:32 pm
Forum: Balancing Redox Reactions
Topic: 6K5A
Replies: 3
Views: 84

### Re: 6K5A

To add to the previous answer, the oxidizing agent is the species being reduced, or gaining electrons, and the reducing agent is the species being oxidized, or losing electrons.
Wed Feb 26, 2020 6:16 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.3b
Replies: 2
Views: 33

### Re: 6L.3b

The Pt and C do not participate in the reaction as they are inert. Thus, they are not included in the half-reaction, but they are included in the cell diagram.
Sat Feb 22, 2020 8:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Finding n
Replies: 6
Views: 71

### Re: Finding n

Hi- n does refer to moles in electrochem, just like before. An example of this is the delta G standard=-nFEcell equation. N can usually be found in electrochem questions just by looking at the redox reaction or balancing the given equation.
Sat Feb 22, 2020 8:19 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Textbook progress
Replies: 3
Views: 39

### Re: Textbook progress

The lectures don’t exactly match the textbook, as Professor Lavelle has mentioned some topics that are further on in the book, past topics we haven’t discussed yet. As the other poster mentioned, I think reading through til the end of 6N is a good estimate of where we are.
Sat Feb 22, 2020 8:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 10
Views: 136

### Re: Salt Bridge

In order to maintain electron flow between the anode and cathode, the sites need to be neutrally charged. They are not neutrally charged naturally, because ions are removed from either side as the electrons flow. Thus, the salt bridge allows anions to flow to the anode and cations to flow to the cat...
Sat Feb 22, 2020 8:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Clarifying from textbook
Replies: 2
Views: 44

### Re: Clarifying from textbook

In Galvanic cells the electrodes flow from cathode to anode. Actually, that’s incorrect - in galvanic cells the electrodes flow from anode to cathode, or from the site of the oxidation reaction to the site of the reduction reaction, in other terms. However, to keep the electrodes neutrally charged,...
Sat Feb 22, 2020 8:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L. 9
Replies: 2
Views: 67

### Re: 6L. 9

The acidified solution just means that H20 and H+ are present and can be used on either side of the half reaction to balance it.
Sun Feb 16, 2020 10:59 pm
Forum: Balancing Redox Reactions
Topic: Electrochemisty
Replies: 10
Views: 119

### Re: Electrochemisty

The answer to this might be obvious but how does this connect to batteries? At a basic level, batteries are storage places for chemical reactions to occur. These chemical reactions can be used to generate electrical energy for our usage. In addition, Professor Lavelle mentioned on Friday that when ...
Sun Feb 16, 2020 10:56 pm
Forum: General Science Questions
Topic: homework for week 7
Replies: 7
Views: 91

### Re: homework for week 7

Yes, you can work on any recent topic, which still includes thermodynamics. If you have not yet submitted homework from topic 5G onwards (or any of the material that was not on the midterm), you can do so for Week 7 Homework.
Sun Feb 16, 2020 10:54 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: ΔU Equal 0
Replies: 4
Views: 213

### Re: ΔU Equal 0

There is another similar question about change in internal energy for isothermal processes. Hopefully this gives some insight: Internal energy, or U, is a state function dependent on temperature. This means that for a process that is isothermal (delta T is 0), even if it is an expansion of a gas, th...
Sun Feb 16, 2020 10:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: isothermal reactions
Replies: 8
Views: 213

### Re: isothermal reactions

Just to clarify - isothermal means there is no temperature. As others have said, internal energy is a state function, which depends on temperature. Thus, without a temperature change, even if you have isothermal expansion, compression, or pressure change, the internal energy will be 0. Delta U = q+w...
Sun Feb 16, 2020 10:42 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: 3/2R & 5/2R
Replies: 9
Views: 218

### Re: 3/2R & 5/2R

I believe Cp and Cv could be used when finding the entropy change of an ideal monatomic gas, such as in Pizza Rolls 5: We are given the initial mass and volumes of two gases, told that they are ideal monatomic gases, and asked to find the change in entropy as they are mixed and the temperature incre...
Sun Feb 16, 2020 10:37 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: wmax = delta G
Replies: 1
Views: 52

### Re: wmax = delta G

This is probably referring to when Professor Lavelle taught us on Friday that the maximum work done at constant temperature and pressure is equal to delta G, which is the amount of free energy the system has to do work. (delta G = delta H - T*delta S at constant temperature and pressure).
Sun Feb 16, 2020 10:32 pm
Forum: Balancing Redox Reactions
Topic: Charge of permanganate
Replies: 5
Views: 92

### Re: Charge of permanganate

Yes, oxidation rules follow a hierarchy when determining oxidation numbers. For example, the oxidation number of oxygen in compounds is usually -2, which pertains to this question about permanganate. I believe a list of the rules is in our textbook, or online.
Sun Feb 16, 2020 10:29 pm
Forum: Calculating Work of Expansion
Topic: Choosing work equation
Replies: 10
Views: 266

### Re: Choosing work equation

As on the midterm, I expect that we will be told on the exams when a reaction is reversible or irreversible. However, a useful thing to keep in mind is that if the arrow on a reaction is not pointing at the reverse as well as the forward, this probably means that the products cannot become reactants...
Sun Feb 16, 2020 10:22 pm
Forum: Phase Changes & Related Calculations
Topic: Negative Work
Replies: 18
Views: 340

### Re: Negative Work

You should use the context clues of the question to figure out if work is meant to be negative or not. If the system is doing work on the surroundings, such as expansion against a constant pressure, then it is right for your value to be negative.
Sun Feb 16, 2020 10:20 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Writing a reaction for a buffer?
Replies: 1
Views: 85

### Writing a reaction for a buffer?

How do we write out the reaction used to make a buffer? What are some good resources for learning how to write these types of reactions?
Sun Feb 16, 2020 10:16 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work
Replies: 14
Views: 317

### Re: Work

In thermodynamics, work is the energy transferred from the system to the surroundings. So, when the system transfers energy to the surroundings by doing work, the work is negative. When the surroundings transfer energy to the system by doing work on it, the work is positive.
Sun Feb 16, 2020 10:10 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: q=n*delta H
Replies: 5
Views: 130

### Re: q=n*delta H

Whether you use delta H or C*delta T depends on the information you are given. If you have delta H reaction, for example, then you will use that value. If you don’t have that information and instead just have the material and it’s specific heat, as well as the temperature change, you will use that v...
Sun Feb 16, 2020 10:02 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Acids/Bases in non-neutral solutions
Replies: 2
Views: 44

### Re: Acids/Bases in non-neutral solutions

I believe the way to find dissociation would be to calculate the percent ionization of the weak acid or base. So you would use the Ka or Kb and make an ICE table with the initial amount of the weak acid or base to calculate the concentration of H3O+ or OH- in the equilibrium mixture, which you can d...
Sun Feb 16, 2020 9:58 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated versus closed
Replies: 7
Views: 184

### Re: Isolated versus closed

An isolated system does not exchange matter or energy with the surroundings, but a closed system exchanges energy and not matter with the surroundings. This relates to the laws of thermodynamics in that the first law states that the internal energy of an isolated system stays constant, and the secon...
Sun Feb 16, 2020 9:37 pm
Forum: General Science Questions
Topic: Studying
Replies: 19
Views: 302

### Re: Studying

I would recommend the homework and just browsing the solutions manual. The methods of answering the questions are very helpful for trying to answer similar questions on the test. It even includes extra explanations about the equations and the concepts that are written really densely in the textbook.
Wed Jan 22, 2020 12:54 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: exothermic reactions
Replies: 19
Views: 226

### Re: exothermic reactions

To remember this concept easily, you can think of this in simplified terms: You can think of heat as a reactant in endothermic reactions, and a product in exothermic reactions. Thus, if you increase the temperature (adding heat) to an exothermic reaction, you will favor the reactants, just like with...
Wed Jan 22, 2020 12:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Why does changing the stoichiometric coefficients by a factor also change the value of K?
Replies: 3
Views: 60

### Re: Why does changing the stoichiometric coefficients by a factor also change the value of K?

To add to the previous reply: Changing the stoichiometric coefficients is NOT the same thing as changing the concentrations of the products and reactants. Changing the coefficients is fundamentally changing the equilibrium reaction itself, which means that the ratio of the products and reactants wil...
Wed Jan 22, 2020 12:44 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: suggestions
Replies: 16
Views: 159

### Re: suggestions

Hi! Khan Academy, Bozeman, and Organic Chemistry Tutor are very good options, but if you want something more interactive you can try PhET simulations. I find them very helpful because controlling what happens helps me understand what factors affect the strength of an acid or base and the dissociatio...
Wed Jan 22, 2020 12:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Determining pH
Replies: 3
Views: 30

### Re: Determining pH

Hi there, just a clarification - you can tell that C6H5NH2 is a base because it has an NH2 group at the end. This group is an amine, which accepts H+ to become C6H5-NH3+. It is also a weak base because amines make weak bases. Similarly, CH3NH3Cl is a strong acid, because the conjugate base, a Cl- io...
Wed Jan 22, 2020 12:29 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solids and Liquids
Replies: 6
Views: 52

### Re: Solids and Liquids

Solids and liquids are pure substances, and thus are not included in the equilibrium constant. A good example of this is that H20 is a liquid, which is often the solvent in the reaction and is not part of the reaction itself, so it is not included in the equilibrium constant.
Wed Jan 15, 2020 1:42 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: strong vs weak
Replies: 4
Views: 45

### Re: strong vs weak

I think both equations can be used for strong and weak acids, it's just that the pKa and pKb equation gives us information about the strength of an acid or base, and that information is not as useful or necessary when we are working with a strong acid or base. The pH and pOH equation definitely can ...
Wed Jan 15, 2020 1:35 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 6
Views: 43

### Re: Le Chatelier's Principle

As an addition to the earlier replies: Although changing the pressure changes the concentration of the products and reactants, their ratio will return to the equilibrium constant, Kp. Only a change in temperature changes Kp, not the pressure or concentration of products and reactants.
Wed Jan 15, 2020 1:32 pm
Forum: Ideal Gases
Topic: Combined gas law
Replies: 3
Views: 59

### Re: Combined gas law

Just as a clarification to the earlier reply: the combined gas law is P1V1/T1 = P2V2/T2. So, there is no way for you to convert between moles and liters using the combined gas law (instead you would use the ideal gas law, PV = nRT). The combined gas law is used to find the conditions under which ano...
Wed Jan 15, 2020 1:25 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8195
Views: 1429211

### Re: Post All Chemistry Jokes Here

Q: What should you do if no one laughs at your chemistry jokes?
A: Keep telling them till you get a reaction!

Q: Want to hear a joke about Sodium, Bromine, and Oxygen?
A: NaBrO
Wed Jan 15, 2020 1:20 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 1 Topics
Replies: 4
Views: 66

### Re: Test 1 Topics

I think doing the further problems from the first two outlines would be useful. In addition, it might be a good idea to look at the examples in the book and the ones from class and redo those, as they directly relate to topics Professor Lavelle has taught us, and is likely to test.
Fri Jan 10, 2020 6:56 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q and speed of reaction
Replies: 5
Views: 48

### Q and speed of reaction

Does Q affect the speed of the forward and reverse reactions in an equilibrium reaction? For example, does the forward reaction proceed more rapidly when Q is greater than K?
Wed Jan 08, 2020 3:46 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reverse reaction
Replies: 6
Views: 63

### Re: Reverse reaction

Just to clarify, the reverse reaction can only occur when there is some amount of products to turn back into reactants. So, the reverse reaction cannot begin until the forward reaction has produced some products. After that, the reverse reaction will continue to occur, even while the reaction is at ...
Wed Jan 08, 2020 3:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: partial pressure
Replies: 2
Views: 41

### Re: partial pressure

To add to the previous answer, we use partial pressure for the Kp of a reaction at equilibrium depending on which form, pressure or molar concentration, the quantities of the reactants and products are given in. So if we are given partial pressures of the reactants and products, we will use that to ...
Wed Jan 08, 2020 3:31 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Composite Equations
Replies: 3
Views: 46

### Re: Composite Equations

For composite equations, the product of one reaction must correspond to the reactant of the other reaction that you are trying to combine. As the other reply stated, you would want to use the two equations in the chart that cancel out Cl2 to give you the desired equation. As it happens, these are bo...
Wed Jan 08, 2020 1:21 pm
Forum: Ideal Gases
Topic: Dynamic Equilibrium
Replies: 10
Views: 120

### Re: Dynamic Equilibrium

We know when something is in dynamic equilibrium when the forward and reverse reactions are still occurring, despite the composition of the products and reactants being the same. One possible way to test this is to remove an amount of products and if the reaction produces more products to reestablis...