## Search found 39 matches

Sat Mar 17, 2018 8:17 pm
Forum: Administrative Questions and Class Announcements
Topic: Roomie Love <3
Replies: 1
Views: 328

### Re: Roomie Love <3

;) love u my lovely roommate thank u for the constant support throughout this rough time we WILL slay tomorrow xoxo gossip girl
Sat Mar 17, 2018 1:39 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: 2009 Practice Final Q6A (m)
Replies: 1
Views: 221

### Re: 2009 Practice Final Q6A (m)

Numbers 2 and 4 are kinetically controlled because they have a large activation energy barrier, even though the products have a lower standard Gibbs Free energy. Because the reaction would have to overcome this barrier, the reaction is governed by kinetics. This is much like the reaction of diamond ...
Wed Mar 14, 2018 11:30 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre Equilibrium Approach Question
Replies: 1
Views: 169

### Pre Equilibrium Approach Question

For the example we used in class for the pre-equilibrium approach involving the reaction of NO and O2 to form 2NO2, the coefficient (2) was taken into consideration due to the unique rate law rule. I was curious as to whether that was necessary to solve other pre-equilibrium approach problems, as th...
Wed Mar 14, 2018 7:33 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: HW 15.49
Replies: 2
Views: 163

### Re: HW 15.49

Because it is not the rate determining step, we can write out the intermediate in the rate law for that specific step.
Wed Mar 14, 2018 7:32 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: thermodynamically stable
Replies: 1
Views: 193

### Re: thermodynamically stable

A thermodynamically stable reaction is one where delta G (free energy) is negative, which would indicate a spontaneous reaction (energy state of the reactants is higher than the energy state of the products and reaction will proceed spontaneously without added energy. Thus, this leaves delta H to be...
Wed Mar 14, 2018 7:27 pm
Forum: Reaction Mechanisms, Reaction Profiles
Replies: 2
Views: 204

### Re: Question about today's lecture?

If your first step had matched, then you would be finished with the problem, as that step would match the mechanism and would not experience bottlenecking like the second step. But because our first step did not match, we then had to go ahead and go through the procedure of converting our second ste...
Tue Mar 06, 2018 12:00 am
Forum: General Rate Laws
Topic: 15.17
Replies: 3
Views: 240

### Re: 15.17

Most likely would be marked wrong, as C being zero order indicates that it will not affect the rate law. If you wrote it, you would prob have to put a 0 as the exponent for it, otherwise it would look like it was being included as first order according to C.
Mon Mar 05, 2018 11:49 pm
Forum: First Order Reactions
Topic: When to use rate equations
Replies: 3
Views: 224

### Re: When to use rate equations

Integrated rate laws are used when describing change in concentrations over time (finding [A]t when given [A]0 and k, for example), while regular rate laws are just used when you are given concentrations and a rate and need to calculate k.
Mon Mar 05, 2018 11:44 pm
Forum: Experimental Details
Topic: Rate Constant
Replies: 4
Views: 566

### Re: Rate Constant

All of the experiments are valid for finding k (the rate constant)
Wed Feb 28, 2018 7:58 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: units of K
Replies: 5
Views: 308

### Re: units of K

The units of K change based on what gets cancelled out in the rate law equations; this is why the value of K is different based on the order of the reaction.
Wed Feb 28, 2018 7:57 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Half-life
Replies: 4
Views: 303

### Re: Half-life

It's not that t (the time) itself is necessarily equal to 1/2; the notation simply tells you that you must find the time required for any specified concentration or amount to decrease by half.
Wed Feb 28, 2018 7:50 pm
Forum: Balancing Redox Reactions
Topic: Textbook 14.1
Replies: 3
Views: 269

### Re: Textbook 14.1

H- does not exist on its own, so this would most likely be an error in the textbook.
Wed Feb 21, 2018 9:50 pm
Forum: Balancing Redox Reactions
Topic: 14.5
Replies: 1
Views: 258

### Re: 14.5

The trick I use is to first balance everything else. So, add a two in front of Br03. Br2--> 2BrO3 Now we have to balance the oxygens. Add H20 to the side that needs oxygen to balance it out. 6H2O+Br2--> 2BrO3 (6 oxygens total, so we add 6 H2O molecules to balance it out) Now we have a surplus of hyd...
Tue Feb 20, 2018 9:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 3
Views: 170

### Re: Cell Diagram

Commas are used to separate like states of matter on the same side (cathode or anode), while slashes separate different states of matter on the same side. For instance, Fe 2+ (aq), Fe 3+ (aq) || Ag + (aq) | Ag (s) where the two iron ions on the anode side are like states of matter, and the silver io...
Tue Feb 20, 2018 9:19 pm
Forum: Balancing Redox Reactions
Topic: Homework Question 14.5
Replies: 2
Views: 228

### Re: Homework Question 14.5

O3 has an oxidation number of 0, as it is a neutral substance that contains atoms of only one element. The same would therefore be true of P4.
Tue Feb 20, 2018 9:13 pm
Forum: Balancing Redox Reactions
Topic: 3A Determining reduction vs oxidation
Replies: 4
Views: 226

### Re: 3A Determining reduction vs oxidation

In determining the oxidized element and reduced element, you look at which element's oxidation number becomes more positive (oxidized) and which one becomes more negative (reduced). For instance, in 3a, the reaction given is Cl2 + S2O3 2- -> Cl - + SO4 2-. Chlorine is the reduced element (AKA oxidiz...
Tue Feb 13, 2018 7:12 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Units for Gibbs Free Energy
Replies: 3
Views: 280

### Re: Units for Gibbs Free Energy

Oh! Your units for delta G should be in kilojoules or joules per mole, as it is calculated from a delta H and a delta S value that is written as kj or j per mol. This would cancel out with the mole unit in R :) sorry about that, hope that helps
Tue Feb 13, 2018 7:09 pm
Forum: Phase Changes & Related Calculations
Topic: U = 3/2 nRT
Replies: 3
Views: 1369

### U = 3/2 nRT

I am a little confused as to when we would utilize this equation. It is present on the constants and equations sheet as calculating U for an ideal gas. I remember using it in 8.103, with the problem involving calculations of molar kinetic energy in j/mol for krypton at 55.85 degrees and 54.85 degree...
Tue Feb 13, 2018 6:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Iced tea and water problem
Replies: 2
Views: 589

### Iced tea and water problem

"In order to make iced-tea, a 30.0 g ice cube at 0 degrees c is added to 250 ml of tea at 20.0 degrees c. What is the final temperature of the iced-tea once it has reached thermal equilibrium? Assume no heat is transferred to and from the surroundings. The density of water (and iced tea) is 2.0...
Mon Feb 12, 2018 7:04 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Units for Gibbs Free Energy
Replies: 3
Views: 280

### Re: Units for Gibbs Free Energy

When calculating K using ΔGº = -nRTlnK, your units should cancel out, as K is unitless. ΔGº utilizes units of joules (if your value is in kilojoules from a prior calculation, you need to concert it to joules), n is units of moles, R is units of joules per kelvin per mole (J/K*n), and T utilizes unit...
Mon Feb 12, 2018 6:59 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 1
Views: 133

### Re: Gibbs Free Energy

Conceptually, the Gibbs Free Energy of a reaction represents the energy that is free and available to do useful work. When it is a negative value, it indicates that the reaction is able to use up the energy created and is spontaneous. When the value is positive, it represents the excess energy avail...
Mon Feb 12, 2018 6:55 pm
Forum: Van't Hoff Equation
Topic: Confusion on different versions of the Van't Hoff equation?
Replies: 4
Views: 532

### Confusion on different versions of the Van't Hoff equation?

The textbook has the Van't Hoff equation as lnK2/K1= delta H/R + {1/T1-1/T2}, while the version we talked about in class has lnK2/K1=-delta H/R + {1/T2-1/T1}. Aside from the delta H factor being negative, and the T's being switched, which are the two differences, which version should we be using in ...
Mon Feb 05, 2018 10:04 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: The sign of the change in Gibb's Free Energy
Replies: 6
Views: 383

### Re: The sign of the change in Gibb's Free Energy

A negative value for Gibb's free energy indicates that no energy is needed to be added to the system to have the reaction occur spontaneously. Therefore, the reaction is spontaneous. If it was a positive value, that indicates that that quantity of energy must be added in order for the reaction to oc...
Mon Feb 05, 2018 9:45 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Conceptual Help on Cv vs Cp
Replies: 1
Views: 170

### Re: Conceptual Help on Cv vs Cp

Cv is change in internal energy/change in temperature because at constant volume, the gas can do no work as w=p*delta V. If w is zero, then delta U=q. We then can use the specific heat capacity relationship q=nCvdeltaT. For Cp, we can use change in enthalpy/change in temperature because the pressure...
Mon Feb 05, 2018 9:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode and Cathode [ENDORSED]
Replies: 4
Views: 375

### Re: Anode and Cathode[ENDORSED]

Much like how CATion is a positive ion, and ANion is a negative ion, a cathode is the positively charged electrode, while the anode is the negatively charged electrode.
Mon Feb 05, 2018 9:07 pm
Forum: Balancing Redox Reactions
Topic: acronym for reduction
Replies: 5
Views: 516

### Re: acronym for reduction

On a related note, to remember where oxidation and reduction occur on a battery model, you can remember that oxidation occurs on the anode (An OX, like the animal), and reduction occurs on the cathode (RED Cat) :)
Wed Jan 31, 2018 10:31 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Class Example
Replies: 6
Views: 244

### Re: Class Example

Because we are solving for a single variable (T) and there are two unknowns (T and G), we set G=0 in order to find the boiling point at which the liquid and gas state can coexist. Once we find the T at which they coexist, we know that a T higher than the one we found will allow for only gases to exi...
Wed Jan 31, 2018 10:27 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Homework 9.13
Replies: 2
Views: 168

### Re: Homework 9.13

Under ideal gas conditions, the textbook assumes 1.00 moles of gas. The sentence "assume ideal behavior" offers this clue. Hopefully, things are worded more clearly on other assignments and exams :)
Wed Jan 31, 2018 10:23 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Sign of ΔS
Replies: 3
Views: 212

### Re: Sign of ΔS

The q value in the numerator indicates whether heat is flowing to the system or being released by the system. If your system is releasing heat, the entropy in the system decreases and the entropy in your surroundings increase.
Wed Jan 31, 2018 10:16 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: q(REV)
Replies: 3
Views: 177

### Re: q(REV)

qREV is just used to remind us that the reaction we are conducting has the heat transfer undertaken reversibly.
Mon Jan 22, 2018 8:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.45- why do you multiply?
Replies: 5
Views: 236

### Re: 8.45- why do you multiply?

The delta H value tells you the kj of heat per 1 mol of S8/4 mol of C/4 mol of CS2. If you were to have the same reaction occur with 1.25 moles of S8, you know the kj required for 1 mol (it was given to you). Thus, you would multiply the delta H value by 1.25 to get the kj for 1.25 moles of S8.
Mon Jan 22, 2018 8:53 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.3
Replies: 3
Views: 221

### Re: 8.3

When you push in the piston on the bicycle pump, you are doing work on the system, and therefore, adding more energy to the internal system. This, in turn, indicates that the work would be a positive value, as you are adding energy.
Mon Jan 22, 2018 8:49 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: the sign of q
Replies: 5
Views: 198

### Re: the sign of q

The wording in the problem will give you a hint as to whether or not the value of q is positive or negative. When a system requires energy, the value of q is positive (endothermic, system absorbs energy). When a system releases energy, the value of q is negative (exothermic, system releases energy)....
Thu Jan 18, 2018 4:56 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Replies: 8
Views: 570

Simple terms: In an adiabatic process, q (heat) is always equal to zero. Therefore, you can assume that if q is zero, then change in internal energy equals the work done by or on the system.
Thu Jan 18, 2018 4:54 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 8.1 question
Replies: 8
Views: 440

### Re: 8.1 question

A bomb calorimeter would be considered an isolated system because the system is closed off to the external environment, being incased within the exterior, insulating walls. Therefore, there is no transfer of heat to the outside surroundings; thus, it is an isolated system.
Tue Jan 16, 2018 6:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Chapter 8 8.57
Replies: 1
Views: 145

### Chapter 8 8.57

"Determine the reaction enthalpy for the hydrogenation of ethyne to ethane, C2H2(g) + H2(g) --> C2H6(g), given the following standard enthalpies of combustion: C2H2(g)= -1300 KJ/mol; C2H6(g)= -1560 KJ/mol; H2(g)= -286 KJ/mol." While I was able to obtain the correct answer (-312 KJ) by maki...
Sat Jan 13, 2018 1:31 pm
Forum: Phase Changes & Related Calculations
Topic: Intensive vs. Extensive
Replies: 4
Views: 254

### Re: Intensive vs. Extensive

Extensive variables depend on how much there is of something (such as mass, volume, etc), while intensive variables don't rely on the quantity of the material/substance/element/object present (density will always be the same in an object regardless of how much there is of it, for example). In regard...
Sat Jan 13, 2018 1:24 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Methods of Finding Enthalpy
Replies: 1
Views: 124

### Re: Methods of Finding Enthalpy

The method used would vary based on the values you are given. If you are given a table with bond enthalpies, you would utilize that information and use that method; if you are given the delta H value for the formation of one molecule and the delta H value for the formation of another molecule, you c...
Sat Jan 13, 2018 1:16 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: enthalpy
Replies: 2
Views: 139

### Re: enthalpy

The enthalpy of a reaction is measured when the reaction is carried out with constant pressure. A calorimeter can ensure that the pressure and volume is held constant. When you measure the energy in the system, it is the internal energy; to convert it to the enthalpy of the reaction, you add the cha...