## Search found 60 matches

Sat Mar 14, 2020 3:24 pm
Forum: Zero Order Reactions
Topic: Equations for 0, 1st, and 2nd order reactions
Replies: 4
Views: 69

### Re: Equations for 0, 1st, and 2nd order reactions

Another important equation for first order that my TA said we should know too, is the derivation of the 1st order equation (noted above). It makes it easier to work out problems in the HW too. When you derive the above equation for 1st order you get:
[A] = [A] initial x e^(-kt)
Sat Mar 14, 2020 3:21 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 7A.17
Replies: 2
Views: 71

### Re: 7A.17

i think this is a typo in the book, because I saw that me and some others got 2.85 with the same units you did, just not with the 10^12 part. I think your answer is fine
Sat Mar 14, 2020 3:19 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Finding k 7B.3
Replies: 1
Views: 47

### Re: Finding k 7B.3

What i did for this one was set up an ICE table for the equation, 2A ---> B + C, with the "end" category being after 115secs, rather than at equilibirium like we normally do. Once you put all the information in, you see that the end concentrations of A and B are .153 - 2x and x respectivel...
Sat Mar 14, 2020 3:09 pm
Forum: General Rate Laws
Topic: 7A.15a
Replies: 4
Views: 87

### Re: 7A.15a

the above comment is absolutely correct. Always remember that the rates are gonna be different depending on the changing concentrations, so if you look at two concentrations changing at once, you can't really calculate the impact the concentration has on the overall rate change. So if you want to se...
Sat Mar 14, 2020 3:03 pm
Forum: General Rate Laws
Topic: HW 7C.7
Replies: 2
Views: 30

### Re: HW 7C.7

When you right the overall reaction, all you do is look at the two steps and add up all the reactants on one side and all the products on the other. Any intermediates (anything that was made as a product of one step that was later used up as a reactant in the following step) should be cancelled out ...
Wed Mar 04, 2020 1:18 pm
Forum: Balancing Redox Reactions
Replies: 4
Views: 36

try to remember the order in which we balance everything: 1. balance all the elements (that aren't Oxygen or Hydrogen) 2. add H20 to balance oxygen 3. add H+ to balance the Hydrogens 4. ADD ELECTRONS TO BALANCE THE CHARGES 5. scale the reactions so electrons cancel out like it was said before you ha...
Wed Mar 04, 2020 1:12 pm
Forum: Balancing Redox Reactions
Topic: Acidic and Basic Redox Reactions
Replies: 9
Views: 69

### Re: Acidic and Basic Redox Reactions

the test specified for us if it will be basic or acidic, and I imagine that they'll advise us also on the final, because of the extra steps we have to calculate in basic solutions.
Wed Mar 04, 2020 1:04 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 6N.17
Replies: 2
Views: 62

### Re: 6N.17

Your Q should be .005/.15, giving you the correct E(cell) to plug into the work equation.
Wed Mar 04, 2020 1:00 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Cell Potential of H2 Redox Rxn
Replies: 3
Views: 73

### Re: Cell Potential of H2 Redox Rxn

In regards to any rule, just remember that this particular half reaction represents a sort of ground level for the other half reduction reactions. In other words, the electronegativities were calculated by comparing their interaction with a hydrogen electrode.
Wed Mar 04, 2020 12:54 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Strongest Reducing Agent
Replies: 5
Views: 80

### Re: Strongest Reducing Agent

Also on the same topic of strength of reducing agents, sometimes you see metals that have two different E values (eg. Ag+/Ag2+ E=.80 or E=1.98),and sometimes this can make things a little confusing. But when comparing these kinds of elements I try to just look at these different electronegativities ...
Fri Feb 28, 2020 4:26 pm
Forum: Balancing Redox Reactions
Topic: Test 2
Replies: 10
Views: 88

### Re: Test 2

if you are ever worried about what material will on a test or exam, just check the announcements on the class website page, that helps keep you updated.
Fri Feb 28, 2020 4:11 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Problem 4I.5
Replies: 2
Views: 128

### Re: Problem 4I.5

the way I understand it, both the cold water and the hot water have the exact same specific heat capacity, so when we set them to one another (q of cold = - q of hot) it just makes it simpler knowing that we can divide both sides without having to do any extra calculations I imagine that if you do e...
Fri Feb 28, 2020 3:59 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 4J.5 Part c
Replies: 2
Views: 31

### Re: 4J.5 Part c

table 4J2 in the textbook shows examples of the most stable forms of some elements. It shows us examples for H2, O2, Cl2, and a few others. Just really helpful in case you wanted to know!
Fri Feb 28, 2020 3:27 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 5g. 13)
Replies: 3
Views: 42

### Re: 5g. 13)

well, technically speaking, the reaction wasn't at equilibrium at all. when we calculate the reaction quotient, Q, with the given pressures, we realize that Q is a different number than K so its not at equilibrium. the previous response is correct; the problem is just a matter of plugging in the var...
Fri Feb 28, 2020 3:18 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: HW question 5G.15
Replies: 4
Views: 91

### Re: HW question 5G.15

So it took me a while to work this one out but you basically do it in 3 steps 1. use the partial pressures to calculate the reaction quotient, Q 2. use the equation delta G naught = - RTlnK and substitute it for delta g naught in the equation delta g = delta g naught + RTlnQ, so you get: delta G = (...
Fri Feb 21, 2020 10:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Ways to Calculate Standard Cell Potentials
Replies: 3
Views: 68

### Re: Ways to Calculate Standard Cell Potentials

You only reverse one of the reactions and change the sign of one of the standard potentials with the first method. If you try reversing and changing the signs with the second method, you get a different value entirely.
Fri Feb 21, 2020 10:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Why is Plt and Iron on the same side of the cell diagram??
Replies: 2
Views: 39

### Why is Plt and Iron on the same side of the cell diagram??

So I ended up getting to lecture a little late today and I missed Professor Lavelle's explanation on cell diagrams. His example in class was the equation: 2 Fe (3+)(aq) + Cu(s) -> Cu(2+)(aq) + 2 Fe(2+)(aq) with an inert conductor of Platinum. I understand that you need to write down the Anode half r...
Fri Feb 21, 2020 10:13 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Delta G and spontaneous process
Replies: 2
Views: 32

### Re: Delta G and spontaneous process

I would kind of like to know if there is some sort of cut off professor lavelle could give us. It just helped me learning the Reaction Quotient (K) knowing what was "large" and "small", and making assumptions and all. If the professor ever specifies anything further about "v...
Fri Feb 21, 2020 10:09 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Reaction quotient
Replies: 3
Views: 65

### Re: Reaction quotient

I might be wrong about this but I think have a larger reaction quotient actually makes the E smaller, considering the Nernst equation. We know that E is equal to the E standard minus (RT/nF)*(lnQ). So if the lnQ was to grow in number, the E standard would keep subtracting larger and larger values. I...
Fri Feb 21, 2020 10:05 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concepts
Replies: 3
Views: 38

### Re: Concepts

the equation itself is explaining to us how the nature of a battery is, essentially. if you want to know how much work (how much energy aka its potential power), then you have to consider three things - the max potential energy possible (E), faraday's constant (F, aka the charge of 1 mole of electro...
Wed Feb 12, 2020 9:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneous
Replies: 23
Views: 367

### Re: Spontaneous

professor lavelle said that every time we're asked whether or not something is spontaneous we know that delta g has to be negative. that's it really.
Wed Feb 12, 2020 9:23 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Four Cases
Replies: 2
Views: 66

### Re: Four Cases

in a discussion of mine for another class we also studied the Gibbs Free Energy equation and what conditions make it more negative and more positive. We made a cross diagram of when delta h was + or - crossed with when delta s was + or - to see which ones were more likely to create a negative delta ...
Wed Feb 12, 2020 9:18 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Question 4J.7
Replies: 5
Views: 91

### Re: Question 4J.7

Enthalpy of formation of O2 is zero because it's in its most stable form of oxygen How would you know that it's the most stable form? Would you have to memorize it? Yeah, it's kind of a memorization thing. It's a gas, bonded between two identical atoms. And O2 as a gas is literally one of the simpl...
Wed Feb 12, 2020 9:14 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Textbook question 4J.7
Replies: 2
Views: 39

### Re: Textbook question 4J.7

just remember that delta h / enthalpy is a state function. Therefore calculations will always be the Final State minus the Initial State.
Wed Feb 12, 2020 9:11 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Joules or KJ?
Replies: 14
Views: 206

### Re: Joules or KJ?

Also, it also kinda helps to look at the answer you have and see which one (J/KJ) just makes more sense. Like, for some answers I would get something long like 1000000 J and that would be appropriate for the question. But like it just made more sense to shorten it to 1000 kj. But yeah, they're both ...
Fri Feb 07, 2020 1:31 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4A.11
Replies: 5
Views: 50

### Re: 4A.11

for calorimeters we're usually just worried about the heat capacity, q / delta t, so you don't have to worry about any other formulas like that. Calorimeters are nice because usually we have a ton of info to plug in with other systems and whatnot, but calorimeters are literally just simple specific ...
Fri Feb 07, 2020 1:27 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Expansion work/ Compression
Replies: 7
Views: 73

### Re: Expansion work/ Compression

Expansion and compression both denote work, but they exert that work in opposite directions. It helps me keep in mind the visual of a balloon expanding and deflating. Both require a change of energy or movement, but one obviously has a positive growth and the other a negative. You just have to remem...
Fri Feb 07, 2020 1:22 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Topics on the Midterm
Replies: 22
Views: 273

### Re: Topics on the Midterm

Friday's (today's) lecture IS included on the midterm, but it cuts off there, at Gibbs free energy. He explained in class that the Midterm will include everything up to today. In the outline of thermodynamics, there are two sheets of learning objectives; the midterm will have everything on the first...
Fri Feb 07, 2020 1:17 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Textbook question 4A.13
Replies: 5
Views: 59

### Re: Textbook question 4A.13

try to think of the - and + signs as how we express the energy change from one perspective. Like it was said before, the reaction is exothermic so it'll leave to it's surroundings, lessening the amount of heat available. From this perspective, heat is being taken away and moved somewhere else.
Fri Feb 07, 2020 1:13 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: ∆U and ∆H
Replies: 6
Views: 81

### Re: ∆U and ∆H

Delta H is the change in enthalpy and it can be used to calculate the delta u (aka the change in internal energy of the system). The equation is delta u = delta h - (temperature)(delta S or entropy).
Thu Jan 30, 2020 7:45 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy of sublimation?
Replies: 8
Views: 68

### Re: Enthalpy of sublimation?

Understanding that you calculate the enthalpy of sublimation with the enthalpy of fusion and of vaporization lets you understand that enthalpy is additive, a state property. So for our purposes, it is helpful in that sense. However, you'll probably see that we don't actually calculate the enthalpy o...
Thu Jan 30, 2020 7:34 pm
Forum: Phase Changes & Related Calculations
Topic: internal energy
Replies: 11
Views: 130

### Re: internal energy

Yup, internal energy is the delta u = q + w. just remember, if the reaction has a constant volume, then no expansion work is done, and delta u is equal to q subscript v.
Thu Jan 30, 2020 7:31 pm
Forum: Phase Changes & Related Calculations
Topic: Open vs Isolated System
Replies: 15
Views: 646

### Re: Open vs Isolated System

You can also think of it on a physical level - open: literally open to pass energy in between system and environment (open-flask experiment etc) closed: physically closed (with a lid or piston) but clear to see that elements such as heat can still pass in and out of reaction isolated: physically clo...
Thu Jan 30, 2020 7:27 pm
Forum: Phase Changes & Related Calculations
Topic: Units
Replies: 16
Views: 151

### Re: Units

It is a little confusing because we know Kelvin and Celsius to be different, but just remember that a majority of the calculations of temperature we do in this section are just asking for the CHANGE OF TEMPERATURE. Temp change the same way in Celsius and in Kelvin, by degrees. So it doesn't really h...
Thu Jan 30, 2020 7:22 pm
Forum: Phase Changes & Related Calculations
Topic: State Functions
Replies: 9
Views: 85

### Re: State Functions

My TA explained that when we think of state reactions, it's like asking someone what floor of a building they're on. You say, "What floor are you on?" and the person responds with "first floor" or "second floor" or something like that. In order to know the answer to you...
Thu Jan 23, 2020 7:12 pm
Forum: Phase Changes & Related Calculations
Replies: 6
Views: 55

### Re: Adding and subtracting properties

State properties, as said above, are not dependent on the "in between"; rather, we only focus on the initial and final measurements to make calculations and assumption. State properties include energy, pressure, volume, temperature, density and heat capacity Non state properties (or proper...
Thu Jan 23, 2020 7:09 pm
Forum: Phase Changes & Related Calculations
Topic: Steam vs liquid
Replies: 7
Views: 75

### Re: Steam vs liquid

It helps for me to understand why steam burns more than liquid water if I remember the graph he showed us in class. I think everyone else did a fantastic job already of explaining it, but when dealing with the phase changes, at least for me, it helped seeing the comparison of energy change water und...
Thu Jan 16, 2020 3:16 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Calculating Q
Replies: 16
Views: 182

### Re: Calculating Q

Q and K require aqueous solutions because their concentrations do change in the system depending on the rate of reaction
Thu Jan 16, 2020 3:13 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ICE Tables
Replies: 4
Views: 55

### Re: ICE Tables

You can usually tell if you have to make an ICE box because the question will specify an initial concentration of some sort ("x amount of moles was place into x amount of liters and allowed to reach equilibrium....") and then itll ask you for the equilibrium concentration. If you're ever a...
Thu Jan 16, 2020 3:11 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Quotient
Replies: 11
Views: 81

### Re: Reaction Quotient

Reaction quotient is just you looking at the same system, at a certain point in time, and comparing it to what it should be at equilibrium. If they match up, great! your system's chilling at equilibrium. If not, you can see the direction in which its progressing to equilibrium.
Thu Jan 16, 2020 3:08 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: How to make ICE box
Replies: 17
Views: 311

### Re: How to make ICE box

Pure liquids and solids are always left out. And to find the change column, its just -x/+x with the molar ratios considered
Thu Jan 16, 2020 3:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Replies: 6
Views: 65

Do yourself a favor and just practice the quadratic formula as much as you can. it just helps make it that much easier, solving everything
Thu Jan 16, 2020 2:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Units in ICE Table
Replies: 8
Views: 90

### Re: Units in ICE Table

Definitely use molarity which is moles/L. This is important because for the K and Q expressions work with concentrations and partial pressures, and for the most part the hypothetical experiments use varying volumes for their processes.
Thu Jan 16, 2020 2:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Approximation
Replies: 2
Views: 26

### Re: Approximation

I understand it as being less than 10^-3. It's a little tricky with 10^-4, but i think we're safe just saying that its less than 10^-3
Thu Jan 16, 2020 2:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Approximation
Replies: 8
Views: 65

### Re: Approximation

In class Dr Lavelle told us to use approximation for sure when K is less than 10^-3. But its a little tricky if we have 10^-4. Definitely use approximation with 10^-5, but its a little uncertain for 10^-4
Thu Jan 09, 2020 7:22 pm
Forum: Ideal Gases
Topic: Ideal Gases
Replies: 3
Views: 34

### Re: Ideal Gases

In terms of ideal gases, I just know we need it to make assumptions and judgments about what's happening to the gases during equilibrium. Someone else asked which gases were considered to be more "ideal" but I don't think we need to focus so much on the gases being ideal, rather we should ...
Thu Jan 09, 2020 7:16 pm
Forum: Ideal Gases
Topic: kc to kp
Replies: 2
Views: 36

### Re: kc to kp

I know that in the Video Modules and pre/post assessments, the questions make us convert the PV=nRT equation to show how we can get Concentrations from given pressure; and then in another question we convert the equation, but this time to get Pressure from given concentration. So I imagine that it i...
Thu Jan 09, 2020 7:08 pm
Forum: Ideal Gases
Topic: R constant in PV=nRT
Replies: 9
Views: 68

### Re: R constant in PV=nRT

You don't have to worry too much though about which one of the R constant values to use, because (like everyone else said) the units will match up to the one we're supposed to use. So if you end up plugging in one of the other R values to the equation, not all of the units will cancel out and your a...
Thu Jan 09, 2020 7:03 pm
Forum: Ideal Gases
Topic: 5G.11
Replies: 6
Views: 48

### Re: 5G.11

Just think of the Reaction Quotient like you proofing the equation. You do just calculate it the same way you find K (with the concentrations raised to the power of their coefficients), but you're trying to see if the value of Q, with the given concentrations, will give you K. Because if it gives yo...
Thu Jan 09, 2020 6:56 pm
Forum: Ideal Gases
Topic: What is the Importance of homogeneous vs heterogeneous equilibria [ENDORSED]
Replies: 12
Views: 168

### Re: What is the Importance of homogeneous vs heterogeneous equilibria[ENDORSED]

From what I understand, yeah, pretty much we learn homogeneous and heterogeneous to know what to include in the K or Q calculations. Because, really, we already recognize the phases of the molecules anyway, it just helps specifying where we include all the concentrations/partial pressures (as we do ...
Thu Mar 16, 2017 1:51 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8047
Views: 1413215

### Re: Post All Chemistry Jokes Here

Thu Mar 16, 2017 1:49 pm
Forum: Ideal Gases
Topic: R constant
Replies: 2
Views: 592

### Re: R constant

The R constant has a lot of different values and whatnot, but we mostly only use the first one, 8.314 J*K^(-1)*mol^(-1). I think we mostly use this one because we focus on primarily on energy change while the other R values pertain to volume in Liters. Joules and kilojoules are usually the units we ...
Thu Mar 16, 2017 1:41 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Transition States
Replies: 2
Views: 369

### Re: Transition States

Another way you can look at the differences between transition states and intermediates is in their role when it comes to writing out reaction mechanisms. Transitions states, when drawn out in mechanisms, usually show whatever compounds and elements in the reaction are reacting with one another and ...
Wed Mar 15, 2017 6:38 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: Calculating energy and Plotting Relative Energy differences
Replies: 1
Views: 352

### Calculating energy and Plotting Relative Energy differences

I missed class the day we went over Ethane and Butane and how to calculate energy as a function of a dihedral angle (page 106 of the course reader). Can someone explain to me where we got the values plotted on the two graphs? Were they values we calculated in class? Or were they simply given to us?
Wed Mar 15, 2017 6:19 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Two Step Reactions
Replies: 3
Views: 549

### Two Step Reactions

small question on finding out which step of a reaction is the rate determining step.

The rate determining step IS the slowest step. Does that mean that this step takes more energy to be carried out in comparison to the faster step?
Fri Mar 03, 2017 10:50 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8047
Views: 1413215

### Re: Post All Chemistry Jokes Here

Thu Feb 23, 2017 7:29 pm
Forum: *Enzyme Kinetics
Topic: Intermediates vs. Catalysts
Replies: 1
Views: 290

### Intermediates vs. Catalysts

From what I heard in lecture intermediates have to be produced in the reaction and then used up. Whereas, catalysts are needed for the reaction to get started and then are somehow regenerated later in the reaction? Can someone verify that this is accurate for me? I don't want to go onto the next top...
Thu Feb 16, 2017 9:03 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Homework Problems 17 and 19
Replies: 1
Views: 375

### Homework Problems 17 and 19

Maybe I'm not reading the Course Reader correctly but I'm having a hard time figuring out the orders for each reactants just by looking at the initial concentrations and Initial rates given to us in the tables??? How do we know which two experiments to use when comparing the concentrations and tryin...
Thu Feb 02, 2017 8:02 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8047
Views: 1413215

### Re: Post All Chemistry Jokes Here

Wed Jan 18, 2017 5:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Memorizing Enthalpies???
Replies: 2
Views: 389

### Memorizing Enthalpies???

I was just wondering if we would have to memorize some standard reaction enthalpies for quizzes or the final? Maybe not for some of the intense or complex formations, but for things like the formation of water molecules maybe???