## Search found 30 matches

Mon Mar 12, 2018 2:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: concentration cell
Replies: 2
Views: 168

### concentration cell

in the concentration cell, why do we always make the side with lower concentration the product? I am a little bit confused. How do we derive that? Thanks.
Mon Mar 12, 2018 2:06 pm
Forum: General Rate Laws
Topic: Deriving rate laws?
Replies: 3
Views: 231

### Re: Deriving rate laws?

Yes, I think we should. We can derive the rate law by setting unique reaction rate of R on the left side while k*[R]^n on the right side. Hope it helps.
Mon Mar 12, 2018 1:59 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediate
Replies: 6
Views: 354

### Re: Intermediate

An intermediate is a product in the former step and is consumed as a reactant in later step(s). And it won't show up in the overall reaction equation. Hope it helps.
Mon Mar 12, 2018 1:51 pm
Forum: *Aldehydes
Topic: Carbonyl -> Aldehydes and Ketones [ENDORSED]
Replies: 5
Views: 1277

### Re: Carbonyl -> Aldehydes and Ketones[ENDORSED]

yes, i believe so. Aldehydes is the one with C bonded to one or two H, and Ketones is the one with C bonded to two C. I think they share the structure "C=O" where two atoms can be bonded to the left of the C to make a total of four bonds around C. Hope it helps.
Mon Mar 05, 2018 2:52 pm
Forum: First Order Reactions
Topic: 15.23 c
Replies: 2
Views: 212

### Re: 15.23 c

according to unique reaction rate law: -(1/a)*delta[A]/delta t= (1/b)*delta[B]/delta t, we can cancel delta t on both sides since they are the same, then we know that a=2, b=1, and we also know delta[B] =0.034mol/L since [B]initial is zero. Then we can derive delta[A] from the equation. since we als...
Mon Mar 05, 2018 2:36 pm
Forum: General Rate Laws
Topic: 3rd order, 4th order, etc.
Replies: 5
Views: 749

### Re: 3rd order, 4th order, etc.

I don't believe we need to know the half-life reaction of third or fourth order reaction. But we should be able to tell if it is a third or fourth order reaction based on the experimental data that are given. Hope it helps.
Mon Mar 05, 2018 2:33 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units of k
Replies: 8
Views: 671

### Re: Units of k

you can write the rate law (with units) first and then cancel units on both sides, then whatever units that are not cancelled should be the units of k. the units of k depends on the order of reaction. And pay more attention when writing the rate law if any concentration is to be squared (or higher),...
Mon Mar 05, 2018 2:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Which Step is Slower?
Replies: 8
Views: 365

### Re: Which Step is Slower?

As the slowest step always determines the overall reaction, find the elementary step whose rate law is the same as the overall reaction rate law, then that elementary step would be the slowest and be the rate determining step. Hope it helps.
Sun Feb 18, 2018 9:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anodes vs. Cathodes
Replies: 3
Views: 197

### Re: Anodes vs. Cathodes

But how are we supposed to know whether the rxn is spontaneous or not?
Sun Feb 18, 2018 9:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order in Cell Diagrams
Replies: 4
Views: 245

### Re: Order in Cell Diagrams

same question. I noticed that some cell diagrams put reactant of the half-rxn first and then product, while others put product of the half-rxn first and then reactant. Just want to know whether the order matters. And how are we supposed to know which is the reactant and which is product in the half-...
Sat Feb 10, 2018 10:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: cell diagram (hw14.11)
Replies: 3
Views: 186

### Re: cell diagram (hw14.11)

Thank you! But i am wondering about the "O2(g)|H+(aq)" part. I didn't find anything related to this part back in appendix. I think is should be O2|H2O?
Sat Feb 10, 2018 10:04 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: cell diagram (hw14.11)
Replies: 3
Views: 186

### cell diagram (hw14.11)

for the cell diagram (e.g., a|b||c|d ) if we know that the left side of the salt bridge represents oxidation and the right side represent reduction, does "a" have to be the reactant and "b" be the product of the oxidation half-reaction? Or is there any way to figure out which is ...
Sat Feb 10, 2018 5:02 pm
Forum: Balancing Redox Reactions
Topic: 14.5
Replies: 4
Views: 256

### Re: 14.5

But why can't we assume the reduction of O3 to BrO3-? I thought the oxidation number would then be decreased from 0 to -2. Can the BrO3- be a product of both oxidation and reduction? I am a little bit confused.
Sat Feb 10, 2018 3:10 pm
Forum: Balancing Redox Reactions
Topic: Salt Bridges
Replies: 14
Views: 512

### Re: Salt Bridges

salt bridges are designed to make a complete electrical circuit. Without the salt bridges, as anode keeps losing e-, it becomes less negative, and as cathode keeps accepting e-, it becomes less positive; after a period of time, anode and cathode go to equilibrium and become neutral where no e- will ...
Tue Feb 06, 2018 5:12 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: hw9.59 standard reaction entropy
Replies: 3
Views: 227

### Re: hw9.59 standard reaction entropy

thanks!!
Tue Feb 06, 2018 10:55 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: hw9.59 standard reaction entropy
Replies: 3
Views: 227

### hw9.59 standard reaction entropy

when we are asked to calculate the standard reaction S/H/G, does the stoichiometric coefficient of one product must be 1? Or we can calculate these standard reaction entropy/enthalpy/ free energy just by balancing the reaction regardless of the product's stoichiometric coefficient ? Since in 9.59, t...
Mon Feb 05, 2018 3:23 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: hw9.47b
Replies: 1
Views: 124

### hw9.47b

in the hw 9.47b, why does the delta S of surroundings equal 0? why does work=0? Can somebody help me with this? thanks!
Mon Feb 05, 2018 1:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Max Potential
Replies: 2
Views: 180

### Re: Max Potential

For the reversible process, I personally believe that professor Lavelle just wanted to emphasize that the transfer of e- for each step is very small, which makes the potential difference change slowly. And it doesn't mean that the flow of e- is reversible I guess. But I am not sure if my answer is c...
Fri Feb 02, 2018 4:36 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Change in vol and temp
Replies: 2
Views: 173

### Re: Change in vol and temp

You can calculate the entropy change resulting from temp change and volume change together separately and then add them up. Use delta S=nRln(v2/v1) to calculate the detla S for volume change and then use detlaS=nCln(T2/T1) to get the entropy change for temp change.
Wed Jan 31, 2018 10:15 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: q(REV)
Replies: 3
Views: 177

### Re: q(REV)

same question!
Wed Jan 31, 2018 10:12 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: homework 9.19
Replies: 4
Views: 227

### homework 9.19

"Calculate the standard entropy of vaporization of water at 85 C, given that its standard entropy of vaporization at 100. C is 109.0 J K 1 mol 1 and the molar heat capacities at constant pressure of liquid water and water vapor are75.3 J K 1 mol 1 and 33.6 J K 1 mol 1, respectively, in this ran...
Mon Jan 22, 2018 2:58 pm
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 for BFCl2 in the lecture example
Replies: 1
Views: 180

### W for BFCl2 in the lecture example

in the lecture, for the last example to calculate the W of BFCl2, if there are four moles of this molecules, does that mean w= 3^4NA? and therefore S=4Rln3? I am a little bit confused. Thanks!
Mon Jan 22, 2018 2:48 pm
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: N: number of particle [ENDORSED]
Replies: 4
Views: 272

### Re: N: number of particle[ENDORSED]

So for the last example of BFCl2, if there are 4 moles of this molecules, then does w=3^4NA? or just w=3^4?
Mon Jan 22, 2018 1:51 pm
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(degeneracy) in isolated system [ENDORSED]
Replies: 1
Views: 171

### W(degeneracy) in isolated system[ENDORSED]

In today's lecture, professor Lavelle mentioned that for an isolated system (constant energy) at equilibrium, W is maximum. Does anyone know why it is maximum? Thanks.
Sat Jan 20, 2018 1:44 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Enthalpy Equation
Replies: 3
Views: 277

### Re: Enthalpy Equation

according to U=q+w, under constant P(delta H=qp),when there is an expansion, work is done by the system, therefore w=-P*delta V (P is constant so only V changes, and since work is done by the system, there is a negative sign in the front); and: U=q+w =delta H+w =delta H+(-P*delta V) =delta H- P*delt...
Sat Jan 20, 2018 1:12 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Internal Energy
Replies: 4
Views: 272

### Re: Internal Energy

According to U=q+w, under constant pressure (deltaH=q),U=delta H+w. With that being said, the internal energy equals sum of enthalpy change and the work done by/on the system.
Sat Jan 13, 2018 9:33 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: hw 8.49
Replies: 1
Views: 90

### hw 8.49

How should we solve this problem? I am super confused. Why does it have to do with PV=nRT?
Fri Jan 12, 2018 3:00 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: What type of system is a Bomb Calorimeter?
Replies: 4
Views: 1029

### Re: What type of system is a Bomb Calorimeter?

A bomb calorimeter is the one with constant V, while the simple calorimeter is just the one with constant P and not sealed.
Tue Jan 09, 2018 9:26 pm
Forum: Administrative Questions and Class Announcements
Replies: 5
Views: 379