Search found 30 matches

by Yutian Zhao -1J
Mon Mar 12, 2018 2:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: concentration cell
Replies: 2
Views: 120

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.
by Yutian Zhao -1J
Mon Mar 12, 2018 2:06 pm
Forum: General Rate Laws
Topic: Deriving rate laws?
Replies: 3
Views: 153

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.
by Yutian Zhao -1J
Mon Mar 12, 2018 1:59 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediate
Replies: 6
Views: 229

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.
by Yutian Zhao -1J
Mon Mar 12, 2018 1:51 pm
Forum: *Aldehydes
Topic: Carbonyl -> Aldehydes and Ketones [ENDORSED]
Replies: 5
Views: 872

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.
by Yutian Zhao -1J
Mon Mar 05, 2018 2:52 pm
Forum: First Order Reactions
Topic: 15.23 c
Replies: 2
Views: 154

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...
by Yutian Zhao -1J
Mon Mar 05, 2018 2:36 pm
Forum: General Rate Laws
Topic: 3rd order, 4th order, etc.
Replies: 5
Views: 308

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.
by Yutian Zhao -1J
Mon Mar 05, 2018 2:33 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units of k
Replies: 8
Views: 328

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),...
by Yutian Zhao -1J
Mon Mar 05, 2018 2:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Which Step is Slower?
Replies: 8
Views: 231

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.
by Yutian Zhao -1J
Sun Feb 18, 2018 9:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anodes vs. Cathodes
Replies: 3
Views: 123

Re: Anodes vs. Cathodes

But how are we supposed to know whether the rxn is spontaneous or not?
by Yutian Zhao -1J
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: 151

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-...
by Yutian Zhao -1J
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: 144

Re: cell diagram (hw14.11)

PranithaPrasad wrote:that

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?
by Yutian Zhao -1J
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: 144

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 ...
by Yutian Zhao -1J
Sat Feb 10, 2018 5:02 pm
Forum: Balancing Redox Reactions
Topic: 14.5
Replies: 4
Views: 185

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.
by Yutian Zhao -1J
Sat Feb 10, 2018 3:10 pm
Forum: Balancing Redox Reactions
Topic: Salt Bridges
Replies: 14
Views: 378

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 ...
by Yutian Zhao -1J
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: 169

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...
by Yutian Zhao -1J
Mon Feb 05, 2018 3:23 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: hw9.47b
Replies: 1
Views: 89

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!
by Yutian Zhao -1J
Mon Feb 05, 2018 1:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Max Potential
Replies: 2
Views: 111

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...
by Yutian Zhao -1J
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: 102

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.
by Yutian Zhao -1J
Wed Jan 31, 2018 10:15 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: q(REV)
Replies: 3
Views: 137

Re: q(REV)

same question!
by Yutian Zhao -1J
Wed Jan 31, 2018 10:12 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: homework 9.19
Replies: 4
Views: 153

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...
by Yutian Zhao -1J
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: 116

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!
by Yutian Zhao -1J
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: 172

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?
by Yutian Zhao -1J
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: 114

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.
by Yutian Zhao -1J
Sat Jan 20, 2018 1:44 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Enthalpy Equation
Replies: 3
Views: 197

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...
by Yutian Zhao -1J
Sat Jan 20, 2018 1:12 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Internal Energy
Replies: 4
Views: 183

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.
by Yutian Zhao -1J
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: 83

hw 8.49

How should we solve this problem? I am super confused. Why does it have to do with PV=nRT?
by Yutian Zhao -1J
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: 512

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.
by Yutian Zhao -1J
Tue Jan 09, 2018 9:26 pm
Forum: Administrative Questions and Class Announcements
Topic: reading textbook
Replies: 5
Views: 286

reading textbook

Since Professor Lavelle would cover topics in the order listed in outline, then if we read the textbook by following the lecture materials, there would be lots of things that we haven't learnt and are related to the previous parts. Should we pass them or read from the beginning of Chapter 8 by ourse...
by Yutian Zhao -1J
Tue Jan 09, 2018 9:04 pm
Forum: Phase Changes & Related Calculations
Topic: Endothermic Reaction
Replies: 10
Views: 1014

Re: Endothermic Reaction

The ice would be the system, and the hand would be its surroundings. When the ice absorbs energy(heat) and reaches to its melting point, it melts, therefore the heat absorbed comes from surroundings, and the phase change is endothermic, and the hand that loses heat would cool down.

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