Search found 38 matches

by Xin He 2L
Fri Mar 16, 2018 6:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Winter Final 2012 #3
Replies: 1
Views: 73

Re: Winter Final 2012 #3

The resulting charge of the anode and the cathode needs to be positive if it's a galvanic cell, so find the equations for the two metals and then pick which is the anode and which is the cathode based on that information.
by Xin He 2L
Thu Mar 15, 2018 11:44 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2 question 6
Replies: 2
Views: 92

Re: Test #2 question 6

To find the oxidizing and reducing agents, you need to find which is the cathode and which is the anode first, you can't just assume. You should've used the half reaction sheet at the end to find the potential and then seen which one was which. The cathode is the oxidizing agent and the anode is the...
by Xin He 2L
Thu Mar 15, 2018 11:32 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2 question 4
Replies: 4
Views: 98

Re: Test #2 question 4

You don't flip the signs of the cell potential when you flip the equation.
by Xin He 2L
Thu Mar 15, 2018 11:28 pm
Forum: *Alkanes
Topic: How much Org Chem do we need to know for the final
Replies: 1
Views: 198

How much Org Chem do we need to know for the final

I was looking over the old finals, and theres a lot more organic chem on those than what we're doing. So I'm wondering if anyone knows how much organic chem we need to know for our final.
by Xin He 2L
Thu Mar 15, 2018 11:26 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: What's up with Torrs
Replies: 2
Views: 187

Re: What's up with Torrs

Don't know fam, but the final is in two days, I feel we have other stuff to worry about lol.
by Xin He 2L
Thu Mar 15, 2018 11:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Could someone explain 14.55 please?
Replies: 2
Views: 123

Re: Could someone explain 14.55 please?

According to the learning objectives, electrolysis, which is problem 14.55, isn't going to be on the final, so I don't think you need to do it.
by Xin He 2L
Thu Mar 15, 2018 11:11 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: Winter 2011 Final #1C
Replies: 1
Views: 165

Re: Winter 2011 Final #1C

NO can be arranged into NO and ON, while BF3 has no such other arrangements, so since NO has two different arrangements, it's residual entropy is higher according to the equation S=kb*lnW.
by Xin He 2L
Wed Mar 14, 2018 9:08 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Do we need to know pH stuff for the test
Replies: 1
Views: 78

Do we need to know pH stuff for the test

So for our final, to what extent do we need to know pH things? I was going over some old tests, and there were several questions about buffers and pH.
by Xin He 2L
Thu Mar 08, 2018 3:01 am
Forum: Second Order Reactions
Topic: 15.35
Replies: 6
Views: 320

Re: 15.35

You use the half-life equation for second order reactions. You then just plug the values into the equation 1/A=kt+1/A0, which can be rearranged into (1/A+1/A0)/k=t to find out the time needed.
by Xin He 2L
Thu Mar 08, 2018 2:58 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.23 part C
Replies: 3
Views: 109

Re: 15.23 part C

We would subtract B from A because B is created from A, so when B increases, A decreases. After the subtraction, you'll find the new value for A which you then plug into the equation and solve for the time elapsed.
by Xin He 2L
Thu Mar 08, 2018 2:56 am
Forum: First Order Reactions
Topic: Question 15.23
Replies: 3
Views: 119

Re: Question 15.23

You use stoichiometry to figure out how much of A is used up to form B. From the equation you gave, A should be used up half as fast as B is created, so you would multiply B by 2 and subtract it from A. Then you use the equation ln([A]/[A0]=-kt to find how much time has elapsed.
by Xin He 2L
Sun Mar 04, 2018 5:40 pm
Forum: First Order Reactions
Topic: Half-life of first order reactions [ENDORSED]
Replies: 4
Views: 159

Re: Half-life of first order reactions [ENDORSED]

The half life of any substance would be the time required for the substance to decay to half it's original value.
by Xin He 2L
Fri Mar 02, 2018 1:25 am
Forum: General Rate Laws
Topic: Test 3
Replies: 3
Views: 127

Re: Test 3

To be safe, I think you should finish up the section of homework for integrated rate laws, so up to about number 43.
by Xin He 2L
Fri Mar 02, 2018 1:23 am
Forum: General Rate Laws
Topic: Determining Order [ENDORSED]
Replies: 8
Views: 163

Re: Determining Order [ENDORSED]

Page 619 includes a lot of helpful information on the orders of the reactions.
by Xin He 2L
Sat Feb 24, 2018 3:15 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15c [ENDORSED]
Replies: 3
Views: 92

Re: 14.15c [ENDORSED]

I'm not completely sure, but I think the K might've come from the solution that the metals are in?
by Xin He 2L
Sat Feb 24, 2018 3:13 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate constant (k)
Replies: 4
Views: 111

Re: Rate constant (k)

The K of a reaction is always the same, but Q is different depending on how close the reaction is to completion.
by Xin He 2L
Sat Feb 24, 2018 3:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 (b)
Replies: 3
Views: 77

Re: 14.13 (b)

I2 isn't a conductor, so the platinum is still needed.
by Xin He 2L
Sun Feb 18, 2018 1:23 am
Forum: Balancing Redox Reactions
Topic: 14.1 Part D
Replies: 4
Views: 95

Re: 14.1 Part D

To balance an equation, you split them up into oxidation and reduction half equations. Then you balance those equations out with electrons and then make sure to cancel the electrons when you add the equations back together.
by Xin He 2L
Sun Feb 18, 2018 1:22 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: reversible system
Replies: 9
Views: 309

Re: reversible system

Whenever there's a reversible system, delta S total would be zero, also remember that internal energy is zero when the system is reversible
by Xin He 2L
Sun Feb 18, 2018 1:20 am
Forum: Van't Hoff Equation
Topic: Van't Hoff equation
Replies: 4
Views: 328

Re: Van't Hoff equation

You can derive them from those two equations, but you have to remember to subtract the values at the first temp, equilibrium constant from the second equilibrium constant. It's probably easier to remember it than derive it.
by Xin He 2L
Sun Feb 11, 2018 11:31 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test #7
Replies: 7
Views: 231

Re: Test #7

The final answer I got was 15.9 degrees Celsius, and he should be posting the answers to the review guide soon
by Xin He 2L
Sun Feb 11, 2018 1:50 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: closed vs isolated
Replies: 11
Views: 445

Re: closed vs isolated

You don't want to assume anything, but if the question says that the reaction happens in a bomb calorimeter, you can assume it's constant volume.
by Xin He 2L
Sun Feb 11, 2018 1:47 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test #7
Replies: 7
Views: 231

Re: Test #7

I haven't done the question yet, but you put the enthalpy of fusion onto the ice side of the equation since it's the energy required to melt the ice. The equation should look like this, Calculations for Ice Calculations for water [Heat of Fusion of Ice+ n*C*delta T]= [n*C*deltaT]
by Xin He 2L
Sun Feb 11, 2018 1:42 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: conceptual entropy questions
Replies: 5
Views: 139

Re: conceptual entropy questions

Bromine is a larger molecule, so it will have more electrons, meaning there are more orientations for the micro states. This means there's higher entropy.
by Xin He 2L
Sun Feb 04, 2018 3:06 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneous
Replies: 14
Views: 320

Re: Spontaneous

Reactions are spontaneous whenever the delta G of the reaction is a negative value.
by Xin He 2L
Sun Feb 04, 2018 3:04 am
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: Standard molar entropy
Replies: 1
Views: 71

Re: Standard molar entropy

The first graph is just a graph for the heat capacities at any given temperature. The second graph gives the heat capacity over the temperature value against the temperature. The area up to a given temperature on the second graph is the entropy values given on the third graph.
by Xin He 2L
Sun Feb 04, 2018 2:57 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reversible vs. Irreversible
Replies: 1
Views: 65

Re: Reversible vs. Irreversible

We can't use that equation for irreversible reactions, we have to use equation three which is given in the book.
by Xin He 2L
Sat Jan 27, 2018 11:22 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Question 8.31
Replies: 7
Views: 253

Re: Question 8.31

Since we're adding 273 to both the initial and final value of temperature, it doesn't matter if we use celsius or kelvin.
by Xin He 2L
Sat Jan 27, 2018 11:18 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: The second law ?
Replies: 3
Views: 98

Re: The second law ?

The second law is pretty much an extension of the first law. While energy cannot be created or destroyed, as stated by the first law, the second law states that the more energy is transformed or transferred, more of it will become wasted and unusable. It also talks about how energy in an isolated sy...
by Xin He 2L
Sat Jan 27, 2018 11:14 pm
Forum: Calculating Work of Expansion
Topic: The integral equation
Replies: 8
Views: 192

Re: The integral equation

You don't need to use calculus, you just need the use the equation given in the book for isothermal reversible expansion. I believe the equation is w=nRT log(Vfinal/Vinitial )
by Xin He 2L
Sat Jan 20, 2018 11:30 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Heat v Thermal Energy
Replies: 3
Views: 106

Re: Heat v Thermal Energy

All heat is thermal energy but not all thermal energy is heat. Heat only refers to the thermal energy that is transferred between objects.
by Xin He 2L
Sat Jan 20, 2018 11:27 pm
Forum: Phase Changes & Related Calculations
Topic: Test 1 topics
Replies: 2
Views: 155

Re: Test 1 topics

There isn't any specific homework questions, but we know that only the chapter 8 materials covered in the first two weeks are covered in the tests. Dr. Lavelle also posted on his website that there will be no isothermal, reversible reactions and that there will only be concept questions involving wo...
by Xin He 2L
Wed Jan 17, 2018 8:48 pm
Forum: Phase Changes & Related Calculations
Topic: Compression (Question 8.3)
Replies: 4
Views: 110

Re: Compression (Question 8.3)

Whenever work is being done on the system, in this case the air in the pump, it is positive. If, for example, the air becomes decompressed and does work on its surroundings, the work would be negative.
by Xin He 2L
Wed Jan 17, 2018 8:44 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Self-Test 8.5B
Replies: 3
Views: 126

Re: Self-Test 8.5B

The system did 450 J(-450) of work. We can find this by doing -150(change in internal energy)=x(work done on system)+300(heat). Regarding the question about how we know 300 is negative or positive, the 300 is negative if the system gives off heat(exothermic) and is positive if the system takes in he...
by Xin He 2L
Wed Jan 10, 2018 7:44 pm
Forum: Phase Changes & Related Calculations
Topic: Reaction in a Flask
Replies: 5
Views: 207

Re: Reaction in a Flask

An endothermic reaction requires heat(energy) to occur, so the reaction draws heat from its surrounding, making it cool.
by Xin He 2L
Mon Jan 08, 2018 7:15 pm
Forum: Administrative Questions and Class Announcements
Topic: Extra Chapter Covered in Dr. Lavelle's Class
Replies: 4
Views: 174

Extra Chapter Covered in Dr. Lavelle's Class

Hi I was a student in Dr. Casey's class last quarter, and I heard from a friend that Dr. Lavelle covered an extra chapter (we only covered up to chapter 13). I was wondering if we were going to quickly go over that chapter in class or if we need it read it ourselves.
by Xin He 2L
Mon Jan 08, 2018 5:48 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Strength of Interactions in a Solid
Replies: 3
Views: 134

Re: Strength of Interactions in a Solid

I think the answer has to do with the extra energy that is put into the system when a solid becomes a liquid. Although the bonds within the system stay just as strong, the extra energy allows for bonds between particles to break and move freely.

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