Search found 21 matches

by Christina_F_3F
Wed Mar 15, 2017 11:42 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Ion-Selective Electrodes/finding pH
Replies: 2
Views: 382

Ion-Selective Electrodes/finding pH

Hi, I'm still a little bit confused on what ion selective electrodes are and how they relate to the Nernst equation. I'm also not sure how the pH of a solution may be determined from the Nernst equation. Basically, the top half of page 54 in the course reader, the section titled "Applications o...
by Christina_F_3F
Wed Mar 15, 2017 11:38 pm
Forum: Van't Hoff Equation
Topic: Van't Hoff Eq.
Replies: 5
Views: 398

Van't Hoff Eq.

For the Van't Hoff equation, we are given two different versions of the same equation: -ln(K2/K1) = -(deltaH*/RT2) + (deltaH*/R) where one assumes delta S naught is constant -ln (K2/K1) = -deltaH*/R(1/T2-1/T1) where one assumes delta H naught is constant My question is under what conditions are delt...
by Christina_F_3F
Wed Mar 08, 2017 2:03 pm
Forum: *Alkanes
Topic: Quiz 3 Drop -- do I show up? [ENDORSED]
Replies: 3
Views: 405

Quiz 3 Drop -- do I show up? [ENDORSED]

Hi. I plan on dropping quiz three as my lowest score and having it replaced with my highest quiz score. Do I need to show up to take my quiz, even if all I do is put my name on it? Or can I just not show up?
Thanks in advance!
by Christina_F_3F
Sun Mar 05, 2017 12:31 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7581
Views: 1012901

Re: Post All Chemistry Jokes Here

How can you tell the difference between a plumber and a chemist?

Ask them to pronounce "unionized"
by Christina_F_3F
Tue Feb 21, 2017 1:20 am
Forum: Administrative Questions and Class Announcements
Topic: 14C
Replies: 4
Views: 439

Re: 14C

I know someone who actually wasn't even enrolled in the class fall quarter, but showed up on the first day, and Professor Hardinger let them in. Of course it can't be said he'll do it again, but maybe just to reassure you you might be able to get a spot :-)
by Christina_F_3F
Tue Feb 21, 2017 1:17 am
Forum: Second Order Reactions
Topic: 15.35
Replies: 1
Views: 284

15.35

"The half-life for the second order reaction of a substance A is 50.5 s when [A]naught=0.84 M. Calculate the time needed for concentration of A to decrease to a) one sixteenth, b) one-fourth, c) one-fifth it's original value." For this question, after looking at the solutions manual, I cou...
by Christina_F_3F
Mon Feb 20, 2017 9:57 pm
Forum: First Order Reactions
Topic: Rate 1st Order Rxn
Replies: 3
Views: 459

Re: Rate 1st Order Rxn

Whoops, I did mean the integrated rate law. On page 64 of the course reader, ln [A] = -kt + ln [A]naught is then exponentiated and reads "RATE 1ST ORDER RXN = k[A] = k [A]naught e^-kt. So I was just curious if the k value that is next to [A] and the one that is being expoentiated are the same/r...
by Christina_F_3F
Mon Feb 20, 2017 8:00 pm
Forum: First Order Reactions
Topic: Rate 1st Order Rxn
Replies: 3
Views: 459

Rate 1st Order Rxn

The equation for the rate of a first order reaction is k [A] = k [A](naught)e^-kt

I was just wondering if there is a difference between the two k values on the right side of the equation?
Does the k being multiplied by [A] have a different meaning/value than the one in e^-kt?
by Christina_F_3F
Tue Feb 14, 2017 4:36 pm
Forum: Balancing Redox Reactions
Topic: Redox
Replies: 4
Views: 408

Re: Redox

Are you asking if the method for balancing redox half reactions is the same in acidic and basic solution?
If so, I'd be happy to reply again and give an explanation :-)
by Christina_F_3F
Tue Feb 14, 2017 3:11 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: function of a salt bridge
Replies: 2
Views: 425

Re: function of a salt bridge

My understanding of a salt bridge is that it is meant to keep both solutions neutral. There is electron flow between the cathode and the anode; electrons flow from the anode, the site of oxidation, to the cathode, the site of reduction. If there was no salt bridge, as electrons were removed from the...
by Christina_F_3F
Tue Feb 14, 2017 2:51 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: w=-delta(nRT)
Replies: 2
Views: 537

Re: w=-delta(nRT)

In midterm 2013 question 3A, the temperature is constant and the delta sign applies to the number of moles. I believe that when you are asked to calculate the work done by a certain system and use this equation, it will be at a specific temperature (i.e. boiling/melting point) and the change is in r...
by Christina_F_3F
Tue Feb 14, 2017 2:47 am
Forum: Balancing Redox Reactions
Topic: 2016 Midterm Q3
Replies: 1
Views: 193

2016 Midterm Q3

"1.00 mile of ideal gas is compressed reversibly and isothermally at constant temperature T=500K and w= 1000 J. Find the following quantities for this process." For question 3A, you are asked to find delta U. I'm just really confused why delta U is equal to zero? When I did this problem, I...
by Christina_F_3F
Sun Feb 12, 2017 4:26 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Course reader example pg. 7 electrochemistry
Replies: 4
Views: 396

Re: Course reader example pg. 7 electrochemistry

After doing some research online, I believe that it is actually correct on the course reader and not on the laminated constant sheet. The number on the laminated sheet should be 96,485.3 C/mol, not 96,4853 C/mol (this number doesn't make any sense because the apostrophe is not in the right place). T...
by Christina_F_3F
Sun Feb 05, 2017 3:26 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration cells
Replies: 3
Views: 322

Re: Concentration cells

n=1 because if you look at the half reactions there is 1 mol of electrons involved in the reaction. Ag(s) --> Ag+(0.1M) + e- e- + Ag+(1.0M) --> Ag (s) Because there is the same number of mols of electrons in both reactions, you do not need to multiply by any coefficients. Therefore, just one mol of ...
by Christina_F_3F
Sun Jan 29, 2017 1:46 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy dependence on enthalpy and entropy
Replies: 2
Views: 206

Gibbs free energy dependence on enthalpy and entropy

In class, we discussed how a reaction with a negative enthalpy change (aka an exothermic reaction) and a positive entropy change (increase in "randomness" or "disorder") will cause the Gibbs free energy to be negative and thus the reaction will be spontaneous at all temperatures....
by Christina_F_3F
Sun Jan 22, 2017 9:49 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.31
Replies: 2
Views: 287

8.31

Q 8.31: "Calculate the heat released by 5.025 g of Kr (g) at 0.400 atm as it cools from 97.6 degrees C to 25 degrees C at a constant pressure" The solution for this question says "The molar heat capacity of a monatomic ideal gas at constant is C=5/2R." Where was this number deriv...
by Christina_F_3F
Sun Jan 22, 2017 5:27 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: HW 8.41
Replies: 3
Views: 281

Re: HW 8.41

For this problem, I was curious why the grams of water used to calculate the heat of the water is 400g, rather than 450g? I understand that the reaction started with 400g of water, but by the time it is over, won't the 50g of ice have melted, resulting in 0g of ice and 450g of water in total?
by Christina_F_3F
Sun Jan 22, 2017 3:38 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Unit Question [ENDORSED]
Replies: 4
Views: 417

Re: Unit Question [ENDORSED]

I had the same question, Teddy. I think that depending on the units of pressure and volume given, you may have to use a conversion to get to joules/kilojoules. If the pressure is given in kilograms per meter and the volume in meters cubed per second squared, then you don't really need to do any conv...
by Christina_F_3F
Sun Jan 22, 2017 2:17 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy of Formation lecture example [ENDORSED]
Replies: 1
Views: 205

Standard Enthalpy of Formation lecture example [ENDORSED]

In lecture/the course reader (pg. 17), there is an example provided for standard reaction enthalpy that involves solid graphite, hydrogen gas, oxygen gas, and liquid ethanol. In the example, the delta H naught rxn is provided as -555.38 kJ. I was just curious how this number was found, or if we need...
by Christina_F_3F
Sun Jan 15, 2017 1:18 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculating Standard Enthalpy of Reaction
Replies: 1
Views: 296

Calculating Standard Enthalpy of Reaction

In class, we discussed how if there is a solid in a chemical reaction for which you are trying to find the standard enthalpy of reaction. you must consider the fact that there is both a phase change as well as an enthalpy change for that solid. My question is, why does this apply to just solids? Mig...

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