Search found 61 matches

by David Zhou 1L
Thu Mar 15, 2018 9:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.17 [ENDORSED]
Replies: 3
Views: 253

Re: 14.17 [ENDORSED]

For this though, couldn't the Fe be oxidized into Fe2+? Why does it have to be Fe2+ oxidized into Fe3+?
by David Zhou 1L
Thu Mar 15, 2018 9:14 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Rate Constant Units
Replies: 9
Views: 610

Re: Rate Constant Units

Remember that multiplying my L/mol is the same thing as dividing by M, or multiplying by M-1.
by David Zhou 1L
Thu Mar 15, 2018 9:12 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: mechanisms
Replies: 3
Views: 311

Re: mechanisms

Rate laws are determined experimentally generally rather than by analyzing the chemical equation, so it's often a difficult task to figure out the specific mechanism for a specific rate law.
by David Zhou 1L
Fri Mar 09, 2018 6:17 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Negative k? [ENDORSED]
Replies: 4
Views: 394

Re: Negative k? [ENDORSED]

Since there can't be a negative amount of products or reactants that exists in a chemical equilibrium, the rate constant must be positive.
by David Zhou 1L
Fri Mar 09, 2018 6:13 pm
Forum: Experimental Details
Topic: Homework Problem 15.3 Part C
Replies: 5
Views: 576

Re: Homework Problem 15.3 Part C

It's the rate that's unique to that reaction, separate from the coefficients you multiply to get to the reaction rates with regards to species in the reaction.
by David Zhou 1L
Fri Mar 09, 2018 6:01 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Electroplating
Replies: 2
Views: 245

Re: Electroplating

Looking over the hw problems and chapter outlines will always give a good overview of what we need to know.
by David Zhou 1L
Fri Mar 09, 2018 5:56 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Ion-selective electrode
Replies: 2
Views: 238

Re: Ion-selective electrode

Any idea how those work though? Does it have something to do with the reduction potentials of different ions?
by David Zhou 1L
Fri Mar 09, 2018 5:54 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: The Chromium example
Replies: 2
Views: 343

Re: The Chromium example

This common type of process is called electroplating, in case you wanted to read more about it!
by David Zhou 1L
Fri Mar 09, 2018 5:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacities of Gases
Replies: 3
Views: 344

Re: Heat Capacities of Gases

Know that Cv = 3/2 *R, because the v and the 3 make a heart! <3
by David Zhou 1L
Fri Mar 09, 2018 5:42 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Equations
Replies: 4
Views: 409

Re: Equations

It's always useful to be very familiar with all the equations you might use, so that you don't have to spend time flipping to the first page and searching for them!
by David Zhou 1L
Fri Mar 09, 2018 5:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.77
Replies: 2
Views: 177

Re: 8.77

It's more stable because the electrons are delocalized.
by David Zhou 1L
Fri Mar 09, 2018 5:35 pm
Forum: Calculating Work of Expansion
Topic: external pressure
Replies: 2
Views: 164

Re: external pressure

Problems will supply you with the constant external pressure if that's the case. Often times that value is 1 atm.
by David Zhou 1L
Fri Mar 09, 2018 5:31 pm
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: Biological systems
Replies: 2
Views: 571

Re: Biological systems

Many of the reaction pathways that are taught in biology are long chains of these connected reactions, like in glycolysis, the Krebs/Citric acid cycle, and the Calvin cycle. These metabolic pathways are crucial to the survival of an enormous number of organisms, and are happening all the time.
by David Zhou 1L
Fri Mar 09, 2018 5:26 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: infinitesimal change
Replies: 3
Views: 542

Re: infinitesimal change

Infinitesimal doesn't necessarily have to do with time, it's just denoting a mathematical value smaller than anything measurable. A change that's infinitesimal can refer to time, pressure, volume, temperature, or anything you want to assign it to since it's unitless.
by David Zhou 1L
Fri Mar 09, 2018 5:05 pm
Forum: Van't Hoff Equation
Topic: Derivation
Replies: 5
Views: 390

Re: Derivation

It doesn't take too long to learn it, it's just the combination of a couple equations for delta G that are given to you.
by David Zhou 1L
Fri Mar 09, 2018 4:55 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Review Session Question
Replies: 2
Views: 173

Re: Review Session Question

Isothermal, reversible processes would be an example of this.
by David Zhou 1L
Fri Mar 09, 2018 4:50 pm
Forum: General Rate Laws
Topic: 15.23 b
Replies: 3
Views: 210

Re: 15.23 b

It's just algebraic manipulation; flipping the numerator and denominator will give you the negative log value.
by David Zhou 1L
Fri Mar 09, 2018 4:47 pm
Forum: General Rate Laws
Topic: 15.13
Replies: 4
Views: 262

Re: 15.13

Gases spread to fill the entire container that they're housed in, unlike liquids and solids. So if the volume of the vessel they're in is .75 L, that's their volume.
by David Zhou 1L
Fri Mar 09, 2018 4:44 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Stopped Flow Technique
Replies: 2
Views: 283

Re: Stopped Flow Technique

Attoseconds are much faster than what's controllable by a stopped syringe - they're 10^-18 seconds. That's a unit of time that's completely unheard of in science, except at quantum level.
by David Zhou 1L
Fri Mar 09, 2018 4:41 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: activation energy [ENDORSED]
Replies: 3
Views: 365

Re: activation energy [ENDORSED]

Activation energy has to do with kinetics. Thermodynamics is concerned with the difference in internal energy before and after the reaction, which is a different concept, and mathematical value from the activation energy for the same reaction.
by David Zhou 1L
Fri Mar 09, 2018 1:21 am
Forum: Zero Order Reactions
Topic: Definition of Reaction Rate
Replies: 4
Views: 351

Definition of Reaction Rate

Why is reaction rate given the units M/s? Why not something like moles/s or g/s? Or even %mass/s? Is this just an arbitrary decision or is there some deeper meaning baked into this definition?
by David Zhou 1L
Thu Mar 08, 2018 7:09 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7951
Views: 1213689

Re: Post All Chemistry Jokes Here

What do you do when you find a questionable amount of sulfur, tungsten, and silver in your backpack?

Keep calm and SWAg on!!!!!!!11!!!11!!!!!

-- Andrew Nguyen
by David Zhou 1L
Thu Mar 08, 2018 7:07 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7951
Views: 1213689

Re: Post All Chemistry Jokes Here

If you're not a part of the solution, you're a part of the precipitate.
by David Zhou 1L
Fri Feb 16, 2018 1:31 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Using Kelvin [ENDORSED]
Replies: 3
Views: 202

Re: Using Kelvin [ENDORSED]

It's generally better to use more sig figs in your constants so your final answer is more accurate, but if the number of sig figs are low (<3) for any other value that you plug into the problem, then you'll be fine as well since your final answer won't have a lot of sig figs anyways.
by David Zhou 1L
Mon Feb 12, 2018 11:30 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Standard molar entropy of cyclopentane vs 1-pentene
Replies: 2
Views: 201

Re: Standard molar entropy of cyclopentane vs 1-pentene

Bonds in the cyclopentane can't rotate freely in any way since that would break the ring. However, in 1-pentene, the molecules aren't bound into a shape, and are relatively free to rotate while still maintaining the same structure.
by David Zhou 1L
Mon Feb 12, 2018 11:20 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: change in entropy total
Replies: 2
Views: 229

Re: change in entropy total

Also, with q/T, if there's any heat transfer, there must be some change in entropy.
by David Zhou 1L
Mon Feb 12, 2018 11:09 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.99
Replies: 1
Views: 104

Re: 9.99

9.99 doesn't have a part b, maybe you were referring to 101?
by David Zhou 1L
Sat Feb 03, 2018 1:40 am
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: Heat Capacity [ENDORSED]
Replies: 4
Views: 1038

Re: Heat Capacity [ENDORSED]

Intermolecular forces also play a large role in determining heat capacity; for example, water has a pretty high specific heat due to hydrogen bonding between the atoms. This is somewhat related to molecular complexity.
by David Zhou 1L
Sat Feb 03, 2018 1:28 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Work and Reversible Process [ENDORSED]
Replies: 2
Views: 161

Re: Work and Reversible Process [ENDORSED]

It's convenient also to think of reversible processes as the ideal situation; the system should be thermally insulated from its surroundings.
by David Zhou 1L
Sat Feb 03, 2018 12:52 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy vs. Potential Energy
Replies: 2
Views: 811

Gibbs Free Energy vs. Potential Energy

What's the difference between Gibbs Free Energy and Potential Energy? Is there a general equation for Potential Energy? In physics, U = mgh is used very often to represent it, so I'm curious if there's any unifying equation for Potential Energy...
by David Zhou 1L
Fri Jan 26, 2018 10:08 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Formation of Snow in Clouds [ENDORSED]
Replies: 5
Views: 1814

Re: Formation of Snow in Clouds [ENDORSED]

Heat transfer always involves something getting hotter and another thing getting colder so that the first law of thermodynamics is obeyed and the universe stays functioning. When water turns into ice, it's getting colder, and so the surroundings must get warmer to balance out the heat transfer. When...
by David Zhou 1L
Fri Jan 26, 2018 9:56 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: What is the pressure value for standard states?
Replies: 2
Views: 231

Re: What is the pressure value for standard states?

1 atm = 1.01325 bar
1 bar = 100,000 Pa

For most questions that don't require extremely accurate measurements, though, there's not enough difference to necessitate this distinction.
by David Zhou 1L
Fri Jan 26, 2018 9:47 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.99
Replies: 3
Views: 217

Re: 8.99

Also, if you're ever unable to find the enthalpy value or any other kind of experimental value, you can always Google it. There's another earlier homework problem in which you needed to use the specific heat capacity of Cu, and for that I just Ok Google'd it because that's really the fastest way to ...
by David Zhou 1L
Wed Jan 17, 2018 9:35 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.1 systems
Replies: 4
Views: 246

Re: 8.1 systems

I just think of the exhaust pipes and the exhaust fumes that come out of the car; instantly then it becomes obvious that the car engine is an open system.
by David Zhou 1L
Wed Jan 17, 2018 9:29 pm
Forum: Phase Changes & Related Calculations
Topic: Heating Curves
Replies: 1
Views: 123

Re: Heating Curves

For the purposes of doing HW and acing tests, I don't think this is very pertinent to the scope of this class. However, if you're interested, take a look at these links:

https://en.wikipedia.org/wiki/Superheating
https://en.wikipedia.org/wiki/Supercooling
by David Zhou 1L
Wed Jan 17, 2018 9:26 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.19 heating water in a copper kettle
Replies: 3
Views: 240

Re: 8.19 heating water in a copper kettle

So long as the problem doesn't tell you to disregard the container the water is in, it's a good idea to incorporate the given mass of the container into the problem-solving process. Everything has a specific heat capacity; in fact, glass has a higher specific heat capacity than copper. Copper: 0.385...
by David Zhou 1L
Sat Jan 13, 2018 12:29 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpies of Formation of Diatomic Molecules
Replies: 6
Views: 2073

Re: Standard Enthalpies of Formation of Diatomic Molecules

It's also of note that standard enthalpy refers to when the pressure is at 1 atm and 25 degrees C (298 K).
by David Zhou 1L
Fri Jan 12, 2018 9:53 pm
Forum: Phase Changes & Related Calculations
Topic: Ideal Gas
Replies: 5
Views: 283

Re: Ideal Gas

No gas behaves completely like an ideal gas; however, in many situations, especially those with relatively low pressure and small gas particles, gases behave close enough to ideal gas behavior that the ideal gas law is a very good approximation for the situation.
by David Zhou 1L
Fri Jan 12, 2018 9:47 pm
Forum: Phase Changes & Related Calculations
Topic: Isothermal Expansion
Replies: 2
Views: 220

Re: Isothermal Expansion

Isothermal expansion is when a system remains at the same temperature. It's in contact with a heat reservoir like a water bath, which keeps the temperature constant, and this process is done slowly enough that the system can continually adjust to maintain the right temperature.
by David Zhou 1L
Sun Dec 10, 2017 3:12 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: 12.53 b
Replies: 1
Views: 288

Re: 12.53 b

The methyl group of acetic acid has greater electron donating power than the single H in formic acid, meaning it destabilizes the carboxylate anion - the anion already has a negative charge on it, and so the slightly higher electron donating power of the methyl group repels against that.
by David Zhou 1L
Sun Dec 10, 2017 3:00 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Problem 12.127 [ENDORSED]
Replies: 2
Views: 817

Re: Problem 12.127 [ENDORSED]

Wouldn't the answer be something electronegativity of the oxygens, because they want to keep hold of their electron pairs? I still don't understand what's going on here.
by David Zhou 1L
Sat Dec 02, 2017 11:31 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Conceptual Kc Problem
Replies: 2
Views: 166

Re: Conceptual Kc Problem

Then will we have to know solubility rules at any point? Like memorizing how soluble nitrates, sulfates, carbonates, etc. are?
by David Zhou 1L
Sat Dec 02, 2017 11:23 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.7 Part C
Replies: 2
Views: 186

Re: 11.7 Part C

But the actual amount of substance has in fact increased if you define the amount of substance as the number of molecules. The number of atoms doesn't change because it's a closed container, but because some of the gas molecules break down, there is an increase in the number of molecules in the cont...
by David Zhou 1L
Sat Dec 02, 2017 11:15 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Gases [ENDORSED]
Replies: 3
Views: 249

Re: Gases [ENDORSED]

Increasing the concentration of gases also decreases the ideal nature of gases; this also causes inter-molecular forces to become more of a factor.
by David Zhou 1L
Fri Nov 17, 2017 7:58 pm
Forum: Hybridization
Topic: sigma/pi bond
Replies: 4
Views: 336

Re: sigma/pi bond

Yes, since the s orbital can only hold two electrons due to the Pauli Exclusion Principle, only the first bond will be a sigma bond.
by David Zhou 1L
Fri Nov 17, 2017 7:54 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Radicals
Replies: 4
Views: 284

Re: Radicals

Elements that are more electronegative will attract the electrons more so than less electronegative elements. Therefore, the single unpaired electron will tend to be on the less electronegative element, since the more electronegative elements will likely attract full valence shells. Also, it's alway...
by David Zhou 1L
Sun Nov 12, 2017 3:48 pm
Forum: Resonance Structures
Topic: Delocalized electrons
Replies: 4
Views: 304

Re: Delocalized electrons

Does this mean that radicals can also have resonance structures, and thus have delocalized electrons?
by David Zhou 1L
Wed Nov 08, 2017 1:19 pm
Forum: Bond Lengths & Energies
Topic: Bond Length
Replies: 8
Views: 1582

Re: Bond Length

Also, shorter bond lengths will result from smaller ions bonding together.

In the example with HF<HCl<HI, because atomic radii increase down the periodic table, the larger the halogen, the longer the bond length.
by David Zhou 1L
Fri Nov 03, 2017 6:52 pm
Forum: Quantum Numbers and The H-Atom
Topic: 2.39
Replies: 4
Views: 381

Re: 2.39

Due to Hund's Rule, the electron configuration isn't the ground state. One of the electrons in the single filled 2p orbital should move to an empty p-orbital, with spin up or down, whichever the one remaining in the first orbital is oriented in; they should be parallel. Excited doesn't have to mean ...
by David Zhou 1L
Fri Nov 03, 2017 6:45 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Homework Problem 2.37
Replies: 2
Views: 197

Re: Homework Problem 2.37

In the textbook on page 37, it states that at "l = 0, there is no orbital angular momentum to fling the electron away from the nucleus." This, of course, corresponds to the s-orbital, which means that the probability density of s-orbitals is closer to the nucleus than other orbitals. Then,...
by David Zhou 1L
Fri Oct 27, 2017 11:47 pm
Forum: Trends in The Periodic Table
Topic: f-orbitals
Replies: 6
Views: 1968

Re: f-orbitals

Lanthanides and Actinides tend to be confusing because they're usually shown all on their own at the bottom, seemingly separate from the rest of the periodic table when in reality the periodic table is just made that way so that it has a nice aspect ratio that can be easily printed/copied. If you ta...
by David Zhou 1L
Fri Oct 27, 2017 11:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Why I3 is linear?
Replies: 2
Views: 1215

Re: Why I3 is linear?

If it's I3-, it's because of the 3 lone pairs in the middle and 2 bonds, making it trigonal bipyramidal. The 3 lone pairs around the central I atom make it linear.
by David Zhou 1L
Sat Oct 21, 2017 1:10 pm
Forum: Properties of Light
Topic: the quantum world [ENDORSED]
Replies: 3
Views: 298

Re: the quantum world [ENDORSED]

Particles are thought of as point sources of mass. In math, particularly geometry and calculus, you've probably learned that points are defined as a very specific location on a line or on a plane or surface. They are of zero dimensions and thus have no length, area, or volume; they are just that ver...
by David Zhou 1L
Sat Oct 21, 2017 12:45 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation! [ENDORSED]
Replies: 8
Views: 797

Re: Rydberg Equation! [ENDORSED]

Electromagnetic radiation can't have a negative frequency because that would mean it oscillates negative times a second, which doesn't make sense; the least it could oscillate is zero times a second. Frequency isn't like velocity, where a negative sign implies movement in the opposite direction, it'...
by David Zhou 1L
Fri Oct 13, 2017 11:49 am
Forum: Einstein Equation
Topic: General Question about Joules [ENDORSED]
Replies: 7
Views: 763

Re: General Question about Joules [ENDORSED]

Also for the purpose of problem-solving in this unit, it's extremely helpful to keep the kg*(m^2/s^2) definition of the Joule in mind in order to make error checking much easier. If at the end of a problem you see that your units are wrong, you know somewhere along the line something went wrong. For...
by David Zhou 1L
Fri Oct 13, 2017 11:27 am
Forum: DeBroglie Equation
Topic: De Broglie Wavelength
Replies: 23
Views: 1614

Re: De Broglie Wavelength

What does it intuitively mean when we find the wavelength of large everyday objects? For example, in problem 1.35, what does it really mean when we compare the wavelengths of a 60kg person vs an 80kg person? Or if we calculate the wavelength of a baseball traveling 92 mph in problem 1.39? Do these h...
by David Zhou 1L
Fri Oct 13, 2017 11:24 am
Forum: Properties of Light
Topic: de Broglie's Relation
Replies: 1
Views: 147

Re: de Broglie's Relation

Oops sorry guys! Wrong topic... I'll move this over.
by David Zhou 1L
Fri Oct 13, 2017 11:22 am
Forum: Properties of Light
Topic: de Broglie's Relation
Replies: 1
Views: 147

de Broglie's Relation

What does it intuitively mean when we find the wavelength of large everyday objects? For example, in problem 1.35, what does it really mean when we compare the wavelengths of a 60kg person vs an 80kg person? Or if we calculate the wavelength of a baseball traveling 92 mph in problem 1.39? Do these h...
by David Zhou 1L
Thu Oct 05, 2017 9:04 pm
Forum: Balancing Chemical Reactions
Topic: Nitrogen
Replies: 5
Views: 412

Re: Nitrogen

I've found there's no need at all for a complicated mnemonic to memorize which gases form diatomic molecules; that just makes things harder, because you have to recall the entire string of elements in your word or phrase to pick out the single one you need. To me, it's far easier to just look at the...
by David Zhou 1L
Thu Oct 05, 2017 8:52 pm
Forum: Balancing Chemical Reactions
Topic: incomplete combustion
Replies: 3
Views: 592

Re: incomplete combustion

Incomplete combustion just means that instead of your reactant, in this case heptane gas, reacting with oxygen gas to form carbon dioxide and water, it forms carbon monoxide and water. Complete combustion skeleton equation: reactant + O2 --> CO2 + H2O Incomplete combustion skeleton equation: reactan...

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