Search found 63 matches
- Sat Mar 09, 2019 9:00 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Test 2 Gibbs Free Energy
- Replies: 5
- Views: 713
Re: Test 2 Gibbs Free Energy
Ice melting will occur spontaneously without any input of energy, so you can assume the reaction is exergonic/spontaneous, and thus delta G will be negative.
- Sat Mar 09, 2019 8:44 am
- Forum: Balancing Redox Reactions
- Topic: Test #2
- Replies: 10
- Views: 1142
Re: Test #2
If you're looking for increasing oxidizing power, you need to see which elements have a higher chance of being reduced. In other words, you'd see which values have the highest standard reduction potential and are the most positive. If you're looking for increasing reducing power, you need to see whi...
- Sat Mar 09, 2019 8:41 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneity
- Replies: 4
- Views: 491
Re: Spontaneity
Try to look at the situations given and determine whether or not it'll happen without an input of energy.
- Sat Mar 09, 2019 8:40 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Determining Spontaneity
- Replies: 7
- Views: 990
Re: Determining Spontaneity
Spontaneity is associated with the delta G values. If you are given delta H and you want to find if something is spontaneous or not, plug in values for T and delta S.
- Sat Mar 09, 2019 8:38 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Work done vs work on system
- Replies: 18
- Views: 3925
Re: Work done vs work on system
When work is done on a system, the work has a positive value. When work is done by a system, the work has a negative value.
- Sat Mar 09, 2019 8:37 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Remembering Equations
- Replies: 5
- Views: 485
Re: Remembering Equations
It might be helpful to categorize equations based on what circumstances they're used in. Aside from that, it's helpful to see how you can derive useful equations from equations given on the constants/equations sheet.
- Sat Mar 09, 2019 8:33 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Increasing/Decreasing temp
- Replies: 8
- Views: 1125
Re: Increasing/Decreasing temp
I always think about it in regards to endothermic reactions. Increasing temperature will always favor endothermic reaction, and thus decreasing temperature will favor the exothermic reaction. Make sure you pay attention to the delta H, and then you can figure out the effect of a temperature change.
- Sat Mar 09, 2019 8:31 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Injecting noble gasses
- Replies: 7
- Views: 796
Re: Injecting noble gasses
Introducing noble gases will not change the equilibrium constant.
- Fri Mar 08, 2019 12:50 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Units of Kp
- Replies: 9
- Views: 3696
Re: Units of Kp
The partial pressures of the gases will be in atm or bar, but the Kp will not have units, as it is the equilibrium constant.
- Fri Mar 08, 2019 12:49 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Stability of reactants and products Midterm question
- Replies: 3
- Views: 689
Re: Stability of reactants and products Midterm question
Because the equilibrium constant is large, the products will be more stable than the reactants.
- Fri Mar 08, 2019 12:48 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Midterm Ice Table
- Replies: 6
- Views: 701
Re: Midterm Ice Table
Yes, Dr. Lavelle told us to not use approximations on the midterm, so you'd just do the ICE tables keeping x in the equations.
- Fri Mar 08, 2019 12:46 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium constant
- Replies: 3
- Views: 308
Re: Equilibrium constant
Yes! The equilibrium constant, k, does not have units.
- Fri Mar 08, 2019 12:46 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kp equilibrium constant
- Replies: 6
- Views: 1669
Re: Kp equilibrium constant
Don't worry too much about the difference between bar and atm -- the numbers would be relatively similar, so it won't matter too much.
- Fri Mar 08, 2019 12:45 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Midterm
- Replies: 4
- Views: 579
Re: Midterm
Just know that strong acids are 100% dissociated, and be comfortable with equilibrium questions regarding weak acids/bases.
- Fri Mar 08, 2019 12:42 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Midterm
- Replies: 5
- Views: 556
Re: Midterm
The products will be more stable than the reactants because the equilibrium concentration is large!
- Fri Mar 08, 2019 12:39 pm
- Forum: Second Order Reactions
- Topic: Final
- Replies: 32
- Views: 2465
Re: Final
It's all cumulative, and assuming from the 14A final from his class last quarter, there should be a relatively equal distribution of questions. :)
- Fri Mar 08, 2019 12:37 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Test 2
- Replies: 12
- Views: 1129
Re: Test 2
The Gibbs free energy of the combustion of gas would be negative, as the reaction is exergonic. This is because gas will have more energy than the water and CO2 molecules released after the combustion, and thus the reaction will be spontaneous.
- Fri Mar 08, 2019 12:34 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Test 2
- Replies: 4
- Views: 480
Re: Test 2
Use Van't Hoff to find the new kw with the temperature change. Then, take the square root of the new kw to find the concentration of H3O+. Then, you can take -log[H3O+] to find pH, which you can now compare to the pH of 7! Hope this helps!
- Mon Feb 04, 2019 4:47 pm
- Forum: Ideal Gases
- Topic: breaking bond - heat released and gained
- Replies: 5
- Views: 913
Re: breaking bond - heat released and gained
In LS7A, we learned that the overall reaction would be exergonic, because it goes from a higher free energy to a lower free energy, thus resulting in a negative delta G. However, it is also true that breaking bonds requires energy.
- Mon Feb 04, 2019 4:45 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Adding Inert Gas
- Replies: 10
- Views: 4623
Re: Adding Inert Gas
Because the inert gases do not really interact with anything else, adding inert gases does not have an astounding effect on the concentrations.
- Mon Feb 04, 2019 4:43 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Decreasing volume and chemical equilibrium
- Replies: 8
- Views: 938
Re: Decreasing volume and chemical equilibrium
When you decrease the volume, the reaction will favor the side with fewer moles of gas.
- Mon Feb 04, 2019 4:42 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Le Chateliers Priniciple
- Replies: 9
- Views: 942
Re: Le Chateliers Priniciple
A change in pressure results in the reaction favoring the side with fewer moles of gas.
- Mon Feb 04, 2019 4:41 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: ignoring x
- Replies: 16
- Views: 3373
Re: ignoring x
If the K value is less than 10^-3, you can ignore the x in the denominator if it is being added or subtracted to the initial concentration. This is because it'll make such a minute difference in the equilibrium concentration as a whole. Be careful that you don't just substitute all the x values with...
- Mon Feb 04, 2019 4:38 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Midterm
- Replies: 12
- Views: 2162
Re: Midterm
Homework questions are a great resource for the midterm. Also, I find that the UA sessions throughout the week are really helpful to do some more practice problems.
- Mon Feb 04, 2019 4:36 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Degeneracy
- Replies: 2
- Views: 234
Re: Degeneracy
Degeneracy is more about the number of different arrangements for the particles, whereas entropy is the chaos which is largely dependent on degeneracy.
- Mon Feb 04, 2019 4:34 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Cup of Tea
- Replies: 17
- Views: 2562
Re: Cup of Tea
A cup of tea would be an open system because matter and energy can be transferred between the system and the surroundings.
- Mon Feb 04, 2019 4:33 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed and Isolated
- Replies: 10
- Views: 753
Re: Closed and Isolated
In a closed system, heat can still be transferred even though the system can't add or remove anything. However, in an isolated system, there is no heat exchange.
- Sun Jan 20, 2019 4:21 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Understanding Q
- Replies: 9
- Views: 779
Re: Understanding Q
Comparing Q and K allows us to see whether or not the system is at equilibrium. If Q=K, then the system is at equilibrium. Otherwise, we can see if Q>K or if K>Q to determine whether the reaction favors the reactants or the products.
- Sun Jan 20, 2019 4:16 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Concentrations Effect on K
- Replies: 8
- Views: 556
Re: Concentrations Effect on K
If both increased by the same amount, K would still remain the same.
- Sun Jan 20, 2019 4:06 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sig figs in pH
- Replies: 7
- Views: 841
Re: Sig figs in pH
If you're being asked to find pH, make sure to see how many sig figs are in the initial number. The final answer should have the same number of decimal places as the number of sig figs in the initial number.
- Fri Jan 11, 2019 10:38 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K, Kc and Kp
- Replies: 8
- Views: 604
Re: K, Kc and Kp
K is the generic term for the equilibrium constant, Kc is specifically for concentrations, and Kp is specifically for partial pressures.
- Fri Jan 11, 2019 10:35 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: defining Q
- Replies: 6
- Views: 599
Re: defining Q
Yes, the reaction will continue for a certain amount of time before it reaches dynamic equilibrium.
- Fri Jan 11, 2019 10:32 am
- Forum: General Science Questions
- Topic: Lecture Powerpoints
- Replies: 9
- Views: 761
Re: Lecture Powerpoints
No, they won't be accessible online. They weren't available for 14A last quarter either.
- Wed Dec 05, 2018 4:42 pm
- Forum: DeBroglie Equation
- Topic: De Brogile Application
- Replies: 4
- Views: 802
Re: De Brogile Application
You can use de Broglie for anything with mass, so that would include electrons. However, you can't use the equation for photons, because photons don't have mass. In this case, you would use an equation with the speed of light.
- Wed Dec 05, 2018 4:41 pm
- Forum: Photoelectric Effect
- Topic: Test #2 Question #2b
- Replies: 4
- Views: 781
Re: Test #2 Question #2b
If the electron is ejected, then increasing the intensity of the light will increase the number of ejected photons, but this does not have an effect on the speed of the ejected electron.
- Wed Dec 05, 2018 4:36 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: bond angle
- Replies: 6
- Views: 527
Re: bond angle
Because you would only be able to find the exact bond angle through an experiment, it's totally fine to put <120 degrees for the test!
- Wed Dec 05, 2018 4:34 pm
- Forum: Hybridization
- Topic: pi vs sigma
- Replies: 12
- Views: 1233
Re: pi vs sigma
The end-to-end overlap of the sigma bond is far more significant than the side-to-side overlap of the pi bond. As a result, the sigma bond is stronger.
- Wed Dec 05, 2018 4:33 pm
- Forum: Hybridization
- Topic: Pi bonds in triple bond
- Replies: 17
- Views: 1899
Re: Pi bonds in triple bond
In a triple bond, there are two pi bonds!
- Wed Dec 05, 2018 4:31 pm
- Forum: Hybridization
- Topic: Radical Placement
- Replies: 3
- Views: 438
Re: Radical Placement
It typically goes on the element like Nitrogen, in which the placement of the radical ensures stability of the atom. See whichever placement gives you a formal charge of 0 for each atom.
- Mon Nov 26, 2018 5:58 pm
- Forum: Bond Lengths & Energies
- Topic: Why Are Double Bonds Shorter
- Replies: 16
- Views: 6218
Re: Why Are Double Bonds Shorter
Double bonds would be shorter (and thus stronger) because there are more electrons that are bonding, and as a result, the atoms are pulled closer together.
- Mon Nov 26, 2018 5:57 pm
- Forum: Sigma & Pi Bonds
- Topic: Which bond would break first.
- Replies: 15
- Views: 2740
Re: Which bond would break first.
Yes, the pi bond would break first, because it has less strength (the electron density is more spread out within pi bonds).
- Mon Nov 26, 2018 5:55 pm
- Forum: Ionic & Covalent Bonds
- Topic: Bond Lengths
- Replies: 10
- Views: 1103
Re: Bond Lengths
Because there is resonance here, the bond length is the average of the bond lengths of the two structures.
- Mon Nov 19, 2018 8:17 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular Shape Patterns
- Replies: 5
- Views: 602
Re: Molecular Shape Patterns
Unfortunately, I think we just have to purely memorize the different shapes and the names of them. However, if you're a visual learner, there are a bunch of helpful charts online that helped me! Here's one: https://chemstuff.co.uk/academic-work/a ... molecules/
- Mon Nov 19, 2018 8:13 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: lone pair influence on shape
- Replies: 12
- Views: 4416
Re: lone pair influence on shape
Because lone pairs have a high electron density, they take up more space. As a result, lone pairs are able to push the angles of the other bonds away from the lone pairs, thus changing the shape.
- Mon Nov 19, 2018 8:12 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Naming the Shape
- Replies: 16
- Views: 1283
Re: Naming the Shape
Personally, I think that visualizing the shapes really allowed me to memorize the names of them. If you're a visual learner, there are many charts online that might help elucidate the connection between number of bonds, number of lone pairs, shapes, and the names of the shapes. One example is this c...
- Fri Nov 09, 2018 10:19 pm
- Forum: Bond Lengths & Energies
- Topic: MIDTERM Bond Length Question
- Replies: 15
- Views: 1615
Re: MIDTERM Bond Length Question
Due to resonance blending, the bond length will be 130 pm (or really any value in between 120pm and 140pm)!
- Fri Nov 09, 2018 10:03 pm
- Forum: Resonance Structures
- Topic: Resonance Lewis Structures
- Replies: 3
- Views: 427
Re: Resonance Lewis Structures
So far, we've primarily just looked at resonance structures in the context of delocalized bonding pairs :)
- Fri Nov 09, 2018 9:54 pm
- Forum: Resonance Structures
- Topic: Resonance with formal charge
- Replies: 6
- Views: 627
Re: Resonance with formal charge
Yes, the molecules can still have resonance as long as the number of electrons still works in the Lewis structure! The lowest formal charge just indicates the stability of the structure.
- Sat Nov 03, 2018 8:33 am
- Forum: Resonance Structures
- Topic: Resonance structures on the midterm
- Replies: 3
- Views: 450
Re: Resonance structures on the midterm
I believe we just need to put the most stable resonance structure. To find this, use the formal charge equation to see which structure has the formal charge closest to zero.
- Sat Nov 03, 2018 8:29 am
- Forum: Lewis Structures
- Topic: How to determine central atom
- Replies: 8
- Views: 1503
Re: How to determine central atom
You can look at whatever has the lowest ionization energy, the lowest electronegativity, and whichever shows up the least in the formula.
- Fri Nov 02, 2018 2:30 pm
- Forum: Lewis Structures
- Topic: Lewis Structures- formal charge
- Replies: 4
- Views: 496
Re: Lewis Structures- formal charge
In order to calculate formal charge, use this equation:
FC= V - (L+ (S/2)), where V is the number of valence electrons, L is the number of electrons in lone pairs, and S is the number of shared electrons.
Hope this helps! :)
FC= V - (L+ (S/2)), where V is the number of valence electrons, L is the number of electrons in lone pairs, and S is the number of shared electrons.
Hope this helps! :)
- Sat Oct 27, 2018 6:15 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg- In relation to wavelength
- Replies: 7
- Views: 742
Re: Heisenberg- In relation to wavelength
Question: If the uncertainty in the momentum increases for a given particle what does this mean for the uncertainty in its wavelength? I was wondering what the relationship between these two uncertainties are and how one can potentially affect the other? Because there's an inverse relationship betw...
- Sat Oct 27, 2018 6:13 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Meaning of Z
- Replies: 5
- Views: 588
Re: Meaning of Z
Z is the atomic number for an element, and thus, it is also the number of protons!
- Sat Oct 27, 2018 6:12 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Calculating Velocity
- Replies: 4
- Views: 576
Re: Calculating Velocity
Is there any type of indicator that you may have not converted right or messed up somewhere in the equation when calculating velocity? For example should you ever get like 3.4 x 10 ^ -12 m/s as your velocity? Is it possible to be that small? Yes, it is possible for the number to be that small, beca...
- Sat Oct 20, 2018 9:06 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Lecture Question
- Replies: 4
- Views: 483
Re: Lecture Question
There are other levels that exist, but we'll just need to focus on s, p, d, and f, because those are the four main orbital types.
- Sat Oct 20, 2018 9:02 pm
- Forum: Properties of Light
- Topic: Wavelengths and frequencies
- Replies: 10
- Views: 710
Re: Wavelengths and frequencies
Nope! It would probably be a good idea to know the general order of the lights' wavelengths, but you won't need to know the specific ranges for anything other than visible light! :)
- Sat Oct 20, 2018 8:54 pm
- Forum: Properties of Light
- Topic: Calculating the wavelength of light
- Replies: 7
- Views: 1223
Re: Calculating the wavelength of light
Either option would work for tests and/or homework, but 2.998 * 10^8 is more accurate! :)
- Sat Oct 13, 2018 8:03 pm
- Forum: DeBroglie Equation
- Topic: DeBroglie Equation
- Replies: 5
- Views: 530
Re: DeBroglie Equation
The de Broglie equation is used to calculate the wavelength of any moving particle. In most of the worked examples completed during lecture, some questions have asked specifically for "the de Broglie" wavelength, whereas other questions might just mention components of momentum and/or wave...
- Sat Oct 13, 2018 7:59 pm
- Forum: Photoelectric Effect
- Topic: Properties of Light
- Replies: 5
- Views: 350
Re: Properties of Light
The intensity of a light source can be determined by looking at the amplitude of the wave, whereas the energy of the light wave can be determined using the equation E = h*v (E is energy in Joules, h is Planck's constant, and v is velocity of the wave).
- Sat Oct 13, 2018 7:52 pm
- Forum: Properties of Light
- Topic: De Brogile Equation
- Replies: 6
- Views: 349
Re: De Brogile Equation
The De Broglie equation enables us to see the wave-like properties of moving objects. We can use the equation ( λ=h/(m*v)) to calculate the wavelength of moving objects/particles (λ is wavelength, h is Planck's constant, m is the mass of a particle, moving at a velocity v).
- Fri Oct 05, 2018 1:48 pm
- Forum: Significant Figures
- Topic: Scientific Notation
- Replies: 7
- Views: 423
Re: Scientific Notation
How do we know when to write solutions using scientific notation? I usually do so as a default but when checking the solutions manual, I noticed that sometimes answers like (for example) .0623 is left just like that and not written as 6.23 * 10^2. Is there a reason for that? Are there specific rule...
- Fri Oct 05, 2018 1:42 pm
- Forum: Balancing Chemical Reactions
- Topic: Balancing Chemical Reactions with Heat
- Replies: 6
- Views: 1421
Re: Balancing Chemical Reactions with Heat
I know that in a chemical equation the delta symbol above the arrow means that heat is added to the equation. However, I cannot remember whether the heat changes any of the compounds in the reaction or not. Do you add any products or reactants to the equation if you add heat? The delta sign indicat...
- Fri Oct 05, 2018 7:12 am
- Forum: SI Units, Unit Conversions
- Topic: formula units [ENDORSED]
- Replies: 69
- Views: 33006
Re: Rounding Up [ENDORSED]
Hello! I had a question regarding atomic masses. Do we round the atomic masses on the periodic table or leave them as is? We can calculate everything with the atomic masses given on the periodic table, and then we can round after we consider significant figures at the end of the problem! This will ...