Search found 48 matches
- Wed Feb 06, 2019 10:23 pm
- Forum: Calculating Work of Expansion
- Topic: Isothermal processes
- Replies: 2
- Views: 12
Re: Isothermal processes
Isothermal expansion is where temperature stays the same and air is expanded, since heat is lost during work, heat is added.
- Wed Feb 06, 2019 10:16 pm
- Forum: Phase Changes & Related Calculations
- Topic: Symbol inquiry
- Replies: 4
- Views: 15
Re: Symbol inquiry
Change in internal energy: ΔU
Internal energy: U
Internal energy: U
- Wed Feb 06, 2019 10:12 pm
- Forum: Student Social/Study Group
- Topic: Unit Conversion for Temp
- Replies: 2
- Views: 8
Re: Unit Conversion for Temp
A good way to tell is to look at the other units you use in the equation. For example, the gas constant includes the unit, K, so you would need to use temperature in Kelvin's for the problem.
- Tue Jan 29, 2019 12:20 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Enthalpies
- Replies: 7
- Views: 23
Re: Bond Enthalpies
They are the least accurate because they are an average of all the possible molecular structures they can be in. If you actually compare the methods they are actually pretty similar, but the other two covered methods deal with more exact numbers based on the specific structures in the equations.
- Tue Jan 29, 2019 12:16 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Memorizing bond enthalpies
- Replies: 5
- Views: 24
Re: Memorizing bond enthalpies
I would assume that you do not need to memorize any both enthalpies. In 14A, we were not expected to do any hard memorization. I would focus on problem solving skills and more conceptual things. Those are both things that Dr.Lavelle has generally shifted his focus to on past exams.
- Tue Jan 29, 2019 12:13 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Thermal Equilibrium
- Replies: 5
- Views: 30
Re: Thermal Equilibrium
At equilibrium processes do not suddenly stop happening. So, equilibrium is defined as when the rate of transfer between the surrounds and the system are equal. An example could be a steaming cup of water. If you leave in a room at room temperature eventually the water will go to room temperate when...
- Thu Jan 24, 2019 8:45 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Second deprotonation
- Replies: 3
- Views: 32
Re: Second deprotonation
I would assume not just because it wasn’t really covered in lecture or discussion sections.
- Thu Jan 24, 2019 8:44 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Pressure
- Replies: 7
- Views: 31
Re: Pressure
You only look at gases, ignoring solids and liquids.
- Thu Jan 24, 2019 8:41 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Test 1
- Replies: 9
- Views: 64
Re: Test 1
They usually provide all the equations you need to know. I find it best to look at it before the test so you are familiar where everything is.
- Fri Jan 18, 2019 2:57 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Acid and Base
- Replies: 3
- Views: 39
Re: Acid and Base
If you think of the negative log of 1x10^-14, which is 14. The pH of the acid and the base always add up to 14, in a neutral solution both will be 7. (the below table is found at http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch17/ph.php) Pairs of Equilibrium Concentrations of H3O+ and OH- Ion...
- Fri Jan 18, 2019 2:50 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium Arrow
- Replies: 7
- Views: 33
Re: Equilibrium Arrow
Moreover, you use two arrows for weak acids and bases because there will be some sort of equilibrium where not everything is disassociated.
- Fri Jan 18, 2019 2:44 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Inert Gas
- Replies: 3
- Views: 18
Re: Inert Gas
When inert gas is added to a system in equilibrium when pressure is kept constant, the volume will increases and moles on either side will shift. Conversely, if an inert gas is added to a system in equilibrium where volume is kept constant, the pressure will increase but the concentrations will not ...
- Fri Jan 11, 2019 12:56 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Q vs K
- Replies: 5
- Views: 35
Re: Q vs K
Simply put, Q is at any moment and K is when in equilibrium. Q can be used to show change.
- Fri Jan 11, 2019 12:53 am
- Forum: Student Social/Study Group
- Topic: New to Lavelle
- Replies: 32
- Views: 401
Re: New to Lavelle
To post a question you will go to the board index and post under the topic that most closely relates to your question. It will probably be removed or changed if it's posted in the wrong category. After that, you click on the new topic button and ask your question.
- Fri Jan 11, 2019 12:42 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: 5G.11 b
- Replies: 3
- Views: 38
Re: 5G.11 b
Solids and liquids are regarded with a value 1 because their effective concentrations stay the same throughout the reaction.
- Sat Dec 08, 2018 5:03 pm
- Forum: Bronsted Acids & Bases
- Topic: Oxoacids
- Replies: 1
- Views: 27
Oxoacids
Which are stronger oxoacids or binary acids?
For example: ClOH vs. HCl.
For example: ClOH vs. HCl.
- Fri Dec 07, 2018 2:00 am
- Forum: *Crystal Field Theory
- Topic: Crystal Field Theory
- Replies: 3
- Views: 205
Re: Crystal Field Theory
I do not think that we are expected to know this for 14 A.
- Fri Dec 07, 2018 1:57 am
- Forum: Bronsted Acids & Bases
- Topic: Strong Acids vs Weak Acids
- Replies: 2
- Views: 32
Re: Strong Acids vs Weak Acids
These are some common strong acids: HCl - hydrochloric acid HNO3 - nitric acid H2SO4 - sulfuric acid (HSO4- is a weak acid) HBr - hydrobromic acid HI - hydroiodic acid HClO4 - perchloric acid HClO3 - chloric acid @https://www.thoughtco.com/list-of-strong-and-weak-acids-603642 You can also differenti...
- Fri Dec 07, 2018 1:45 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Coordination Complexes
- Replies: 2
- Views: 15
Re: Coordination Complexes
As a side note, a tetrahedral complex is normally formed from AX4, while square planar is usually formed from AX4E2.
- Sun Dec 02, 2018 1:35 pm
- Forum: Administrative Questions and Class Announcements
- Topic: More practice
- Replies: 7
- Views: 112
Re: More practice
If you attended any of the review sessions for the midterm, we were given practice problems (as well as the "garlic bread" packet). Also, you might have gotten back previous tests.
- Sun Dec 02, 2018 1:22 pm
- Forum: Administrative Questions and Class Announcements
- Topic: More practice
- Replies: 7
- Views: 112
Re: More practice
You could also look at the problems on past tests or previous review sessions.
- Sun Dec 02, 2018 1:16 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Monodentates
- Replies: 2
- Views: 31
Re: Monodentates
Yes, monodentates only have one donor atom. Going on, bidentates have two donor atoms.
- Sun Dec 02, 2018 1:05 pm
- Forum: Naming
- Topic: Polydentate
- Replies: 2
- Views: 22
Re: Polydentate
A polydentate has more than two lewis base sites.
- Tue Nov 27, 2018 12:21 am
- Forum: Lewis Acids & Bases
- Topic: Difference Between Acids and Bases
- Replies: 4
- Views: 48
Re: Difference Between Acids and Bases
Some other indicators are pH values (above 7 is alkaline [base] and less than 7 is acid), and that H+ is usually found in relation to acids, while OH- is usually found in relation to bases.
- Tue Nov 27, 2018 12:17 am
- Forum: Hybridization
- Topic: s-character
- Replies: 6
- Views: 104
Re: s-character
It is the ratio of the s orbital to other orbitals. It is usually described by a percentage of s character. For example, sp3 hybrid has 25% s character.
- Tue Nov 27, 2018 12:13 am
- Forum: Dipole Moments
- Topic: Dipole Moment Calculation
- Replies: 3
- Views: 42
Re: Dipole Moment Calculation
If we didn't do it in class and it was never talked abut in sections, we probably don't have to do it on the test.
- Thu Nov 15, 2018 2:26 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Formal Charge
- Replies: 10
- Views: 107
Re: Formal Charge
It depends on whether or not an element can have an expanded octet. Some elements can only have eight electron so formal charge does not matter because you can't add electrons (however, you might be able to go to a double or triple bond), while others can improve their formal charge (closer to zero)...
- Thu Nov 15, 2018 2:20 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 109.5 Degrees
- Replies: 4
- Views: 32
Re: 109.5 Degrees
This is because it is a three dimensional shape so its wont just be 360 divided by the number of sides. This is a link to a mathematical proof laying out how to come to 109.5 degrees. http://www.ctralie.com/Teaching/Tetrahedron/
- Thu Nov 15, 2018 2:17 pm
- Forum: General Science Questions
- Topic: Audio Visuals
- Replies: 6
- Views: 107
Re: Audio Visuals
I do not believe so. Lavelle said that he only did them on the topics that he finds students struggle with the most. The most fundamental things.
- Thu Nov 08, 2018 1:32 am
- Forum: Bond Lengths & Energies
- Topic: MIDTERM Bond Length Question
- Replies: 15
- Views: 157
Re: MIDTERM Bond Length Question
The experimentally determined bond lengths of all the bonds are the same. Bonds lengths are the average of all of the resonance structures. I also got 130.
- Thu Nov 08, 2018 1:17 am
- Forum: Administrative Questions and Class Announcements
- Topic: Test during Thanksgiving Week?
- Replies: 2
- Views: 55
Re: Test during Thanksgiving Week?
The syllabus says "Test 3 Starting Tuesday November 27 in discussion section."
Thanksgiving break is the week prior.
Thanksgiving break is the week prior.
- Thu Nov 08, 2018 1:06 am
- Forum: Dipole Moments
- Topic: Polar and Nonpolar
- Replies: 7
- Views: 71
Re: Polar and Nonpolar
Polar: there is an uneven distribution of charge
Nonpolar: there is a completely symmetric distribution of charge
Video explaining this: https://www.youtube.com/watch?v=SiZXRScxbl0
Nonpolar: there is a completely symmetric distribution of charge
Video explaining this: https://www.youtube.com/watch?v=SiZXRScxbl0
- Fri Nov 02, 2018 12:10 am
- Forum: Lewis Structures
- Topic: How does nitrogen form 4 bonds?
- Replies: 3
- Views: 76
Re: How does nitrogen form 4 bonds?
https://i.stack.imgur.com/Z2n1k.png If you look at the above image you can see that when nitrogen has a positive charge (one less electron), it can form four covalent bonds. Either with single, double, or triple bonds. It is similar to phosphorus in this regard because they both have five valence el...
- Fri Nov 02, 2018 12:01 am
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Ionization energy
- Replies: 1
- Views: 14
Re: Ionization energy
It is harder to remove the second electron and ever harder to remove the third due to an increase in effective nuclear charge when electrons are removed. The effective nuclear charge is a positive force attracting valence electrons. Therefore, when one electron is removed, the same amount of positiv...
- Thu Nov 01, 2018 11:52 pm
- Forum: Octet Exceptions
- Topic: octet rule exceptions?
- Replies: 5
- Views: 70
Re: octet rule exceptions?
As a general rule, things become more complicated in terms of an expanded octet 3rd row and down, and the first few elements are stable with only two electrons. I found a more cut and dry rule for octet rule exceptions at this link: https://saylordotorg.github.io/text_general-chemistry-principles-pa...
- Fri Oct 26, 2018 1:02 am
- Forum: Lewis Structures
- Topic: Drawing Lewis Structures
- Replies: 3
- Views: 60
Re: Drawing Lewis Structures
You bond the atoms where there is either an excess or lack of valence electrons, you know this by placing the electrons in the structure or by visualizing it. The following are two helpful links with step-by-step instructions: http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch01/ch1-3depth.html htt...
- Fri Oct 26, 2018 12:57 am
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: atomic spectra Rydberg
- Replies: 3
- Views: 95
Re: atomic spectra Rydberg
Final state - Initial state
We talked about how this is not always so, but for the most part, this is the correct way of thinking about it.
We talked about how this is not always so, but for the most part, this is the correct way of thinking about it.
- Fri Oct 26, 2018 12:53 am
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Electron Configuration and Unfilled Orbitals
- Replies: 2
- Views: 47
Re: Electron Configuration and Unfilled Orbitals
Another explanation for this is that the most balanced state might not be the one that goes in order with the set rules. Lower energy fills before higher energy, and the most balanced state is strived for as well.
- Fri Oct 19, 2018 3:35 pm
- Forum: Photoelectric Effect
- Topic: Test 2
- Replies: 16
- Views: 245
Re: Test 2
You'll still have to know unit analysis and other basic concepts from Test1, but the general concepts tested will be everything up until lecture Friday.
- Fri Oct 19, 2018 3:33 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Chem Community Due Date
- Replies: 6
- Views: 107
Re: Chem Community Due Date
I've heard various things like before lecture Friday or Sunday night. My TA told me to just get it done by Thursday night to be safe.
- Fri Oct 19, 2018 3:31 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Equation sheet
- Replies: 4
- Views: 76
Re: Equation sheet
It's probably a lot like the equation sheet on the front on test 1, which you should have.
- Fri Oct 19, 2018 3:29 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Electron Configuration Clarification
- Replies: 2
- Views: 21
Re: Electron Configuration Clarification
I believe this is because "l" has to be n-1. n=the first quantum number, and l=the second quantum number.
- Thu Oct 11, 2018 10:55 pm
- Forum: Significant Figures
- Topic: sig figs in periodic table
- Replies: 6
- Views: 150
Re: sig figs in periodic table
You always look to the least amount of sig figs in any problem. It makes practical sense because the least number of sig figs determines how precise you can be in your calculations.
- Thu Oct 11, 2018 10:53 pm
- Forum: Balancing Chemical Reactions
- Topic: Writing Chemical Equations
- Replies: 2
- Views: 104
Re: Writing Chemical Equations
We haven't gone over it in class yet, but there are a series of procedures for writing the names of chemical formulas. If you are curious, this is a website that goes over how to write chemical formulas: http://www.kentchemistry.com/links/nami ... riting.htm
- Thu Oct 11, 2018 10:50 pm
- Forum: Einstein Equation
- Topic: Units for v(frequency)
- Replies: 11
- Views: 90
Re: Units for v(frequency)
They can both be used (and are basically the same thing), but make sure that all units cancel when you reach the end of the problem.
- Fri Oct 05, 2018 9:20 pm
- Forum: Balancing Chemical Reactions
- Topic: Balancing reactions tips
- Replies: 29
- Views: 505
Re: Balancing reactions tips
I usually start with what occurs the least and work through trial and error if I have to. It something is taking too long or not working out make sure you wrote it down correctly because a small mistake at first can turn into a huge hassle in the long run.
- Fri Oct 05, 2018 9:17 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: G13
- Replies: 1
- Views: 52
Re: G13
To get you started, you will be using the equation M1V1=M2V2, to calculate what you are missing. This link is for a helpful youtube video on dilution: https://www.youtube.com/watch?v=v6dnEp58mVk
- Fri Oct 05, 2018 9:07 pm
- Forum: General Science Questions
- Topic: Rounding up with Sig Figs
- Replies: 3
- Views: 108
Rounding up with Sig Figs
When rounding for sig figs with a number that ends in a five, do you round up or round down? Does it depend on whether it is preceded by an even or odd number? For example, does the number 2.65 for two sig figs go to 2.7 or 2.6? thanks