Search found 33 matches
- Tue Mar 14, 2017 3:10 pm
- Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
- Topic: Difference Between torsional strain, steric strain, and bond angle strain
- Replies: 2
- Views: 5375
Re: Difference Between torsional strain, steric strain, and bond angle strain
Torsional strain is caused by unfavorable electrostatic interaction. When molecules are eclipsed (as when the carbon atoms are in a planar geometry), the regions of electron density from the eclipsed atoms are closer together, thus leading to higher energy and less stability of the molecule. Steric ...
- Tue Mar 14, 2017 2:36 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Saying Thank You to Dr. Lavelle
- Replies: 490
- Views: 513354
Re: Saying Thank You to Dr. Lavelle
Dear Dr. Lavelle, Thank you so much for truly devoting yourself to giving your students the best academic experience we could possibly have! You exude such genuine passion for chemistry and it has positively influenced my learning experience. It is definitely refreshing to learn from a professor who...
- Wed Mar 08, 2017 6:57 pm
- Forum: *Cycloalkanes
- Topic: How much of Common naming do we need to know for Quiz 3?
- Replies: 4
- Views: 1716
Re: How much of Common naming do we need to know for Quiz 3?
Technically, every molecule can be named with IUPAC naming. However, naming becomes complicated without the use of common naming for instances such as multiple substituents on a substituent. This is why you should know and become familiar with the common names and what they would like like in line s...
Re: Numbering
Hey! When numbering multiple constituents, always aim for the lowest sum total. If there is equal numbering between constituents (for example 2,3 or 3,2) then apply the lowest number to the first alphabetical constituent, not including the prefixes.
- Wed Mar 01, 2017 1:01 am
- Forum: *Electrophiles
- Topic: Electrophile Vs. Nucleophile
- Replies: 3
- Views: 893
Re: Electrophile Vs. Nucleophile
Just look at whether there are electron deficiency or electron surplus. Molecules/Elements that have many electrons are most likely negatively charged (Nucleophiles). Electrophiles are electron deficient and are attracted to positive charges. The "obvious" comes from whether the molecule/e...
- Thu Feb 23, 2017 11:06 am
- Forum: General Rate Laws
- Topic: Units for Reaction Rate and the Rate Constant
- Replies: 3
- Views: 1136
Re: Units for Reaction Rate and the Rate Constant
The reaction rate units is usually in the form mol L^-1 s^-1 (the time unit can vary - s, min, hr, etc). The rate constant depends on the order of the reaction. For example, if first order, the rate constant will be s^-1. You can find this by dividing the units of the reaction rate by the unit of th...
- Thu Feb 23, 2017 11:03 am
- Forum: First Order Reactions
- Topic: 15.29
- Replies: 3
- Views: 2494
Re: 15.29
B is a product so the concentration of B increasing means that more product is being formed. Since .018 M of B is formed, using stoichiometric calculations, 0.018M B(1 mol A/3 mol B) = .006M A is lost because reactant concentration lessens as products are formed and product concentration is increase...
- Tue Feb 14, 2017 7:59 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Galvanic Cells
- Replies: 4
- Views: 869
Re: Galvanic Cells
When there is no solid available for either anode or cathode. A solid is needed as the electrode for the reaction to occur.
- Tue Feb 07, 2017 1:11 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation [ENDORSED]
- Replies: 4
- Views: 1421
Re: Oxidation [ENDORSED]
OIL RIG is a simple pneumonic device I use to remember the difference between Oxidation and Reduction. Oxidation Is Losing (OIL) and Reduction is Gaining (RIG). Oxidation loses electrons, and so the charge of an element increases. Reduction gains electrons, and this brings in more negative value, de...
- Tue Feb 07, 2017 1:05 pm
- Forum: Balancing Redox Reactions
- Topic: Intensive Property
- Replies: 2
- Views: 686
Re: Intensive Property
Just think about voltage as a set measurement for certain reactions. For instance, 2 Ag+ (aq) + 2 e- ------> 2 Ag (s) will have a certain voltage value. It does not matter how much of the reactants or products there are. It is a set measurement independent of the amount.
- Fri Feb 03, 2017 2:45 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: question on U=q+w equation
- Replies: 2
- Views: 690
Re: question on U=q+w equation
If the pressure is not constant, you are calculating the work for a reversible pathway. If you are in isothermal conditions (temp is constant) and you have a system that is being compressed with changing volume, the work expression would be -nrtln(V2/V1), where V2 is the final volume and V1 is the i...
- Fri Feb 03, 2017 2:40 pm
- Forum: Calculating Work of Expansion
- Topic: Amount of work done
- Replies: 2
- Views: 681
Re: Amount of work done
Yes, the reversible pathway calculates the maximum value for work. However, most reactions, including biological reactions, use the irreversible pathway because it is more efficient and quicker.
- Wed Jan 25, 2017 12:42 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: "Favorable" chemical reaction
- Replies: 3
- Views: 1510
Re: "Favorable" chemical reaction
This reaction is exothermic, meaning that the products are at a lower energy state than the reactants are. Usually, molecules will want to achieve the lowest energy state possible, and in this reaction, exactly that is happening. This reaction was favorable because it happened by itself, making it a...
- Wed Jan 25, 2017 12:37 pm
- Forum: Calculating Work of Expansion
- Topic: Irreversible process
- Replies: 2
- Views: 618
Re: Irreversible process
Free expansion is saying that the particles, let's say from a reaction, is diffusing outwards freely. There is no work involved because these particles do not need to exert any energy (do work) to freely expand.
- Wed Jan 18, 2017 11:54 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: relationship between delta H and q [ENDORSED]
- Replies: 4
- Views: 3179
Re: relationship between delta H and q [ENDORSED]
If pressure is held constant, q will have a subscript p (qp), making it interchangeable with delta H.
- Wed Jan 18, 2017 11:50 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Units of Reaction Enthalpies
- Replies: 11
- Views: 2071
Re: Units of Reaction Enthalpies
To give an example, we used kj/mol for the standard enthalpy of formation of ethanol for the example (page 17 of the course reader) because the definition of the standard enthalpy of formation has to do with 1 mol of the product that was formed from the reactants. The same goes for the second exampl...
- Tue Nov 29, 2016 10:53 pm
- Forum: Polyprotic Acids & Bases
- Topic: Writing Reaction Equation for Polyprotic Acids/Bases
- Replies: 2
- Views: 842
Re: Writing Reaction Equation for Polyprotic Acids/Bases
Writing out the two steps for polyprotic acids is usually very helpful in visualizing what cancels out and what is added together. However, if you are just finding the K value for the overall equation, you can just multiply the individual Ka or Kb values.
- Thu Nov 17, 2016 11:06 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Identifying Polydentates? [ENDORSED]
- Replies: 8
- Views: 2297
Re: Identifying Polydentates? [ENDORSED]
Identifying a ligand as polydentate has two criteria. 1) The ligand must have at least 2 atoms that have lone pairs. This can be found through simply drawing the Lewis structure. 2) The atoms must be in the correct geometry to bind to the Transition metal cation in more than one place at the same ti...
- Thu Nov 17, 2016 8:56 am
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: What is MO theory for? [ENDORSED]
- Replies: 20
- Views: 8861
Re: What is MO theory for? [ENDORSED]
Molecular Orbital Theory gives us more understanding of molecules we may not be able to know just through Lewis structures. It mainly gives us context on bond strength and magnetic properties. We can figure out the bond order through MO theory, and the higher the bond order, the stronger the bond. W...
- Tue Nov 08, 2016 9:45 am
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: Bond Order
- Replies: 2
- Views: 1564
Re: Bond Order
The greater the bond order, the greater the stability of the molecule. For example, O2+ has a bond order of 2.5. When drawing out the Lewis structure for O2+, the 2 indicates a double bond and the .5 indicates a resonance structure. Double bonds are shorter, and thus stronger. If the bond order was ...
- Tue Nov 08, 2016 9:40 am
- Forum: Hybridization
- Topic: Hybridization
- Replies: 2
- Views: 648
Re: Hybridization
Hybridized orbitals allow atoms to have enough orbitals to bond with unpaired electrons. For example, the s and p orbitals will combine to form a new shape that allows the atom to bond with electrons. Carbon only has two unpaired electrons, but with the hybridized orbital sp^3, Carbon is able to hav...
- Thu Nov 03, 2016 8:39 am
- Forum: Dipole Moments
- Topic: Polar and Non-polar bond
- Replies: 8
- Views: 2081
Re: Polar and Non-polar bond
I usually draw out the lewis structure and determine from there. If the central atom of the lewis structure has all bonding pairs (ex. linear, trigonal planar, tetrahedral, etc.) and all atoms that are bonded to the central atom are the same, the molecule is non-polar because the equal and opposite ...
- Thu Nov 03, 2016 8:26 am
- Forum: Hybridization
- Topic: Hybridization Beyond sp3
- Replies: 2
- Views: 766
Re: Hybridization Beyond sp3
It's better to understand that usually when the atom, more specifically the central atom, has an expanded octet, we need to utilize a hybridization beyond sp3. For example, XeF4 has an expanded octet and a hybridization sp^3d^2 because it has 6 electron density regions. Molecules such as XeF4 are pr...
- Thu Oct 27, 2016 8:53 pm
- Forum: Electronegativity
- Topic: Electronegativity in Quiz 2 [ENDORSED]
- Replies: 3
- Views: 807
Re: Electronegativity in Quiz 2 [ENDORSED]
If the electronegativities are given, the calculated difference in electronegativity for the molecule can determine whether the molecule is ionic or covalent. However, if the numbers are not given, the trends for electronegativity or polarizability based on the size of the atoms and charges(if it is...
- Thu Oct 27, 2016 8:51 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: VSEPR Diagram
- Replies: 3
- Views: 1791
Re: VSEPR Diagram
It is safe to assume that whenever you see a single bond, it is a sigma bond because sigma bonds overlap two orbitals end to end, creating one single bond. There is only one overlap, and within this overlap is the single area of electron density. This one overlap gives you a single bond.
- Fri Oct 21, 2016 2:27 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Px, Py, Pz [ENDORSED]
- Replies: 5
- Views: 13926
Re: Px, Py, Pz [ENDORSED]
Px, Py, Pz are the different orbitals that are within the p subshell. Each one is a different orientation and each is linked to a different number for the magnetic quantum number m_l. For example, let's say n = 2. Then l = 0, 1. For l = 1 (the p orbital), m_l = -1, 0, 1. These three numbers correspo...
- Tue Oct 18, 2016 8:52 am
- Forum: Lewis Structures
- Topic: Resonance [ENDORSED]
- Replies: 5
- Views: 1081
Re: Resonance [ENDORSED]
Resonance is when there are delocalized electrons within a molecule. This means that the bonding of the atoms within the molecule cannot be expressed with exactly one Lewis structure. For example, in NO3-, N has one double bond with one O in structural format. In actuality, the delocalized electrons...
- Thu Oct 13, 2016 8:42 am
- Forum: Photoelectric Effect
- Topic: Work Function and Threshold Energy [ENDORSED]
- Replies: 3
- Views: 4783
Re: Work Function and Threshold Energy [ENDORSED]
The work function and the threshold energy both refer to the energy required to eject an electron from the metal surface. In the formula, E(photon)=E(energy remove electron) = E(excess), the E(energy remove electron) is the amount of work that needs to be put in the system in order to eject the elec...
- Thu Oct 13, 2016 8:32 am
- Forum: DeBroglie Equation
- Topic: Conceptual Question on DeBroglie
- Replies: 3
- Views: 770
Re: Conceptual Question on DeBroglie
When you execute the DeBroglie equation with the mass of something like a baseball or car, the resulting wavelength is so extremely small that it is physically impossible to detect. All matter has wavelike properties, but we can only notice these wavelike properties for very small objects with high ...
- Thu Oct 06, 2016 3:48 pm
- Forum: DeBroglie Equation
- Topic: Post Module Question [ENDORSED]
- Replies: 3
- Views: 840
Re: Post Module Question [ENDORSED]
The speed of light is what we can compare to in terms of velocity. The answer cannot be reasonable if the speed is greater than the actual speed of light. It is similar to the concept of comparison when we are calculating the uncertainty in velocity. If the uncertainty is greater than the speed of l...
- Thu Oct 06, 2016 3:40 pm
- Forum: Properties of Electrons
- Topic: Wavelike Properties? [ENDORSED]
- Replies: 2
- Views: 856
Re: Wavelike Properties? [ENDORSED]
Even though we cannot literally see that something like a car would have wavelike properties, all matter has wavelike properties. However, we can only notice or detect these wavelike properties in extremely small moving objects such as electrons.
- Wed Sep 28, 2016 9:39 pm
- Forum: Properties of Light
- Topic: Photons
- Replies: 4
- Views: 852
Re: Photons
The shorter the wavelength, the higher the frequency. Shorter wavelengths mean increased energy for each photon in a beam of light. In order to reach the threshold of energy to eject electrons from the metal, the photons must have enough energy. If the photons in a beam of light do not have enough e...
- Wed Sep 28, 2016 9:31 pm
- Forum: General Science Questions
- Topic: Rusty on High School Chem [ENDORSED]
- Replies: 347
- Views: 416246
Re: Rusty on High School Chem [ENDORSED]
I took AP Chem in my junior year and I have a couple of review books and notes that I brought with me that actually really supplemented my learning while watching the modules and taking the pre/post assessments. I recommend that you refresh your memory with notes or even specific youtube videos. Wat...