Search found 50 matches
- Wed Mar 14, 2018 3:44 pm
- Forum: *Alkanes
- Topic: Naming compounds
- Replies: 3
- Views: 3619
Re: Naming compounds
I do not believe we will have to draw the functional groups, I think we will just have to recognize one given a structure or chemical formula of a molecule.
- Wed Mar 14, 2018 3:42 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Elementary reactions
- Replies: 6
- Views: 859
Re: Elementary reactions
Elementary reactions are the specifics of an overall reaction. They're elementary in that there may be species seen, such as intermediates and catalysts, that are not seen in the net reaction that takes place.
- Wed Mar 14, 2018 3:41 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts vs Intermediates
- Replies: 2
- Views: 454
Re: Catalysts vs Intermediates
Intermediates are produced in one of the elementary steps, and consumed in another, thereby cancelling it out. Catalysts, however, are not produced in between and are at the beginning of the reaction and are at the end of the elementary steps to cancel out.
- Sun Mar 11, 2018 7:05 pm
- Forum: Second Order Reactions
- Topic: the slope
- Replies: 12
- Views: 1545
Re: the slope
If the slope were to be positive for the first order reaction, we would have to look at -ln(concentration) on the y axis, which doesn't conceptually make sense, so I don't think we would have to calculate a positive slope for equations that are given with a slope w a -k value.
- Sun Mar 11, 2018 7:01 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: 15.69
- Replies: 2
- Views: 431
Re: 15.69
In the equation, rate=K[reactants], K is directly related to the rate. Keep in mind, however, that K depends ONLY on the reaction and the temperature and will not change if the reactant concentrations change.
- Sun Mar 11, 2018 6:58 pm
- Forum: Second Order Reactions
- Topic: Half life of second order reactions
- Replies: 8
- Views: 1298
Re: Half life of second order reactions
I wouldn't worry too much about deriving the half life of a second order process. If we ever needed to use the equation, we would need 2 of the 3 unknowns: k, initial concentration, or the half life.
- Wed Feb 28, 2018 9:45 pm
- Forum: Zero Order Reactions
- Topic: Negative order
- Replies: 4
- Views: 815
Re: Negative order
I wouldn't worry too much about it when you're studying, since we will only be tested on 1st, 2nd and zeroth order.
- Wed Feb 28, 2018 9:44 pm
- Forum: General Rate Laws
- Topic: Half life
- Replies: 3
- Views: 477
Re: Half life
Today in class we derived that t1/2= 1/(k[A]sub0)
- Wed Feb 28, 2018 9:42 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Units of Reaction Rate
- Replies: 7
- Views: 901
Re: Units of Reaction Rate
We will use gas constant, R, when we talk more about activation energy and its relationship to k and A.
- Fri Feb 23, 2018 1:02 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: ln vs log [ENDORSED]
- Replies: 5
- Views: 920
Re: ln vs log [ENDORSED]
They are both just different ways to write the Nernst Equation, but they should yield the same answer
- Fri Feb 23, 2018 1:01 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell diagram [ENDORSED]
- Replies: 4
- Views: 601
Re: Cell diagram [ENDORSED]
You only use commas when they are in the same phase, such as when they're both aqueous. All other times a single line should be used.
- Fri Feb 23, 2018 1:00 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Spontaneous Directions [ENDORSED]
- Replies: 7
- Views: 1006
Re: Spontaneous Directions [ENDORSED]
Redox reactions are spontaneous when standard potential is positive. This makes sense if you think about the equation G=-nFE. If E is positive, G will be negative, indicating a spontaneous process.
- Fri Feb 16, 2018 5:41 pm
- Forum: Balancing Redox Reactions
- Topic: Salt Bridge Versus Pourous Disk
- Replies: 6
- Views: 777
Re: Salt Bridge Versus Pourous Disk
There isn't an overall difference, because both maintain neutrality in the solutions
- Fri Feb 16, 2018 5:39 pm
- Forum: Balancing Redox Reactions
- Topic: Salt Bridges
- Replies: 14
- Views: 1292
Re: Salt Bridges
Salt bridges keep both solutions neutral as reduction and oxidation are occurring
- Fri Feb 16, 2018 5:38 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode/ Cathode
- Replies: 6
- Views: 792
Re: Anode/ Cathode
Usually the anode is on the left and the cathode is on the right, and we see the electrons flow from left to right. If this isn't the case, though, just remember that oxidation (loss of elections) occurs at the anode and reduction (gain of electrons) occurs at the cathode.
- Sun Feb 11, 2018 12:29 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Sig Figs in 11.19
- Replies: 2
- Views: 454
Re: Sig Figs in 11.19
It should be two sig figs, but I wouldn't worry too much about it since we won't be penalized for improper sig figs on tests.
- Sun Feb 11, 2018 12:25 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Non-spontaneous
- Replies: 4
- Views: 653
Re: Non-spontaneous
The forward reaction is favored when there doesn't need to be an outside source, such as increasing temperature, to catalyze the reaction. If the forward reaction is favored, then the reverse reaction is not favored (and vice versa).
- Sun Feb 11, 2018 12:22 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 913
- Replies: 2
- Views: 373
Re: 913
Ideal gas behavior assumes that the ideal gas has a quantity of 1 mol.
- Wed Jan 31, 2018 11:26 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 9.3
- Replies: 5
- Views: 686
Re: 9.3
When heat is leaving a system, it's energy sign is negative. When it is entering a system, its energy sign is positive. This can also be applied when you're doing problem 9.5 when heat is being transferred from one reservoir to another.
- Wed Jan 31, 2018 11:24 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Question 9.5
- Replies: 3
- Views: 431
Re: Question 9.5
Heat is being given off in the 800K reservoir, which makes the energy sign negative, and it's being absorbed in the 200K reservoir, which makes its energy sign positive.
- Wed Jan 31, 2018 11:22 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: 9.5
- Replies: 5
- Views: 577
Re: 9.5
Heat is leaving the large reservoir at 800K, which explains why the entropy is negative.
- Wed Jan 24, 2018 4:57 pm
- Forum: Phase Changes & Related Calculations
- Topic: Combustion of liquids
- Replies: 4
- Views: 724
Re: Combustion of liquids
In combustion reactions, the products normally come in the form of gaseous CO2 and liquid H20, unless otherwise specified.
- Wed Jan 24, 2018 4:55 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Positive and Negative Signs 8.21
- Replies: 3
- Views: 417
Re: Positive and Negative Signs 8.21
It ends up not mattering which side gets the negative. What's important to know (as seen in the solutions manual) is that
heat lost=-(heat gained).
heat lost=-(heat gained).
- Wed Jan 24, 2018 4:52 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm
- Replies: 2
- Views: 307
Re: Midterm
I think it depends on how far we get into the Second & Third Laws and if we move on to Electrochemistry before the midterm. We'll probably learn more about it as the midterm gets closer.
- Thu Jan 18, 2018 12:00 pm
- Forum: Phase Changes & Related Calculations
- Topic: Question about Problem 8.41
- Replies: 5
- Views: 603
Re: Question about Problem 8.41
Yes because there is a transfer of heat from the water to the ice
- Thu Jan 18, 2018 11:59 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.29 heat capacity
- Replies: 3
- Views: 363
Re: 8.29 heat capacity
The solutions manual explains that as more atoms are present in the molecule, there are more possible bond vibrations that can absorb added energy
- Wed Jan 17, 2018 11:08 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: R value in equation
- Replies: 4
- Views: 339
Re: R value in equation
The R value depends on the units you're working with
- Fri Jan 12, 2018 11:26 am
- Forum: Phase Changes & Related Calculations
- Topic: Ideal Gas
- Replies: 5
- Views: 416
Re: Ideal Gas
An ideal gas means the gas follows the properties of gases "ideally." For example, an ideal gas contains random particle motion, and each particle collision is completely elastic (no energy is lost during the collision). An ideal gas follows the ideal gas law PV=nRT.
- Fri Jan 12, 2018 9:56 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: 4823
Re: Standard Enthalpies of Formation of Diatomic Molecules
O2 is the most stable form of oxygen and therefore has an enthalpy equal to zero. This is the same for other diatomic elements, such as nitrogen (N2), chlorine (Cl2), etc.
- Fri Jan 12, 2018 9:42 am
- Forum: Phase Changes & Related Calculations
- Topic: Constant Temperature
- Replies: 4
- Views: 383
Re: Constant Temperature
Because heat is needed for a phase change, the temperature of the sample will remain the same even though heat is being supplied because the heat is being used to break bonds.
- Tue Dec 05, 2017 11:24 am
- Forum: Bronsted Acids & Bases
- Topic: Proton Transfer Equilbria
- Replies: 2
- Views: 479
Re: Proton Transfer Equilbria
In an acid-base equilibrium reaction, a proton is transferred (bronsted), or another way to thing about it is that an electron is donated (Lewis).
- Tue Dec 05, 2017 11:20 am
- Forum: Lewis Acids & Bases
- Topic: Memorizing Acids and Bases
- Replies: 7
- Views: 857
Re: Memorizing Acids and Bases
I think it's important just to know the trends on the periodic table, which will help you determine which acids/bases are strong. For example, group 1 and group 2 hydroxides are generally strong bases. In addition, we learned that as the atomic radius increases (weaker bonds), it's easier for acids ...
- Thu Nov 30, 2017 10:58 am
- Forum: Naming
- Topic: Cobalt-cobaltate
- Replies: 2
- Views: 398
Re: Cobalt-cobaltate
-ate is added when the overall complex has a negative charge. Remember for iron instead of it becoming ironate it becomes ferrate.
- Thu Nov 30, 2017 10:55 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: TM cations in solutions
- Replies: 1
- Views: 253
Re: TM cations in solutions
TM cations in solution form complexes with H2O. Some ligands, however, bind more easily than others. Adding NH3 or KCN (electron rich species) will replace H20 ligands because it's an easier way to make coordination compounds.
- Wed Nov 29, 2017 3:08 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: T Shape or Trigonal Pyramidal
- Replies: 3
- Views: 533
Re: T Shape or Trigonal Pyramidal
T shape structures have the VSEPR formula AX3E2, which means there are 2 lone pairs on the central atom. Trigonal pyramidal structures have the VSEPR formula AX3E, which means there's one lone pair on the central atom.
- Wed Nov 29, 2017 2:59 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular v Electron Arrangement
- Replies: 2
- Views: 481
Re: Molecular v Electron Arrangement
Yes, the electron arrangement takes into account the lone pairs (same as looking at the amount of regions of electron density). For example, NH3 has 4 regions of electron density (tetrahedral arrangement), but has a molecular shape of trigonal pyramid.
- Tue Nov 21, 2017 10:26 am
- Forum: Hybridization
- Topic: lone pair effect on hybridization
- Replies: 3
- Views: 314
Re: lone pair effect on hybridization
A lone pair (like a single, double, or triple bond) counts as a region of electron density when determining hybridization. For example, oxygen in a water molecule has two single bonds and two lone pairs. 2+2=4 regions of electron density, creating the sp3 hybrid.
Re: Diaqaua
Diaqua means there are two water molecules (H2O) in the coordination complex
- Tue Nov 14, 2017 5:07 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Memorizing Shapes
- Replies: 2
- Views: 283
Re: Memorizing Shapes
We definitely need to know the shapes we learned in class, and also the shapes of molecules based on the regions of electron density before lone pairs are taken into account. Even though we didn't go over T-shaped, we had homework problems assigned that incorporated that shape, so I would definitely...
- Tue Nov 14, 2017 5:00 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Most Favorable Formal Charge
- Replies: 5
- Views: 3059
Re: Most Favorable Formal Charge
It's most favorable for the central atom to have a formal charge of zero. This is why an expanded octet on the central atom can be more stable than a regular octet. For example, SF6 has an expanded octet on the sulfur atom, but that is the most stable lewis structure.
- Tue Nov 07, 2017 11:28 am
- Forum: Lewis Structures
- Topic: Central atom
- Replies: 2
- Views: 272
Re: Central atom
If you think about trends on the periodic table, ionization energy decreases to the left, as does electronegativity (so you can think about it both ways). For SCN-, the overall trend for ionization energy is that it decreases down and to the left of the periodic table (carbon is further left, and th...
- Tue Nov 07, 2017 11:21 am
- Forum: Dipole Moments
- Topic: Dipole Moment and Formal Charge
- Replies: 1
- Views: 607
Re: Dipole Moment and Formal Charge
Formal charge changes depending on the way in which you draw the lewis structure of the compound. If the compound is not drawn in its most stable structure, I don't think the formal charge will always accurately display the most electronegative atom. When constructing the dipole moment, the arrow is...
- Tue Oct 31, 2017 10:04 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Difference between subshell and orbital [ENDORSED]
- Replies: 9
- Views: 2626
Re: Difference between subshell and orbital [ENDORSED]
A shell corresponds to the principal quantum number (n). Inside each shell are subshells, which are the angular momentum quantum numbers (l). Depending on the subshell, there is a specific amount of orbitals. For example, in the subshell l=1 (p-orbital) there are 3 orbitals where 6 electrons can occ...
- Tue Oct 31, 2017 10:02 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: d and s blocks
- Replies: 16
- Views: 2090
Re: d and s blocks
You write the electron configuration in order of increasing energy. Since n=3 is lower energy than n=4, 3d is written before 4s even though 4s comes first in the periodic table.
- Thu Oct 26, 2017 12:43 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Writing Electron Configuration for Excited element [ENDORSED]
- Replies: 2
- Views: 944
Re: Writing Electron Configuration for Excited element [ENDORSED]
Writing the electron configuration for an excited atom IS different than writing it in its ground state. When electron is in an excited state, it's in a higher energy level than its normal ground state. Therefore, when writing the electron configuration, you can put electrons in higher energy levels...
- Thu Oct 26, 2017 12:36 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Possible Quantum numbers given n=6
- Replies: 3
- Views: 725
Re: Possible Quantum numbers given n=6
If given n=6 on our test the correct answer for the possible l values are 0 to n-1. Even though we don't go beyond the f-orbital, there are levels of angular momentum beyond l=3.
- Tue Oct 17, 2017 8:01 pm
- Forum: Properties of Electrons
- Topic: Energy Levels
- Replies: 3
- Views: 555
Re: Energy Levels
Electrons can move up and down energy levels and the changes in energy are modeled by the difference in En for the hydrogen atom. Make sure that when you're finding Efinal-Einitial, the negative sign in the equation for En doesn't get lost.
- Mon Oct 16, 2017 5:58 pm
- Forum: Properties of Light
- Topic: Rydberg's Constant
- Replies: 4
- Views: 881
Re: Rydberg's Constant
I used the one given in Hz or s^-1 for question 1.13, and I think all of them should use the number in those units. When you're working on 1.13, don't forget the negative sign in the equation (this helped me realize a mistake I made in that problem).
- Wed Oct 11, 2017 4:44 pm
- Forum: Properties of Light
- Topic: Clarification on C=λv
- Replies: 10
- Views: 4240
Re: Clarification on C=λv
Since speed of light is constant (3.00 x 10^8 m/s) and therefore cannot change, if wavelength increases, frequency must decrease to keep their product equal to speed of light.
- Mon Oct 09, 2017 11:04 pm
- Forum: General Science Questions
- Topic: Rusty on High School Chem [ENDORSED]
- Replies: 347
- Views: 416347
Re: Rusty on High School Chem [ENDORSED]
I took chemistry in high school too and I still feel behind in some topics we're going to be learning soon. I found that the best way to learn the material was to do as many practice problems as possible and to find random youtube videos that describe processes in a creative way to make it help stic...