Search found 50 matches
- Sun Mar 18, 2018 10:31 pm
- Forum: General Science Questions
- Topic: Grade
- Replies: 8
- Views: 1482
Re: Grade
I think the class is graded.
- Sun Mar 18, 2018 2:59 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3013269
Re: Post All Chemistry Jokes Here
What do you do with a dead chemist?
Barium
Barium
- Sun Mar 18, 2018 2:58 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Putting an Ice cube into a glass of water
- Replies: 4
- Views: 1371
Re: Putting an Ice cube into a glass of water
Yes, need both deltaH fusion and deltaH for warming up liquid water to final temp.
- Sun Mar 18, 2018 2:55 pm
- Forum: Student Social/Study Group
- Topic: Final
- Replies: 11
- Views: 2042
Re: Final
Yeah was confused about that as well. Don't you need two unknown variables for a function?
- Sun Mar 18, 2018 2:42 pm
- Forum: Van't Hoff Equation
- Topic: Van't Hoff
- Replies: 9
- Views: 1135
Re: Van't Hoff
I think that this equation can be used for different temperatures and also different Ea as well.
- Sun Mar 18, 2018 2:38 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: isothermal = no internal energy change
- Replies: 4
- Views: 756
Re: isothermal = no internal energy change
Only isothermal reactions have u = 0 so q = -w. T being 0 does not always mean that q = 0. Isothermal reaction is when T = 0. This is because as work may be done by or done on the system, there is a supply or removal of heat from the system so that T = 0 and that the internal energy of the system re...
- Sun Mar 18, 2018 2:32 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3013269
Re: Post All Chemistry Jokes Here
Making bad chemistry jokes because all the good ones Argon
- Sun Mar 18, 2018 2:31 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3013269
Re: Post All Chemistry Jokes Here
What is the chemical formula for "coffee"?
CoFe2
CoFe2
- Sat Mar 17, 2018 8:47 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: What has greater residual entropy at 0K?
- Replies: 5
- Views: 1100
Re: What has greater residual entropy at 0K?
I think NO has resonance meaning that there has multiple possible structures. So there are more possible structures for NO than for BF3 which is why there is more residual entropy.
- Fri Mar 16, 2018 4:51 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: What has greater residual entropy at 0K?
- Replies: 5
- Views: 1100
Re: What has greater residual entropy at 0K?
Things to look for when comparing entropy. The following will usually have higher entropy:
Gases in larger volume>smaller volume
Gases>liquids>solids
Larger mass>smaller mass
Greater complexity>less complex
Gases in larger volume>smaller volume
Gases>liquids>solids
Larger mass>smaller mass
Greater complexity>less complex
- Fri Mar 16, 2018 4:48 pm
- Forum: General Rate Laws
- Topic: Writing out states for rate laws
- Replies: 4
- Views: 827
Re: Writing out states for rate laws
I'm pretty sure that we don't have to.
- Fri Mar 16, 2018 4:45 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: What has greater residual entropy at 0K?
- Replies: 5
- Views: 1100
Re: What has greater residual entropy at 0K?
Yes, you should draw out the lewis structures. If you do, you will see that NO is non-symmetric and has resonance. BF3 is symmetric and only has one configuration, so NO should have greater residual entropy.
- Fri Mar 16, 2018 4:06 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Substitution Reactions
- Replies: 2
- Views: 411
Re: Substitution Reactions
What do we have to know about the Sn2 organic reaction substitution nucleophile 2? I get that an atom is replaced by another, but what is the nucleophile?
- Fri Mar 16, 2018 4:01 pm
- 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: Microstate Determination
- Replies: 2
- Views: 564
Re: Microstate Determination
If the problem asks for calculating the number of microstates for one mole, make sure you use Avogadro's number for the number of atoms as the power.
- Fri Mar 16, 2018 3:48 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Collision Theory
- Replies: 3
- Views: 533
Re: Collision Theory
For the activated complex model, I think we need to know how to identify the slowest step (rate determinant step), which will be the highest peak. Additionally, to know the position of the atoms in a reaction as it progresses, like if the transition state will have atoms closer to the position that ...
- Fri Mar 16, 2018 3:40 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Collision Theory
- Replies: 3
- Views: 533
Re: Collision Theory
I think we need to know the 3 concepts
(1) molecules must collide
(2) must collide with sufficient energy to break bonds-overcome energy barrier or activation energy
(3) must collide in the correct orientation
(1) molecules must collide
(2) must collide with sufficient energy to break bonds-overcome energy barrier or activation energy
(3) must collide in the correct orientation
- Wed Mar 14, 2018 7:03 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Slow Step
- Replies: 4
- Views: 478
Re: Slow Step
I don't think the second step would be considered to be in equilibrium. If the first step is the slow step, the second step would just proceed normally. The rate is determined by the slow step so just the first. The reason why when the second step is slower, that the first step is considered to be i...
- Wed Mar 14, 2018 4:09 pm
- Forum: *Enzyme Kinetics
- Topic: Catalysts and Intermediates
- Replies: 5
- Views: 1170
Re: Catalysts and Intermediates
The main difference is that catalysts occur in the beginning and the end of the reaction. They may both be cancelled out, but catalysts occur in the beginning and may be consumed in one of the elementary steps, but in the end the catalyst will reform as it was in the beginning. An intermediate will ...
- Wed Mar 14, 2018 4:05 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Elementary reactions
- Replies: 6
- Views: 860
Re: Elementary reactions
It says in the lecture notes that the rate law for each elementary step follows directly from molecularity, which is the number of species. Because of that, we can determine that an elementary step with a first order rate law is unimolecular meaning one species, a second order rate law is bimolecula...
- Wed Mar 14, 2018 3:58 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Chapter 15.12?
- Replies: 4
- Views: 463
Re: Chapter 15.12?
I think that the equation is lnk = -Ea/RT + lnA with the negative sign.
- Wed Mar 14, 2018 3:57 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Chapter 15.12?
- Replies: 4
- Views: 463
Re: Chapter 15.12?
Also know that there in a graph with lnk and 1/T as its axes, the slope will be linear and will equal -Ea/R.
- Wed Mar 14, 2018 3:39 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts vs Intermediates
- Replies: 2
- Views: 455
Re: Catalysts vs Intermediates
The catalyst usually appears in the beginning of the reaction and the end of the reaction. So if it is consumed, it will reappear in the end. The intermediate does not appear in the beginning or the end of the reaction-it is both formed and consumed in the middle of the reaction.
- Wed Mar 14, 2018 3:34 pm
- Forum: General Rate Laws
- Topic: Test #3 Q3
- Replies: 3
- Views: 967
Re: Test #3 Q3
When we use the (change in concentration)/(change in time) equation does that mean that it is 1st order?
- Wed Mar 14, 2018 3:28 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: units
- Replies: 4
- Views: 743
Re: units
Also for kinetics specifically make sure you know that the units for a rate constant can vary depending on the order of the equation. The rate should be in mol/L*s so you can determine the rate constant from there depending on the order. Or we might have to get the order of a reaction when we are gi...
amine
Today in lecture, Dr. Lavelle said that for amines each atom that the N is bonded to could be replaced with a CH3, so it was drawn a single N with a lone pair and three CH3 groups. But in my notes it shows a that the functional group has a NH2. Does the N not have to be bonded to two H atoms?
- Wed Mar 14, 2018 3:14 pm
- Forum: *Alkanes
- Topic: Naming compounds
- Replies: 3
- Views: 3620
Re: Naming compounds
Will we be required to draw the functional groups?
- Tue Mar 06, 2018 9:06 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: K'
- Replies: 7
- Views: 884
Re: K'
Sorry, the equation is k = k'/([B initial]m [C initial]l)
- Tue Mar 06, 2018 9:03 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: K'
- Replies: 7
- Views: 884
Re: K'
There is also an equation if you are solving for k' for rate = k [A] [C], k = k'/[initial B]m [initial C]l[/b] when [B] and [C] are in surplus,
- Tue Feb 20, 2018 11:32 am
- Forum: Balancing Redox Reactions
- Topic: Balancing REDOX reactions
- Replies: 5
- Views: 662
Re: Balancing REDOX reactions
Because Eo is an intensive property, voltage difference is the same and does not depend on how many times the reaction occurs.
- Tue Feb 20, 2018 11:27 am
- Forum: Balancing Redox Reactions
- Topic: Anode vs Cathode and their Equations
- Replies: 2
- Views: 360
Re: Anode vs Cathode and their Equations
The anode has the element that is most likely oxidized while the cathode has the element that is reduced. The half-reaction with the element that is most likely reduced has a higher standard potential (more V) so it forms the cathode. The half-reaction with the element that is less likely reduced ha...
- Sun Dec 10, 2017 9:05 pm
- Forum: Conjugate Acids & Bases
- Topic: % Ionization [ENDORSED]
- Replies: 3
- Views: 852
Re: % Ionization [ENDORSED]
Is the hydrogen proton concentration the same as the conjugate base concentration for an acid?
- Sun Dec 10, 2017 9:02 pm
- Forum: Lewis Acids & Bases
- Topic: Strength [ENDORSED]
- Replies: 5
- Views: 1120
Re: Strength [ENDORSED]
Stronger acids tend to have a greater percent ionization because its conjugate base will tend to stay in that form and be more stable.
- Sun Dec 10, 2017 8:53 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Strong Bases? [ENDORSED]
- Replies: 2
- Views: 721
Re: Strong Bases? [ENDORSED]
Yes, strong bases have very stable conjugate acids because the strength of a base can be measured in how likely the conjugate acid is to stay an acid. This is because a strong base completely dissociates
- Sun Dec 10, 2017 8:44 pm
- Forum: Amphoteric Compounds
- Topic: Amphoteric [ENDORSED]
- Replies: 4
- Views: 933
Re: Amphoteric [ENDORSED]
Yes, amphiprotic compounds are included in amphoteric compounds because they can act as an acid or base. Amphiprotic compounds act as acids or bases by either donating or receiving protons.
- Sun Dec 03, 2017 11:42 pm
- Forum: Ideal Gases
- Topic: Q and K [ENDORSED]
- Replies: 35
- Views: 3025
Re: Q and K [ENDORSED]
Q is the formula for concentration of products/reactants at any time. K is the ratio of products to reactants at equilibrium and they use the same formulas
- Sun Dec 03, 2017 11:39 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Chemical Equilibrium
- Replies: 3
- Views: 537
Re: Chemical Equilibrium
The solvent is the material that contains the solute and concentration change in the solvent is assumed to be negligible, so it is not included in the chemical equilibrium expressions
- Sun Nov 26, 2017 10:46 pm
- Forum: Hybridization
- Topic: 4.41
- Replies: 4
- Views: 1944
Re: 4.41
I think a good way to look at it is also remembering the regions of electron density. Sp2 has three regions of electron density so it is trigonal planar. Sp has two regions of electron density so it is linear
- Sun Nov 26, 2017 10:38 pm
- Forum: Hybridization
- Topic: Filling the hybrid orbitals?
- Replies: 12
- Views: 1794
Re: Filling the hybrid orbitals?
Doesn't sp^2 hybridization have three regions of electron density?
- Sun Nov 19, 2017 11:28 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Octahedral vs Trigonal Bypyramidal family
- Replies: 3
- Views: 549
Re: Octahedral vs Trigonal Bypyramidal family
Yes pretty sure there is axial and equatorial plane. Lone pairs start occupying axial planes to make square pyramidal and square planar.
- Sun Nov 19, 2017 11:17 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Predicting bond angles
- Replies: 4
- Views: 656
Re: Predicting bond angles
After figuring out how many bonding areas there are, you still need to distinguish from atoms and lone pairs. Can't just rely on geometric shape to find bond angles because lone pairs affect the angles but only atoms are used to name the shape
- Sun Nov 12, 2017 9:49 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Formal Charge and stability [ENDORSED]
- Replies: 7
- Views: 8213
Re: Formal Charge and stability [ENDORSED]
Also important to note that the most stable structures are those that have lower energy. Atoms form bonds in order to reach a state of lower energy which is why it takes energy to break bonds.
- Sun Nov 12, 2017 6:15 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Formal Charge
- Replies: 8
- Views: 1080
Re: Formal Charge
It is also really rare to have a formal charge of -2 in a stable lewis structure, so if the formal charge ends up being -2, try reducing the formal charge by adding bonds or drawing them a different way.
- Sun Nov 05, 2017 11:53 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: Paramagnetic- Q3F 2013 Final
- Replies: 3
- Views: 781
Re: Paramagnetic- Q3F 2013 Final
Does the first electron to enter an orbital always have an upwards magnetic spin?
- Sun Nov 05, 2017 11:48 pm
- Forum: Hybridization
- Topic: Atomic orbitals [ENDORSED]
- Replies: 3
- Views: 694
Re: Atomic orbitals [ENDORSED]
It's also interesting because s has a magnetic quantum number of 0. And there's only one orbital for s because it is the orbital with symmetrical e- density. However p would have magnetic quantum numbers of -1, 0, and 1 because it has orbitals in the orientation of xy, yz. xz that line up on those n...
- Sun Oct 29, 2017 11:10 pm
- Forum: Hybridization
- Topic: Principle Quantum Number in D-Block [ENDORSED]
- Replies: 4
- Views: 1039
Re: Principle Quantum Number in D-Block [ENDORSED]
Why do electrons fill up the 4s shells before the 3d shells in Potassium and Scandium if 3d is lower energy?
- Sun Oct 29, 2017 11:04 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: Relationship between Electronegativity and Orbital Energy
- Replies: 4
- Views: 3862
Re: Relationship between Electronegativity and Orbital Energy
I think that the more electronegative an atom is, the more easy it is to attract electrons. This goes up in a diagonal trend, so increase as group goes to the right and as period goes up, disregarding noble gases. The atomic radius will increase as group goes to the left and period goes down. There ...
- Sun Oct 15, 2017 4:18 pm
- Forum: Properties of Light
- Topic: Understanding the Rydberg Formula [ENDORSED]
- Replies: 6
- Views: 997
Re: Understanding the Rydberg Formula [ENDORSED]
Frequency should always be positive so the negative sign is used when the change between initial and final is negative
- Sun Oct 15, 2017 4:13 pm
- Forum: Properties of Light
- Topic: How to use the Rydberg Formula? [ENDORSED]
- Replies: 6
- Views: 1290
Re: How to use the Rydberg Formula? [ENDORSED]
I'm pretty sure all equations that we need on the test will be provided on the equations sheet. It is negative because some people switch the n1 with the n2 and to keep frequency as a positive number, they use the negative sign.
- Tue Oct 03, 2017 10:46 pm
- Forum: Balancing Chemical Reactions
- Topic: Balancing Process
- Replies: 11
- Views: 1190
Re: Balancing Process
Yes I think it's just a guideline to follow to make it easier. I think when he says balance first the element that appears the least, he means the amount of times in the equation, not the number of moles.
- Tue Oct 03, 2017 10:34 pm
- Forum: Significant Figures
- Topic: All students read this sig fig post [ENDORSED]
- Replies: 170
- Views: 33599
Re: All students read this sig fig post [ENDORSED]
Hi, when there are numerous instances in a problem when multiplication/division is needed, can we just find the final answer and do the sig fig in the end after all the multiplication? Also, is a problem with both addition and multiplication different because you have to recount the sig figs after ...