Search found 63 matches
- Thu Mar 14, 2019 7:34 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Arrhenius Equation.
- Replies: 4
- Views: 535
Re: Arrhenius Equation.
Basically, you will use the equation to solve for the rate, temperature, or activation energy. Also, you may use the equation to compare the reaction under different temperature. When using Arrhenius equation, typically all but one conditions would be given.
- Thu Mar 14, 2019 7:25 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Intermediate vs catalyst
- Replies: 8
- Views: 857
Re: Intermediate vs catalyst
Intermediates exists to show the reaction mechanism and it cancels out if you combine the separate steps together. However, catalyst is consumed and will be regenerated in the next step, and it functions to lower the activation energy.
- Thu Mar 14, 2019 7:21 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Pre Equilibrium Approach
- Replies: 3
- Views: 723
Re: Pre Equilibrium Approach
Usually, we use a pre equilibrium approach when the reaction is separated into a few steps in which the a fast step is followed by a slow step. In this case, we can assume that the faster step reaches equilibrium.
- Wed Mar 06, 2019 8:48 pm
- Forum: General Rate Laws
- Topic: Rate Laws and Temperature
- Replies: 4
- Views: 453
Re: Rate Laws and Temperature
Depending on what reaction's happening, the change of temperature would affect the rate of reaction. Therefore, we can conclude that since the concentration stays the same, k has to change.
- Wed Mar 06, 2019 8:40 pm
- Forum: First Order Reactions
- Topic: Units
- Replies: 3
- Views: 409
Re: Units
Essentially, the final unit for all reaction is M/s or mol/(L*s). Therefore, you can start from the end and make it back to the unit of k based on the orders.
- Wed Mar 06, 2019 8:34 pm
- Forum: General Rate Laws
- Topic: Unit for reaction rates
- Replies: 4
- Views: 489
Re: Unit for reaction rates
The final rate would always be M/s or mol/(L*s). Therefore, if the order of the reaction changes, in order to reach the final unit of M/s, the unit of k will have to change.
- Fri Mar 01, 2019 9:26 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: speed of reaction based on activation energy
- Replies: 6
- Views: 673
Re: speed of reaction based on activation energy
Yes. To add on that, when adding catalyst, you increase the rate of reaction because the activation energy barrier is lowered so that the reaction can proceed faster.
- Fri Mar 01, 2019 9:23 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Activation energy
- Replies: 8
- Views: 867
Re: Activation energy
Kinetic control means that even the reaction is favorable in terms of thermodynamics(gibbs free energy is zero), but kinetics trumps that because there is a huge activation energy barrier between the reactant and product.
- Fri Mar 01, 2019 9:21 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Kinetically Stable
- Replies: 3
- Views: 570
Re: Kinetically Stable
Kinetically stable means that the reactants need a lot of activation energy to turn into products. Thermodynamically stable means the reaction is favorable(gibbs free energy would be negative).
- Fri Feb 22, 2019 12:41 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Favor ability of Cell portential
- Replies: 5
- Views: 646
Re: Favor ability of Cell portential
Technically, if the galvanic cell is running properly and measured correctly, the cell potential should always be positive. This also means that the reaction would be spontaneous according to the equation since delta G would be negative.
- Fri Feb 22, 2019 12:36 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode and Cathode
- Replies: 4
- Views: 492
Re: Anode and Cathode
Anode is oxidation while cathode is reduction. When trying to identify them in the galvanic cell, preferably, you would write down the half reactions and identify the transfer of e-.
- Fri Feb 22, 2019 12:31 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 5
- Views: 579
Re: Salt Bridge
e- transfer from one "reaction beaker" to another will stop due to charge buildup. Therefore, a salt bridge is necessary to allow ion transfer so that the two solutions would stay neutral.
- Fri Feb 15, 2019 5:20 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy and Equilibrium
- Replies: 5
- Views: 530
Re: Gibbs Free Energy and Equilibrium
When the gibbs free energy is zero, the reaction is at equilibrium because neither the forward nor the reverse reaction is favored.
- Fri Feb 15, 2019 5:18 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Stability
- Replies: 3
- Views: 367
Re: Stability
For a specific compound, if it's gibbs free energy of formation is negative, then it's relatively stable.
- Fri Feb 15, 2019 5:13 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy
- Replies: 7
- Views: 729
Re: Gibbs free energy
This is the gibbs free energy equation: deltaG = deltaH - TdeltaS
when deltaG is negative, the reaction is spontaneous; when it's positive, the reaction is non spontaneous.
when deltaG is negative, the reaction is spontaneous; when it's positive, the reaction is non spontaneous.
- Sat Feb 09, 2019 9:41 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Predict entropy change
- Replies: 3
- Views: 578
Predict entropy change
Without performing any calculations, predict whether there is an increase or a decrease in entropy for each of the following processes: (a) Cl2 (g) + H2O (l) --> HCl (aq) + HClO (aq) The answer says that entropy decreases because there's not as many moles of gas on the right side of the equation. Do...
- Thu Feb 07, 2019 8:42 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Molar Entropy
- Replies: 9
- Views: 1287
Re: Molar Entropy
The mass is definitely a determining factor. However, we usually consider degeneracy first then the mass of the molecule.
- Thu Feb 07, 2019 8:37 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: 4G.3
- Replies: 1
- Views: 209
4G.3
Which would you expect to have a higher molar entropy at T=0, single crystals of BF3 or of COF2? Why?
- Thu Feb 07, 2019 7:52 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 4F.11
- Replies: 1
- Views: 224
4F.11
During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5 degrees Celsius was compressed suddenly and irreversibly to 0.500 L by driving in a piston. In the process, the temperature of the gas increased to 28.1 degrees Celsius. Assume ideal behavior. What is the change in entr...
- Fri Feb 01, 2019 12:19 pm
- Forum: Calculating Work of Expansion
- Topic: Reversible Expansion
- Replies: 3
- Views: 350
Re: Reversible Expansion
For example, the volume of the gas inside the container would not be fixed. It would increase/decrease depending on the pressure. We calculate the work of reversible expansion by using integral since the pressure keeps changing. The final equation would be w=-nRTln(V2/V1).
- Wed Jan 30, 2019 4:53 pm
- Forum: Calculating Work of Expansion
- Topic: calculation of work of irreversible and reversible expansion
- Replies: 5
- Views: 439
calculation of work of irreversible and reversible expansion
In order to calculate work, do we use internal or external pressure? For example, in the case of irreversible expansion, when the external pressure is smaller than the internal one, do we use the external or the internal? Do we always use the external/internal pressure when calculating the work?
- Wed Jan 30, 2019 4:26 pm
- Forum: Calculating Work of Expansion
- Topic: reversible & irreversible expansion
- Replies: 2
- Views: 278
reversible & irreversible expansion
Why that the maximum work is done by the reversible expansion?
- Thu Jan 24, 2019 10:51 pm
- Forum: Phase Changes & Related Calculations
- Topic: Water heating curve
- Replies: 7
- Views: 774
Re: Water heating curve
The heat is used in breaking the bonds. In order to break the bond, a lot of energy would be required. Therefore, the temperature will not increase since all the heat is used up.
- Thu Jan 24, 2019 10:47 pm
- Forum: Phase Changes & Related Calculations
- Topic: Change in Enthalpy
- Replies: 3
- Views: 322
Re: Change in Enthalpy
The change in enthalpy would be positive in this case because in order to have the liquid water change phase into vapor, the process requires heat. The final enthalpy minus initial would generate a positive change of enthalpy.
- Thu Jan 24, 2019 10:45 pm
- Forum: Phase Changes & Related Calculations
- Topic: Why steam causes severe burns
- Replies: 9
- Views: 1997
Re: Why steam causes severe burns
Because the steam undergoes condensation, a phase change, in which it releases a lot of energy. This energy would burn a lot more than just, for example, boiling water dropped on the skin because boiling water would only under go temperature change.
- Thu Jan 17, 2019 1:58 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Conjugates
- Replies: 4
- Views: 322
Re: Conjugates
The conjugate parts are usually the products. In order to identify the conjugates in the products, you need to know if the reactants are acids or base. In terms of that, you should see whether the reactants accept or donate protons. Acids generally lose protons, therefore, having conjugate base in t...
- Thu Jan 17, 2019 1:54 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: homework help
- Replies: 1
- Views: 221
Re: homework help
First of all, you should turn all the mass into concentration. Then you should set up an ICE table. The initial concentration of ammonium carbamate can be calculated, and we know at initial point, there's only ammonium carbamate in the flask. For the change of concentration, it should be -x, +2x, +x...
- Thu Jan 17, 2019 1:48 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Percent Ionization
- Replies: 3
- Views: 261
Re: Percent Ionization
We'll have to use the quadratic formula to calculate the exact value of x.
- Thu Jan 10, 2019 2:49 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: The Response of Equilibria to Changes in Conditions 11.79
- Replies: 1
- Views: 95
Re: The Response of Equilibria to Changes in Conditions 11.79
You need to write out the balanced equation. Then you can calculate Kc out of it. After, you set up an ICE table in which the initial for PN2, PH2, and PNH3 should be 3.11+1.57=4.68 bar, 1.64 bar, and 23.72 bar respectively. I 4.68 1.64 23.72 C -x -3x +2x E 4.68-x 1.64-3x 23.72+2x You will be able t...
- Thu Jan 10, 2019 2:36 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: how to write the formula for K
- Replies: 6
- Views: 449
Re: how to write the formula for K
If you are calculating Kp, then you need to write P subscript to indicate you are using the partial pressure. However, when you are calculating Kc, you can simply use the bracket to show the concentration.
- Wed Jan 09, 2019 9:21 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Calculating Kp
- Replies: 2
- Views: 78
Calculating Kp
When calculating Kp, do we have to change the unit of pressure into a standard one (bars or atm) or just use the unit that the question gives?
- Wed Dec 05, 2018 10:41 pm
- Forum: Identifying Acidic & Basic Salts
- Topic: Neutral salt
- Replies: 3
- Views: 511
Neutral salt
So I know that salts that contain conjugate acids of weak bases produce acidic solution, and salts that contain conjugate bases of weak acids produce basic solution. But how do you know when the salt is neutral? For example, KBr is a neutral salt. Is it that if it doesn't fit into any of the categor...
- Tue Dec 04, 2018 9:38 am
- Forum: Lewis Acids & Bases
- Topic: Ionic equation
- Replies: 1
- Views: 216
Ionic equation
When writing the complete ionic equation for a salt produced from the acid-base neutralization reaction, do we write all acids/bases in dissociated form(ions) or just the strong acids/bases? For example, homework J9 in 7th edition, I believe phosphoric acid, bromous acid, and hydrosulfuric acid are ...
- Mon Dec 03, 2018 5:53 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: CO3 2-
- Replies: 2
- Views: 388
CO3 2-
Why that CO3 2- can be either mono or bidentate ligands? Why that it can't be tridentate with the third oxygen atom?
- Thu Nov 29, 2018 1:01 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Single Electron in Terms of Shape
- Replies: 2
- Views: 283
Re: Single Electron in Terms of Shape
A single electron will affect the shape. However, because there's only one electron, the lone electron repulsion generated would be much smaller than the lone pair(two electrons). Therefore, the degree of angle distortion would be less significant.
- Thu Nov 29, 2018 12:56 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Angular Shape
- Replies: 3
- Views: 371
Re: Angular Shape
Angular shape is the same as bent shape. So it would be slightly less than 120 degrees.
- Mon Nov 26, 2018 6:37 pm
- Forum: Sigma & Pi Bonds
- Topic: Resonance structure
- Replies: 2
- Views: 246
Resonance structure
For the molecules that have resonance structures, for example SO3 2-, how many sigma and pi bonds does it have?
- Thu Nov 22, 2018 10:36 pm
- Forum: Dipole Moments
- Topic: Dipole-dipole & dipole-induced dipole
- Replies: 1
- Views: 270
Dipole-dipole & dipole-induced dipole
For assigned problem 3F.9, it asks us to place ion-dipole, dipole-induced dipole, dipole dipole in the gas phase, ion-ion, dipole-dipole in the solid phase in order of increasing strength. The answer shows that dipole induced dipole is similar to dipole dipole. I don’t quite understand why.
- Thu Nov 22, 2018 10:05 pm
- Forum: Ionic & Covalent Bonds
- Topic: Ionic & covalent character
- Replies: 6
- Views: 1248
Ionic & covalent character
When we are talking about ionic or covalent compounds/bonds, is it that we are saying the compound/bond has more ionic/covalent characters? Is it that essentially, there’s no clear cut between ionic/covalent?
- Mon Nov 19, 2018 9:27 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular shape on test
- Replies: 5
- Views: 418
Re: Molecular shape on test
I believe we need to predict the bond angle based on the lewis structure as well as hybridization.
- Sat Nov 17, 2018 5:46 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Formula for determining bond angle
- Replies: 6
- Views: 634
Re: Formula for determining bond angle
There is no formula for determining bond angle. A lot of the times we can only know the approximate bond angles because it differ based on the electron pair repulsion.
- Wed Nov 14, 2018 11:48 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Trigonal planar and bent shape
- Replies: 2
- Views: 1239
Trigonal planar and bent shape
If the lewis structure of a molecule, for example ClO2+, has a lone pair, does it make the shape a trigonal planar or bent? I thought it would be bent, since the lone pair repulsion would make the bond angle slightly less than 120 degrees, but the answer says it should be trigonal planar.
- Tue Nov 13, 2018 8:25 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: dipole dipole and london forces
- Replies: 2
- Views: 286
dipole dipole and london forces
How to distinguish between dipole dipole and london forces?
- Thu Nov 08, 2018 8:20 pm
- Forum: Bond Lengths & Energies
- Topic: Formula/ Memorization of Bond lengths?
- Replies: 3
- Views: 394
Re: Formula/ Memorization of Bond lengths?
I don't think we need to memorize any bond length. However, we do need to understand how to calculate the average bond length based on the lewis structure(such as resonance structures) and the value of bond length given.
- Thu Nov 08, 2018 7:59 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Polarizability
- Replies: 3
- Views: 160
Re: Polarizability
Polarizability gets higher as the number of electrons increases. This is because the nuclear charge has less control over the electrons due to the shielding effect. Therefore, the outer electrons are more easily distorted.
- Tue Nov 06, 2018 5:21 pm
- Forum: Bond Lengths & Energies
- Topic: Bond Lengths
- Replies: 6
- Views: 578
Re: Bond Lengths
When the molecule has resonance structures, you need to find the average bond length. For example, if the molecule has a single bond in one form of resonance and a double bond in the other, you need to calculate the average of the two.
- Wed Oct 31, 2018 8:08 pm
- Forum: Octet Exceptions
- Topic: 7th Edition 2C5.A
- Replies: 2
- Views: 312
Re: 7th Edition 2C5.A
I have the same question too. I think one possible reason would be that oxygen has a higher electronegativity, therefore pulling the electron to it. But I'm not sure if this explanation is right. I went to a chemistry drop in session today and the tutor there wasn't sure either.
- Wed Oct 31, 2018 8:04 pm
- Forum: Lewis Structures
- Topic: Most stable lewis
- Replies: 3
- Views: 396
Re: Most stable lewis
In order to know the most stable lewis structure, you should calculate the formal charge. The most stable lewis structure has the least formal charge on each atom.
- Tue Oct 30, 2018 7:17 pm
- Forum: Trends in The Periodic Table
- Topic: Electron affinity homework 1F.11
- Replies: 2
- Views: 401
Electron affinity homework 1F.11
The problem asks what element of each of the following pairs has the higher electron affinity: gallium or indium; beryllium or magnesium. The answer for both is equal. I don't quite understand how that works.
- Thu Oct 25, 2018 9:20 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Degeneracy
- Replies: 4
- Views: 465
Re: Degeneracy
For multi-electron, orbitals with same l but different ml are said to be degenerate. For hydrogen, orbitals with different n are degenerate because it only has one electron. This rule would not apply to multi-electron model because multi-electron model is more complicated and need to take the electr...
- Thu Oct 25, 2018 12:21 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Nodal Planes
- Replies: 6
- Views: 574
Re: Nodal Planes
The shape of s orbital is spherically symmetrical and there is no point of region where you can find that the electron probability density is zero.
- Tue Oct 23, 2018 2:29 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Significance of XYZ to PDF orbitals
- Replies: 6
- Views: 566
Re: Significance of XYZ to PDF orbitals
It is just to show the orbital orientations. X, Y, Z can be used to show different planes.
- Wed Oct 17, 2018 11:15 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: 7th Edition, 1B.27
- Replies: 3
- Views: 232
Re: 7th Edition, 1B.27
Does this rule also apply to the uncertainty in position? For example, when it's +-5m, is it that we should use 10m in the equation for uncertainty in position?
- Wed Oct 17, 2018 10:50 pm
- Forum: Lewis Structures
- Topic: ClO and ClNO3 Lewis Structure
- Replies: 1
- Views: 662
ClO and ClNO3 Lewis Structure
These are from homework 2C 5. The solution manual shows that for ClO, the lewis structure would be a single bond between Cl and O, however, leaving five valence electrons on Cl. I don't understand why there are only five valence electrons left in this lewis structure for Cl since Cl has seven valenc...
- Tue Oct 16, 2018 2:19 pm
- Forum: Lewis Structures
- Topic: Radicals
- Replies: 2
- Views: 275
Radicals
So according to the definition, the radicals have unpaired electrons. When it comes to odd number of electrons, the molecules would be seen as a radical while those have even number of electrons are not radicals. However, there's also the concept of paramagnetism and diamagnetism. What is the differ...
- Wed Oct 10, 2018 6:13 pm
- Forum: Photoelectric Effect
- Topic: Threshold Energy Question
- Replies: 2
- Views: 204
Re: Threshold Energy Question
This problem is asking for the energy required to remove an electron from ONE sodium atom. The work function given is the threshold energy needed to remove the electron from one mole of sodium atom. Therefore, in order to get the energy required to remove an electron from one sodium atom, you need t...
- Wed Oct 10, 2018 5:56 pm
- Forum: Properties of Light
- Topic: Diffraction patterns
- Replies: 2
- Views: 128
Re: Diffraction patterns
Thank you. This helps a lot!
- Tue Oct 09, 2018 7:11 pm
- Forum: Properties of Light
- Topic: Diffraction patterns
- Replies: 2
- Views: 128
Diffraction patterns
How does interacting waves give rise to diffraction patterns? Also, does the diffraction experiment(the slit experiment) need to be conducted under vacuum condition?
- Mon Oct 08, 2018 11:18 am
- Forum: Properties of Light
- Topic: Intensity of Light and Wavelength
- Replies: 3
- Views: 165
Intensity of Light and Wavelength
In the class, Dr. Lavelle talks about how increasing the intensity of light would increase the number of photons. I am little confused about the concept of light intensity. Is it related to the amplitude of wavelength? Does increasing/decreasing the amplitude of wavelength result to the increase/dec...
- Tue Oct 02, 2018 5:14 pm
- Forum: Significant Figures
- Topic: Accepted range of answers
- Replies: 2
- Views: 259
Accepted range of answers
For some of the multistep problems, I got answers that are slightly off from the ones on the solution manual due to significant figures. For example, 0.001-0.002 off for a three significant figure problem. I am wondering if my answer would be acceptable. What is generally the accepted range for the ...
- Tue Oct 02, 2018 4:30 pm
- Forum: SI Units, Unit Conversions
- Topic: Units for the answers
- Replies: 2
- Views: 155
Units for the answers
Some of the solutions give the answers that convert units like kg or mg into grams. Do we have to convert the units for answers in the homework/test into more frequently used units or it is fine as long as the significant figure are right?
- Sat Sep 29, 2018 8:12 pm
- Forum: Empirical & Molecular Formulas
- Topic: Formula unit
- Replies: 3
- Views: 511
Re: Formula unit
For example, E 25 asks for the number of KNO3 formula units in 0.750 mol KNO3.
- Sat Sep 29, 2018 7:38 pm
- Forum: Empirical & Molecular Formulas
- Topic: Formula unit
- Replies: 3
- Views: 511
Formula unit
There are several practice problems that ask for the formula unit of a molecule or ion. I am not sure what that means.