Search found 56 matches
- Sat Mar 17, 2018 8:11 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Catalysts
- Replies: 3
- Views: 581
Catalysts
How do we know if there is a catalyst in a reaction mechanism?
- Sat Mar 17, 2018 8:10 pm
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: 14.55
- Replies: 3
- Views: 872
Re: 14.55
I believe you should get a positive voltage since the cell is electolytic.
- Thu Mar 15, 2018 10:06 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Question 14.41 [ENDORSED]
- Replies: 2
- Views: 1316
Re: Question 14.41 [ENDORSED]
This is what I did: Cathode: 2H+ + 2e- --> H2 Anode: H2 --> 2H+ + 2e- Overall: 2H+ + 2e- + H2 --> 2H+ + 2e- + H2 If you cancel the H2 out you get: 2H+ + 2e- --> 2H+ + 2e- So I guess you are supposed to factor out the 2 to get only 1 electron being transferred. I think H2 cancels out because they are...
- Thu Mar 15, 2018 9:49 pm
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: 14.55
- Replies: 3
- Views: 872
Re: 14.55
The +1.23 volts is for the oxidation reaction. The standard reduction potential is actually -1.23 V so the solution manual is correct. And you want to get the most negative value of E because in an electrolytic cell, the reaction is non spontaneous.
- Thu Mar 15, 2018 9:41 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: 14.101 Concentration Cells
- Replies: 1
- Views: 278
Re: 14.101 Concentration Cells
I think its because when you have the same species with different concentrations, the higher concentration of the species indicates that its the reactant while the lower concentration is the products. It's because the higher concentration will shift to the lower concentration to reach equilibrium, m...
- Fri Mar 09, 2018 1:42 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3665865
Re: Post All Chemistry Jokes Here
Heisenberg is driving when he gets pulled over. When the police officer asks how fast he was driving, Heisenberg replies "No, but I know exactly where I am!".
- Fri Mar 09, 2018 1:34 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: 15.85
- Replies: 1
- Views: 221
Re: 15.85
I think we did something like this in class today, but I found this link which had the same question. Hope this helps! viewtopic.php?t=2561
- Fri Mar 09, 2018 1:24 pm
- Forum: Second Order Reactions
- Topic: Units [ENDORSED]
- Replies: 5
- Views: 857
Re: Units [ENDORSED]
The unit for k in a 0 order reaction is mol/(L*s). In a first order reaction, k is in 1/s. In a second order reaction, k is L/(mol*s).
- Fri Mar 02, 2018 10:34 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3665865
Re: Post All Chemistry Jokes Here
What did the police molecule say to the suspect molecule? I got my ion you.
- Fri Mar 02, 2018 10:27 pm
- Forum: First Order Reactions
- Topic: Psuedo 1st order rate law [ENDORSED]
- Replies: 2
- Views: 447
Re: Psuedo 1st order rate law [ENDORSED]
It's considered a pseudo rate law because the if the normal rate law is Rate=k*A*B*C, we have to change the concentrations of B and C to see how A affects the rate. So under the assumption that B and C are in excess and are constants, we use the psuedo rate law Rate=kprime*A, where kprime=k*B*C. I t...
- Fri Mar 02, 2018 10:23 pm
- Forum: Zero Order Reactions
- Topic: Relation between rate law and zero order [ENDORSED]
- Replies: 3
- Views: 529
Re: Relation between rate law and zero order [ENDORSED]
Since the CO wasn't present we were able to assume it was a 0 order because it wasn't in the rate law. I think Dr. Lavelle mentioned that not all reactants actually affect the rate so in those cases they should have a 0 order as well.
- Thu Feb 22, 2018 11:18 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Diagrams [ENDORSED]
- Replies: 7
- Views: 862
Re: Cell Diagrams [ENDORSED]
These species that are added to the ends of the cell diagrams, like Pt, are inert electrodes that simply act as a way to transport the electrons.
- Thu Feb 22, 2018 11:14 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 14.13c
- Replies: 1
- Views: 232
Re: 14.13c
I think it is because HCl is a strong acid, so it dissociates completely into H+ and Cl- ions.
- Thu Feb 22, 2018 11:11 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Pressure in calculating Q
- Replies: 4
- Views: 545
Re: Pressure in calculating Q
I think Q is still calculated the same, but instead of using concentrations you are using pressures.
- Sun Feb 18, 2018 9:23 pm
- Forum: Balancing Redox Reactions
- Topic: Skeletal equation
- Replies: 2
- Views: 337
Skeletal equation
When we write out a skeletal equation, do we only include the species being reduced or oxidized?
- Tue Feb 13, 2018 8:39 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Iced tea and water problem
- Replies: 2
- Views: 1255
Re: Iced tea and water problem
I think that what you did is right since the ice melts so it becomes liquid water, so you have to use the specific heat capacity of water at a liquid. Was the enthalpy of vaporization in kJ/mol because that could effect how you convert the units. Hope this helps!
- Tue Feb 13, 2018 8:33 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: isothermal and deltaU=0
- Replies: 3
- Views: 653
Re: isothermal and deltaU=0
Using U=(3/2)*R*T, we know that this is the internal energy for an ideal gas. So that means the only thing changing U is temperature since (3/2) and R are constants. So since isothermal means the temperature doesn't change, deltaU=0.
- Tue Feb 13, 2018 8:30 pm
- Forum: Phase Changes & Related Calculations
- Topic: U = 3/2 nRT
- Replies: 3
- Views: 2060
Re: U = 3/2 nRT
I think that would be one of the only instances to use it. Dr. Lavelle has also used it to show that deltaU is 0 during isothermic processes, but I don't think we will use the equation too much.
- Fri Feb 09, 2018 2:07 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: What makes E an intrinsic property? [ENDORSED]
- Replies: 1
- Views: 287
What makes E an intrinsic property? [ENDORSED]
What makes the cell potential an intrinsic property since we don't multiply it by anything when we do problems with half reactions?
- Fri Feb 09, 2018 2:01 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Self test 8.12A
- Replies: 1
- Views: 443
Re: Self test 8.12A
I used those same numbers and got the answer from the book. I plugged in
-3920 kJ = deltaU + (-3 mol) * (.008314 kJ/Kmol) * 298K. Then I solved for deltaU.
-3920 kJ = deltaU + (-3 mol) * (.008314 kJ/Kmol) * 298K. Then I solved for deltaU.
- Thu Feb 08, 2018 12:10 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Standard Conditions
- Replies: 3
- Views: 424
Re: Standard Conditions
Standard conditions are usually noted with a ° like in S° or H°.
- Fri Feb 02, 2018 2:07 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Question 3b on the test
- Replies: 4
- Views: 661
Re: Question 3b on the test
Since the system is isothermal, we know that the change in internal energy is 0. So q+w=0, and q=-w. Since the balloon is expanding its volume against a changing pressure, work is being done. This also means that the energy lost during work is gained as heat, because the internal energy must stay 0....
- Fri Feb 02, 2018 2:04 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: dS, dV, dW
- Replies: 2
- Views: 359
dS, dV, dW
When deriving equations, the book changes terms from delta S to dS or dq because they say the change is infinitesimal. What does this mean?
- Fri Feb 02, 2018 1:56 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: How to tell what happens to entropy by seeing a reaction?
- Replies: 6
- Views: 1037
Re: How to tell what happens to entropy by seeing a reaction?
Normally, combustion reactions result in an increase in entropy. Based on the phase changes, we see that a solid changed into a gas and liquid, which means an increase in entropy.
- Sat Jan 27, 2018 12:28 pm
- Forum: Calculating Work of Expansion
- Topic: Irreversible Work Chart
- Replies: 5
- Views: 486
Re: Irreversible Work Chart
I think it was just used to show that a reversible reaction does more work than an irreversible reaction.
- Sat Jan 27, 2018 12:27 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3665865
Re: Post All Chemistry Jokes Here
What do you do with a dead chemist? You barium.
- Sat Jan 27, 2018 12:21 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy Units
- Replies: 2
- Views: 750
Entropy Units
Since entropy is the number of states a system can have, is there units for entropy?
- Mon Jan 22, 2018 10:32 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Problem 8.49
- Replies: 3
- Views: 458
Re: Problem 8.49
You use 298 K because you assume the system is at standard conditions, so the temperature is 25 degrees Celsius.
- Mon Jan 22, 2018 10:27 pm
- Forum: Phase Changes & Related Calculations
- Topic: Question on Cv(vap)
- Replies: 2
- Views: 237
Re: Question on Cv(vap)
Cv(vap) is a constant, 2.01 (J/C*g). It was in table 8.2.
- Mon Jan 22, 2018 10:21 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Isothermal Expansion
- Replies: 1
- Views: 223
Re: Isothermal Expansion
I think that delta U is only 0 for isothermal expansion on ideal gases.
- Thu Jan 18, 2018 3:36 pm
- Forum: Calculating Work of Expansion
- Topic: Self-Test 8.1A
- Replies: 1
- Views: 183
Self-Test 8.1A
Water expands when it freezes. How much work does 100 g of water do when it freezes at 0.0 degrees Celsius and pushes back the metal wall of a pipe that exerts an opposing pressure of 1070 atm? The densities of water and ice at 0 degrees Celsius are 1 g/cm3 and 0.92 g/cm3 respectively. I am having t...
- Thu Jan 18, 2018 3:22 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Homework 8.15
- Replies: 3
- Views: 441
Re: Homework 8.15
Since it is an adiabatic process, no heat is transferred, so q must be 0 always. q would be negative if heat was allowed to transfer from the system to the surroundings, making the reaction exothermic.
- Thu Jan 18, 2018 3:16 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Lewis structures for bond enthalpies
- Replies: 3
- Views: 274
Re: Lewis structures for bond enthalpies
I think we do need to know which bonds are formed and are broken because it will affect the value of the enthalpy of the reaction. The lewis structures are helpful to see which bonds are broken and formed.
- Fri Jan 12, 2018 12:51 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Hess's Law
- Replies: 8
- Views: 1426
Re: Hess's Law
I think in Hess's Law problems, the stoichiometric coefficients are often fractions to make the math easier. Multiplying by fractions just means you multiply the enthalpy by the same fraction as well.
- Fri Jan 12, 2018 12:30 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy Change Signs
- Replies: 5
- Views: 1443
Re: Enthalpy Change Signs
To add on, if a reaction was exothermic, the enthalpy sign would be negative. So the reverse reaction would be endothermic, making the enthalpy sign positive.
- Fri Jan 12, 2018 12:27 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard Enthalpy of Formation vs Standard Enthalpy of Reaction
- Replies: 3
- Views: 402
Standard Enthalpy of Formation vs Standard Enthalpy of Reaction
What is the difference between the standard enthalpy of formation and the standard enthalpy of the reaction?
- Sat Dec 09, 2017 9:36 pm
- Forum: Ideal Gases
- Topic: Kc and shifting of reaction
- Replies: 3
- Views: 773
Re: Kc and shifting of reaction
I think if you are given Q with Kc, then you can see how the reaction will shift. If Q<K, the reaction shifts right. If Q>K, the reaction shifts left.
- Mon Dec 04, 2017 4:32 pm
- Forum: Biological Examples
- Topic: Cooridnate compound dentate
- Replies: 2
- Views: 585
Re: Cooridnate compound dentate
I think to find the type of dentate a compound is you look at how many atoms have lone pairs. It helps to see the Lewis Structure and find those sites. For example, water has one atom, oxygen, with two lone pairs. Water is a monodentate because it only has one atom with a binding site.
- Fri Dec 01, 2017 4:47 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Double bonds and poldentates
- Replies: 1
- Views: 268
Re: Double bonds and poldentates
A molecule is a polydentate if it has more than one atom that can bind to a central metal atom/ion at different sites. For example, ethylenediamine is a bidentate because if you look at the lewis structure, there are lone pairs on 2 different nitrogen atoms. In water, there are two lone pairs on the...
- Fri Dec 01, 2017 4:39 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3665865
Re: Post All Chemistry Jokes Here
A neutron walks into a bar and orders a drink. When the neutron asks how much the drink was, the bartender replies "For you, no charge".
- Fri Dec 01, 2017 4:36 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Kw= [H30+]*[OH-]
- Replies: 4
- Views: 615
Kw= [H30+]*[OH-]
In lecture today we found the equation for kw, which was Kw= [H30+]*[OH-], from the chemical reaction 2H20 --> H30+ + OH-. Is H2O not part of the equation for Kw because it is in a liquid state? Dr. Lavelle also mentioned that it was because there was a large amount of water but I'm not sure what he...
- Thu Nov 23, 2017 4:26 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3665865
Re: Post All Chemistry Jokes Here
What fish is made of two atoms? 2Na
- Thu Nov 23, 2017 4:21 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Solids when using ICE [ENDORSED]
- Replies: 8
- Views: 3386
Solids when using ICE [ENDORSED]
When we calculate the equilibrium constant I know that we ignore solids and liquids. Do we also do this when using the ICE method? Thank you!
- Mon Nov 20, 2017 3:59 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3665865
Re: Post All Chemistry Jokes Here
Did you hear oxygen went on a date with potassium? It went OK.
- Mon Nov 20, 2017 3:56 pm
- Forum: Ideal Gases
- Topic: PV=nRT [ENDORSED]
- Replies: 4
- Views: 611
Re: PV=nRT [ENDORSED]
If the pressure isn't given in atm, then you can use 760 mmHg = 1 atm and 101.325 kPa = 1 atm.
- Mon Nov 20, 2017 3:51 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Coordination Number
- Replies: 2
- Views: 325
Re: Coordination Number
The coordination number is just the number of bonds attached to the central metal atom.
- Wed Nov 15, 2017 4:24 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3665865
Re: Post All Chemistry Jokes Here
If the Silver Surfer and Iron Man team up, they’d be alloys.
- Wed Nov 15, 2017 4:22 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3665865
Re: Post All Chemistry Jokes Here
I don't trust atoms... they make up everything.
- Wed Nov 15, 2017 4:18 pm
- Forum: Dipole Moments
- Topic: SiO2
- Replies: 2
- Views: 418
Re: SiO2
My reasoning for putting SiO2 as polar was because of the slight difference in electronegativity. Since there was a slight difference in electronegativity, the compound did have ionic properties, but was not completely ionic.
- Thu Nov 09, 2017 1:42 pm
- Forum: Lewis Structures
- Topic: NO3- vs NF3 [ENDORSED]
- Replies: 2
- Views: 1662
Re: NO3- vs NF3 [ENDORSED]
When you are drawing a Lewis structure, I think you have to look at the formal charges. NO3- has a double bond to minimize the formal charges of each atom because if there were lone pairs, the formal charge would not match the charge of the nitrate ion. Without the double bond, the formal charge of ...
- Fri Nov 03, 2017 4:50 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: The configuration of tungsten
- Replies: 2
- Views: 678
Re: The configuration of tungsten
From what I've looked at online, its another exception, so only Chromium and Molybdenum have different electron configurations.
- Fri Nov 03, 2017 4:47 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Trigonal planar vs. Trigonal bipyramidal
- Replies: 4
- Views: 1742
Re: Trigonal planar vs. Trigonal bipyramidal
Hi, just to add on, molecules that have a trigonal bipyramidal shape have more regions of electron density so these bonds are as far away as possible. A trigonal planar is only on one plane while the trigonal bipyramidal adds a 3rd dimension.
- Sat Oct 14, 2017 3:57 pm
- Forum: Properties of Light
- Topic: Light as a wave or a particle [ENDORSED]
- Replies: 2
- Views: 304
Light as a wave or a particle [ENDORSED]
Hello, I am still confused on when light acts as a wave or a particle. In the photoelectric effect, light acted as photons to remove electrons, but in other experiments, light can act as a wave. Can someone clarify this? Thank you!
- Sat Oct 14, 2017 3:47 pm
- Forum: Photoelectric Effect
- Topic: Confused about photoelectric effect! [ENDORSED]
- Replies: 6
- Views: 986
Re: Confused about photoelectric effect! [ENDORSED]
So was the fact that light can act as a particle the unexpected effect or was it something else?
- Tue Oct 03, 2017 9:48 pm
- Forum: SI Units, Unit Conversions
- Topic: Appendix 1D & 1E
- Replies: 3
- Views: 322
Re: Appendix 1D & 1E
I don't think there will be questions specifically on 1B and 1C, but the concepts might be used in problems on the tests. My TA told us that knowing the unit conversions can save time when doing stoichiometry. For 1C, it might be helpful to know the rules for significant figures when writing your an...
- Tue Oct 03, 2017 9:39 pm
- Forum: SI Units, Unit Conversions
- Topic: Molecules [ENDORSED]
- Replies: 10
- Views: 1381
Re: Molecules [ENDORSED]
The textbook says that a mole of something has the same number of atoms in carbon-12, which is 6.02x10^23 atoms.