Search found 56 matches

by Andy Nguyen 1A
Sat Mar 17, 2018 8:11 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalysts
Replies: 3
Views: 224

Catalysts

How do we know if there is a catalyst in a reaction mechanism?
by Andy Nguyen 1A
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: 319

Re: 14.55

I believe you should get a positive voltage since the cell is electolytic.
by Andy Nguyen 1A
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: 998

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...
by Andy Nguyen 1A
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: 319

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.
by Andy Nguyen 1A
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: 103

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...
by Andy Nguyen 1A
Fri Mar 09, 2018 1:42 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 918761

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!".
by Andy Nguyen 1A
Fri Mar 09, 2018 1:34 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.85
Replies: 1
Views: 70

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
by Andy Nguyen 1A
Fri Mar 09, 2018 1:24 pm
Forum: Second Order Reactions
Topic: Units [ENDORSED]
Replies: 5
Views: 325

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).
by Andy Nguyen 1A
Fri Mar 02, 2018 10:34 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 918761

Re: Post All Chemistry Jokes Here

What did the police molecule say to the suspect molecule? I got my ion you.
by Andy Nguyen 1A
Fri Mar 02, 2018 10:27 pm
Forum: First Order Reactions
Topic: Psuedo 1st order rate law [ENDORSED]
Replies: 2
Views: 122

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...
by Andy Nguyen 1A
Fri Mar 02, 2018 10:23 pm
Forum: Zero Order Reactions
Topic: Relation between rate law and zero order [ENDORSED]
Replies: 3
Views: 120

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.
by Andy Nguyen 1A
Thu Feb 22, 2018 11:18 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams [ENDORSED]
Replies: 7
Views: 259

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.
by Andy Nguyen 1A
Thu Feb 22, 2018 11:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13c
Replies: 1
Views: 89

Re: 14.13c

I think it is because HCl is a strong acid, so it dissociates completely into H+ and Cl- ions.
by Andy Nguyen 1A
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: 158

Re: Pressure in calculating Q

I think Q is still calculated the same, but instead of using concentrations you are using pressures.
by Andy Nguyen 1A
Sun Feb 18, 2018 9:23 pm
Forum: Balancing Redox Reactions
Topic: Skeletal equation
Replies: 2
Views: 85

Skeletal equation

When we write out a skeletal equation, do we only include the species being reduced or oxidized?
by Andy Nguyen 1A
Tue Feb 13, 2018 8:39 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Iced tea and water problem
Replies: 2
Views: 305

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!
by Andy Nguyen 1A
Tue Feb 13, 2018 8:33 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: isothermal and deltaU=0
Replies: 3
Views: 183

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.
by Andy Nguyen 1A
Tue Feb 13, 2018 8:30 pm
Forum: Phase Changes & Related Calculations
Topic: U = 3/2 nRT
Replies: 3
Views: 839

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.
by Andy Nguyen 1A
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: 111

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?
by Andy Nguyen 1A
Fri Feb 09, 2018 2:01 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Self test 8.12A
Replies: 1
Views: 135

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.
by Andy Nguyen 1A
Thu Feb 08, 2018 12:10 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Standard Conditions
Replies: 3
Views: 171

Re: Standard Conditions

Standard conditions are usually noted with a ° like in S° or H°.
by Andy Nguyen 1A
Fri Feb 02, 2018 2:07 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question 3b on the test
Replies: 4
Views: 197

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....
by Andy Nguyen 1A
Fri Feb 02, 2018 2:04 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: dS, dV, dW
Replies: 2
Views: 93

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?
by Andy Nguyen 1A
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: 227

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.
by Andy Nguyen 1A
Sat Jan 27, 2018 12:28 pm
Forum: Calculating Work of Expansion
Topic: Irreversible Work Chart
Replies: 5
Views: 166

Re: Irreversible Work Chart

I think it was just used to show that a reversible reaction does more work than an irreversible reaction.
by Andy Nguyen 1A
Sat Jan 27, 2018 12:27 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 918761

Re: Post All Chemistry Jokes Here

What do you do with a dead chemist? You barium.
by Andy Nguyen 1A
Sat Jan 27, 2018 12:21 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Units
Replies: 2
Views: 86

Entropy Units

Since entropy is the number of states a system can have, is there units for entropy?
by Andy Nguyen 1A
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: 164

Re: Problem 8.49

You use 298 K because you assume the system is at standard conditions, so the temperature is 25 degrees Celsius.
by Andy Nguyen 1A
Mon Jan 22, 2018 10:27 pm
Forum: Phase Changes & Related Calculations
Topic: Question on Cv(vap)
Replies: 2
Views: 106

Re: Question on Cv(vap)

Cv(vap) is a constant, 2.01 (J/C*g). It was in table 8.2.
by Andy Nguyen 1A
Mon Jan 22, 2018 10:21 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Isothermal Expansion
Replies: 1
Views: 93

Re: Isothermal Expansion

I think that delta U is only 0 for isothermal expansion on ideal gases.
by Andy Nguyen 1A
Thu Jan 18, 2018 3:36 pm
Forum: Calculating Work of Expansion
Topic: Self-Test 8.1A
Replies: 1
Views: 105

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...
by Andy Nguyen 1A
Thu Jan 18, 2018 3:22 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Homework 8.15
Replies: 3
Views: 158

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.
by Andy Nguyen 1A
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: 112

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.
by Andy Nguyen 1A
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: 327

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.
by Andy Nguyen 1A
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: 195

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.
by Andy Nguyen 1A
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: 126

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?
by Andy Nguyen 1A
Sat Dec 09, 2017 9:36 pm
Forum: Ideal Gases
Topic: Kc and shifting of reaction
Replies: 3
Views: 368

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.
by Andy Nguyen 1A
Mon Dec 04, 2017 4:32 pm
Forum: Biological Examples
Topic: Cooridnate compound dentate
Replies: 2
Views: 254

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.
by Andy Nguyen 1A
Fri Dec 01, 2017 4:47 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Double bonds and poldentates
Replies: 1
Views: 141

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...
by Andy Nguyen 1A
Fri Dec 01, 2017 4:39 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 918761

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".
by Andy Nguyen 1A
Fri Dec 01, 2017 4:36 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Kw= [H30+]*[OH-]
Replies: 4
Views: 219

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...
by Andy Nguyen 1A
Thu Nov 23, 2017 4:26 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 918761

Re: Post All Chemistry Jokes Here

What fish is made of two atoms? 2Na
by Andy Nguyen 1A
Thu Nov 23, 2017 4:21 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Solids when using ICE [ENDORSED]
Replies: 8
Views: 483

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!
by Andy Nguyen 1A
Mon Nov 20, 2017 3:59 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 918761

Re: Post All Chemistry Jokes Here

Did you hear oxygen went on a date with potassium? It went OK.
by Andy Nguyen 1A
Mon Nov 20, 2017 3:56 pm
Forum: Ideal Gases
Topic: PV=nRT [ENDORSED]
Replies: 4
Views: 226

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.
by Andy Nguyen 1A
Mon Nov 20, 2017 3:51 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Number
Replies: 2
Views: 137

Re: Coordination Number

The coordination number is just the number of bonds attached to the central metal atom.
by Andy Nguyen 1A
Wed Nov 15, 2017 4:24 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 918761

Re: Post All Chemistry Jokes Here

If the Silver Surfer and Iron Man team up, they’d be alloys.
by Andy Nguyen 1A
Wed Nov 15, 2017 4:22 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 918761

Re: Post All Chemistry Jokes Here

I don't trust atoms... they make up everything.
by Andy Nguyen 1A
Wed Nov 15, 2017 4:18 pm
Forum: Dipole Moments
Topic: SiO2
Replies: 2
Views: 197

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.
by Andy Nguyen 1A
Thu Nov 09, 2017 1:42 pm
Forum: Lewis Structures
Topic: NO3- vs NF3 [ENDORSED]
Replies: 2
Views: 303

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 ...
by Andy Nguyen 1A
Fri Nov 03, 2017 4:50 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: The configuration of tungsten
Replies: 2
Views: 260

Re: The configuration of tungsten

From what I've looked at online, its another exception, so only Chromium and Molybdenum have different electron configurations.
by Andy Nguyen 1A
Fri Nov 03, 2017 4:47 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Trigonal planar vs. Trigonal bipyramidal
Replies: 4
Views: 294

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.
by Andy Nguyen 1A
Sat Oct 14, 2017 3:57 pm
Forum: Properties of Light
Topic: Light as a wave or a particle [ENDORSED]
Replies: 2
Views: 166

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!
by Andy Nguyen 1A
Sat Oct 14, 2017 3:47 pm
Forum: Photoelectric Effect
Topic: Confused about photoelectric effect! [ENDORSED]
Replies: 6
Views: 364

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?
by Andy Nguyen 1A
Tue Oct 03, 2017 9:48 pm
Forum: SI Units, Unit Conversions
Topic: Appendix 1D & 1E
Replies: 3
Views: 230

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...
by Andy Nguyen 1A
Tue Oct 03, 2017 9:39 pm
Forum: SI Units, Unit Conversions
Topic: Molecules [ENDORSED]
Replies: 10
Views: 497

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.

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