## Search found 50 matches

Sun Mar 18, 2018 2:37 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Electrolytic cells vs Galvanic Cells
Replies: 3
Views: 698

### Re: Electrolytic cells vs Galvanic Cells

A galvanic cell (left) transforms the energy released by a spontaneous redox reaction into electrical energy that can be used to perform work. In an electrolytic cell (right), an external source of electrical energy is converted to chemical energy.
Sun Mar 18, 2018 2:29 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: isothermal = no internal energy change
Replies: 4
Views: 384

### Re: isothermal = no internal energy change

I believe it applies to just isothermal reactions.
Sat Mar 17, 2018 8:56 pm
Forum: General Rate Laws
Topic: Test #3 Q. 3
Replies: 2
Views: 387

### Re: Test #3 Q. 3

Could you the post the question as I think there are different test versions?
Sun Mar 11, 2018 11:03 pm
Forum: Calculating Work of Expansion
Topic: Midterm 4a
Replies: 5
Views: 402

### Re: Midterm 4a

The question is: A piston containing 0.10 mol of nitrogen gas at 298 K has an initial volume of 2.24 L and undergoes an expansion against 0.5 atm external pressure until its volume doubles. Calculate the work involved in Joules. The key here is that it states there is an external pressure of 0.5 atm...
Sun Mar 11, 2018 10:55 pm
Forum: Calculating Work of Expansion
Topic: Midterm Q3B
Replies: 7
Views: 443

### Re: Midterm Q3B

I believe that molar mass would still be considered an intensive property. Since it is still the mass of one mole of a given substance and thus does not depend on the amount of substance.
Sun Mar 11, 2018 10:41 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal Processes
Replies: 2
Views: 280

### Re: Isothermal Processes

Internal energy is due to motion of particles in a system which depends on temperature. As you mentioned, temperature in isothermal process is constant, so the internal energy will also be constant. Therefore, the change in internal energy 0. Hope that helps!
Sun Mar 04, 2018 11:56 pm
Forum: Zero Order Reactions
Topic: Will we need to know how to derive equations? [ENDORSED]
Replies: 9
Views: 506

### Re: Will we need to know how to derive equations?[ENDORSED]

While Dr. Lavelle has said that he wouldn't directly ask us to derive equations in the past, it would be a good idea to know how to derive the order of reaction equations.
Sun Mar 04, 2018 11:53 pm
Forum: Second Order Reactions
Topic: Week 9 HW and test promblems
Replies: 5
Views: 420

### Re: Week 9 HW and test promblems

As the above poster mentioned, all assigned homework questions are fair game. In terms of finding posts by TAs/UAs, I would try using the search user function and search for "Chem Mod"
Sun Mar 04, 2018 11:33 pm
Forum: First Order Reactions
Topic: Derivations
Replies: 6
Views: 342

### Re: Derivations

I think that there is possibility that we will be asked to derive on not just the final, but the quiz as well.
Mon Feb 26, 2018 12:04 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Nernst Equation
Replies: 6
Views: 419

### Re: Nernst Equation

To find the moles of electrons transferred, you'll want to look at the two balanced half reactions and make sure that the electron change is same in both.
Wed Feb 21, 2018 1:43 am
Forum: Balancing Redox Reactions
Topic: Finding half reactions
Replies: 4
Views: 258

### Re: Finding half reactions

I believe the two half reduction reactions were found in Appendix 2B.
Wed Feb 21, 2018 1:28 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: calculating n
Replies: 9
Views: 522

### Re: calculating n

You have to look at how many electrons are transferred in the balanced half-reactions. In other words, find the number of electrons in each balanced half-reaction. If they match, that is n. If they don't match, take the lowest common multiple, and that is n.
Sun Feb 18, 2018 8:43 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Q
Replies: 7
Views: 352

### Re: Q

If Q is greater than K, the reaction will shift to the left and if it's less than K then the reaction will shift to the right!
Sun Feb 18, 2018 8:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell reactions
Replies: 3
Views: 189

### Re: Cell reactions

Yes. Generally speaking, the left side of the cell diagram will correspond to the anode (oxidation) while the right side will correspond to the cathode (reduction). Hope that helps!
Sun Feb 18, 2018 8:21 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic vs. Voltaic
Replies: 5
Views: 236

### Re: Galvanic vs. Voltaic

The two actually refer to the same type of electrochemical cell. That is that they both convert chemical energy into electrical energy. Hope that helps!
Sun Feb 11, 2018 2:23 pm
Forum: Balancing Redox Reactions
Topic: Oxidation vs. reduction
Replies: 8
Views: 289

### Re: Oxidation vs. reduction

Another way to remember this is OIL RIG. Oxidation is Loss. Reduction is Gain. So you'll want to compare the reactants and products and see if the oxidation number decreases or increases to help determine whether or not it was oxidized or reduced.
Sun Feb 11, 2018 1:34 pm
Forum: Balancing Redox Reactions
Topic: cat/anions
Replies: 2
Views: 160

### Re: cat/anions

Both! For example, a common material for salt bridges is KCl. The K+ ions dissociate into the cation end, and the Cl- ions dissociate into the anion end to counter charge buildup.
Sat Feb 10, 2018 5:10 pm
Forum: Calculating Work of Expansion
Topic: Reversible reaction and Detla U
Replies: 3
Views: 215

### Re: Reversible reaction and Detla U

Are you referring to delta u in an isothermal reaction? This is because for an ideal gas U = 3/2 nRT. Therefore, if the moles of gas stay the same, n is constant, R is the gas constant, and if T is constant (which is what isothermal means) then U is constant which means delta U = 0.
Sun Feb 04, 2018 11:00 pm
Forum: Phase Changes & Related Calculations
Topic: The universe
Replies: 9
Views: 438

### Re: The universe

You might be getting confused with the entire universe vs the "observable" universe. The entire universe is isolated because it contains everything by definition, and has no surroundings as a result. It literally is everything. However, if you are referring to the universe that we can see,...
Sun Feb 04, 2018 10:53 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: change in entropy with change in temperature
Replies: 2
Views: 150

### Re: change in entropy with change in temperature

Just adding onto the above post. The first equation is looking at when the change in volume is positive; therefore entropy is increasing. The second one occurs under constant pressure and we are looking at the change in temperature. Here, lower temperature means higher entropy. Hope that helps!
Wed Jan 31, 2018 8:04 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Celsius or Kelvin
Replies: 5
Views: 248

### Re: Celsius or Kelvin

You should convert to Kelvin as it is no longer ΔT in the equation, but T (The general formula for change in entropy being ΔS = qrev/T).
Sun Jan 28, 2018 1:03 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy and Gravity
Replies: 1
Views: 140

### Re: Entropy and Gravity

I believe the answer to your question is yes. Entropy is still increased because of the kinetic energy being given off as heat, so while the entropy is low in terms of less positions/dispersed, the total entropy is higher because of the change in temperature. Hope that helps!
Sun Jan 28, 2018 12:49 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: More Entropy vs. Less Entropy
Replies: 3
Views: 165

### Re: More Entropy vs. Less Entropy

Dr. Lavelle has been making a point to avoid using the word "disorder" when discussing entropy, so I believe avoiding that terminology might help with understanding it. Based on the two principles mentioned above, a system is stable when the internal energy is at its minimum and the entrop...
Sun Jan 28, 2018 12:26 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Increasing temperature to make G negative
Replies: 3
Views: 236

### Re: Increasing temperature to make G negative

Generally this should be true for all endothermic processes as raising the temperature of the reaction favors the products. This means that the reverse reaction is favored which is exothermic. Hope that helps!
Sun Jan 21, 2018 3:28 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Intensive vs. Extensive
Replies: 3
Views: 373

### Re: Intensive vs. Extensive

An extensive property depends on the amount of matter in a sample (Ex: Volume). In contrast, an intensive property is independent of the amount of matter in a sample (Ex: Density). Hope that helps!
Sun Jan 21, 2018 12:31 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.31
Replies: 3
Views: 129

### Re: 8.31

Just to add on that R represents the gas constant which varies depending on what units you are using. As mentioned above, it can be found on the constant and equations sheet on Dr. Lavelle's website.
Sun Jan 21, 2018 12:20 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.49
Replies: 1
Views: 87

### Re: 8.49

I believe we are assuming the reaction takes place at room temperature (25 ºC/298 K).
Sun Jan 14, 2018 12:40 pm
Forum: Phase Changes & Related Calculations
Topic: Extensive vs Intensive
Replies: 2
Views: 181

### Re: Extensive vs Intensive

One way that I think of to remember it is that INtensive properties are INdependent of mass. Meanwhile, an EXtensive property will increase if an EXtra amount is added as it does depend on mass. Hope that helps!
Sun Jan 14, 2018 12:34 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Calorimeter
Replies: 10
Views: 581

### Re: Calorimeter

A calorimeter is how we measure specific heat capacity. The coffee cup calorimeter measures heat under conditions of constant pressure while the bomb calorimeter measures heat under constant volume. Not sure about your second question, but I do suspect that we'll see more of it in problems and appli...
Sun Jan 14, 2018 12:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law: Method 1
Replies: 3
Views: 218

### Re: Hess's Law: Method 1

Hess's Law can be defined as: The overall reaction enthalpy is the sum of the reaction enthalpies of the steps into which the reaction can be divided. In that example, we're looking at two steps of the reaction, Nitrogen oxide formation (N2 + O2 --> 2NO) and then its reaction with oxygen (2NO + O2 -...
Thu Dec 07, 2017 8:10 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Midterm Question
Replies: 2
Views: 322

### Re: Midterm Question

As you know, Heisenberg's uncertainty principle is: Δp x Δx ≥ h/4π Now, the question gives us the mass of the marble as well as the uncertainty in velocity which allows us to find Δp. Since momentum is mass x velocity, you take 1.5 x 10^-3 kg (converted from grams) x 1.1 m/s (because +/-). This will...
Tue Dec 05, 2017 10:57 pm
Forum: Trends in The Periodic Table
Topic: Second Ionization Energy
Replies: 1
Views: 224

### Re: Second Ionization Energy

Mg will actually have a smaller second ionization energy than Na because the first ionization energy of Na results in Na+ having a full valence shell (similar to Ne). As having a full valence shell is very favorable, it will be more difficult to remove a second electron from Na in comparison to Mg (...
Sun Dec 03, 2017 2:39 pm
Forum: Hybridization
Topic: Clarification on hybridization
Replies: 3
Views: 316

### Re: Clarification on hybridization

Yes, lone pairs also contribute to the type of hybridization. For example, BrF3 has a Br with two lone pairs bonded to three F atoms making it sp^3d (5 areas of electron density). Hope that helps!
Sat Dec 02, 2017 3:21 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strong acid vs weak acid [ENDORSED]
Replies: 7
Views: 435

### Re: Strong acid vs weak acid[ENDORSED]

What makes a strong acid completely ionize or disassociate as opposed to a weak one? Strong acids have mostly ions in solution, therefore the bonds holding H and A together must be weak. In other words, strong acids easily break apart into ions allowing them to completely dissociate in contrast to ...
Sat Dec 02, 2017 2:24 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Conceptual question about pH / pOH [ENDORSED]
Replies: 1
Views: 173

### Re: Conceptual question about pH / pOH[ENDORSED]

The pH of a solution is related to its concentration of hydrogen ions - the higher the concentration of hydrogen ions H+ the lower the pH. At the same concentration of acid, the concentration of hydrogen ions will be higher in a strong acid than in a weak acid. This is because a strong acid will don...
Sun Nov 26, 2017 11:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solids and Liquids
Replies: 3
Views: 276

### Re: Solids and Liquids

Solids and liquids are not included in the K expression because their concentrations stay constant throughout the reaction. Therefore, they do not affect the reactant amount at equilibrium in the reaction. Hope that helps!
Sat Nov 25, 2017 8:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium
Replies: 2
Views: 141

### Re: Equilibrium

Even though there is no net change at equilibrium, both the forward and reverse reactions are still taking place. In other words the reactants are being formed as fast as they are consumed. Hope that helps!
Sat Nov 25, 2017 12:40 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: IF7
Replies: 2
Views: 297

### Re: IF7

It is a pentagonal bipyramidal because there are 7 bonding electron pairs with 0 lone pairs. Hope that helps!
Sat Nov 11, 2017 3:38 pm
Forum: Trends in The Periodic Table
Topic: Isoelectronic [ENDORSED]
Replies: 4
Views: 360

### Re: Isoelectronic[ENDORSED]

To clarify the above post. Isoelectronic atoms or ions have both the same number of valence electrons (8 in this case for F-) and the same electronic structure. As [He] only has 2 valence electrons it cannot be isoelectronic to F-. Hope that helps!
Sat Nov 11, 2017 2:30 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Isoelectronic [ENDORSED]
Replies: 4
Views: 523

### Re: Isoelectronic[ENDORSED]

Remember that atoms or ions are considered isoelectronic only when they have both the same number of valence electrons and the same electronic structure. Hope that helps!
Sat Nov 04, 2017 11:48 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Magnetic Quantum Number
Replies: 6
Views: 409

### Re: Magnetic Quantum Number

Hi, I don't believe there is a way for us to determine the magnetic quantum number (ml) a specific electron has without doing an experiment. Thus, we will most likely not be asked about a specific ml number. Rather it is more likely that we will be asked about the range such as on the previous quiz....
Sat Nov 04, 2017 11:13 pm
Forum: Lewis Structures
Topic: Formal Charge
Replies: 1
Views: 114

### Re: Formal Charge

Hi! The formula for finding formal charge is actually Valence Electrons - (Lone Pair Electrons + Shared Electrons/2). Hope that helps!
Sat Oct 28, 2017 8:15 pm
Forum: Ionic & Covalent Bonds
Topic: Lewis Structure [ENDORSED]
Replies: 3
Views: 192

### Re: Lewis Structure[ENDORSED]

Hi there, multiple bonds (such as a double bond) are shorter than single bonds between the same two elements because the additional bonding electrons attract the nuclei more strongly and pull the atoms closer together. Hope that helps!
Sat Oct 28, 2017 7:57 pm
Forum: Quantum Numbers and The H-Atom
Topic: Zeff [ENDORSED]
Replies: 1
Views: 158

### Re: Zeff[ENDORSED]

I believe that this refers to the proximity of the electrons in an orbital to the nucleus. Therefore when it says "the s orbital penetrate the nucleus" they are saying how close the electrons in the s orbital are to the nucleus. The textbook then goes on to say that p orbital "penetra...
Sun Oct 22, 2017 9:26 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electronic Configuration for d-block elements [ENDORSED]
Replies: 9
Views: 767

### Re: Electronic Configuration for d-block elements[ENDORSED]

Hi! The reason why the nodal planes are different once you reach the d orbital is because there are more orbitals. While p has 3 orbitals, d has 5 orbitals of a given energy.
Sun Oct 22, 2017 8:54 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Different d and f orbitals
Replies: 3
Views: 270

### Re: Different d and f orbitals

Hi, yes there are different nodal planes for these orbitals as well. D orbitals have 5 while F orbitals have 7. I believe that Dr. Lavelle said during lecture that we won't be going over F orbitals, so I'll just list the D orbitals. dxy, dyz, dxz, dz^2, and dx^2y^2. Hope this helps!
Sat Oct 14, 2017 1:56 pm
Topic: Black Body Relevance [ENDORSED]
Replies: 1
Views: 424

### Re: Black Body Relevance[ENDORSED]

In terms of relevance, I believe that experiments involving black bodies eventually led to the Quantum theory as experiment results could not be explained by classical mechanics. This issue wasn't solved until Planck came along and suggested that the exchange of energy occurs in quanta (packets) of ...
Tue Oct 10, 2017 9:40 pm
Topic: Wien's law $$\lambda max$$ [ENDORSED]
Replies: 1
Views: 265

### Re: Wien's law $$\lambda max$$[ENDORSED]

In Wien's law, lambda is still used to represent wavelength. Lambda max refers to the wavelength in the absorption spectrum where the absorbance is maximum. In other words, lambda max is the wavelength that corresponds to the maximum in the intensity which is where you might have gotten confused. Ho...
Tue Oct 03, 2017 1:29 pm
Forum: Empirical & Molecular Formulas
Topic: Problem E.15 Confusion [ENDORSED]
Replies: 1
Views: 239

### Re: Problem E.15 Confusion[ENDORSED]

I believe the M is indeed a variable that represents the unknown metal in the compound. Since you can calculate the molar mass of (OH)2, you can then subtract that from the given molar mass of the compound to find out the molar mass of "M". After checking the periodic table you will discov...
Mon Oct 02, 2017 2:16 pm
Forum: Limiting Reactant Calculations
Topic: % yield [ENDORSED]
Replies: 2
Views: 305

### Re: % yield[ENDORSED]

Theoretical yield is what you calculate with Stoichiometry and is the maximum amount of product that can be produced. The percent yield is the fraction of the theoretical yield that is actually produced aka the amount of the theoretical yield that you obtained, expressed as a percentage. You would f...