Search found 62 matches
- Sat Mar 09, 2019 12:14 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneity
- Replies: 4
- Views: 459
Re: Spontaneity
You can determine the spontaneity of a reaction by calculating delta G using standard reaction gibbs free energy values or by comparing the signs for enthalpy and entropy at fixed temperature values.
- Sat Mar 09, 2019 12:10 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Reaction mechanisms
- Replies: 2
- Views: 322
Re: Reaction mechanisms
No, I don't think we would explicitly need to know what the intermediates are. However, like the example done in class, if a compound is in the chemical equation but not in the experimentally derived rate law, it is evident that it is an intermediate in the reaction.
- Sat Mar 09, 2019 12:08 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: catalyst/enzyme
- Replies: 4
- Views: 475
Re: catalyst/enzyme
A catalyst/enzyme does change the rate of the reaction by changing the activation energy needed for the reaction to proceed to completion.
- Sat Mar 09, 2019 12:05 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Test 2 Gibbs Free Energy
- Replies: 5
- Views: 671
Re: Test 2 Gibbs Free Energy
The cold/heat pack is considered to be spontaneous because the question said that heat is being released. Since the reaction is exothermic, it is thermodynamically favorable, thus making the reaction spontaneous.
- Tue Feb 26, 2019 8:49 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: 6th edition, #89
- Replies: 1
- Views: 210
6th edition, #89
I didn't really understand the solution manual's answer for this question, if anyone can explain the answer in clearer terms that would be great!
Question: Some entries for Sm in Appendix 2A are negative. What is common about these entries, and why would the entropy be negative?
Question: Some entries for Sm in Appendix 2A are negative. What is common about these entries, and why would the entropy be negative?
- Mon Feb 25, 2019 12:51 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Potential Value
- Replies: 1
- Views: 406
Re: Cell Potential Value
E does not change because if you look at the equation it is evident that delta G doubles when the stoichometric coefficients are doubled. However, the change in the number of moles, or delta n, also doubles. Since both delta G and delta n doubles, it does not affect delta E in the equation, meaning ...
- Mon Feb 25, 2019 12:50 pm
- Forum: Balancing Redox Reactions
- Topic: Single Reactant in Redox
- Replies: 2
- Views: 298
Re: Single Reactant in Redox
You can tell which one is the oxidation and reduction reaction based on the oxidation numbers on the product side of the equation.
- Mon Feb 25, 2019 12:48 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing Redox Reactions in Basic Solutions
- Replies: 1
- Views: 229
Balancing Redox Reactions in Basic Solutions
Can someone clarify the procedure for balancing O and H for redox reactions in basic solutions?
- Mon Feb 25, 2019 12:47 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing Charges
- Replies: 4
- Views: 348
Re: Balancing Charges
I think you can assume that oxygen will always be a charge of -2 and hydrogen will always be a charge of -1. Using the charge for this "given" elements, you can find the charge of the other elements, like manganese in this case.
- Fri Feb 15, 2019 2:40 pm
- Forum: Calculating Work of Expansion
- Topic: Free Expansion
- Replies: 3
- Views: 437
Free Expansion
What does free expansion mean? Does it just mean that there was a change in volume, and hence work was present in the system?
- Fri Feb 15, 2019 2:39 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: 3/2R vs 5/2R
- Replies: 8
- Views: 2006
Re: 3/2R vs 5/2R
3/2 R is used for Cv of an ideal monoatomic atom. 5/2R is for Cv of a linear molecule and for Cp of an ideal monoatomic atom.
- Fri Feb 15, 2019 2:38 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Cp vs. Cv heat capacity
- Replies: 1
- Views: 295
Cp vs. Cv heat capacity
With regards to the different types of motion, rotation, translational, and vibrational, what changes between Cp and Cv causing the use of two different formulas (3/2R and 5/2R)?
- Fri Feb 15, 2019 2:36 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: ΔS=q/t
- Replies: 8
- Views: 904
Re: ΔS=q/t
Why can you only calculate delta S, when the q for the reaction is reversible?
- Wed Feb 13, 2019 9:10 pm
- Forum: Phase Changes & Related Calculations
- Topic: ΔH vs ΔU?
- Replies: 8
- Views: 1364
Re: ΔH vs ΔU?
Yes, this can occur when there is no volume change (free expansion), but generally speaking, delta H will only equal delta U when there is no work done and pressure is held constant
- Thu Jan 31, 2019 11:43 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bomb Calorimeter
- Replies: 2
- Views: 285
Bomb Calorimeter
In lecture yesterday, what did Dr. Lavelle say the limitations are for using a bomb calorimeter as an isolated system?
- Thu Jan 31, 2019 11:41 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Heat Capacity
- Replies: 1
- Views: 235
Heat Capacity
When is heat capacity calculated? Is it for the slopes or the stagnant portions of the phase diagram?
- Thu Jan 31, 2019 11:39 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Enthalpies
- Replies: 2
- Views: 373
Bond Enthalpies
Are both bond enthalpies and standard enthalpies of formation given by mol, meaning that we always have to multiply by the stoichometric coefficients? Also, for which method is do we say that the enthalpy of a pure substance is zero?
- Sat Jan 26, 2019 5:59 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy
- Replies: 2
- Views: 220
Enthalpy
Why is enthalpy defined to be a state function?
- Sat Jan 26, 2019 5:55 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Signs in bond enthalpies
- Replies: 4
- Views: 432
Re: Signs in bond enthalpies
Yes, this is because energy is released when bonds are broken, which is what occurs in the reactants. On the other hand, energy is needed to put the bonds back together, which is what occurs in the products.
- Sat Jan 26, 2019 3:58 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Enthalpies
- Replies: 3
- Views: 313
Re: Bond Enthalpies
Yes, you only account for the bonds broken and re-formed. However, Dr. Lavelle mentioned in class that you can also just break down all the bonds in the reacts and re-form all the bonds in the products to get the same answer though it might be a longer process for the calculations.
- Sat Jan 26, 2019 3:56 pm
- Forum: Phase Changes & Related Calculations
- Topic: Modules
- Replies: 17
- Views: 1234
Re: Modules
The modules give you a score on the post-assessment and tell you which questions you got wrong, but they do not show the correct answer.
- Mon Jan 21, 2019 12:05 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Inert gas effect on Equilibrium constant
- Replies: 4
- Views: 1006
Re: Inert gas effect on Equilibrium constant
Pressure, even when volume is changed, will not change your equilibrium constant, K. Temperature is the only physical parameter that can change K, concentration and pressure can shift the direction to which the equilibrium will go towards, but they will not change K.
- Mon Jan 21, 2019 12:03 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Partial Pressure
- Replies: 2
- Views: 260
Re: Partial Pressure
If you are given Kp then it is evident that all your gases will be represented in an partial pressures. If you are given Kc, then report them as concentrations. You can easily convert between partial pressures and concentrations using the derivativion made from PV=nRT that we were shown in class.
- Mon Jan 21, 2019 12:01 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Pressure
- Replies: 7
- Views: 632
Re: Pressure
For any concept associated with Le Chatelier's principle, such as pressure, temperature, or concentration, you do not include any solids or liquids.
- Sun Jan 13, 2019 2:20 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Gas Phase Reactants and Products
- Replies: 2
- Views: 121
Gas Phase Reactants and Products
When given gas phase reactants and products, is it best to put the concentrations in terms of atm and make the equilibrium constant Kp or put it in molarity and make the equilibrium constant Kc?
- Sun Jan 13, 2019 2:18 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Changes in Pressure
- Replies: 2
- Views: 125
Changes in Pressure
Other than pumping in an inert gas into a system, are there any other ways that the pressure of a system will not shift toward the reactants or products?
- Sun Jan 13, 2019 2:16 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: vant Hoff factor and equation
- Replies: 3
- Views: 208
Re: vant Hoff factor and equation
I think Dr. Lavelle said that we are covering this topic later on in thermodynamics. The outline for the textbook reading given on his website also omits these pages!
- Sun Jan 13, 2019 2:15 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE table question
- Replies: 2
- Views: 257
Re: ICE table question
Basically, you can use an ICE table when you do not have the change in concentration given between the initial and equilibrium concentrations. By finding the change in concentrations, we can figure out the equilibrium concentrations, from only the initial concentrations and the equilibrium constant.
- Wed Jan 09, 2019 8:33 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Q vs. K
- Replies: 2
- Views: 367
Q vs. K
We know that when Q<K products are favored and reactants are favored when Q>K. What happens when Q=K?
- Wed Jan 09, 2019 8:32 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Table
- Replies: 4
- Views: 157
ICE Table
For the ICE table that Dr. Lavelle mentioned in class today, why/do we always assume that products start at 0 if no numbers are given at the beginning for the initial condition?
- Mon Jan 07, 2019 10:42 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Post Assessment #27 Part 2
- Replies: 1
- Views: 163
Post Assessment #27 Part 2
I wasn't sure how to answer this question, since the concentration of H2O is only given before the reaction has reached equilibrium. A mixture of 2.5 moles H2O and 100 g of C are placed in a 50 L container and allowed to come to equilibrium subject to the following reaction: C(s) + H2O (g) ⇌ CO (g) ...
- Mon Dec 03, 2018 1:06 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: Comparing Weak vs. Strong Acids and Bases
- Replies: 3
- Views: 323
Comparing Weak vs. Strong Acids and Bases
What is another way to distinguish between strong and weak acids and bases other than comparing dissociation constants (Ka and Kb)?
- Mon Dec 03, 2018 12:59 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: Stabilizing an Acid [ENDORSED]
- Replies: 1
- Views: 231
Stabilizing an Acid [ENDORSED]
What are other ways of stabilizing an acid other than delocalizing the electrons? Also, does the concept of delocalizing the electrons only apply for oxoacids or for all compounds?
- Mon Dec 03, 2018 12:58 pm
- Forum: Amphoteric Compounds
- Topic: Amphoteric Oxides
- Replies: 1
- Views: 204
Amphoteric Oxides
Are all the metalloids considered to be amphoteric oxides or are they just a subset? Are there any other examples that we should know that are not in the diagonal band mentioned in class?
- Mon Dec 03, 2018 12:53 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Electronegativity and delocalization
- Replies: 1
- Views: 302
Re: Electronegativity and delocalization
High electronegativity means high delocalization power because the more an element wants to gain an electron, the more likely it is to want to delocalize a pair of electrons from another element.
- Mon Dec 03, 2018 12:50 pm
- Forum: Lewis Acids & Bases
- Topic: Lewis v. Bronsted
- Replies: 2
- Views: 293
Re: Lewis v. Bronsted
The difference is in the way that they defined acids and bases. The Bronsted Acid is a proton donor, and the Bronsted base definition is a proton acceptor. According to the Lewis definition, and acid is an electron pair acceptor, and a base is an electron pair donor.
- Mon Dec 03, 2018 12:48 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: KB values
- Replies: 1
- Views: 220
Re: KB values
I think that he is planning on covering that on Wednesday when he talks more about chemical equilibria.
- Mon Dec 03, 2018 12:47 pm
- Forum: Bronsted Acids & Bases
- Topic: Bronsted Acids/Bases Vs. Arrhenius Acids/Bases
- Replies: 1
- Views: 305
Re: Bronsted Acids/Bases Vs. Arrhenius Acids/Bases
The difference between Arrhenius and Bronsted Lowry definition is that in the Arrhenius definition an acid is characterized by anything that has a H+ ion and a base as anything that has a OH- ion. The Bronsted Lowry definition is that acid is anything that is a proton donor, and a base is a proton a...
- Sun Nov 18, 2018 11:11 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 2
- Views: 259
Bond Angles
When do the bond angles of a molecular slightly differ from the expected one (ex. for some structures that are tetrahedral the bond angle is less than 109.5)?
- Sun Nov 18, 2018 10:58 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular shape vs. Electron Geometry [ENDORSED]
- Replies: 2
- Views: 411
Molecular shape vs. Electron Geometry [ENDORSED]
What is the difference between molecular shape and electron pair geometry?
- Sun Nov 18, 2018 10:55 am
- Forum: Sigma & Pi Bonds
- Topic: usage of sigma/pi
- Replies: 6
- Views: 667
Re: usage of sigma/pi
By knowing how many sigma and pi bonds there are in a molecule, we can know the strength of the interactions, since sigma bonds are generally stronger than pi bonds. Also, they are the result of overlapping orbitals in hybridization so they can predict the behavior of molecules.
- Sun Nov 11, 2018 4:55 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Different States of Matter based on Polarizability
- Replies: 1
- Views: 152
Different States of Matter based on Polarizability
Why does differences in the strength of polarizability give rise to different states of matter, (ex. pentane is a mobile fluid while octadecane is a waxy solid)?
- Sun Nov 11, 2018 4:53 pm
- Forum: Bond Lengths & Energies
- Topic: Interaction Potential Energies
- Replies: 1
- Views: 109
Interaction Potential Energies
What is interaction potential energies and why is it dependent on (r), the distance between two atoms or molecules?
- Sun Nov 11, 2018 4:42 pm
- Forum: Octet Exceptions
- Topic: Number of electrons in relation to Octet
- Replies: 3
- Views: 336
Re: Number of electrons in relation to Octet
Sometimes, octet formation is impossible as in the case of compounds such as SF6 where the octet rule is exceeded. The octet rule here is numerically impossible to satisfy but the idea is to keep the formal charges to zero. The only elements that are totally bounded by the octet rule are those in pe...
- Sun Nov 11, 2018 4:22 pm
- Forum: Lewis Structures
- Topic: Formal Charge
- Replies: 14
- Views: 1222
Re: Formal Charge
Obviously there are exceptions, but I think that it is better to have no formal charge on the central atom in order to have the Lewis Structure of the lowest energy and most stability. Also, if you add up the formal charges of all the elements it should equal the charge of the compound.
- Sun Nov 11, 2018 4:20 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: Dissociation Energy
- Replies: 1
- Views: 232
Dissociation Energy
Why is dissociation energy always positive in a reaction?
- Sun Nov 11, 2018 4:18 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: Hydrogen Bonding Question
- Replies: 3
- Views: 381
Re: Hydrogen Bonding Question
With regards to why the energy is negative, I think it is because it takes a huge amount of energy to break the hydrogen bonds due to the difference in electronegativities. Since Fluorine is the most electronegative atom, the closer you bond hydrogen with an element next to fluorine, the higher the ...
- Sun Nov 11, 2018 1:27 pm
- Forum: Dipole Moments
- Topic: Bonding
- Replies: 3
- Views: 303
Bonding
In class, we said that Van der Waals forces and London Dispersion forces are synonymous when talking about nonpolar bonds. However, in high school chem I remember that Van der Waals encompassed a broader category which included even those with weak dipoles, so I was just wondering whether these term...
- Sun Nov 11, 2018 1:19 pm
- Forum: Electronegativity
- Topic: Electronegativity
- Replies: 4
- Views: 559
Electronegativity
Can the differences in electronegativity be used to figure out any information about the structure of the molecule or is it solely used to determined the type of bond?
- Sun Nov 11, 2018 1:10 pm
- Forum: Resonance Structures
- Topic: Resonance Structures
- Replies: 3
- Views: 361
Resonance Structures
Does the concept of resonance structures only apply to shifting the strength (double/triple) bonds around the atom, or can it also apply to the shifting of the lone pairs?
- Sun Nov 11, 2018 1:07 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Octet Exceptions
- Replies: 4
- Views: 1094
Re: Octet Exceptions
Yes, it does. We covered in class these two elements as exceptions but also when we did electron configurations of ions, such as Cu+ we only removed the 4s1 electron, which proves that valence electrons are being affected.
- Sun Nov 11, 2018 12:58 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Polar vs Nonpolar
- Replies: 5
- Views: 640
Re: Polar vs Nonpolar
In addition to looking at the Lewis Structure for the dipole moments, I think the difference in electronegativity can be calculated to differentiate between polar and nonpolar molecules. For example, polar molecules tend to have higher differences in electronegativities than nonpolar ones.
- Sun Oct 21, 2018 2:23 pm
- Forum: Properties of Light
- Topic: SI Units
- Replies: 6
- Views: 586
SI Units
What other unit conversions are important to know for Test 2 other than that of nm to m?
- Sun Oct 21, 2018 2:21 pm
- Forum: Properties of Light
- Topic: Wavelengths and frequencies
- Replies: 10
- Views: 643
Re: Wavelengths and frequencies
No, I don't think the specific wavelengths are necessary. Rather, maybe just knowing the spectrum in order of increasing wavelength/frequency might be helpful since you can check if your answers are reasonable. Also, knowing that visible light is between 400-900 nm is important.
- Sun Oct 21, 2018 2:10 pm
- Forum: Photoelectric Effect
- Topic: Question from Post-Assessment Module
- Replies: 2
- Views: 144
Question from Post-Assessment Module
I wasn't sure of the answer for this question on the module assessment, if anyone knows!
When the energy per photon is equal to the energy required to remove an electron what is this energy called?
When the energy per photon is equal to the energy required to remove an electron what is this energy called?
- Sat Oct 13, 2018 5:34 pm
- Forum: Properties of Light
- Topic: Rydberg Equation
- Replies: 3
- Views: 170
Rydberg Equation
In class, Professor Lavelle mentioned to not use the Rydberg Equation when doing problems that had a change in energy state (ex. n=4 to n=2). When will this equation be used, and in what capacity if so?
- Sat Oct 13, 2018 5:31 pm
- Forum: DeBroglie Equation
- Topic: DeBroglie Equation
- Replies: 5
- Views: 500
DeBroglie Equation
When is the DeBroglie equation used in a problem, and will a problem specify if we need to use it? I'm wondering because the example in class mentioned "find the DeBroglie wavelength..."?
- Sat Oct 13, 2018 5:28 pm
- Forum: Einstein Equation
- Topic: Energy of a Photon
- Replies: 2
- Views: 244
Energy of a Photon
What is the difference between the term "energy released by a photon" and the "E" in the equation E=hv?
- Sun Oct 07, 2018 4:14 pm
- Forum: Significant Figures
- Topic: Sig Figs & Molar Mass
- Replies: 4
- Views: 576
Re: Sig Figs & Molar Mass
I think its best to keep the molar mass from the periodic table, and round it when doing calculations according to the number given in the problem. False accuracy should not occur because the molar mass values are standardized for all the problems.
- Sat Oct 06, 2018 2:37 pm
- Forum: Balancing Chemical Reactions
- Topic: Combustion Question on Modules
- Replies: 3
- Views: 238
Re: Combustion Question on Modules
I think the formulas for the hydrocarbons will be provided, but we need to know that when a question says combustion/oxidation/burning it will have a hydrocarbon + O2 --> CO2 + H2O.
- Sat Oct 06, 2018 2:33 pm
- Forum: Significant Figures
- Topic: Sig Figs: Addition and Subtraction
- Replies: 3
- Views: 494
Re: Sig Figs: Addition and Subtraction
For addition, the rule is to go with the number that has the least digits after the decimal point, so 12345.6 + 1.008 would have an answer that has only one digit after the decimal point, so the answer will be 12346.6. The rule about having the least amount of sig figs in the answer is for multiplic...
- Sat Oct 06, 2018 2:28 pm
- Forum: Limiting Reactant Calculations
- Topic: Section L, #35
- Replies: 2
- Views: 172
Section L, #35
Sodium bromide, NaBr, which is used to produce AgBr for use in photographic lm, can itself be prepared as follows. Fe + Br2 --> FeBr2 FeBr2 + Br2 --> Fe3Br8 Fe3Br8 + Na2CO3 --> NaBr + CO2 + Fe3O4 What mass of iron, in kilograms, is needed to produce 2.50 t of NaBr? I understand the stoichometry for ...