Search found 51 matches
- Sat Mar 17, 2018 11:15 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: why is the entropy change at constant pressure greater than the entropy change at constant volume?
- Replies: 3
- Views: 2337
Re: why is the entropy change at constant pressure greater than the entropy change at constant volume?
Beyond the fact that C(p,m) > C(v,m), it could be that when pressure remains constant that there's no relief in the force acting on the molecules, as when volume changes pressure will change inversely. That's my best bad guess. Maybe it could have to do with the fact that (delta)S=(delta)H/T at cons...
- Sat Mar 17, 2018 11:08 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Final
- Replies: 3
- Views: 1643
Final
Beyond memorizing the names and structures of the functional groups, is there anything else we need to know about/how to do in O Chem?
- Fri Mar 16, 2018 6:13 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Kinetics Formulas for the Final
- Replies: 2
- Views: 620
Kinetics Formulas for the Final
For the final, are we going to have to work with collision theory and its formulas (both collision frequency, relative velocity, and molar mass formulas), or do we just have to understand the concepts behind these formulas?
- Sun Mar 11, 2018 7:38 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Kinetics Test Scores [ENDORSED]
- Replies: 3
- Views: 776
Kinetics Test Scores [ENDORSED]
For those who have discussions later on in the week (Thursday and Friday) will we be getting our tests back earlier (in class) so that we have more time to review before the final on Sunday?
- Sun Mar 11, 2018 7:35 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Reversible or irreversible?
- Replies: 2
- Views: 727
Re: Reversible or irreversible?
Isothermal reactions should be reversible.
- Thu Mar 08, 2018 1:27 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Homework Problems
- Replies: 3
- Views: 623
Homework Problems
Did Dr Lavelle mention the extent of the questions in the textbook that are necessary/will be covered by the Kinetics test? If so, which ones?
- Sat Mar 03, 2018 3:00 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: example 15.4: Measuring a Rate Constant
- Replies: 2
- Views: 595
Re: example 15.4: Measuring a Rate Constant
My TA said that it could end up on Test 3 and/or the Final, but I believe he mentioned that the numbers involved wouldn't be difficult to work with.
- Sat Mar 03, 2018 2:56 pm
- Forum: Zero Order Reactions
- Topic: Zero Order Reactions and Rate of Reaction
- Replies: 5
- Views: 821
Re: Zero Order Reactions and Rate of Reaction
A zero order reaction also indicates that the rate of that specific reaction is at its maximum (usually due to the introduction of an enzyme) which is why changing the concentration of the reactant will not have an effect on the rate, but only the duration.
- Sat Mar 03, 2018 2:49 pm
- Forum: First Order Reactions
- Topic: Naming Orders
- Replies: 3
- Views: 567
Re: Naming Orders
Usually you can determine through the data given for each individual compound concentration's effect on the rate of the reaction.
- Thu Feb 22, 2018 12:30 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Difference between galvanic and electrolytic cells
- Replies: 1
- Views: 372
Re: Difference between galvanic and electrolytic cells
Yes. The Flow of electrons go from negative to positive, where they leave the anode (negatively charged) because it's getting oxidized (losing electrons), and travel over to the cathode (positively charged) where the cathode is reduced (gaining/accepting electrons).
- Thu Feb 22, 2018 12:28 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Oxidizing and Reducing Agents
- Replies: 2
- Views: 403
Re: Oxidizing and Reducing Agents
You'll find the standard cell potentials on the electrochemistry series (page 579 of textbook).
- Thu Feb 22, 2018 12:27 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Concentration Cells
- Replies: 2
- Views: 359
Concentration Cells
How does a potential difference arise in a concentration cell if each electrode has the same substance? A conceptual explanation would be preferred.
- Sun Feb 18, 2018 5:44 pm
- Forum: Balancing Redox Reactions
- Topic: Addition of H3O+ or OH-
- Replies: 4
- Views: 1880
Addition of H3O+ or OH-
How can we tell when to add H3O+ or OH- when balancing half reactions, and how do we know what side of the equation to add it to?
- Sun Feb 18, 2018 5:41 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Conc. Cells
- Replies: 2
- Views: 469
Re: Conc. Cells
Because the addition of the electron into the products cause the ions to aggregate into solids, which will accumulate on the electrode that's in the solution- so you're making more of the inert substance.
- Sun Feb 18, 2018 5:40 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: E equations
- Replies: 3
- Views: 643
Re: E equations
There isn't. Both equations are equal to each other, one simply uses a natural log, and the other uses a log base 10 and simplifies/integrates the constant into the equation required to make both equations equal.
- Sun Feb 11, 2018 6:38 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Derivation of Formulas
- Replies: 5
- Views: 806
Derivation of Formulas
Will we be expected to derive the formulas we've learned in class on the midterm?
- Sun Feb 11, 2018 6:36 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Practice Midterm [ENDORSED]
- Replies: 5
- Views: 908
Practice Midterm [ENDORSED]
Where can I find the practice midterm exam?
- Sun Feb 11, 2018 6:36 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Practice Midterm
- Replies: 1
- Views: 364
Practice Midterm
Where can I find the practice midterm?
- Sun Feb 11, 2018 6:31 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: Finding entropy of vaporization for water at room temp
- Replies: 2
- Views: 629
Re: Finding entropy of vaporization for water at room temp
It depends on the pressure acting on the system (the water). If you lower the pressure, then the energy required to vaporization should be less.
- Sun Feb 04, 2018 10:24 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat Transfer Test 1 Concept Question
- Replies: 2
- Views: 458
Re: Heat Transfer Test 1 Concept Question
If it's being held at constant temperature, increasing volume will lead to a decrease in temperature. However, to maintain a constant T, energy/heat must be supplied to the system.
- Sun Feb 04, 2018 10:22 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Q or Qc when calculating Gibbs Free Energy
- Replies: 1
- Views: 621
Re: Q or Qc when calculating Gibbs Free Energy
If you're only provided with partial pressures then you can use that to find Q, either way, as long as you calculate Q correctly (when delta G is not equal to zero) then it shouldn't matter whether you've used partial pressures or concentrations to come to the solution. Most of the time it will depe...
- Sun Feb 04, 2018 10:19 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Sig Figs
- Replies: 6
- Views: 756
Re: Sig Figs
They shouldn't be anymore or less important than the topics we've covered in the past. However, they'll matter more on the test and/or in a lab.
- Sun Jan 28, 2018 11:27 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Test question [ENDORSED]
- Replies: 16
- Views: 1807
Re: Test question [ENDORSED]
I also put the equation (delta)E(univ)= (delta)E(sys) + (delta)E(surroundings), but I'm not sure if that was redundant in lieu of stating that matter and energy are neither created nor destroyed.
- Sun Jan 28, 2018 11:21 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Exothermic vs Exergonic and Endothermic vs Endergonic
- Replies: 3
- Views: 25257
Re: Exothermic vs Exergonic and Endothermic vs Endergonic
Exo/Endothermic represents the relative change in heat/enthalpy in a system, whereas Exer/Endergonic refers to the relative change in the free energy of a system.
- Sun Jan 28, 2018 11:20 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: entropy property? [ENDORSED]
- Replies: 2
- Views: 325
Re: entropy property? [ENDORSED]
I think it would be extensive because it changes based on the volume, or the number of particles- these would affect the number of microstates possible.
- Sun Jan 21, 2018 9:06 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: delta n
- Replies: 3
- Views: 3731
Re: delta n
The focus should be on the change in moles of gaseous particles, as this is will sometimes be the cause of the change in volume (which will help you solve for work). As for whether it's Ps-Rs or vice versa, it's more or less focusing on the change in the number of moles due to how the initial and fi...
- Sun Jan 21, 2018 9:02 pm
- Forum: Phase Changes & Related Calculations
- Topic: Test 1 [ENDORSED]
- Replies: 7
- Views: 970
Re: Test 1 [ENDORSED]
There should be a link posted on Lavelle's website that goes over the concepts and formulas that will be covered on the test. However, (delta)U= (delta)q + (delta)w, w = -P(delta)V, q = mC(delta)T / q = nC(delta)T (formula differs whether you're using specific heat, or molar heat capacity), are the ...
- Sun Jan 21, 2018 8:57 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Specific enthalpy
- Replies: 1
- Views: 245
Re: Specific enthalpy
Beyond understanding what it means, it should be provided on the test.
- Sun Jan 14, 2018 10:36 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Recording Lectures
- Replies: 2
- Views: 408
Re: Recording Lectures
You can also check any modules he has on his website.
- Sun Jan 14, 2018 10:26 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard States
- Replies: 4
- Views: 1209
Re: Standard States
I believe we should be told on the test, but beyond that, a table of standard enthalpy of formation would have a zero next to a compound in its standard state.
- Sun Jan 14, 2018 9:02 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: q equations
- Replies: 2
- Views: 508
Re: q equations
The first equation applies to Molar Heat Capacity, which is designated by the Cm symbol, and why the symbol for moles ("n") is included in the formula- when solving for q, the moles will "cancel" out during dimensional analysis. Csp, on the other hand, refers to the specific heat...
- Sun Dec 10, 2017 9:48 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Final [ENDORSED]
- Replies: 4
- Views: 1424
Re: Final [ENDORSED]
What I did was find the molarity of both the H+ and OH- ion in the 1.00 L solution, and then took the difference in molarities between the two ions, because I wanted to find the net concentration of a certain ion. I chose to find the net concentration, because I believed that the H+ and OH- ion woul...
- Sun Dec 10, 2017 9:44 pm
- Forum: Amphoteric Compounds
- Topic: Finals Question about Glycine? [ENDORSED]
- Replies: 1
- Views: 726
Re: Finals Question about Glycine? [ENDORSED]
It asked whether or not it was amphiprotic, and I said yes, because the N atom had a lone pair, and the H connected to the Oxygen seemed that it would likely dissociate in a solution. Therefore, it could both gain, and donate a proton (H+ ion).
- Sun Dec 03, 2017 9:39 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Noble Gas increasing pressure
- Replies: 3
- Views: 976
Re: Noble Gas increasing pressure
The only time the equilibrium constant will change, will be when temperature changes. All other variables like Pressure, n (moles), and Volume, do not have an effect on the constant itself.
- Sun Dec 03, 2017 9:37 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Question 11.89 Part A
- Replies: 2
- Views: 327
Re: Question 11.89 Part A
It could possibly be that they are trying to balance the coefficients on each side, so if A is a reactant, and B and C are the products, then there needs to be two (lets say) moles on the reactant and product side of the equation.
- Sun Nov 26, 2017 10:48 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kc or Kp for a heterogenenous equilibrium?
- Replies: 2
- Views: 370
Re: Kc or Kp for a heterogenenous equilibrium?
You have to convert either to only gas (giving you Kp) or only molarity (Kc), so you will need to use the ideal gas law to convert from one to the other.
- Sun Nov 26, 2017 10:46 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: convertine to partial pressure
- Replies: 2
- Views: 525
Re: convertine to partial pressure
If you already have a substance in gas form you shouldn't have to convert to partial pressure.
- Sun Nov 19, 2017 11:19 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3890961
Re: Post All Chemistry Jokes Here
Did you know that you can cool yourself to -273.15˚C and still be 0k?
- Sun Nov 19, 2017 11:15 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Octahedral vs Trigonal Bypyramidal family
- Replies: 3
- Views: 576
Re: Octahedral vs Trigonal Bypyramidal family
For the Octahedral shape, there will be four atoms on one plane, and two axial atoms bonded to the central atom.
- Sun Nov 12, 2017 11:58 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Where to put the lone pairs?
- Replies: 3
- Views: 530
Re: Where to put the lone pairs?
A tetrahedral shape shouldn't have any lone pairs, only trigonal pyramidal will have a singular lone pair above the central atom.
- Sun Nov 12, 2017 11:54 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: VSEPR Formula
- Replies: 2
- Views: 967
Re: VSEPR Formula
A corresponds to the central atom, the X with its subscript symbol represents the number of bonded atoms, and the E and its subscript applies to the number of lone pairs.
- Sun Nov 05, 2017 10:46 pm
- Forum: Lewis Structures
- Topic: 3.25 part d
- Replies: 2
- Views: 292
Re: 3.25 part d
Hydrogen is allowed to act like a cation with no electrons- this hydrogen ion is common, and is what makes (for example) HCl an acids, as it disassociates into H+ and OH-.
- Sun Nov 05, 2017 10:41 pm
- Forum: SI Units, Unit Conversions
- Topic: Si Unit for molar mass
- Replies: 3
- Views: 2148
Re: Si Unit for molar mass
Yes, because the units for molar mass is g*mol^-1.
- Sun Oct 29, 2017 10:11 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Direction of the Spin Magnetic Quantum Number
- Replies: 5
- Views: 960
Re: Direction of the Spin Magnetic Quantum Number
Postive 1/2 has an upward spin/arrow, and negative 1/2 has a downward spin/arrow.
- Sun Oct 29, 2017 10:07 pm
- Forum: Trends in The Periodic Table
- Topic: Electron Affinity [ENDORSED]
- Replies: 3
- Views: 627
Re: Electron Affinity [ENDORSED]
Usually specific values will be provided through experimental data, but for the Chlorine vs. Bromine example, Chlorine would have the greater eletron affinity, as it is above Bromine in the periodic table.
- Sun Oct 22, 2017 10:53 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: P orbitals
- Replies: 4
- Views: 1906
Re: P orbitals
The first three electrons in the P orbital will all have a positive spin, and will occupy the Px, then Py, then Pz, orbital. Then the next three will all have negative spins, and will fill in that order. When filling orbitals (usually) we go from left to right with a positive spin first, and then on...
- Sun Oct 22, 2017 10:46 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Quantum Numbers - Magnetic Quantum Number
- Replies: 2
- Views: 417
Re: Quantum Numbers - Magnetic Quantum Number
For this quantum number, the reason that it can have negative numbers for the orbitals is because it mirrors whatever positive number you get based off what l equals: therefore if you get m= 1, then it can be 1, 0, and -1, and if m=2 then it can be 2, 1, 0, -1, -2.
- Sun Oct 15, 2017 4:39 pm
- Forum: Photoelectric Effect
- Topic: General Q about photoelectric effect terms [ENDORSED]
- Replies: 2
- Views: 483
Re: General Q about photoelectric effect terms [ENDORSED]
Threshold energy, unless specified otherwise.
- Sun Oct 15, 2017 4:26 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Variation of Empirical Equation of H-atom [ENDORSED]
- Replies: 2
- Views: 537
Re: Variation of Empirical Equation of H-atom [ENDORSED]
The first is equation is referring to the change in energy (either released or absorbed) during the transition state of an electron from energy level to the next. So, (delta)E actually equals [(-hR)/(n(final))^2 - (-hR)/(n(initial))^2], because "delta" refers to "the change in" w...
- Thu Oct 05, 2017 9:44 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: E7 [ENDORSED]
- Replies: 9
- Views: 1301
Re: E7 [ENDORSED]
Prof. Lavelle said that he isn't stressing sig figs as much as the content/information. Although, it's a better idea to round off at the end, because truncating your numbers too early can drastically change your answer.
- Thu Oct 05, 2017 9:38 pm
- Forum: Limiting Reactant Calculations
- Topic: Percent Yield [ENDORSED]
- Replies: 5
- Views: 6120
Re: Percent Yield [ENDORSED]
Also, another reason a high yield is important is if you're preparing a solution or a chemical that is an intermediate step to a larger experiment, the lower the yield the worse off the entire experiment becomes. If you think about it mathematically, it's similar to the function p= (C)^x where C is ...