Search found 199 matches
- Sat Mar 13, 2021 4:32 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Textbook 7D.7
- Replies: 2
- Views: 269
Textbook 7D.7
I was wondering for 7D.7 part c, why does raising the temperature increase the rate constant of the forward reaction even more than it does for the rate constant of the reverse reaction?
- Fri Mar 12, 2021 8:09 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Saying Thank You to Dr. Lavelle
- Replies: 490
- Views: 512942
Re: Saying Thank You to Dr. Lavelle
Thank you Dr. Lavelle for being a great teacher for the last two quarters! I really appreciate how much effort you put into making sure we do well with all the office hours/workshops and chemistry community. I'm thankful for how much I've learned in your class and how much I've gained confidence in ...
- Wed Mar 10, 2021 12:34 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Focus 6.57
- Replies: 1
- Views: 150
Focus 6.57
How do we know which half-reaction to use for the other half-reaction that wasn't specified for focus 6.57 and why did the answer key take the square root of Ka to get K? Shouldn't they be the same value?
- Wed Mar 10, 2021 12:32 am
- Forum: Administrative Questions and Class Announcements
- Topic: Final Distribution
- Replies: 5
- Views: 397
Re: Final Distribution
I'd say since each outline has about the same number of questions we should study each outline for an equal amount of time, but there are certain sections within these outlines that are shorter which will probably be tested less on based on last quarter.
- Tue Mar 09, 2021 6:54 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: strong reducing agent textbook 6.45
- Replies: 2
- Views: 211
strong reducing agent textbook 6.45
For problem 6.45, I know that a stronger reducing agent is good at oxidizing and has a low standard E value. However, I don't know which standard e value we use for a given element since there's multiple depending on how many electrons are transferred.
- Mon Mar 08, 2021 11:06 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Textbook 6N.23a cathodic protection
- Replies: 2
- Views: 209
Textbook 6N.23a cathodic protection
For textbook 6N.23 a, we're asked to suggest two metals that could be used for the cathodic protection of a titanium pipeline. I know we're supposed to look for standard reduction potentials smaller than that of titanium. However, when I looked up the titanium reaction in the table I saw that two el...
- Mon Mar 08, 2021 6:28 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Textbook Problem 6N.13
- Replies: 6
- Views: 577
Re: Textbook Problem 6N.13
I got the same answer too! I think it's because they used ln instead of log.
- Mon Mar 08, 2021 6:27 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Textbook Problem 6N.13
- Replies: 6
- Views: 577
Re: Textbook Problem 6N.13
I got the same answer too! I think it's because they used ln instead of log.
- Mon Mar 08, 2021 2:48 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell notation rules
- Replies: 4
- Views: 694
Re: Cell notation rules
The left side of the reaction is the anode side (oxidation reaction), and the right is the cathode side (reduction). These two reactions are separated by the double line, or the salt bridge. We add Pt to whichever half reaction is missing a solid in its reaction. Single lines represent different pha...
- Mon Mar 08, 2021 2:44 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: n in ∆G = -nFE
- Replies: 80
- Views: 3802
Re: n in ∆G = -nFE
You would have to write the two half reactions and multiply both by any coefficients necessary to get the same number of electrons to cancel out. This is because the number of electrons lost has to be the number of electrons gained. This number of electrons is the number you should use.
- Mon Mar 08, 2021 2:43 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K
- Replies: 33
- Views: 1242
Re: K
They're the same thing. K is the equilibrium constant, and the c just specifies that it's calculated from the concentrations rather than the partial pressure (for gases).
- Mon Mar 08, 2021 2:41 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: What is the purpose of having a salt bridge?
- Replies: 16
- Views: 674
Re: What is the purpose of having a salt bridge?
Salt bridges help allow the redox reaction to keep occuring. As reduction and oxidation occur, the charges will build up on both sides, which is unfavorable and would cause the reaction to stop. However, since we have a salt bridge that replenishes the ion concentrations on both sides, this keeps th...
- Mon Mar 08, 2021 2:40 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: About k
- Replies: 26
- Views: 2735
Re: About k
If k is large, the concentration of products is greater than the concentration of the reactants so product formation is favored.
- Mon Mar 08, 2021 12:16 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Textbook 6N.9
- Replies: 3
- Views: 222
Textbook 6N.9
For textbook problem 6N.9, they gave us that the molarity of Sn(NO3)2 was 0.015 M. I was wondering when we calculated Q in the Nernst equation and we had to plug in the value for Sn2+ why we used the same concentration of 0.015 M when they're different compounds.
- Sun Mar 07, 2021 12:14 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell diagram but no phases given
- Replies: 1
- Views: 155
Cell diagram but no phases given
For Textbook Problem 6M.11a, I was wondering how we would be able to write the cell diagram when the phases of the reactants and products aren't given in the problem or in the standard reduction table.
- Sat Mar 06, 2021 8:28 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Higher reduction potential Textbook 6M.7a
- Replies: 2
- Views: 198
Higher reduction potential Textbook 6M.7a
For textbook 6M.7 part a, I was wondering how we would know which standard reduction potentials to compare. For example if we were looking for the standard reduction potential of Cu, would we use the potential given when 2 electrons are transferred to form Cu or 3 etc.?
- Sat Mar 06, 2021 3:52 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 6M.5 Pt on both sides?
- Replies: 3
- Views: 259
6M.5 Pt on both sides?
I was wondering for 6M.5 part a, why they included Pt on only one side instead of both sides of the cell diagram since both the reactant and product side of the reaction are missing a solid?
- Thu Mar 04, 2021 1:03 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Conducting solid
- Replies: 1
- Views: 139
Conducting solid
Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions: Cd (s) + 2Ni(OH)3 (s) → Cd(OH)2 (s) + 2Ni(OH)2 (s), the reaction in the nickel−cadmium cell the half-reactions: anode: Cd (s) + 2 OH- (aq) → Cd(OH)2 (s) + 2 e- cathode: 2 Ni(OH)3 (s) ...
- Wed Mar 03, 2021 7:36 pm
- Forum: Student Social/Study Group
- Topic: Office hour links not working
- Replies: 2
- Views: 340
Re: Office hour links not working
Chem_Mod wrote:Which office hour was this?
It was Colin Bertz's Wednesday office hour at 3 and 4 pm.
- Wed Mar 03, 2021 4:13 pm
- Forum: Student Social/Study Group
- Topic: Office hour links not working
- Replies: 2
- Views: 340
Office hour links not working
I've tried to go to two different office hour sessions today and I made sure that they were the right day and time but each time zoom tells me to wait for the host to start the meeting even though about 8 minutes have passed. I was wondering if this is happening to anyone else?
- Wed Mar 03, 2021 1:29 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell diagram coefficients
- Replies: 1
- Views: 181
Cell diagram coefficients
I was wondering why we don't need to add coefficients in the cell diagram?
- Wed Mar 03, 2021 1:02 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: standard E in textbook problems
- Replies: 2
- Views: 200
standard E in textbook problems
I was wondering why for textbook problems like 6L.5, the answer key calculates the standard E when it doesn't say to do so in the instructions. Should we do that too?
- Tue Mar 02, 2021 12:47 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: To Pt(s) or not to Pt(s)? - cell diagrams
- Replies: 6
- Views: 392
Re: To Pt(s) or not to Pt(s)? - cell diagrams
You add Pt(s) if you don't have a conducting solid in the redox reaction. Platinum is a common conducting solid, so it's typically used.
- Tue Mar 02, 2021 12:46 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: -d[R]/dT versus d[P]/dt
- Replies: 13
- Views: 857
Re: -d[R]/dT versus d[P]/dt
Yes, they're the same! d[R] will be a negative value because the concentration of the reactants are decreasing, so we add a negative sign to this result to make it positive like d[P] in d[P]/dt. This makes the rates of change comparable because they would have the same sign.
- Tue Mar 02, 2021 12:44 am
- Forum: Student Social/Study Group
- Topic: Book Recommendations
- Replies: 135
- Views: 11938
Re: Book Recommendations
Educated by Tara Westover and Book Thief are really good!
- Tue Mar 02, 2021 12:43 am
- Forum: Student Social/Study Group
- Topic: Book Recommendations
- Replies: 135
- Views: 11938
Re: Book Recommendations
Educated by Tara Westover and Book Thief are really good!
- Tue Mar 02, 2021 12:42 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Textbook 6L.3 part b
- Replies: 1
- Views: 80
Textbook 6L.3 part b
For 6L.3 part b in the textbook, I was wondering what the gr next to the carbon on the anode half of the cell diagram means.
- Mon Mar 01, 2021 9:21 pm
- Forum: Balancing Redox Reactions
- Topic: Textbook 6K.5
- Replies: 1
- Views: 128
Textbook 6K.5
For textbook problem 6K.5, I was wondering why for the O3--> O2 half-reaction we have to add water on the products side. Both sides have the same elements already so I don't know why this is necessary.
- Mon Mar 01, 2021 2:03 am
- Forum: Balancing Redox Reactions
- Topic: adding H+ and H2O
- Replies: 9
- Views: 700
adding H+ and H2O
For acidic redox reactions, if we add water to one side do we have to add H+ to the other side? Or could we add water molecules to the other side instead?
- Fri Feb 26, 2021 12:58 am
- Forum: Balancing Redox Reactions
- Topic: adding water in the reaction
- Replies: 13
- Views: 598
adding water in the reaction
For Textbook Problem 6K.3, I was wondering why water was added to the oxidation half of the reaction specifically and not the reduction half? And why was it added in the first place?
- Fri Feb 26, 2021 12:08 am
- Forum: Balancing Redox Reactions
- Topic: Textbook 6K.1 [ENDORSED]
- Replies: 2
- Views: 236
Textbook 6K.1 [ENDORSED]
I was wondering for 6K.1 how we would know carbon was oxidized from -2 to -1 in the redox reaction?
- Mon Feb 22, 2021 2:04 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Calculating Disorder based on molecule size
- Replies: 12
- Views: 678
Re: Calculating Disorder based on molecule size
Yes because they have more subatomic particles which means that they have a higher degeneracy, and therefore a higher entropy.
- Mon Feb 22, 2021 2:00 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Standard reduction potentials
- Replies: 2
- Views: 159
Standard reduction potentials
Could someone explain what standard reduction potentials are?
- Mon Feb 22, 2021 1:58 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidizing vs Reducing
- Replies: 55
- Views: 2243
Re: Oxidizing vs Reducing
The oxidizing agent is becoming oxidized, so it is losing electrons. The reducing agent is becoming reduced, so it's gaining electrons. I like to think of reduction as reducing a positive charge to become more negative. Hope this helps!
- Mon Feb 22, 2021 1:56 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated Systems
- Replies: 15
- Views: 772
Re: Isolated Systems
I believe it's theoretical because you can't completely prevent energy from entering or leaving a system because of the natural design of the container. We can get close to doing this though using a bomb calorimeter.
- Mon Feb 22, 2021 1:55 pm
- Forum: Balancing Redox Reactions
- Topic: salt bridge?
- Replies: 8
- Views: 356
Re: salt bridge?
The salt bridge keeps the reaction on both sides neutral by replacing anions on the anode side and replacing cations on the cathode side. It does this because if the reaction didn't remain neutral electrons would no longer flow to the cathode side since it would be increasingly unfavorable to keep i...
- Sun Feb 21, 2021 8:13 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Advice from a Medical Student - Part II [ENDORSED]
- Replies: 298
- Views: 244748
Re: Advice from a Medical Student - Part II [ENDORSED]
I was wondering what particular classes made you interested in medicine/ particular clubs?
- Thu Feb 18, 2021 10:11 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: When to use delta H of formation and when to use delta H
- Replies: 4
- Views: 234
When to use delta H of formation and when to use delta H
I was wondering when delta H of formation of a compound should be equal to delta H of the reaction, and when would we have to multiply the moles of a reactant or compound by the delta H of formation to get delta H of the reaction instead.
- Thu Feb 18, 2021 6:27 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: 4J.5 Standard change in gibbs free energy
- Replies: 6
- Views: 350
4J.5 Standard change in gibbs free energy
I was wondering why for 4J.5 in the textbook, we can't use the standard gibbs free energy of formation given in Appendix 2A as the answer for the standard gibbs free energy of the reaction since they tell us to use the table in Appendix 2A.
- Wed Feb 17, 2021 10:29 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Larger mass= higher molar entropy
- Replies: 4
- Views: 274
Larger mass= higher molar entropy
For Textbook Problem 4H number 1, I was wondering why HBr has a higher molar entropy than HF, both of which are gases. The answer key said that it's because Br has a larger mass but how does this relate to having a higher entropy?
- Wed Feb 17, 2021 2:09 pm
- Forum: Van't Hoff Equation
- Topic: Delta H naught VS delta H
- Replies: 28
- Views: 2330
Re: Delta H naught VS delta H
ΔH° is the change in enthalpy under standard conditions, while ΔH is just the change in enthalpy.
- Wed Feb 17, 2021 2:06 pm
- Forum: Balancing Redox Reactions
- Topic: lecture 17 question
- Replies: 3
- Views: 327
Re: lecture 17 question
MnO4- is being reduced and Fe2+ is being oxidized. Oxygen has a oxidation number of 2- since it tends to gain two electrons to complete its valence shell. Therefore O4 has a 8- charge and since the overall charge of MnO4- is 1- that must mean that Mn originally has a 7+ oxidation number. MnO4- becom...
- Wed Feb 17, 2021 2:04 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Textbook 4F.13
- Replies: 1
- Views: 125
Textbook 4F.13
For textbook problem 4F.13, I was wondering why cooling the products back to 85 degrees Celsius would be one of the steps that we have to take into account since the question is asking for the standard change in entropy of the vaporization of water at 85 degrees Celsius.
- Tue Feb 16, 2021 3:23 pm
- Forum: Phase Changes & Related Calculations
- Topic: Focus 4.5 10 hrs versus 10.5 hours
- Replies: 4
- Views: 288
Focus 4.5 10 hrs versus 10.5 hours
For Textbook Problem 4.5, I was wondering why the answer key took the ratio of heat absorbed by the liquid water,3135 J/0.5 hr, and multiplied it by 10 hrs. Shouldn't it be 10.5 hours?
- Tue Feb 16, 2021 2:31 pm
- Forum: Phase Changes & Related Calculations
- Topic: Focus 4.1
- Replies: 1
- Views: 211
Focus 4.1
For focus problem 4.1, I was wondering why we can use delta H to calculate heat absorbed for each step of the reaction. Why can we assume that heat absorbed was at a constant pressure when it wasn't mentioned?
- Mon Feb 15, 2021 2:20 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Textbook 4D.9
- Replies: 1
- Views: 151
Textbook 4D.9
I was wondering why for problem 4D.9, the change in enthalpy of the reaction was made positive by the answer key when it was originally negative.
- Sat Feb 13, 2021 11:52 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: standard change in enthalpy vs. change in enthalpy
- Replies: 4
- Views: 252
standard change in enthalpy vs. change in enthalpy
Is standard change in enthalpy kJ per one mol, while change in enthalpy is just in moles?
- Sat Feb 13, 2021 6:08 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Textbook 4C.7
- Replies: 2
- Views: 177
Textbook 4C.7
Could someone explain why in Problem 4C.7 in the textbook we calculate the change in enthalpy by finding the heat supplied divided by the moles? I don't remember this being a formula.
- Sat Feb 13, 2021 1:18 am
- Forum: Administrative Questions and Class Announcements
- Topic: tips if you're struggling!
- Replies: 77
- Views: 4382
Re: tips if you're struggling!
This was really helpful. Thank you!
- Sat Feb 13, 2021 1:18 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Textbook 4C. 3 [ENDORSED]
- Replies: 2
- Views: 179
Textbook 4C. 3 [ENDORSED]
I was wondering for Problem 4C.3a in the textbook, why the answer key wrote n*Cp*deltaT and replaced Cp with 5/2 *R.
- Fri Feb 12, 2021 12:54 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Textbook 4A.13
- Replies: 1
- Views: 117
Textbook 4A.13
Could someone explain how to do 4A.13?
- Wed Feb 10, 2021 1:32 am
- Forum: Calculating Work of Expansion
- Topic: Textbook 4A.3
- Replies: 1
- Views: 102
Textbook 4A.3
For Problem 4A.3 in the textbook, when calculating for the change in volume, the answer key multiplied by 1L=1000cm^3. I was wondering how we would know that 1L is equal to 1000 cm^3 based off of the equation sheet.
- Wed Feb 10, 2021 1:31 am
- Forum: Calculating Work of Expansion
- Topic: 1L=1000cm^3
- Replies: 4
- Views: 291
1L=1000cm^3
For Problem 4A.3 in the textbook, when calculating for the change in volume, the answer key multiplied by 1L=1000cm^3. I was wondering how we would know that 1L is equal to 1000 cm^3 based off of the equation sheet.
- Mon Feb 08, 2021 1:28 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: dT versus ΔT
- Replies: 8
- Views: 737
dT versus ΔT
I was wondering what the difference is between dT versus ΔT?
- Mon Feb 08, 2021 1:17 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Does phase matter in Hess's Law?
- Replies: 21
- Views: 1848
Re: Does phase matter in Hess's Law?
Yes, phase does matter in Hess's law. It's not enough to just look for the change in enthalpy of the compound name.
- Mon Feb 08, 2021 1:15 pm
- Forum: Calculating Work of Expansion
- Topic: R constant of an Ideal Gas
- Replies: 16
- Views: 721
Re: R constant of an Ideal Gas
On the equation sheet, looking at the multiple possible values for R, you can look at what units are being used and plug that into whatever problem you're solving to see if the units cancel.
- Mon Feb 08, 2021 1:13 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Work on a system
- Replies: 27
- Views: 1026
Re: Work on a system
Compression is an example of work done onto the system because the energy lost from compression is going into the system.
- Mon Feb 08, 2021 1:11 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed vs Isolated System
- Replies: 30
- Views: 1217
Re: Closed vs Isolated System
A closed system has a fixed amount of matter, meaning that it's sealed off but energy can still go into the system. For example, if you're holding a sealed container, it's a closed system because there's a fixed amount of matter but energy in the form of heat from your hand can still enter the syste...
- Mon Feb 08, 2021 1:09 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Constant temperature
- Replies: 1
- Views: 94
Constant temperature
I was wondering why in today's lecture when Professor Lavelle was explaining dS=dq/T that the temperature would be constant if the change in entropy and heat are infinitesimally small?
- Wed Feb 03, 2021 2:27 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Molecules in gas phase occupying more states
- Replies: 2
- Views: 108
Molecules in gas phase occupying more states
I was wondering why molecules in the gas phase occupy more states than liquids and solids?
- Wed Feb 03, 2021 2:25 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy definition
- Replies: 37
- Views: 2189
Entropy definition
Could someone clarify what entropy is?
- Mon Feb 01, 2021 2:08 pm
- Forum: Student Social/Study Group
- Topic: Work Life Balance
- Replies: 44
- Views: 1451
Re: Work Life Balance
I recommend planning to finish your work each day right before office hours. I feel more motivated to do my work when I know that if I get stuck I can get help right away. I also recommend following guided meditations on Youtube for example to help clear your mind for 15 minutes because those really...
- Mon Feb 01, 2021 1:13 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy reactions
- Replies: 9
- Views: 415
Re: Enthalpy reactions
First, draw the Lewis structure of the reactants and products. Then compare the reactants and products to identify which bonds must have been broken and which must have been formed to get the new molecules. Next, take the bond enthalpies of the broken bonds and the enthalpies of the formed bonds (wh...
- Mon Feb 01, 2021 1:09 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: closed system
- Replies: 43
- Views: 1466
Re: closed system
A closed system has a fixed amount of matter because the system is sealed off, so therefore, substances can't be added or taken away and the volume doesn't change.
- Mon Feb 01, 2021 1:07 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: State Function
- Replies: 22
- Views: 707
Re: State Function
Work isn't a state function because it's necessary to know the intermediate steps and not just the final and initial. For example, with the two hikers on the mountain in Lavelle's old lecture, even if their change in altitude was the same, one path took more work because the hiker hiked a longer pat...
- Mon Feb 01, 2021 1:05 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Delta U
- Replies: 6
- Views: 263
Re: Delta U
Yes, the internal energy is the energy within the system, not in the surroundings. If the internal energy is decreasing that means that the system is losing heat or doing work by expanding. If the internal energy is increasing, that means that the system is gaining heat or having work done onto it t...
- Mon Feb 01, 2021 12:58 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Lecture Closed System but Volume Changes [ENDORSED]
- Replies: 1
- Views: 134
Lecture Closed System but Volume Changes [ENDORSED]
In today's lecture, at around 28:33, Professor Lavelle gave an example where there was a closed system but the volume was still changing and I'm still confused about how the volume could still change if the system is closed.
- Thu Jan 28, 2021 6:42 pm
- Forum: Student Social/Study Group
- Topic: Favorite Music
- Replies: 113
- Views: 9776
Re: Favorite Music
Some of my recommendations are Hozier, Riles, Bruno Major,Duckwrth, Still Woozy, and Claire Rosinkraz!
- Tue Jan 26, 2021 11:48 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 4D.17
- Replies: 3
- Views: 147
4D.17
I was wondering why the answer key didn't include N2 in the calculations for the standard enthalpy of the reaction for 4D Problem 17 in the textbook?
- Tue Jan 26, 2021 12:49 am
- Forum: Student Social/Study Group
- Topic: Sections 4A to 4C on Midterm
- Replies: 3
- Views: 157
Sections 4A to 4C on Midterm
I know Professor Lavelle said that sections 4D and 4E are most relevant to the midterm, but I was wondering if we need to do problems 4A to 4C at all still or if we will come back to them later since they weren't lectured on.
- Mon Jan 25, 2021 2:55 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: qsys v. qsurr
- Replies: 7
- Views: 303
Re: qsys v. qsurr
The reaction is within the system and the surroundings are whatever is outside the system, or doesn't include the reaction.
- Mon Jan 25, 2021 2:51 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Ice melting
- Replies: 5
- Views: 300
Re: Ice melting
Ice melting is endothermic because heat is going inside the system, or the ice cube, to melt it. For an exothermic reaction, heat is being released into the surroundings and out of the system so that's why the surroundings are gaining more heat. Hope that helps!
- Mon Jan 25, 2021 2:50 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Acid and Bases
- Replies: 7
- Views: 365
Re: Acid and Bases
Hydronium will be in a higher concentration for an acidic solution, and hydroxide will be in a higher concentration for basic solutions.
- Mon Jan 25, 2021 2:50 pm
- Forum: Phase Changes & Related Calculations
- Topic: when to assume x is insignificant
- Replies: 86
- Views: 6385
Re: when to assume x is insignificant
When the equilibrium constant is less than 10^-4 you can assume x is insignificant and not include it in the denominator. If you really want, you can verify if it was okay to use the approximation for a given problem by checking if the percent ionization is less than 5%.
- Mon Jan 25, 2021 1:26 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Change in Kelvin/Celsius
- Replies: 4
- Views: 229
Change in Kelvin/Celsius
Can someone explain what Professor Lavelle meant in the very beginning of today's lecture that a change in Kelvin is the same as a change in Celsius?
- Sun Jan 24, 2021 10:54 pm
- Forum: Phase Changes & Related Calculations
- Topic: Textbook 4A.1 systems
- Replies: 2
- Views: 107
Textbook 4A.1 systems
For Problem 4A.1 in the textbook, I was wondering if someone could explain parts c and d?
Here's the problem:
Identify the following systems as open, closed, or isolated:
(c) a bomb calorimeter in which benzene is burned
(d) gasoline burning in an automobile engine
Here's the problem:
Identify the following systems as open, closed, or isolated:
(c) a bomb calorimeter in which benzene is burned
(d) gasoline burning in an automobile engine
- Sun Jan 24, 2021 7:53 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: approximating
- Replies: 10
- Views: 387
Re: approximating
x is still equal to some value and not zero. If it was equal to zero the numerator and denominator would be zero and the entire fraction would be zero so it wouldn't make sense. I'm assuming we keep x^2 in the numerator bc although x may be a small value, x^2 is large enough to be included.
- Sun Jan 24, 2021 7:14 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: pH of salt/bases
- Replies: 4
- Views: 207
pH of salt/bases
For the compound CH3NH3Cl in problem 6D.13, how do we know if it's a salt or base? I know weak bases contain ammonia in them but I still can't tell if this would be a salt or not.
- Sat Jan 23, 2021 10:30 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook Problem 6D.5a use tables?
- Replies: 2
- Views: 196
Textbook Problem 6D.5a use tables?
I was wondering if we're supposed to use the tables to solve Problem 6D.5a. I know the pka value was given but when I calculated the ka value from it and then the kb value, it didn't match the answer key.
- Sat Jan 23, 2021 12:21 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Telling Between Salts and Acids/Bases
- Replies: 3
- Views: 206
Telling Between Salts and Acids/Bases
I know what the strong acids and bases are as well as what the weak acids and bases are, but sometimes I can't tell if a compound is a salt or if it's an acid/base. How can I tell the difference?
- Fri Jan 22, 2021 11:59 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook Problem 6D.3b
- Replies: 1
- Views: 129
Textbook Problem 6D.3b
I was wondering for textbook problem 6D.3b how did we know that the compound was a base when writing the reaction? I know we can't just assume that it's a base even when they're asking for the kb value so I was wondering how else would we know.
- Thu Jan 21, 2021 1:38 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Lower pkb is more basic
- Replies: 4
- Views: 626
Lower pkb is more basic
I was wondering if someone could explain why a lower pka means that an acid is stronger and why a lower pkb means that a base is stronger? Also, do higher Ka and Kb values correspond to stronger acids and bases or weaker acids and bases?
- Thu Jan 21, 2021 12:11 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook 6B.11 part ii.
- Replies: 2
- Views: 113
Textbook 6B.11 part ii.
For Problem 6B.11 part ii in the textbook, I used the M*V of the initial solution=M*V of the final solution equation to try to find the molarity of the original solution. I was wondering why the answer key used the 5 ml that was transferred for the volume of the original solution instead of the volu...
- Tue Jan 19, 2021 7:15 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Ka vs. Kb
- Replies: 30
- Views: 4899
Re: Ka vs. Kb
Ka and Kb are both equilibrium constants for reactions, but Ka is used when an acid is involved in the reaction, while Kb is used when a base is involved in the reaction. Their equations are both the ratio of the concentration of products over the concentration of reactants.
- Tue Jan 19, 2021 7:11 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Textbook Question Kw
- Replies: 5
- Views: 183
Re: Textbook Question Kw
They're always the same in concentration because when H3O forms that means that a water molecule donated a proton to H2O, which also must mean that the water molecule became OH once it donated its proton.
- Tue Jan 19, 2021 7:10 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: ICE table values
- Replies: 20
- Views: 798
Re: ICE table values
It can also sometimes be in bars, and in that case, you wouldn't need to convert any units and can just write the number directly into the ICE table.
- Tue Jan 19, 2021 7:08 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Water in Reactions
- Replies: 7
- Views: 273
Re: Water in Reactions
You only include water in reactions when it's not a liquid. Liquids or solids aren't included in k because they're in so much excess that any change to their concentration doesn't change their overall concentration by much so their concentrations would cancel out in the numerator and the denominator...
- Tue Jan 19, 2021 7:05 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: conjugate base
- Replies: 14
- Views: 425
Re: conjugate base
The conjugate base of a weak acid is a strong base, so they are opposites in strength.
- Mon Jan 18, 2021 1:05 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Table- What increases and what decreases
- Replies: 3
- Views: 137
ICE Table- What increases and what decreases
I was wondering whenever we form an ICE Table, how do we know which concentrations will increase and which will decrease? At first, I assumed that products' concentrations will always decrease and reactants' concentrations will always increase, but that doesn't seem to always be the case.
- Mon Jan 18, 2021 12:50 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook 5.35
- Replies: 2
- Views: 88
Textbook 5.35
Can someone explain how to do part a in Number 5.35? I'm confused on how to balance the equation from looking at the graph.
- Mon Jan 11, 2021 2:10 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kw in Lecture
- Replies: 5
- Views: 331
Kw in Lecture
In today's lecture for the example that involved the reaction Ba(OH)2--> Ba+2OH, I was wondering why Professor Lavelle wrote Kw as equal to the hydronium concentration multiplied by the hydroxide equation. Why didn't he include Ba in the equilibrium constant when it's not a solid or liquid?
- Mon Jan 11, 2021 2:11 am
- Forum: Administrative Questions and Class Announcements
- Topic: Participation
- Replies: 18
- Views: 778
Re: Participation
We get points for both.
- Mon Jan 11, 2021 2:08 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: change in K
- Replies: 22
- Views: 805
Re: change in K
Yes, only temperature can change K.
- Mon Jan 11, 2021 2:06 am
- Forum: Student Social/Study Group
- Topic: Study Habits
- Replies: 96
- Views: 5400
Re: Study Habits
Hi! I think breaking up the outline problems in chunks throughout the week makes things a lot more manageable and gives you more time to ask questions if you need to so you can understand the content better, since I personally tended to cram last quarter. I also would recommend to go to workshops to...
- Mon Jan 11, 2021 2:03 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Tables
- Replies: 11
- Views: 627
Re: ICE Tables
You use it usually when you want to solve for the concentrations of the reactants and products at equilibrium given the initial concentrations of the reactants and products and the k value.
- Mon Jan 11, 2021 2:01 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Coefficients for eq constant
- Replies: 9
- Views: 559
Re: Coefficients for eq constant
You raise the concentrations of each reactant and each product to the power of that coefficient in the fraction. Make sure that the reaction is balanced first so you have the right coefficients.
- Mon Jan 11, 2021 2:00 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Favors
- Replies: 10
- Views: 446
Re: Favors
If a reaction favors the left side/reverse reaction, it means that it will try to create more reactants, while if a reaction favors the right side/forward reaction, it will try to create more products.
- Mon Jan 11, 2021 1:57 am
- Forum: Student Social/Study Group
- Topic: Weekly Assignments
- Replies: 5
- Views: 200
Re: Weekly Assignments
Yes, but you should also be working on the outline problems on your own since some of them are on the test and they can pile up if you don't work on them throughout the week.
- Mon Jan 11, 2021 1:56 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Pure substances
- Replies: 9
- Views: 1104
Re: Pure substances
For liquids, their concentrations don't change because they are in so much excess that the change is very minimal in comparison to their concentrations. When we write the expression for k, since their concentrations don't change on the reactant and product side, they would cancel out in the numerato...
- Sun Jan 10, 2021 12:58 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: When to use ice table
- Replies: 4
- Views: 222
When to use ice table
When do we know when to use the ICE table? I'm not sure how to tell if the concentration that's given in a problem is the concentration at equilibrium already or if its a concentration not at equilibrium.