Search found 53 matches
- Mon Mar 15, 2021 9:18 am
- Forum: Administrative Questions and Class Announcements
- Topic: THANK YOU DR LAVELLE!
- Replies: 47
- Views: 6295
Re: THANK YOU DR LAVELLE!
Thank you so much Dr. Lavelle!
- Sat Mar 13, 2021 7:35 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts and intermediates
- Replies: 10
- Views: 577
Re: Catalysts and intermediates
LeanneBagood_2F wrote:in terms of equations/laws, which ones can/cannot have catalysts and/or intermediates in them again?
i saw someone mention that intermediates can't be in rate laws but is there anything else?
I believe you cannot have intermediates in the rate law, but you can have catalysts.
- Sat Mar 13, 2021 7:33 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode and Cathode
- Replies: 25
- Views: 1213
Re: Anode and Cathode
Yes the anode will always be oxidized and the cathode will always be reduced.
- Fri Mar 12, 2021 8:48 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Units for Activation Energy
- Replies: 28
- Views: 1854
Re: Units for Activation Energy
It can be either kj/mol or J/mol, but you should be careful when using the activation energy in the Arrhenius Equation because the R constant is in J/mol K so you should convert your activation energy from kj/mol to J/mol by multiplying by 1000.
- Thu Mar 11, 2021 5:15 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Bottle Neck Effect and Reaction Rate Equation
- Replies: 2
- Views: 186
Re: Bottle Neck Effect and Reaction Rate Equation
In Matthew's Workshop yesterday, he used the pre-equilibrium approach and for the overall rate, we just left the answer as rate = k[a]... where k = (k1 * k2)/k'1. He also posted his answers for the worksheet if you want to see it under Matthew's Workshop Week 10. This is the only way I've seen this ...
- Wed Mar 10, 2021 5:27 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Reaction Intermediates? [ENDORSED]
- Replies: 4
- Views: 309
Re: Reaction Intermediates? [ENDORSED]
Intermediates are species that are in the mechanism, but not in the overall rate law. The way to distinguish intermediates and catalysts is that intermediates are always produced by a reaction, and then consumed immediately after in the next reaction. On the other hand, catalysts are consumed first,...
- Wed Mar 10, 2021 5:24 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: determining order [ENDORSED]
- Replies: 7
- Views: 602
Re: determining order [ENDORSED]
When you use the table to find the order, you essentially have to divide two experiments where one reactant is constant and the other is changing. You can look at the table and formulate the equation in your head to get it without having to write down everything. I find this helpful when the factor ...
- Sat Mar 06, 2021 2:03 pm
- Forum: General Rate Laws
- Topic: Factors Affecting k
- Replies: 83
- Views: 4543
Re: Factors Affecting k
K is affected by a change in temperature!
- Fri Mar 05, 2021 2:57 pm
- Forum: First Order Reactions
- Topic: How to determine the Order of reactions
- Replies: 8
- Views: 397
Re: How to determine the Order of reactions
You can use experimental data or graphs to figure out the order. To the order of the reaction using the experimental data, you should find two trials where all of the reactants except for one is being held constant and then divide those two to find the order. You should do this for all of the other ...
- Thu Mar 04, 2021 6:04 pm
- Forum: General Rate Laws
- Topic: Rate Constant
- Replies: 31
- Views: 1133
Re: Rate Constant
You can change the rate constant by changing the temperature the reaction takes place in or by changing the activation energy ( you can add or remove a catalyst to do this).
- Wed Mar 03, 2021 5:39 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Concentration Cells
- Replies: 2
- Views: 157
Re: Concentration Cells
The standard cell potential will be zero because in a concentration cell, the same reaction is occurring on both sides, there's just a concentration difference between the anode and cathode and that's what drives the electron flow. When calculating E naught of the cell, if you subtract the E anode f...
- Tue Mar 02, 2021 11:42 am
- Forum: Balancing Redox Reactions
- Topic: states of matter
- Replies: 58
- Views: 2121
Re: states of matter
The states of matter are important and Redox reactions and you should include them in your answer for sapling!
- Sun Feb 28, 2021 12:38 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Gibbs Free Energy Equation and n
- Replies: 13
- Views: 575
Re: Gibbs Free Energy Equation and n
In this equation, the n value will the number of electrons transferred between the reactions. The best way to find this out is to separate the oxidation and reduction half reactions and then after balancing them, look at the number of electrons that are transferred to get the n value.
- Sat Feb 27, 2021 9:51 am
- Forum: Balancing Redox Reactions
- Topic: Acidic vs. Basic
- Replies: 20
- Views: 752
Re: Acidic vs. Basic
For acidic solutions, you want to use H+ and H2O to balance out the equations, but for basic solutions, you want to use OH- and H20 instead of H+ because you don't want to have H+ in a basic solution.
- Thu Feb 25, 2021 4:28 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: n in NFE
- Replies: 64
- Views: 2942
Re: n in NFE
Once you balance your oxidation and reduction half reactions, n is going to the number of electrons that transferred in the equation. Since its balanced, it should be the same in both reactions.
- Thu Feb 25, 2021 4:24 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Relationship between E naught and spontaneity
- Replies: 8
- Views: 1052
Re: Relationship between E naught and spontaneity
If the E naught value is positive, then the reaction is spontaneous, but if the E naught value is negative, then the reaction is not spontaneous.
- Thu Feb 25, 2021 4:23 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Relationship between E naught and spontaneity
- Replies: 8
- Views: 1052
Re: Relationship between E naught and spontaneity
If the E naught value is positive, then the reaction is spontaneous, but if the E naught value is negative, then the reaction is not spontaneous.
- Thu Feb 25, 2021 4:20 pm
- Forum: Ideal Gases
- Topic: Conditions
- Replies: 20
- Views: 1476
Re: Conditions
STP is at 1 atm and 273.15 K or 0 C.
- Fri Feb 19, 2021 6:59 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Is thermal mugs an example of an isolated system?
- Replies: 38
- Views: 1900
Re: Is thermal mugs an example of an isolated system?
A thermos or any insulated sealed container would be as close to a real isolated system because no energy can be transferred from the system to the surroundings and no matter can be exchanged either.
- Fri Feb 19, 2021 6:57 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Calculating degeneracy
- Replies: 18
- Views: 3278
Re: Calculating degeneracy
W = (number of equal energy states) ^ (the number molecules). You would then plug this W value into the S = Kb ln W equation to get positional/residual entropy.
- Fri Feb 19, 2021 6:55 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: When does delta H = q?
- Replies: 15
- Views: 4830
Re: When does delta H = q?
Delta H = q when there is constant pressure. In problems, they might say isobaric too, but that also means constant pressure.
- Fri Feb 19, 2021 6:54 am
- Forum: Calculating Work of Expansion
- Topic: unit of w
- Replies: 17
- Views: 1136
Re: unit of w
After calculating work with the P*deltaV equation, you should multiply your answer by 101.325 J/(L atm) because this will convert the value into J. This is super important because q usually ends up in J or kj and you want to be able to add/subtract them for delta U.
- Wed Feb 17, 2021 7:07 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Textbook Question 4.21
- Replies: 3
- Views: 248
Re: Textbook Question 4.21
Yes I believe we are talking about the entropy of the world because that would technically be delta S total. We know that a process is spontaneous only if delta S total is positive, so here the delta S total is negative which makes it not spontaneous.
- Thu Feb 11, 2021 6:43 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Different R Constants
- Replies: 14
- Views: 690
Re: Different R Constants
Keeping track of the units, like everyone said, is super helpful! That's saved me so many times. You should use the 0.08206 L atm/ K mol for PV=nRT because the units of the constant will cancel out and then you want to use the 8.3145 J/mol K for any equation where you're trying to find energy or ent...
- Thu Feb 11, 2021 6:40 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Free Energy
- Replies: 49
- Views: 1889
Re: Free Energy
A state function is where the value doesn't depend on the path taken to get there, but only the final and initial values. Free energy is a state function because we only need the final and initial values to find the change and determine whether the reaction is spontaneous.
- Thu Feb 11, 2021 6:38 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Kelvin conversion
- Replies: 40
- Views: 2892
Re: Kelvin conversion
You should add 273 or 273.15 to the C temperature value to convert to Kelvin and then subtract 273 or 273.15 from the K value to get the C value.
- Wed Feb 10, 2021 8:08 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Sapling Week 5/6 #7
- Replies: 5
- Views: 288
Re: Sapling Week 5/6 #7
I don't remember going over finding the enthalpy of vaporization in our lectures, but I used the units to figure out how to find it. I realized that I needed to convert the heater value with units W to kj (convert from W to J/sec to J to kj), and then I used the masses given to calculate the moles o...
- Mon Feb 08, 2021 10:07 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Using R in thermodynamic equations
- Replies: 24
- Views: 972
Re: Using R in thermodynamic equations
The R constant you should use depends on the units that the question is asking for. Usually if you're using the R to find energy, then I would recommend using 8.3145 J/mol*K, but if you're using PV=nRT to convert values, then I would use the 0.08206 L*atm/mol because that will give you the right uni...
- Fri Feb 05, 2021 3:34 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: External Pressure
- Replies: 32
- Views: 968
Re: External Pressure
The external pressure is the pressure pushing onto the piston from the surroundings.
- Fri Feb 05, 2021 3:32 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Key points of First Law
- Replies: 8
- Views: 190
Re: Key points of First Law
The First Law of Thermo essentially says that energy cannot be created or destroyed. So if we're looking at the system vs surroundings, a release of energy from the system (negative change) will be energy absorbed by the surroundings (positive change) and vice versa.
- Thu Feb 04, 2021 10:24 am
- Forum: Calculating Work of Expansion
- Topic: integral equation
- Replies: 7
- Views: 295
Re: integral equation
The integral equation is used in a reversible system and the external pressure is changing in really small increments (which is the reason we have to use the integral). You won't actually have to use it on a test though thankfully.
- Wed Feb 03, 2021 6:09 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Units
- Replies: 11
- Views: 359
Re: Units
You should use J/g C because that's what the textbook uses, but also just be careful of what units the problem gives temperature in. They might give it in kelvin just to throw you off or something like that.
- Tue Feb 02, 2021 3:02 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated System
- Replies: 16
- Views: 658
Re: Isolated System
All isolated systems are not vacuums, rather they are just systems where no matter or energy can be transferred so the internal energy of the system stays the same.
- Sun Jan 31, 2021 10:42 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Pressure affects only gas reactions?
- Replies: 23
- Views: 1699
Re: Pressure affects only gas reactions?
If there is an equal amount of moles on both sides, then any pressure changes won't affect the reaction because pressure only affects gases, not liquids and solids.
- Thu Jan 28, 2021 3:43 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: x is less than 5% of initial concentration
- Replies: 4
- Views: 224
Re: x is less than 5% of initial concentration
Honestly, since the calculation takes less than a minute I would do it anytime you're unsure if you can use the approximation. If the K is 10^-4 then I would definitely do that but if its 10^-5 you probably won't need to, but it can't hurt.
- Wed Jan 27, 2021 11:58 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: How to understand if -x is insignificant
- Replies: 13
- Views: 470
Re: How to understand if -x is insignificant
You can take out the x in the expression when its (concentration - x) in denominator when the K value for the equation is less than 10^-4. 10^-4 is a safe value for approximation, so if you're unsure you can always go through with the problem to find x and then use the % protonation or deprotonation...
- Tue Jan 26, 2021 4:49 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Memorize bond enthalpies / standard enthalpies of formation?
- Replies: 39
- Views: 1232
Re: Memorize bond enthalpies / standard enthalpies of formation?
We won't have to memorize the bond enthalpy values or anything like that, we should be given this value and then we can use the values to then figure out the standard reaction enthalpy.
- Mon Jan 25, 2021 5:20 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Difference between standard reaction enthalpy, enthalpy of formation, and enthalpy of combustion
- Replies: 2
- Views: 202
Difference between standard reaction enthalpy, enthalpy of formation, and enthalpy of combustion
I'm confused on the difference between the standard reaction enthalpy, enthalpy of formation, and enthalpy of combustion. Can we use the three methods from friday's lecture to find all three or are there specific methods to finding one of them.
- Sat Jan 23, 2021 1:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling Week 2 Hw 5
- Replies: 6
- Views: 321
Re: Sapling Week 2 Hw 5
You can use the 5% rule for percent protonation and deprotonation and then if the rule doesn't work, then I would go back and use the quadratic formula to get the more accurate answer.
- Thu Jan 21, 2021 6:03 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: How to fill in 2nd row of ICE table?
- Replies: 25
- Views: 740
Re: How to fill in 2nd row of ICE table?
Most of the time, the reactants side will have a negative change and the products side will have a positive change. One way to be sure is to calculate Q using the initial concentrations. If K < Q, then the reaction will move towards the reactants which means that the product change is negative and r...
- Wed Jan 20, 2021 11:05 am
- Forum: Ideal Gases
- Topic: PV=nRT and Equilibrium
- Replies: 12
- Views: 539
Re: PV=nRT and Equilibrium
I mostly use PV=nRT in equilibrium to convert gases to concentration and vice versa, depending on the information given in the question. The equation is also helpful for Le Chatelier's Principle because you can see how pressure and volume are related to see volume changes would affect the reaction.
- Wed Jan 20, 2021 11:02 am
- Forum: Ideal Gases
- Topic: Omitting solid/liquid
- Replies: 19
- Views: 692
Re: Omitting solid/liquid
We leave solids and liquids out because they do not have a concentration so we cannot put them into our K expression. We also don't include H20 in the K expression when it acts as a solvent because its concentration is so high on both the reactants and products side that we would see no difference. ...
- Mon Jan 18, 2021 9:24 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: When would K be unchanged?
- Replies: 31
- Views: 1058
Re: When would K be unchanged?
It's a good thing to keep track of the temperatures in the question because if the temperature changes, then K will change as well. Otherwise, if the temperature stays constant for the whole question, then you can assume that K stays the same even though the concentration of reactants or products ch...
- Fri Jan 15, 2021 8:03 am
- Forum: Ideal Gases
- Topic: n/V = concentration
- Replies: 19
- Views: 2155
Re: n/V = concentration
Hi! Since molarity (M) is defined as the concentration over the volume, we can manipulate our ideal gas equation to get (n/v) on one side and get P/rt on the other side. This is super helpful to go between molarity and pressure especially since we use a lot of gases in chemical equilibrium.
- Wed Jan 13, 2021 6:36 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: How to calculate the pKa
- Replies: 14
- Views: 836
Re: How to calculate the pKa
To find pKa, you would need to have the Ka value, which you can get by setting up the equilibrium equation with products at the tops and reactants at the bottom. Once you have Ka, just take the -log(Ka) which will give you the pKa value.
- Tue Jan 12, 2021 9:03 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Neglecting Water
- Replies: 20
- Views: 988
Re: Neglecting Water
The concentration of water is so high on both sides, that the change in water that happens during the reaction is so small so that we don't include it in the K expression. Even if we were to include it, there wouldn't necessarily be a difference in the water value because the value is so small that ...
- Mon Jan 11, 2021 5:40 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kw
- Replies: 7
- Views: 353
Re: Kw
Yes since Kw is dependent on temperature, it will change if the temperature changes.
Also for your second question, a neutral solution is when both [H3O] and [OH] are 1.0*10^-7 (both equal) so water would only be neutral at that time too.
Also for your second question, a neutral solution is when both [H3O] and [OH] are 1.0*10^-7 (both equal) so water would only be neutral at that time too.
- Mon Jan 11, 2021 5:37 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: H30+ and OH-
- Replies: 4
- Views: 431
Re: H30+ and OH-
In a neutral solution (like water), H30 and OH have to be equal. But if the solution is acidic, that means there is more H3O than OH and if the solution is basic, then that means there is more OH than H3O.
- Thu Jan 07, 2021 5:13 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Partial pressure vs concentration
- Replies: 6
- Views: 329
Re: Partial pressure vs concentration
You can use either partial pressure or concentration of the gas, as long as you say Kp and Kc respectively and know which one the problem is asking for.
- Wed Jan 06, 2021 2:41 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: True or False?
- Replies: 4
- Views: 285
Re: True or False?
According to Le Chatelier's Principle, if there is a higher number of reactants, then the system will accommodate for that change by making more products to get to equilibrium. So compared to the original scenario, an increase in the reactants will also cause an increase in the products too.
- Wed Jan 06, 2021 2:38 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: solvent in equilibrium constants
- Replies: 8
- Views: 350
Re: solvent in equilibrium constants
Solvents are usually going to be water but are liquids and have the symbol (l) and they are not included in the equilibrium equation. You want to include aqueous (aq) solutions in the equilibrium equation.
- Tue Jan 05, 2021 2:00 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Q vs K
- Replies: 12
- Views: 549
Re: Q vs K
Hi! What helps me remember the relationship between Q and K is if Q is smaller than K, then the reaction still needs more time to get to the equilibrium value and therefore it needs to make more products (shifts to the right), but if Q is larger than K, then the reaction still needs to go to equilib...
- Mon Jan 04, 2021 3:17 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: How does changing volume impact the equilibrium constant?
- Replies: 7
- Views: 2182
Re: How does changing volume impact the equilibrium constant?
If the volume decreases, then the concentration increases which would shift the equilibrium towards side with less moles of gas. If the volume increases, then the equilibrium will shift towards the side with more moles of gas because the concentrations will decrease. Eventually, the system will adju...