Search found 174 matches
- Tue Mar 16, 2021 8:59 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Pseudo Reaction Orders
- Replies: 2
- Views: 350
Re: Pseudo Reaction Orders
The purpose of a pseudo first order reaction is to help you analyze the rate law of a reaction that depends on the concentration of more than one reactant species. The way it works is that you increase the concentration of one of the reactant species to be so high that any changes in its concentrati...
- Tue Mar 16, 2021 8:48 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts and Intermediates
- Replies: 7
- Views: 553
Re: Catalysts and Intermediates
Catalysts are not consumed during the course of a reaction. They are used to lower the activation energy so that more molecules, at the same temperature, have the minimum required energy to reach the transition state. Catalysts speed up the rate of the forward and reverse reaction, so they do not af...
- Mon Mar 15, 2021 9:52 am
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Phase Diagram and Heat
- Replies: 2
- Views: 356
Re: Phase Diagram and Heat
When you are calculating the heat it takes to change a substance from one phase to another phase, you need to separate it into different steps because of differences in specific heat capacity and due to the presence of phase changes. For example, if you are heating solid ice from -5 C to + 150 C, yo...
- Mon Mar 15, 2021 9:46 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Ecell and G
- Replies: 1
- Views: 240
Re: Ecell and G
Delta G is the maximum amount of work that a cell can perform. At standard conditions, we can use the equation delta G(naught) = -n F E(naught) to see that when E naught is a positive value, then delta G naught is a negative value and the redox reaction is spontaneous so a galvanic cell is used. On ...
- Mon Mar 15, 2021 9:40 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Cell Diagrams
- Replies: 2
- Views: 250
Re: Cell Diagrams
Pt stands for platinum. It should be included in the cell diagram when either or both of sides of the galvanic cell do not have a solid conducting metal as an electrode. Since platinum is inert, it would not be involved in the oxidation and reduction reactions. Some exceptions to this are that Hg (l...
- Mon Mar 15, 2021 9:38 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Is electromotive force the same as Ecellnaught?
- Replies: 3
- Views: 530
Re: Is electromotive force the same as Ecellnaught?
The standard EMF is the maximum potential difference between two electrodes and is denoted as E naught.
- Mon Mar 15, 2021 9:32 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Sapling Week 9/10 #17
- Replies: 5
- Views: 397
Re: Sapling Week 9/10 #17
For this problem, I would suggest drawing a reaction profile or visualizing one. First, the problem states that delta H = + 24kJ. This means the reaction is endothermic and would be represented as the distance from the energy of the reactants to the energy of the products on a reaction profile. Next...
- Sun Mar 14, 2021 9:13 pm
- Forum: Administrative Questions and Class Announcements
- Topic: THANK YOU DR LAVELLE!
- Replies: 47
- Views: 6248
Re: THANK YOU DR LAVELLE!
Thank you Dr. Lavelle!! I will never forget the amazing lessons I learned in your class.
- Sat Mar 13, 2021 8:56 pm
- Forum: Student Social/Study Group
- Topic: Sapling good to review for final?
- Replies: 16
- Views: 881
Re: Sapling good to review for final?
Sapling is a good way to get extra practice and can be helpful if you are struggling on particular kinds of problems since the solutions explains how to do problems step-by-step.
- Sat Mar 13, 2021 8:54 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: K = kforward/kreverse
- Replies: 16
- Views: 1025
Re: K = kforward/kreverse
Yes that is correct. If you increase the rate of the forward reaction, then the equilibrium constant K will increase. If you increase the rate of the reverse reaction, the equilibrium constant K will decrease.
- Sat Mar 13, 2021 8:53 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Oxidation and reduction
- Replies: 12
- Views: 1255
Re: Oxidation and reduction
Oxidation is the loss of electrons. It occurs at the anode of a galvanic cell.
Reduction is the gain of electrons. It occurs at the cathode of a galvanic cell.
Reduction is the gain of electrons. It occurs at the cathode of a galvanic cell.
- Sat Mar 13, 2021 8:50 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Textbook 7.21
- Replies: 1
- Views: 236
Re: Textbook 7.21
e is wrong because k vs temperature is not linear. ln K vs 1/T is linear with a -Ea/R slope. g is linear because in the half life equation for a zero order reaction, [A] is in the numerator and is directly proportional to half life. h is not linear because in the half life equation for second order,...
- Sat Mar 13, 2021 8:45 pm
- Forum: First Order Reactions
- Topic: textbook 7B #5
- Replies: 3
- Views: 335
Re: textbook 7B #5
It is asking for the half life in hours.
Use t = 0.693/k to find the half life in seconds and then divide by 3600 seconds to convert to hours.
Use t = 0.693/k to find the half life in seconds and then divide by 3600 seconds to convert to hours.
- Sat Mar 13, 2021 8:43 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Temperature change effect on rate constant
- Replies: 3
- Views: 389
Re: Temperature change effect on rate constant
Adding heat to a system increases the number of molecules with the minimum energy to overcome the energy barrier. So, raising temperature will increase the rate constant because more molecules are colliding with enough energy to make the reaction occur. Reactions with higher activation energy depend...
- Sat Mar 13, 2021 8:39 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Delta S of Surroundings = 0 in Irreversible Process
- Replies: 1
- Views: 263
Re: Delta S of Surroundings = 0 in Irreversible Process
Delta S surroundings is zero in an isothermal irreversible process (free expansion) because w = 0 since the system is not pushing against an external pressure. Also, since it's isothermal, delta U is 0. Since delta U = q + w, q must also be 0.
- Sat Mar 13, 2021 9:06 am
- Forum: Administrative Questions and Class Announcements
- Topic: Saying Thank You to Dr. Lavelle
- Replies: 490
- Views: 512573
Re: Saying Thank You to Dr. Lavelle
Thank you so much for a wonderful quarter, Dr. Lavelle! I truly enjoyed being a student in your class. Your passion and dedication for teaching is evident through the numerous resources you have made available to us (UA sessions, TA office hours, Sapling, your discussion sections, etc). Thank you fo...
- Fri Mar 12, 2021 6:52 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Does temperature affect A?
- Replies: 9
- Views: 558
Does temperature affect A?
Does temperature affect the frequency factor A? If so, how?
- Fri Mar 05, 2021 8:28 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Concentration vs Cell Potential
- Replies: 5
- Views: 351
Re: Concentration vs Cell Potential
The Nernst equation is key in telling us how concentration affects cell potential. When you increase the concentration of reactants, the Q term decreases. Taking the ln of value below 1 is negative. This means that you are adding E naught to a positive value, so the E cell potential will be more pos...
- Fri Mar 05, 2021 8:22 am
- Forum: Administrative Questions and Class Announcements
- Topic: 14B Final TextBook Questions
- Replies: 5
- Views: 394
Re: 14B Final TextBook Questions
Yes, it's a good idea to look at textbook questions that are listed in the syllabus outlines. These questions may appear on the final exam, as they have appeared on the midterms.
- Fri Mar 05, 2021 8:21 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Diagram Commas
- Replies: 9
- Views: 547
Re: Cell Diagram Commas
The order does not matter when you are using commas. Just be sure to only use a comma if the phases are the same.
You use a Platinum electrode if you do not have a solid electrode for either a cathode or anode. The only exception to this is that Hg (l) can serve as an electrode.
You use a Platinum electrode if you do not have a solid electrode for either a cathode or anode. The only exception to this is that Hg (l) can serve as an electrode.
- Fri Mar 05, 2021 8:17 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: K
- Replies: 10
- Views: 629
Re: K
You can calculate k if you are given other values for the equation. For example, if you are given a data table with concentrations of reactants across different experiments and the initial rates for those experiments, then you can determine the order for each reactant, write a rate law equation, and...
- Fri Mar 05, 2021 8:11 am
- Forum: General Rate Laws
- Topic: Concentration Denotation
- Replies: 7
- Views: 397
Re: Concentration Denotation
Yes, concentration is usually denoted in brackets. The units are typically moles/Liters or Molarity. In kinetics, the units are sometimes mmol/L also.
- Fri Mar 05, 2021 8:10 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: 5J.5 D
- Replies: 3
- Views: 458
Re: 5J.5 D
I think you meant to write 2HD (g)--> H2 (g)+ D2 (g) When you increase the pressure of the system, you expect the reaction to favor the side with the less moles of gas to relieve the pressure (Le Chatelier's principle). However, in this case, there are 2 moles of gas in the reactants and 2 moles of ...
- Fri Mar 05, 2021 8:06 am
- Forum: Balancing Redox Reactions
- Topic: Oxidation and Reduction
- Replies: 11
- Views: 736
Re: Oxidation and Reduction
The same molecule can be an oxidizing and reducing agent if you have two of those molecules as reactants. So, even though the molecule is identical, one is the oxidizing agent and the other is the reducing agent.
- Sat Feb 27, 2021 10:27 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Spontaneity
- Replies: 2
- Views: 257
Re: Spontaneity
Yes, using the delta G (naught) = -nFE(naught) equation, if standard E naught is positive, then delta G naught is negative, so the reaction is spontaneous.
- Sat Feb 27, 2021 10:26 am
- Forum: Balancing Redox Reactions
- Topic: Adding OH-
- Replies: 5
- Views: 347
Re: Adding OH-
Add OH- and H20 in basic solution.
Add H+ and H20 in acidic solution.
If you're not told which solution you are in, assume acidic.
Add H+ and H20 in acidic solution.
If you're not told which solution you are in, assume acidic.
- Sat Feb 27, 2021 10:23 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Moles in ΔG = -nFE
- Replies: 45
- Views: 3645
Re: Moles in ΔG = -nFE
The value of n in this equation is the number of moles of electrons that are exchanged in the oxidation and reduction reactions, so be sure to balance the redox reactions before solving for this.
- Sat Feb 27, 2021 10:22 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Volts in Concentration Cells
- Replies: 2
- Views: 190
Re: Volts in Concentration Cells
The E naught value is 0 if the solution of cathode and anode is at equilibrium.
- Sat Feb 27, 2021 10:21 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: anode / Cathode
- Replies: 9
- Views: 570
Re: anode / Cathode
I believe it depends on which cell you are talking about. For galvanic cells, the anode is negatively charged, but for an electrolytic cell, the anode is positively charged.
- Sat Feb 20, 2021 7:40 am
- Forum: Calculating Work of Expansion
- Topic: Work sign
- Replies: 46
- Views: 1893
Re: Work sign
When a system does work (like pushing a piston to expand the volume), it is losing energy, so the value of work is negative.
When a system has work done on it (like compression), it is gaining energy, so the value of work is positive.
When a system has work done on it (like compression), it is gaining energy, so the value of work is positive.
- Sat Feb 20, 2021 7:35 am
- Forum: Calculating Work of Expansion
- Topic: Work Formula
- Replies: 15
- Views: 743
Re: Work Formula
You are correct, delta n is the number of moles of gas in the products minus the number of moles of gas in the reactants. You do not consider solids, liquids, or aqueous.
Also, delta n can be positive or negative.
Also, delta n can be positive or negative.
- Sat Feb 20, 2021 7:33 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Stable vs Unstable Gibbs Free Energy
- Replies: 16
- Views: 2344
Re: Stable vs Unstable Gibbs Free Energy
A molecule is thermodynamically unstable if its delta G is positive.
A molecule is thermodynamically stable if its delta G is negative.
A molecule is thermodynamically stable if its delta G is negative.
- Sat Feb 20, 2021 7:31 am
- Forum: Calculating Work of Expansion
- Topic: unit of w
- Replies: 17
- Views: 1128
Re: unit of w
When you multiple L and atm, you can use the conversion factor that 101.325 J = 1 L-atm to convert to Joules.
- Sat Feb 20, 2021 7:29 am
- Forum: Administrative Questions and Class Announcements
- Topic: 2/19 lecture
- Replies: 6
- Views: 358
Re: 2/19 lecture
Dr. Lavelle did post a lecture yesterday. We had a Wednesday and Friday lecture this week.
- Tue Feb 16, 2021 7:17 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: Can Delta S of the universe be negative?
- Replies: 1
- Views: 1491
Can Delta S of the universe be negative?
Can Delta S of the universe be negative? I thought that one of the laws of thermodynamics said that entropy of the universe is always increasing and that delta S total is always greater than or equal to 0. However, at one of the UA sessions, we were told that delta S of the universe is negative when...
- Sun Feb 14, 2021 7:53 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: SeO2 versus SeO3
- Replies: 5
- Views: 260
Re: SeO2 versus SeO3
Ryan Hoang 1D wrote:I believe so, since the Se is the central atom, and all the other Os must revolve around it, theres no room for positional entropy. However, if I’m wrong, it’d be nice for someone to correct me!
What about the entropy? Would the entropy of SeO3 be higher because it has more atoms?
- Sun Feb 14, 2021 7:53 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: SeO2 versus SeO3
- Replies: 5
- Views: 260
Re: SeO2 versus SeO3
What about the entropy? Would the entropy of SeO3 be higher because it has more atoms?
- Sun Feb 14, 2021 7:18 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: SeO2 versus SeO3
- Replies: 5
- Views: 260
SeO2 versus SeO3
Would SeO2 and SeO3 both have a W (degeneracy) value of 1 since the atoms around the Selenium are the same, so there would only be one microstate? If not, what would the correct degeneracy be?
- Sun Feb 14, 2021 4:59 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Sapling Number 5
- Replies: 8
- Views: 418
Re: Sapling Number 5
Once you have the number of moles, use the delta S = nC ln T2/T1 equation to find the change in entropy.
- Sun Feb 14, 2021 4:56 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Sapling Question#9
- Replies: 3
- Views: 204
Re: Sapling Question#9
Here is how I solved the problem: To find delta S of the system, use the standard entropy values that are given in the table. We know from the constants and equations sheet, delta S = q / T. At constant pressure, q = delta H of the system. The value of delta H will be equal and opposite for the surr...
- Sun Feb 14, 2021 4:51 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Sign of G,H,S
- Replies: 4
- Views: 262
Re: Sign of G,H,S
This one was tricky. I had to read the question carefully to predict. For delta G: We know if delta G is negative, it indicates that a reaction is spontaneous. In the given description, we are told that water vapor "readily" adsorbs onto the surface of the silica gel. This implies that the...
- Sun Feb 14, 2021 4:43 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Textbook Problem 4I.5
- Replies: 2
- Views: 148
Re: Textbook Problem 4I.5
You are very close. For this question, you are correct to use q = mCdeltaT to find the final temperature of the solution. Then use delta S = n C ln T2/T1 for each of the water solutions. However, make sure to use 75.3 J/K mol as the molar heat capacity of water liquid. You cannot use 4R because that...
- Sun Feb 14, 2021 4:29 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: sapling #7 week 5/6
- Replies: 2
- Views: 222
Re: sapling #7 week 5/6
Here is how I solved question 7 for the the delta H of vaporization: 1. Use the given information in the problem to find kJ. Start by converting the given value of W into J/s (1 W = 1 J/s). Then multiply that by that by 60 sec/1min. Then multiply by the given minute value, so that you have the Joule...
- Sun Feb 14, 2021 4:20 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Temperature and K
- Replies: 21
- Views: 1046
Re: Temperature and K
For an endothermic reaction, adding heat will shift the reaction to the right, causing more products to be formed, so K will increase. For an exothermic reaction, adding heat will shift the reaction to the left, so more reactants will be formed, and K will decrease.
- Sat Feb 06, 2021 9:47 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Work
- Replies: 39
- Views: 1387
Re: Work
A negative sign in front of work means that the system is losing energy in the form of work because it is expanding.
- Sat Feb 06, 2021 9:45 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Sapling 18, Cp and Cv
- Replies: 2
- Views: 147
Re: Sapling 18, Cp and Cv
I solved the problem the same way that you did and got the correct answer, so I think the method works. However it seems that the book uses Cv and Cp because that is what is discussed in 4C with atoms, linear molecules, and nonlinear molecules.
- Sat Feb 06, 2021 9:42 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Example 4B.1 Question
- Replies: 1
- Views: 91
Re: Example 4B.1 Question
I'm not sure about part b, but for part a, we can say that delta U is equal to zero because we are told that the expansion is isothermal, which means that temperature remains constant. For an ideal gas in an isothermal process, internal energy is equal to 0.
- Sat Feb 06, 2021 9:40 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Enthalpy vs Entropy
- Replies: 7
- Views: 201
Re: Enthalpy vs Entropy
Entropy measures the randomness of molecules in a system, and has units J/K.
Enthalpy measures the energy and total heat in a system, and has units kJ/mol usually.
Enthalpy measures the energy and total heat in a system, and has units kJ/mol usually.
- Sat Feb 06, 2021 9:38 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Entropy vs Enthalpy
- Replies: 11
- Views: 495
Re: Entropy vs Enthalpy
Entropy is a measure of disorder in a system, while enthalpy is the measure of total heat in a system. Entropy is denoted by S, but enthalpy is denoted by H. Entropy is normally in J/K, while enthalpy is in kJ/mol.
- Sat Feb 06, 2021 9:32 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Textbook Problem 4C9 (b)
- Replies: 1
- Views: 115
Re: Textbook Problem 4C9 (b)
In part a, you did q(copper) + q(water) to find the total heat. For part b, you should use the value that you got for q when you do mCdeltaT of the water. Divide that by the total amount of heat that you calculated in part a. Multiply by 100%.
- Sun Jan 31, 2021 7:16 pm
- Forum: Phase Changes & Related Calculations
- Topic: Examples of sublimation
- Replies: 12
- Views: 464
Re: Examples of sublimation
This is a really interesting question! I searched the internet and learned that methanol and camphor can also undergo sublimation.
- Sun Jan 31, 2021 7:13 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: delta H vs delta U
- Replies: 11
- Views: 468
Re: delta H vs delta U
By definition, delta U is the change in internal energy, while delta H is the enthalpy change. If there is no work being done, then delta U would be equal to delta H.
- Sun Jan 31, 2021 7:11 pm
- Forum: Phase Changes & Related Calculations
- Topic: H and q
- Replies: 47
- Views: 1530
Re: H and q
q is the heat that is transferred to or from a system, and it is not a state function. However, H is the total heat of the system at constant pressure and it is a state function.
- Sun Jan 31, 2021 7:09 pm
- Forum: Phase Changes & Related Calculations
- Topic: when to assume x is insignificant
- Replies: 86
- Views: 6385
Re: when to assume x is insignificant
You can assume that x is insignificant if the value that you receive for percent ionization is less than 5%. This would mean that your original substance barely dissociated, so the number that you would be subtracting from the initial is negligible.
- Sun Jan 31, 2021 7:07 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Calculus for thermochemistry
- Replies: 5
- Views: 325
Re: Calculus for thermochemistry
That's a good question. From what I've heard, the Math 31,32,33 classes typically go over calculus concepts. However, I am unsure whether there are other calculus classes at UCLA that would better complement the math we use in chemistry.
- Sun Jan 31, 2021 7:04 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: q = nCdeltaT vs q = CdeltaT (sapling q12)
- Replies: 6
- Views: 282
Re: q = nCdeltaT vs q = CdeltaT (sapling q12)
The difference between the two equations is that in the first one, you use mass in grams, but in the second one you use number of moles. The equation you choose will depend on what the problem is asking.
- Sat Jan 30, 2021 7:43 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: q=mCdeltaT
- Replies: 3
- Views: 263
Re: q=mCdeltaT
I believe we started talking about q and heat in Wednesday's lecture this week, but we will most likely do more calculations in Week 5 lectures.
- Sat Jan 30, 2021 7:40 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Strong Ka
- Replies: 8
- Views: 847
Re: Strong Ka
For strong polyprotic acids, you should consider both the first and second dissociation. But the first dissociation is assumed to go to completion (100%), so you only need the second Ka. For weak polyprotic acids, you only need to consider the second dissociation Ka2.
- Wed Jan 27, 2021 7:07 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Clarification about Solids & Liquids for Le Chateliers Principle
- Replies: 7
- Views: 1675
Clarification about Solids & Liquids for Le Chateliers Principle
Is this correct? : If a reaction contains a solid or a liquid substance, then increasing or decreasing the concentration of the solid or liquid will not affect the reaction. Le Chatelier's principle does not apply to solids and liquids? So, the equilibrium concentrations will not change, and the val...
- Sun Jan 24, 2021 12:24 pm
- Forum: Phase Changes & Related Calculations
- Topic: Steam causing severe burns
- Replies: 19
- Views: 767
Re: Steam causing severe burns
I think that whether you get burned by steam or not can depend on how fast the steam is coming out. For example, steam from pressure cookers ejects really fast, and the speed at which those gas water molecules hit your skin could affect whether you are burned. On the other hand, face steamers often ...
- Sun Jan 24, 2021 12:19 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: H, T, and q
- Replies: 1
- Views: 160
Re: H, T, and q
H enthalpy is just the internal energy of a specific reactant or product. When you add delta in front of a symbol, it means "change." Delta H means the change in internal energy of a system (final - initial), or the enthalpy of products minus the enthalpy of reactants. Delta H is equal to ...
- Sun Jan 24, 2021 12:14 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat released/ gained
- Replies: 22
- Views: 936
Re: Heat released/ gained
Breaking a bond requires energy. Forming a bond releases energy. This is due to the fact that bonds form to allow atoms to be in the lowest energy (stable) position. Breaking a bond would cause two previously bound atoms to now be separate, and this may be an unstable position for the atoms. So, bre...
- Sun Jan 24, 2021 12:10 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Direction of arrows
- Replies: 11
- Views: 464
Re: Direction of arrows
If there is only one arrow that points in one direction, it means that the reaction will strongly proceed in that direction, but it does not mean that the reverse won't happen. For example, in a different lecture Professor Lavelle drew a very long arrow going from the reactants to products, and an e...
- Fri Jan 22, 2021 9:58 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: enthalpy of formation vs. enthalpy of combustion
- Replies: 3
- Views: 335
Re: enthalpy of formation vs. enthalpy of combustion
For enthalpy of combustion, it helps me to remember that a combustion reaction has O2 as a reactant. The products are CO2, H2O, and sometimes N2. If your reaction has those reactants and products, then you are likely looking at a combustion reaction. When you are finding the total enthalpy of a comb...
- Fri Jan 22, 2021 9:55 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard State
- Replies: 3
- Views: 303
Re: Standard State
The standard state of an element is its phase at 25 degrees celsius and 1 atm or 1M.
- Wed Jan 20, 2021 5:51 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: steam causing burns
- Replies: 40
- Views: 1212
Re: steam causing burns
Steam causes severe burns because of the large negative enthalpy of condensation.
- Mon Jan 18, 2021 7:38 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Q and K
- Replies: 46
- Views: 1550
Re: Q and K
One way to compare Q and K is that if Q>K then you have more products in the reaction that the amount of products there should be at equilibrium. Therefore, to reach equilibrium, the reaction will shift left. If Q <K then there are more reactants present than the amount of reactants that there shoul...
- Mon Jan 18, 2021 7:36 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Moles vs Concentrations in ICE Box
- Replies: 21
- Views: 742
Re: Moles vs Concentrations in ICE Box
When I use the ice table, I normally start with concentrations because I can directly calculate the equilibrium concentrations and plug them into the K expression to solve a problem. However, if you use moles, then you have to make sure to convert to concentrations later on, which you could possibly...
- Mon Jan 18, 2021 7:31 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: pH, pOH, pKa, pKb
- Replies: 5
- Views: 2490
Re: pH, pOH, pKa, pKb
In addition to what others have said above, you can also compare pH and pKa or pOH and pKb to determine if the dominant species in a reaction will be charged or neutral. We learned this towards the end of Chem 14A, and there are sapling questions on it as well, so it might be helpful to think of wha...
- Mon Jan 18, 2021 7:30 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Chem Community and Sapling Grades
- Replies: 25
- Views: 1055
Re: Chem Community and Sapling Grades
You can find your sapling grade on the sapling website, by clicking gradebook. You can then verify if this grade is correctly entered into myUCLA by logging into your myUCLA and checking "exam and homework grades" for chem 14b.
- Mon Jan 18, 2021 7:28 pm
- Forum: Ideal Gases
- Topic: reversing reactions
- Replies: 83
- Views: 4832
Re: reversing reactions
When you reverse a reaction, you should take the inverse of K, which means computing 1/K.
- Mon Jan 18, 2021 7:27 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Water Being Significant in Equilibria
- Replies: 9
- Views: 392
Re: Water Being Significant in Equilibria
You should include water in your equilibrium concentration expression if water is a product or if it is a reactant in the reaction and there is a solvent that is not water. In this case, water is not in excess and its concentration will not cancel on both sides. Therefore, it does affect the K value...
- Mon Jan 18, 2021 7:23 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: Textbook 6D.7 finding Ka value
- Replies: 2
- Views: 128
Re: Textbook 6D.7 finding Ka value
Tables 6C.1 and 6C.2 include the Ka and Kb values for several chemical formulas. These can be found on page 461 and 462 of the textbook.
- Mon Jan 18, 2021 7:21 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Seeing replies on Chemistry Community
- Replies: 10
- Views: 511
Re: Seeing replies on Chemistry Community
Sometimes, I'll get a notification on the top right if someone has responded to my post. Otherwise, I'll just repeatedly check my account to see the responses.
- Tue Jan 12, 2021 4:32 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Textbook 6B.9 question
- Replies: 4
- Views: 194
Re: Textbook 6B.9 question
The answer key has a mistake; it should include a negative sign. It makes sense for the answer for this to be negative because when the [H30+] > 1 M, then the pH will be below 0. You are correct!
- Tue Jan 12, 2021 4:30 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Super Acids and Super Bases
- Replies: 6
- Views: 254
Re: Super Acids and Super Bases
Super acids are when the concentration of hydronium are above 1M and the concentration of hydroxide is smaller than 10^-14 M. Super bases are when the concentration of hydroxide is above 1M, so the concentration of hydronium is below 10^-14 M.
- Sat Jan 09, 2021 8:40 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Temp Increase on Exothermic Reactions
- Replies: 3
- Views: 243
Re: Temp Increase on Exothermic Reactions
An exothermic reaction is one in which heat is produced. If you think of "heat" as a product, then adding heat to an exothermic reaction would cause there to be more products than reactants so the reaction would shift to the left to produce more reactants.
- Sat Jan 09, 2021 8:38 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Lecture 3 Inert Gas
- Replies: 5
- Views: 175
Re: Lecture 3 Inert Gas
Volume doesn't change when adding an inert gas because you are not changing the amount of physical space there is of the container. You are simply adding gas that is unreactive to the container. There are more gas molecules that will collide (so the pressure has increased) but the space of the conta...
- Sat Jan 09, 2021 8:35 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Adding more to reactant to a reaction?
- Replies: 5
- Views: 190
Re: Adding more to reactant to a reaction?
If you add more reactant to a reaction that is already equilibrium, and you therefore perturb the system away from equilibrium, then according to LeChatelier's principle, the reaction will respond by producing products to minimizing the change and help return to the equilibrium state.
- Sat Jan 09, 2021 8:33 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook 5.35
- Replies: 2
- Views: 133
Re: Textbook 5.35
For this question, the y-axis is shown in kPa. On Dr. Lavelle's constants and equations sheet, there is a conversion that says 101.3 kPa = 1 atm. Very similarly, 100 kPa = 1 bar. The textbook uses the second conversion to change kPa into bar.
- Sat Jan 09, 2021 8:30 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5H 1b
- Replies: 3
- Views: 140
Re: 5H 1b
It's best to not have fractions as coefficients in your balanced chemical reaction. To turn the fractions into whole numbers, you can multiple the entire reaction by a common denominator.
- Sat Jan 09, 2021 8:28 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Changes in Q vs K
- Replies: 6
- Views: 450
Re: Changes in Q vs K
Changing pressure or volume does not change K. They can change the concentration of the substances in the reaction, but by the leChatelier's principle, the reaction will shift to minimize that change and return to the equilibrium concentrations of reactants and products. Changing temperature does ch...
- Sun Dec 13, 2020 7:26 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: What are the bond angles for T shaped?
- Replies: 21
- Views: 8443
What are the bond angles for T shaped?
What are the bond angles for T shaped?
- Sun Dec 13, 2020 6:58 am
- Forum: Amphoteric Compounds
- Topic: Is Silicon an amphoteric element?
- Replies: 5
- Views: 564
Is Silicon an amphoteric element?
Hi, are compounds containing silicon amphoteric (like SiO2)?
It seems like there wasn't a clear list of amphoteric compounds given, so I'm not sure which metalloids to identify as amphoteric.
Thanks
It seems like there wasn't a clear list of amphoteric compounds given, so I'm not sure which metalloids to identify as amphoteric.
Thanks
- Sat Dec 12, 2020 11:30 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Polydentate and Chelating Ligands
- Replies: 2
- Views: 244
Re: Polydentate and Chelating Ligands
Yes the ligand must follow the lone pair spacer spacer lone pair model in order to be a chelating ligand because that is the only formation that allows the ligand to "wrap around" a transitional metal cation
- Sat Dec 12, 2020 11:27 am
- Forum: Naming
- Topic: Oxidation Numbers
- Replies: 3
- Views: 171
Re: Oxidation Numbers
You are correct that the second Chlorine is outside the brackets so it is not a ligand and is not part of the coordination sphere. However, you must take it into account when you are determining the oxidation number of the transition metal because the oxidation number of the transition metal will de...
- Thu Dec 10, 2020 8:38 am
- Forum: Hybridization
- Topic: hybridization orbitals
- Replies: 1
- Views: 111
Re: hybridization orbitals
At least in the case of p orbitals, the px, py, and pz axes are 90 degrees from each other so that is why the orbitals will be at 90 degrees.
- Thu Dec 10, 2020 8:34 am
- Forum: Identifying Acidic & Basic Salts
- Topic: Strong Acid Names
- Replies: 6
- Views: 437
Re: Strong Acid Names
That's a great mneumonic,. Heads up that HClO3 is also a strong acid; you left that out in the list.
- Thu Dec 10, 2020 8:33 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Why is NH2 a bidentate ligand?
- Replies: 1
- Views: 156
Re: Why is NH2 a bidentate ligand?
I'm not sure if you are asking in regards to a particular coordination compound (if you are, it would be helpful if you could write the entire formula), but in ethylenediamine, there are 2 NH2 and they are separated by two spacers so the entire molecule is bidentate because each N has a lone pair th...
- Thu Dec 10, 2020 7:00 am
- Forum: Bronsted Acids & Bases
- Topic: Why is formic acid stronger than acetic acid?
- Replies: 2
- Views: 710
Why is formic acid stronger than acetic acid?
Why is formic acid stronger than acetic acid?
The textbook answer key says this: The Ch3 group in acetic acid has electron donating properties which means that it is less electron withdrawing than the H attached to the carbon in formic acid.
I'm struggling to understand this explanation. Thanks!
The textbook answer key says this: The Ch3 group in acetic acid has electron donating properties which means that it is less electron withdrawing than the H attached to the carbon in formic acid.
I'm struggling to understand this explanation. Thanks!
- Sun Dec 06, 2020 7:45 pm
- Forum: Lewis Acids & Bases
- Topic: Weak/ Strong Acids and Bases
- Replies: 6
- Views: 405
Re: Weak/ Strong Acids and Bases
Here's a list of the strong acids: HCl, HNO3, HI, HBr, H2SO4, HClO3, HClO4
Strong bases usually come from Group 1 and Group 2 hydroxides, like LiOH or Ba(OH)2
Strong bases usually come from Group 1 and Group 2 hydroxides, like LiOH or Ba(OH)2
- Sun Dec 06, 2020 7:42 pm
- Forum: Student Social/Study Group
- Topic: Professor Lavelle's Review Session
- Replies: 4
- Views: 182
Re: Professor Lavelle's Review Session
Here is the link to the Final Review sessions: https://lavelle.chem.ucla.edu/wp-conten ... ns_14A.pdf
You can also locate it on the right of Professor Lavelle's Chem 14A website.
You can also locate it on the right of Professor Lavelle's Chem 14A website.
- Sun Dec 06, 2020 7:41 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Types of Ligands
- Replies: 3
- Views: 329
Re: Types of Ligands
A monodentate ligand is a lewis base that has one lone pair that it can donate, such as NH3. A bidentate or polydentate must follow the "lone pair, spacer, spacer, lone pair" rule. An example of a bidentate ligand is NH2CH2CH2NH2 because the two nitrogens have lone pairs that they can dona...
- Thu Dec 03, 2020 8:43 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Outline 4 Shape and polar and IM forces
- Replies: 1
- Views: 146
Re: Outline 4 Shape and polar and IM forces
Since shape can affect polarity and polarity can determine which intermolecular interactions a molecule can engage in, we can use shape and polar/nonpolar properties to predict IMFs. For example, in the case of water, since the molecular geometry is bent, the dipoles do not cancel, so water can exhi...
- Thu Dec 03, 2020 8:37 am
- Forum: Lewis Acids & Bases
- Topic: Sapling J.7 part b
- Replies: 1
- Views: 183
Re: Sapling J.7 part b
The textbook puts 2 as the subscript for Zn(OH)2 and Zn(NO2)2. You can determine this by asking yourself what the ground state electron configuration of Zn. Since Zn has an e- configuration of [Ar]3d10 4s2, it will lose the two 4s electrons to reach a stable state. This means that Zn will become Zn2...
- Mon Nov 30, 2020 10:14 am
- Forum: Naming
- Topic: Using ido or o
- Replies: 24
- Views: 776
Using ido or o
In the textbook, anionic ligands were named as fluorido, chlorido, or bromido with the -ido at the end. However, in lecture and in the textbook answer key, the ide is completely dropped and replaced with o like chloro. When do you use -ido and when do you use -o?
Thanks!
Thanks!
- Mon Nov 30, 2020 8:05 am
- Forum: Naming
- Topic: 9C.3 textbook problem
- Replies: 3
- Views: 281
Re: 9C.3 textbook problem
Yes, the ligands are in alphabetical order here. In the chemical formula, aqua came before oxalato.
- Sat Nov 28, 2020 3:26 pm
- Forum: Hybridization
- Topic: Hybridization in bonding groups
- Replies: 5
- Views: 302
Re: Hybridization in bonding groups
Yes, double bonds count as only one region of electron density.
- Sat Nov 28, 2020 3:24 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: delocalized pi bond
- Replies: 8
- Views: 479
Re: delocalized pi bond
A delocalized pi bond is present in a molecule that has double bonds and also has resonance. For example, CO3 2- would have delocalized pi bonds because the multiple bond character is spread over three oxygen atoms.
- Sat Nov 28, 2020 3:23 pm
- Forum: Hybridization
- Topic: 2F.3 Other Common Types of Hybridization
- Replies: 1
- Views: 181
Re: 2F.3 Other Common Types of Hybridization
Dr. Lavelle briefly mentioned that hybrid orbitals are made from linear combinations, but he did not go into the details during lecture. The assigned homework problems do not discuss this either, so I would assume that we do not need to know it.