Search found 60 matches
- Sun Mar 14, 2021 12:03 am
- Forum: General Rate Laws
- Topic: Concentration Graphs to Determine Rate Law
- Replies: 4
- Views: 271
Re: Concentration Graphs to Determine Rate Law
I think it's important for us to know, but it's easy if you're given the units for each axis.
- Sun Mar 14, 2021 12:00 am
- Forum: Zero Order Reactions
- Topic: Half Life
- Replies: 11
- Views: 686
Re: Half Life
All the half-life equations are based off the order equations on the equation sheet. Know which integrated equation goes with each order, and you can easily find the half-life equation.
- Sat Mar 13, 2021 11:58 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Kinetic vs Thermodynamic Control
- Replies: 2
- Views: 378
Re: Kinetic vs Thermodynamic Control
It is possible! This happens when the products are at a lower free energy, so are thermodynamically favorable, but have a higher activation energy.
- Sat Mar 13, 2021 11:55 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: lnQ to logK
- Replies: 4
- Views: 626
Re: lnQ to logK
The log equation can only be used under standard conditions, so the units balance out to 0.0592. Under any other conditions, you have to use E = Enaught - (RT/nF)ln Q, but remember you can also use that equation under standard conditions.
- Sat Mar 13, 2021 11:49 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Calculating n
- Replies: 17
- Views: 940
Re: Calculating n
The n refers to the electrons exchanged in a redox reaction rather than moles of a substance. Definitely easy to mix up!
- Sat Mar 13, 2021 11:48 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Electromotive Force
- Replies: 5
- Views: 410
Re: Electromotive Force
I think they're generally the same. A quick online search said that EMF is the voltage induced from a source, but it's measured in volts as is cell potential.
- Sat Mar 13, 2021 11:43 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidizing Vs Reducing agent
- Replies: 39
- Views: 1920
Re: Oxidizing Vs Reducing agent
A reducing agent reduces a reactant while being oxidized itself, and an oxidizing agent oxidizes a reactant while being reduced itself. When looking for each, think about how a reducing agent is oxidized and how an oxidizing agent is reduced.
- Sat Mar 13, 2021 11:41 pm
- Forum: Van't Hoff Equation
- Topic: Van't Hoff Equation Uses
- Replies: 6
- Views: 503
Re: Van't Hoff Equation Uses
We use the Van't Hoff Equation when we're either looking for a second equilibrium constant at a second temperature or a second temperature to go with a second equilibrium constant. It can also be used to find the enthalpy change given the two K's and T's.
- Sat Mar 13, 2021 11:37 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy and Maximum Nonexpansion Work
- Replies: 5
- Views: 372
Re: Gibbs Free Energy and Maximum Nonexpansion Work
I think the above post is correct. I think I read the same thing in the textbook, that non-expansion applies because of the lack of volume change with the electron transfer.
- Sat Mar 13, 2021 11:33 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Mass vs Entropy
- Replies: 8
- Views: 2261
Re: Mass vs Entropy
Atoms with larger mass tend to have more particles, which makes their entropies higher. Molecules with high mass will also tend to have more atoms, which means more positional entropy.
- Sat Mar 13, 2021 11:30 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Problem with change in temperature and pressure
- Replies: 5
- Views: 399
Re: Problem with change in temperature and pressure
I also was wondering this, and the answers help a lot! It's easy to get tripped up on problems like this that involve a change in two different units.
- Sat Mar 13, 2021 11:28 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: Units of W
- Replies: 16
- Views: 731
Re: Units of W
Don't think degeneracy has units. Tried to look back at my notes and on the internet and it doesn't seem like there is a unit.
- Sat Mar 13, 2021 11:23 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy of Surroundings
- Replies: 3
- Views: 325
Re: Entropy of Surroundings
You're right! Irreversible free expansions, when isothermal as well, have no change in enthalpy.
- Sat Mar 13, 2021 11:21 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: adiabatic reactions
- Replies: 6
- Views: 384
Re: adiabatic reactions
Since q = 0 in an adiabatic reaction, there is no temperature change and the final temp = initial temp
- Sat Mar 13, 2021 11:20 pm
- Forum: Calculating Work of Expansion
- Topic: irreversible vs reversible work
- Replies: 6
- Views: 552
Re: irreversible vs reversible work
It's actually the opposite. The small increments done in a reversible reaction need more work than a sudden, large change in pressure.
- Sat Mar 13, 2021 11:18 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: R constant and shape of molecules
- Replies: 2
- Views: 320
Re: R constant and shape of molecules
I don't think that we need to know this, because the gas constant is really only for ideal gases. One thing that is important to remember is to use the right gas constant based on the units provided.
- Sat Mar 13, 2021 11:14 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Constant Pressure in open systems(?)
- Replies: 6
- Views: 717
Re: Constant Pressure in open systems(?)
Open systems have a constant pressure. This is caused by the environment, which unless the system is placed in a very specific place will be relatively the same.
- Sat Mar 13, 2021 11:11 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Concept of qsys=-qsurr
- Replies: 7
- Views: 2502
Re: Concept of qsys=-qsurr
Think of qsys = -qsurr as the heat lost by the system is gained by the surroundings or vice versa. This is assuming a perfect system, but unless otherwise stated I think we should assume a perfect system.
- Sat Mar 13, 2021 11:07 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Clarification on Heat Capacity
- Replies: 4
- Views: 421
Re: Clarification on Heat Capacity
Cp is at constant pressure, while Cv would be at constant volume. In this equation specifically, Cp couldn't be at constant temperature because of the deltaT. If deltaT was 0, Qp would also be zero and Cp wouldn't even be necessary.
- Sat Mar 13, 2021 11:05 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Finding bond enthalpies
- Replies: 6
- Views: 453
Re: Finding bond enthalpies
We add them up because when bonds are formed the deltaH is negative (energy released), while deltaH is positive (energy absorbed) when bonds break.
- Sat Mar 13, 2021 11:03 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy vs Entropy
- Replies: 39
- Views: 3085
Re: Enthalpy vs Entropy
Enthalpy is more about heat transferred, while entropy is about disorder and the number of possible positions for atoms/molecules. It's important to note that they're both state functions.
- Sat Mar 13, 2021 11:01 pm
- Forum: Phase Changes & Related Calculations
- Topic: oxidation number change
- Replies: 7
- Views: 618
Re: oxidation number change
Oxidation number is the number of electrons gained or lost due to forming a bond. A negative oxidation number means the atom gained electrons when forming the bond because it is based on charge.
- Sat Mar 13, 2021 10:59 pm
- Forum: Phase Changes & Related Calculations
- Topic: state properties
- Replies: 13
- Views: 766
Re: state properties
Enthalpy just depends on the initial and final states, while heat is what appears when there is a change in enthalpy or work. Heat depends on the path taken instead of the start and end points.
- Sat Mar 13, 2021 10:56 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Catalyst and exo vs endothermic reactions
- Replies: 7
- Views: 618
Re: Catalyst and exo vs endothermic reactions
Catalysts don't shift the equilibrium of the reaction, but that's a great question! All the catalyst does is lower the activation energy of the reaction, both forward and reverse.
- Sat Mar 13, 2021 10:53 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: catalyst's effect on equilibrium
- Replies: 9
- Views: 810
Re: catalyst's effect on equilibrium
Nothing really changes about the reaction other than the activation energy: the energy needed for the reaction to proceed. The state of the reaction wouldn't change.
- Sat Mar 13, 2021 10:52 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Q Calculations
- Replies: 21
- Views: 954
Re: Q Calculations
It makes the most sense to change it from mmol to mol, because mol/L is the unit for concentration, which is incredibly important for Q or K values.
- Sat Mar 13, 2021 10:50 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Acids and Bases
- Replies: 15
- Views: 820
Re: Acids and Bases
I think the best way is just to memorize them. I've tried to figure out patterns to remember them better, but with no luck. It sucks, but it's the best we can do.
- Sat Mar 13, 2021 10:48 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Determining The Favored Side of an Equilibrium Product
- Replies: 12
- Views: 1180
Re: Determining The Favored Side of an Equilibrium Product
You have to compare the Q value to the K equilibrium constant, and if Q < K, the reaction will proceed towards the products while if Q > K, the reaction will proceed towards the reactants. If Q = K, the reaction is at equilibrium.
- Sat Mar 13, 2021 10:45 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: textbook 5.39a
- Replies: 4
- Views: 514
Re: textbook 5.39a
Not exactly sure where it came from, but it is most likely due to what the x value ended up being. It's a little odd that they use the 1/(6.1 x 10^-3) rather than 1.6 x 10^2, but they're the same value.
- Sat Mar 13, 2021 10:41 pm
- Forum: Ideal Gases
- Topic: Standard temperature
- Replies: 10
- Views: 712
Re: Standard temperature
Standard temperature is 298K, so SATP
- Sat Mar 13, 2021 10:40 pm
- Forum: Ideal Gases
- Topic: R ideal gas constant
- Replies: 31
- Views: 2060
Re: R ideal gas constant
Make sure you check to see what the units are for the question, because the R value depends on the units used.
- Sat Mar 13, 2021 10:38 pm
- Forum: Ideal Gases
- Topic: Torr as a Unit of Pressure
- Replies: 8
- Views: 745
Re: Torr as a Unit of Pressure
It's definitely possible that it shows up, but regardless it's an easy conversion to atm or mmHg using the equation sheet
- Sun Feb 21, 2021 4:48 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: State function?
- Replies: 36
- Views: 1279
Re: State function?
The path that is taken matters with E, unlike H, S, or G. Since those three are all state functions, E is not a state function.
- Sun Feb 21, 2021 4:42 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 6
- Views: 342
Re: Salt Bridge
As those above have said, the salt bridge allows electron flow back to oxidation solution to maintain neutrality and prevent a buildup of electric charge.
- Sun Feb 21, 2021 4:36 pm
- Forum: Balancing Redox Reactions
- Topic: Cathode v Anode
- Replies: 8
- Views: 416
Re: Cathode v Anode
I was also a little confused, but it seems like the anode tends to be positive while the cathode is negative.
- Sun Feb 21, 2021 4:34 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Q and K
- Replies: 40
- Views: 2700
Re: Q and K
You find Q and K the same way, by putting the concentrations of products over concentrations of reactants, taking into account the coefficients. If Q > K, the reaction favors the reactants and if Q < K, the reaction favors the products. Also, if Q = K, the reaction is at equilibrium.
- Sun Feb 21, 2021 4:29 pm
- Forum: Van't Hoff Equation
- Topic: Van't Hoff equation
- Replies: 13
- Views: 1472
Re: Van't Hoff equation
The Van't Hoff equation is derived from deltaG = -RTlnK, but it's used when you find multiple temperatures and are trying to find the K value at one of those temps. Using either one just depends on the information given in a question.
- Sun Feb 21, 2021 4:23 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K vs. Kc
- Replies: 36
- Views: 1240
Re: K vs. Kc
K and Kc are pretty much the same thing, Kc just specifies equilibrium constant K for concentrations, while Kp is K for pressure. For all these versions of K, you can calculate them the same way as well.
- Sun Feb 21, 2021 4:20 pm
- Forum: Ideal Gases
- Topic: Temperature
- Replies: 99
- Views: 5730
Re: Temperature
Yup, you should assume the temperature is at standard conditions of 25 degrees C, or 298 K.
- Sun Feb 14, 2021 4:54 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: temperature
- Replies: 32
- Views: 1230
Re: temperature
I would say that it's good to convert to Kelvin whenever given a temperature in Celsius. Sometimes a question will ask for the final temperature in Celsius, but it's easy to convert back to it and when plugging in temperature into equations it's going to be in Kelvin, especially with ideal gas law.
- Sun Feb 14, 2021 4:40 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy: kJ or J?
- Replies: 30
- Views: 1495
Re: Entropy: kJ or J?
It's usually in Joules/Kelvin, but I find it a lot easier to look at what units the question is asking for so that I know to convert from KJ to J or J to KJ or to not change at all.
- Sun Feb 14, 2021 4:38 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy of gases
- Replies: 7
- Views: 358
Re: Entropy of gases
It helps for me to think about entropy as disorder, especially considering how molecules move around in different states. With gases, molecules have more room to move around as they are not as close together as a liquid, and same with liquids and solids. This goes in hand with Dr. Lavelle's discussi...
- Sun Feb 14, 2021 4:35 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Assumption on type of system
- Replies: 13
- Views: 680
Re: Assumption on type of system
I think it's good to assume the system is closed unless otherwise stated, especially because we've dealt with mostly problems with closed systems so far.
- Sun Feb 14, 2021 4:25 pm
- Forum: Calculating Work of Expansion
- Topic: Ideal gas constant
- Replies: 9
- Views: 783
Re: Ideal gas constant
I was also struggling with this a bit, like the post above said, make sure you keep in mind the units that are given and also the units that you're trying to find in the equation. The unit for pressure is the most important, but K is also good to look at.
- Sun Feb 14, 2021 4:21 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Homework #19
- Replies: 4
- Views: 246
Re: Homework #19
Like the post above said, use ∆G = ∆G˚ + RT*lnQ. To find Q remember it is products/reactants using the values given.
- Sun Feb 14, 2021 3:20 pm
- Forum: Van't Hoff Equation
- Topic: Van't Hoff equation mistake?
- Replies: 6
- Views: 445
Re: Van't Hoff equation mistake?
The only difference is that in the lecture the negative is factored out and in the textbook is not, so it's (1/T1-1/T2) instead of -(1/T2-1/T1)
- Sun Feb 14, 2021 3:08 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Sapling #15
- Replies: 3
- Views: 166
Re: Sapling #15
This problem is similar to the problems we did with enthalpy of formation that were on the last midterm. First you want to balance out the reaction so that there is 2D on each side, which would give A + B + 2D --> 2D + 2C. This cancels out to give the original reaction, A + B --> 2C. Because we flip...
- Sun Nov 01, 2020 11:54 pm
- Forum: Ionic & Covalent Bonds
- Topic: hydrogen
- Replies: 19
- Views: 881
Re: hydrogen
Hydrogen bonds only occur with O, N, and F because of their high electronegativities that interact with the low electronegativity of the H. This results in the partial positive charge on the H interacting with the partial negative of another atom.
- Sun Nov 01, 2020 11:46 pm
- Forum: Ionic & Covalent Bonds
- Topic: Strength of bonds
- Replies: 13
- Views: 580
Re: Strength of bonds
I think that the general order of the strength of bonds is: covalent, ionic, and hydrogen. What I have noticed though is that in some instances people say that ionic bonds are stronger than covalent bonds, but I think this depends on whether the bonds are intramolecular or intermolecular. I think i...
- Sun Nov 01, 2020 11:29 pm
- Forum: Ionic & Covalent Bonds
- Topic: Non Metals
- Replies: 10
- Views: 717
Re: Non Metals
Like what's been posted above, non-metals tend to have a much higher ionization energy and electronegativity than metals, which often leads to the formation of ionic bonds, when the non-metal steals an electron from the metal. This usually leads to both atoms going back to a full outer electron shell.
- Sun Nov 01, 2020 11:23 pm
- Forum: Ionic & Covalent Bonds
- Topic: Nonpolar and polar
- Replies: 16
- Views: 1068
Re: Nonpolar and polar
Polarity in molecules is based on the difference in electronegativity between bonded atoms. Typically, polar molecules will have polar bonds where the two atoms have vastly different electronegativities, so the electron isn't shared equally. However, nonpolar molecules can also have polar bonds, but...
- Sun Nov 01, 2020 11:16 pm
- Forum: Ionic & Covalent Bonds
- Topic: intermolecular vs intramolecular
- Replies: 17
- Views: 1884
Re: intermolecular vs intramolecular
It's important to note the types of forces that occur with intramolecular forces and intermolecular forces, especially considering their strength. For example, individual intramolecular forces such as covalent bonds will be much stronger than individual intermolecular forces such as hydrogen bonds.
- Sun Oct 18, 2020 7:41 pm
- Forum: Properties of Electrons
- Topic: Ionizing Atoms
- Replies: 3
- Views: 199
Re: Ionizing Atoms
Yes, when atoms are ionized they fully lose their electron to another atom. In an ionic bond, the opposite charges of two atoms, one with an extra electron and one with a lost electron, attract to each other, creating the strength of the bond.
- Sun Oct 18, 2020 2:59 pm
- Forum: Properties of Electrons
- Topic: Grading System
- Replies: 7
- Views: 373
Re: Grading System
I don't think there's going to be a curve, but the C- policy just means if you get above a 50% you will get at least a C-.
- Sun Oct 18, 2020 2:40 pm
- Forum: Properties of Electrons
- Topic: Balmer/Lyman/Paschen Series
- Replies: 2
- Views: 173
Re: Balmer/Lyman/Paschen Series
Adding to the post above, each series is part of different regions of the electromagnetic spectrum. The Lyman series is part of the UV light region, the Balmer series is part of the visible light region, and the Paschen series is part of the infrared light region.
- Sun Oct 18, 2020 2:34 pm
- Forum: Student Social/Study Group
- Topic: studying for exams
- Replies: 21
- Views: 2375
Re: studying for exams
I've mostly been using textbook problems for practice, but going back to the textbook to look at things you may be having trouble with helps a lot too. If there's something in particular that I really struggle with, both the sample problems and the textbook problems are very useful. Going over notes...
- Sun Oct 18, 2020 2:25 pm
- Forum: *Black Body Radiation
- Topic: Black Body Radiation
- Replies: 13
- Views: 760
Re: Black Body Radiation
Like those above have said, Dr. Lavelle said in the lecture that we're not going very in-depth on black body radiation, but he used the black body as an example of what something would be like if it could absorb all frequencies of light. If you end up taking physics, it might be an important topic.
- Sun Oct 18, 2020 2:22 pm
- Forum: Photoelectric Effect
- Topic: Light Intensity
- Replies: 23
- Views: 458
Re: Light Intensity
Yup! When they increase the intensity of the light they are increasing the number of photons, which doesn't end up changing the energy, so in the photoelectric experiment the intensity change didn't increase the electrons released. This was how they realized the frequency changes the energy of the p...
- Sun Oct 18, 2020 1:55 pm
- Forum: Properties of Electrons
- Topic: Movement from energy level to energy level
- Replies: 4
- Views: 199
Re: Movement from energy level to energy level
Agreed with the post above. There's a minimum energy required from a photon to excite an electron to the next energy level, so if you have enough energy in the photon to meet multiple energy requirements, the electron can jump multiple energy levels with a single photon.
- Thu Oct 08, 2020 11:46 pm
- Forum: SI Units, Unit Conversions
- Topic: Acronym for prefixes
- Replies: 7
- Views: 477
Re: Acronym for prefixes
Thanks so much for this, it'll be so useful just to know this when trying to remember all of the prefixes.