Search found 56 matches
- Mon Mar 15, 2021 6:54 pm
- Forum: First Order Reactions
- Topic: 1st order equation
- Replies: 8
- Views: 436
Re: 1st order equation
The integrated rate law is used when finding concentration at a some time during the course of the reaction. The equation is linear and arranged in y=mx+b format so that we can find concentration with respect to time.
- Mon Mar 15, 2021 6:49 pm
- Forum: *Free Energy of Activation vs Activation Energy
- Topic: Activation Energy and Catalysts
- Replies: 7
- Views: 3150
Re: Activation Energy and Catalysts
Catalysts lower the activation energy of a reverse reaction, as well as the forward reaction, because it orients the reactant molecules in a way where it can collide with enough energy to overcome the energy barrier.
- Sun Mar 14, 2021 3:14 pm
- Forum: Calculating Work of Expansion
- Topic: irreversible vs reversible work
- Replies: 6
- Views: 494
Re: irreversible vs reversible work
In an irreversible process, entropy is generated within the gas in the system, and whenever entropy is generated within the system, there is less opportunity to perform useful work. So, more work is done in a reversible process.
- Sun Mar 14, 2021 3:10 pm
- Forum: Calculating Work of Expansion
- Topic: when is change in internal energy 0
- Replies: 10
- Views: 1700
Re: when is change in internal energy 0
The change in internal energy will be 0 in an isolated system. No change in volume means that work is 0.
- Sun Mar 14, 2021 3:04 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Free Energy of Activation
- Replies: 6
- Views: 380
Re: Free Energy of Activation
Free energy of activation is Gibbs free energy, which is the free energy difference between the transition state of a reaction and the ground state of the reactants.
- Sun Mar 14, 2021 3:00 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: ΔU
- Replies: 9
- Views: 552
Re: ΔU
In isothermal, reversible reactions
- Sun Mar 14, 2021 2:55 pm
- Forum: Student Social/Study Group
- Topic: On Campus class vs. remote
- Replies: 21
- Views: 1186
On Campus class vs. remote
Do you guys think they'll give us the option to choose fully remote classes next year? If so, would anyone consider doing it? To live abroad, or save money, etc?
- Sun Mar 14, 2021 2:52 pm
- Forum: Student Social/Study Group
- Topic: How do you deal with burnout?
- Replies: 144
- Views: 12718
Re: How do you deal with burnout?
I try to find out why I'm feeling burntout, because normally it's not just being physically tired. For me, it's typically because I'm not doing something I truly enjoy doing, and so doing any work related to it feels like a burden.
- Sun Mar 07, 2021 5:44 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: nernst equation
- Replies: 20
- Views: 737
Re: nernst equation
The moles are found by balancing the oxi-red reactions to see how many moles of electrons are transferred
- Sun Mar 07, 2021 5:38 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Catalyst
- Replies: 30
- Views: 1922
Re: Catalyst
Catalysts aren't considered reactants or products, so they shouldn't be shown on either side. Sometimes they are written above the arrow in the chemical equation.
- Sun Mar 07, 2021 5:33 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Chemical Kinetics
- Replies: 3
- Views: 191
Re: Chemical Kinetics
Adding on, studying chemical kinetics can allow us to know how to increase production of products, and control reaction conditions.
- Sun Mar 07, 2021 5:30 pm
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: pH
- Replies: 17
- Views: 832
Re: pH
A pH meter measures the acidity, or the hydrogen ion activity, in a solution. It determines the pH level, which is from 1 to 14.
- Sun Mar 07, 2021 5:24 pm
- Forum: *Free Energy of Activation vs Activation Energy
- Topic: Definition of Transition State
- Replies: 7
- Views: 1470
Re: Definition of Transition State
Adding on to what was said above, it is at a local energy maximum. Transition state has partial bonds and is highly unstable.
- Mon Mar 01, 2021 9:06 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anodes and Cathodes
- Replies: 22
- Views: 952
Re: Anodes and Cathodes
Adding to what was said above, cathodes attract cations/positive charge.
- Sun Feb 28, 2021 11:02 am
- Forum: Balancing Redox Reactions
- Topic: Sapling #5
- Replies: 2
- Views: 191
Re: Sapling #5
That should be the right equation! Did you include all the phases?
- Fri Feb 26, 2021 7:08 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Writing Cell diagrams
- Replies: 4
- Views: 244
Re: Writing Cell diagrams
Quick question: does it matter what species comes first in writing the cell diagrams? I know that the cathode will be on the right of the double line and the anode reaction will be on the left of the double lines, but does it matter where we put each species? For instance: Are these essentially the...
- Fri Feb 26, 2021 6:38 am
- Forum: Balancing Redox Reactions
- Topic: #8 Sapling Week 7/8
- Replies: 3
- Views: 185
Re: #8 Sapling Week 7/8
Just kidding I switched the two reactions
- Fri Feb 26, 2021 6:33 am
- Forum: Administrative Questions and Class Announcements
- Topic: International Students
- Replies: 3
- Views: 247
Re: International Students
Also currently studying in Asia! There are workshops throughout the day, so there are definitely some that aren't in the middle of night for your time zone. Also lectures are almost always recorded, so my biggest issue isn't even the time zone, it's finding time to watch everything and not fall behi...
- Fri Feb 26, 2021 6:16 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Sapling #9, Week 7/8
- Replies: 8
- Views: 441
Re: Sapling #9, Week 7/8
Relating to this question and standard reduction potentials, conceptually, why does the half reaction with the larger standard reduction potential occur at the cathode? Larger standard reduction potential means that it has a higher tendency to get reduced (gain electrons), and electrons always flow...
- Fri Feb 26, 2021 5:46 am
- Forum: Balancing Redox Reactions
- Topic: #8 Sapling Week 7/8
- Replies: 3
- Views: 185
#8 Sapling Week 7/8
Hi, I can't seem to figure out what I'm doing wrong in this problem. Could anyone help? Thanks in advance :)
- Fri Feb 19, 2021 8:44 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 4F.17 Question
- Replies: 3
- Views: 350
Re: 4F.17 Question
Hey Stella, When approaching problems with a lot of numerical info like these, it helps to translate everything in the problem into a set of mathematical expressions: ΔS o vap @100 o C = 109J/Kmol C P liquid = 75.3J/Kmol C P vapor = 33.6J/Lmol ΔS o vap @85 o C = ? Based on those given values it's g...
- Fri Feb 19, 2021 8:19 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Textbook 4I.9
- Replies: 3
- Views: 151
Re: Textbook 4I.9
The process is irreversible and a free expansion. In a free expansion, the external pressure is 0 because the gas is expanding against no force. You also cannot calculate the change in volume because the gas is expanding freely. So, the work equation Pdv would equal 0.
- Fri Feb 19, 2021 7:58 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Can someone explain to me why work of compression is always negative?
- Replies: 12
- Views: 5586
Re: Can someone explain to me why work of compression is always negative?
If the system compresses, there is a negative change in volume (piston being pushed in), so the work done by the system is positive because work is being done on the system.
- Fri Feb 19, 2021 7:40 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: Degeneracy and Entropy
- Replies: 6
- Views: 465
Degeneracy and Entropy
Why does degeneracy directly relate to entropy? Conceptually, how does this work?
- Fri Feb 19, 2021 7:37 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Non-spontaneous exothermic reaction
- Replies: 14
- Views: 4279
Non-spontaneous exothermic reaction
How can an exothermic reaction be nonspontaneous? What would be an example of this?
- Sun Feb 14, 2021 8:25 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: confusion with notation
- Replies: 11
- Views: 465
Re: confusion with notation
Hi! d represents derivative (dy/dx), which is the rate of change. So for example, dS would be the same thing as ΔS, or the change in entropy.
- Sun Feb 14, 2021 8:19 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: work
- Replies: 9
- Views: 456
Re: work
Knowing whether a system is endothermic or exothermic will only relate to heat but not the direction of work.
- Sun Feb 14, 2021 8:17 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: q equation
- Replies: 21
- Views: 3411
Re: q equation
Both equations are the same, except m is mass in grams and n is moles. If you are given specific heat capacity, it would be easier to use mass, and if you are given molar heat capacity, it would be better to use moles.
- Sun Feb 14, 2021 8:12 pm
- Forum: Calculating Work of Expansion
- Topic: negative vs positive work
- Replies: 21
- Views: 836
Re: negative vs positive work
Yes, when the system is expanding, work is negative because the system is doing work. Work is positive when the system is compressing because work is being done to the system.
- Sun Feb 14, 2021 8:11 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: temperature
- Replies: 32
- Views: 1137
Re: temperature
It depends on the units used, for instance if you are using the gas constant with units J/Kmol it would be better to use temperature in Kelvins to let the units cancel out.
- Sun Feb 07, 2021 7:51 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Spontaneous Process
- Replies: 4
- Views: 161
Re: Spontaneous Process
The entropy of the system can be negative, but the overall change in entropy for spontaneous process will always be positive. If the enthalpy has a large enough negative change, spontaneous reactions can have a negative change in entropy of the system, but the entropy of the surroundings will increa...
- Sun Feb 07, 2021 7:35 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Cv and Cp
- Replies: 3
- Views: 118
Re: Cv and Cp
The equation is derived from the first law of thermodynamics (ΔU = Q - W).
The derivation is long, but basically the equation means that the specific heat capacity of gas at constant pressure (Cp) is greater than the gas' specific heat capacity at constant volume (Cv) by R (8.314 J K-1 mol-1).
The derivation is long, but basically the equation means that the specific heat capacity of gas at constant pressure (Cp) is greater than the gas' specific heat capacity at constant volume (Cv) by R (8.314 J K-1 mol-1).
- Sun Feb 07, 2021 7:10 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat of combustion sign
- Replies: 2
- Views: 107
Heat of combustion sign
If heat of combustion is always negative, when are we supposed to use the absolute value of the heat of combustion in calculations?
- Sun Feb 07, 2021 7:02 am
- Forum: Calculating Work of Expansion
- Topic: Work on the surroundings
- Replies: 4
- Views: 193
Work on the surroundings
How do we determine which systems do work on the surroundings? (Sapling week 3/4 question 13)
- Sun Feb 07, 2021 6:54 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed System
- Replies: 52
- Views: 2476
Re: Closed System
A closed system just means that matter cannot be transferred in or out, but energy still can. For example, if a beaker is sealed, it is a closed system, but work and heat can still be transferred, so it is exchanging energy with its surroundings.
- Sun Jan 31, 2021 11:52 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: pKa and conjugate base
- Replies: 4
- Views: 268
Re: pKa and conjugate base
The pKa tells you how much an acid will dissociate. If the value is low, more acid will dissociate, which means the acid will be stronger. If the pKa value is large, less acid will dissociate, so the acid will be weaker, and the conjugate base will be stronger.
- Sun Jan 31, 2021 11:51 pm
- Forum: Ideal Gases
- Topic: Temperature
- Replies: 99
- Views: 5582
Re: Temperature
Yes, we could assume that temperature would be at standard state, which is 25 degrees C, or 298 K.
- Sun Jan 31, 2021 11:49 pm
- Forum: Ideal Gases
- Topic: Conditions
- Replies: 20
- Views: 1417
Re: Conditions
SamayaJoshi1A wrote:Can someone clarify why we have these numbers set as the STP?
0 degrees Celsius and 1 atm is the freezing point of pure water at sea level atmospheric pressure. Gases are dependent on temperature and pressure, so we use these values as a reference condition.
- Sun Jan 31, 2021 11:48 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Taking the Anti-Log
- Replies: 37
- Views: 2344
Re: Taking the Anti-Log
10^(-pKa) would equal the Ka value. This is important to convert back and forth between between pKa and Ka.
- Sun Jan 31, 2021 11:42 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Water as a Reactant
- Replies: 9
- Views: 337
Re: Water as a Reactant
Yes, we would assume that H2O is a liquid unless otherwise stated, and because water is the solvent, we can ignore it in the equilibrium equation.
- Sun Jan 24, 2021 4:19 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K or Kc?
- Replies: 5
- Views: 313
Re: K or Kc?
In the textbook, K is referring to Kp, so they have to specify whenever they are using Kc, which is the ratio of equilibrium concentrations of products over the equilibrium concentrations of reactants.
- Sun Jan 24, 2021 4:17 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: pH vs pKa in Equilibrium
- Replies: 1
- Views: 204
Re: pH vs pKa in Equilibrium
Hi! If the pH is higher than the pKa for acids, it would want to be more acidic, so it would produce more protons (H3O+), and therefore favor the products. And if the pH is lower than the pKa, it would produce more HA and favor the reactants. For bases, I think that it would be the opposite. If pH i...
- Sat Jan 23, 2021 7:45 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: [B]formal
- Replies: 5
- Views: 320
Re: [B]formal
Bformal is the same as the initial concentration of B. The formal concentration of B is the sum of the concentrations of B and BH+. On sapling, they calculated the concentration of B at equilibrium, not the initial concentration of B, which is why they had to add B (x) and BH+ (B-x) to get to the in...
- Sat Jan 23, 2021 7:42 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: sapling question 5 week 2
- Replies: 2
- Views: 84
Re: sapling question 5 week 2
Hi, I think Bformal is the same as the initial concentration of B. The equation is still [BH+]/[Binitial]. On sapling, they calculated the concentration of B at equilibrium in the solution, not the initial concentration of B, which is why they had to add B (x) and BH+ (B-x) to get to the initial, or...
- Sat Jan 23, 2021 7:24 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Sapling week 2 #9
- Replies: 8
- Views: 361
Re: Sapling week 2 #9
Thank you guys! So is it the opposite for bases? When pH>pka, the neutral species would be predominant?
- Fri Jan 22, 2021 11:45 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Sapling week 2 #9
- Replies: 8
- Views: 361
Sapling week 2 #9
Why is it that when the pH value is above the pKa, the A− will become more predominant in solution?
Do these types of questions have anything to do with the Henderson-Hasselbach Equation?
Do these types of questions have anything to do with the Henderson-Hasselbach Equation?
- Sun Jan 17, 2021 4:09 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: The Quadratic equation
- Replies: 7
- Views: 449
Re: The Quadratic equation
The quadratic formula doesn’t directly have anything to do with the chemical equilibrium itself, it’s just a mathematical formula to figure out the value of x. The formula helps us solve a quadratic equation in the form of ax^2 + bx + c = 0. Because we set up an ICE table to find the value of x, whi...
- Sun Jan 17, 2021 4:02 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Using Ka vs Kb
- Replies: 8
- Views: 443
Re: Using Ka vs Kb
If you have an acid dissociating or when H3O+ is formed, you would use Ka. When a base is dissociating, you would use Kb. Also, Ka x Kb = Kw = 10-14.
- Sun Jan 17, 2021 3:52 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kc vs. Q
- Replies: 5
- Views: 185
Re: Kc vs. Q
They don’t refer to the same value. The reaction quotient measures the amount of product/reactant at any given time in a reaction, while the Kc value is the concentration at equilibrium. Knowing the reaction quotient and comparing it to the equilibrium constant helps figure out what direction the re...
- Sun Jan 17, 2021 3:46 am
- Forum: Ideal Gases
- Topic: Gas constant R
- Replies: 26
- Views: 1024
Re: Gas constant R
Where does the value for the gas constant come from? I understand that the value equals 8.3144598 J/mol·K, however how was this value calculated? Avogadro's Law says that at STP (which is 1.00 atm and 0 degreesC), 1.00 mole of a gas takes up 22.4 L. If you rearrange the ideal gas law PV=nRT, you ge...
- Sun Jan 17, 2021 3:34 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Box method
- Replies: 5
- Views: 1105
Re: ICE Box method
The ice box is just a helpful way of keeping track of changing concentrations or pressures or each specifies in an equilibrium reaction. The I stands for initial concentration/pressure, the C stands for the change in concentration/pressure, and the E is what the value is when the system is at equili...
- Mon Jan 11, 2021 5:00 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Homogeneous and Heterogeneous Equilibrium
- Replies: 13
- Views: 670
Re: Homogeneous and Heterogeneous Equilibrium
In addition, could someone give me an example of a heterogenous equilibrium? I am confused on how we could have one or more product/reactant in "different phases" or what that really means in the context of a reaction. A common reaction that is heterogenous is ice and water at equilibrium...
- Mon Jan 11, 2021 4:58 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: States that effect equilibrium.
- Replies: 4
- Views: 273
Re: States that effect equilibrium.
Thank you for the response, but as a follow up question, why are solids and liquids not affected? I am not clear on that. The molar concentration of a pure substance, such as a solid or a liquid, does not change. So, they aren’t taken into account because their concentrations don’t change throughou...
- Mon Jan 11, 2021 4:56 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: change in K
- Replies: 22
- Views: 760
Re: change in K
K is only affected by temperature changes.
- Mon Jan 11, 2021 4:55 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Effect of Catalyst
- Replies: 7
- Views: 277
Re: Effect of Catalyst
A catalyst helps the reaction proceed faster by lowering the activation energy or changing the reaction mechanism. Equilibrium will be reached faster, but the concentration of reactants and products stays the same, so K won’t change.
- Mon Jan 11, 2021 4:54 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Coefficients for eq constant
- Replies: 9
- Views: 543
Re: Coefficients for eq constant
First you balance your equation, then you raise the concentration or partial pressure of the product to that coefficient.