Search found 58 matches
- Sat Mar 14, 2020 5:56 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: What was your favorite chem topic?
- Replies: 137
- Views: 8623
Re: What was your favorite chem topic?
Thermochemistry! Also catalysts and kinetics are super cool :)
- Fri Mar 13, 2020 4:36 am
- Forum: Balancing Redox Reactions
- Topic: OH vs H
- Replies: 12
- Views: 873
Re: OH vs H
No because H+ is only used in acidic solutions.
- Tue Mar 10, 2020 4:04 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Review Sessions for Final Exam
- Replies: 2
- Views: 256
Review Sessions for Final Exam
Hi all,
So apparently UCLA is moving toward online classes this week and I was wondering if exam review sessions would still be offered?
Thanks
So apparently UCLA is moving toward online classes this week and I was wondering if exam review sessions would still be offered?
Thanks
- Mon Mar 09, 2020 12:51 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: cubic equations, assumption
- Replies: 3
- Views: 285
Re: cubic equations, assumption
Cubic equations are notoriously to difficult to solve, especially without a graphing calcuator, so I think that on the ones that we will be tested on, we can approximate the value of x given a small k value.
- Mon Mar 09, 2020 12:50 pm
- Forum: General Rate Laws
- Topic: Formula for Individual Reactant Order
- Replies: 1
- Views: 167
Re: Formula for Individual Reactant Order
There is a method but not really a formula. You find two reactions where one reactant is held constant and the other is changing and examine the change in rates to determine the order of the changing reactant.
- Mon Mar 09, 2020 12:08 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Intermediates
- Replies: 3
- Views: 242
Re: Intermediates
I think they would give us the slow and fast steps and then have us identify the intermediates, catalysts, and overall reaction.
- Mon Mar 09, 2020 12:06 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Adding a Catalyst
- Replies: 6
- Views: 1522
Re: Adding a Catalyst
A catalyst only lowers the activation energy therefore speeding up the rate of the reaction. However, catalysts are not consumed during the reaction as they are added and then regenerated. As a result, they are not written in the equilibrium expression.
- Mon Mar 09, 2020 12:05 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: k' vs kr
- Replies: 13
- Views: 770
Re: k' vs kr
K’ is the rate of the reverse reaction which equals Kr
- Mon Mar 02, 2020 6:42 am
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: biological examples
- Replies: 3
- Views: 323
Re: biological examples
I think electroylsis is a pretty big one as I am pretty sure it is used in ATP production.
- Mon Mar 02, 2020 6:41 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: inert conductor
- Replies: 2
- Views: 174
Re: inert conductor
Pt is used when the anode or cathode is a liquid or aqueous soln that allows for the transfer of electrons to occur easier.
- Mon Mar 02, 2020 6:21 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Moles in nernst
- Replies: 4
- Views: 286
Re: Moles in nernst
If you balanced the equations right, the moles of electrons in each half reaction are the same so you just use the moles of electrons transferred.
- Mon Mar 02, 2020 6:20 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Stoichiometric Coefficients in Cell Diagrams
- Replies: 3
- Views: 201
Re: Stoichiometric Coefficients in Cell Diagrams
No, you only include them when it says to balance the half reactions. However, make sure you know how many elections are transferred to find deltaG.
- Mon Mar 02, 2020 6:18 am
- Forum: Student Social/Study Group
- Topic: Test 2 Homework Problems, Etc
- Replies: 6
- Views: 399
Re: Test 2 Homework Problems, Etc
I usually re-read the section in the book before doing the problems because usually the hw problems end up utilzing the formulas we learned in lecture. I would say to try to find what the question is asking first and then find the right formula.
- Mon Feb 24, 2020 9:39 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode/ Cathode
- Replies: 3
- Views: 192
Re: Anode/ Cathode
Oxidation occurs at the anode but the thing that is oxidized is called a reducing agent. In contrast, reduction occurs at the cathode but the substance reduced is called an oxidizing agent.
- Mon Feb 24, 2020 9:54 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Platinum
- Replies: 5
- Views: 366
Re: Platinum
Pt is used if the given redox reaction has only aqueous solutions and no solid conductor used in the reaction within a galvanic cell.
- Mon Feb 24, 2020 9:53 am
- Forum: Administrative Questions and Class Announcements
- Topic: Test 2
- Replies: 5
- Views: 457
Re: Test 2
Yes, Test 2 was moved to week 9 and covers the second page of Unit 4 and all of Unit 5.
- Mon Feb 24, 2020 9:53 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Convention for cell diagrams
- Replies: 3
- Views: 208
Re: Convention for cell diagrams
I think what he means is that he writes it using a notation of |anode electrode|anode product||cathode electrode|cathode product in order to help us learn. By convention, a galvanic cell is written as |anode electrode|anode product||cathode product|cathode electrode.
- Mon Feb 24, 2020 9:51 am
- Forum: Administrative Questions and Class Announcements
- Topic: Extra Credit
- Replies: 17
- Views: 910
Re: Extra Credit
I don't believe that any extra credit is offered as there seems to be a strict point system for the class.
- Mon Feb 24, 2020 9:45 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Gibs free energy
- Replies: 3
- Views: 217
Re: Gibs free energy
n stands for moles of electrons transferred during the reaction. You want to look at the substances that are oxidized and reduced and see how the oxidation number changes along with the stoichiometric coefficients.
- Mon Feb 17, 2020 7:56 am
- Forum: Balancing Redox Reactions
- Topic: Acidic conditions- relevant?
- Replies: 1
- Views: 109
Re: Acidic conditions- relevant?
I think acidic conditions are written in the problem to let us know to use H+ and Water to balance the redox reactions instead of OH- and Water. Personally, I do not hydrogen ions can ever be limiting in a solution, unless the solution is very basic.
- Mon Feb 17, 2020 7:54 am
- Forum: Balancing Redox Reactions
- Topic: Why do we split equations?
- Replies: 12
- Views: 746
Re: Why do we split equations?
The method of splitting the redox reactions into the half reactions of oxidation and reduction allows for an easier method of balancing. Balancing each reaction on its own is simpler and less confusing which allows for a more precise answer when the reactions are combined together.
- Mon Feb 17, 2020 7:52 am
- Forum: Administrative Questions and Class Announcements
- Topic: HW7
- Replies: 14
- Views: 781
Re: HW7
Work on/submit problems from the end of Outline 4 and beginning of Outline 5.
- Mon Feb 17, 2020 7:51 am
- Forum: Balancing Redox Reactions
- Topic: Oxidation Number Rules
- Replies: 7
- Views: 466
Re: Oxidation Number Rules
I think that once you do a lot of practice with them you eventually learn how to apply them so there is no need to memorize them.
- Mon Feb 17, 2020 7:49 am
- Forum: General Science Questions
- Topic: Content on Test 2
- Replies: 10
- Views: 658
Re: Content on Test 2
I believe the next test will be on Gibbs Free Energy and how it relates with equilibrium and on electrochemistry and redox reactions.
- Mon Feb 10, 2020 9:30 am
- Forum: Ideal Gases
- Topic: density
- Replies: 5
- Views: 392
Re: density
Density is mass/volume (g/cm^3) and can be substituted into the ideal gas equation using algebra.
- Mon Feb 10, 2020 9:29 am
- Forum: Ideal Gases
- Topic: Kc vs Kp
- Replies: 109
- Views: 4382
Re: Kc vs Kp
You use Kc when you have concentrations in molarity snd use Kp when you have partial pressures.
- Mon Feb 10, 2020 9:28 am
- Forum: Ideal Gases
- Topic: ideal gases
- Replies: 14
- Views: 907
Re: ideal gases
Ideal Gases have no mass and do not have any attractive force between them unlike a real gas which has attractions between molecules.
- Mon Feb 10, 2020 9:27 am
- Forum: Calculating Work of Expansion
- Topic: Constant Volume and Pressure Values
- Replies: 8
- Views: 300
Re: Constant Volume and Pressure Values
I would say to know that Cp=Cv + R so you can quickly derive it to save time.
- Mon Feb 10, 2020 9:26 am
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm
- Replies: 12
- Views: 565
Re: Midterm
The midterm is on Wednesday from 6-8 pm in halls around campus depending on your lecture and last name.
- Mon Feb 10, 2020 9:25 am
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm Material
- Replies: 13
- Views: 663
Re: Midterm Material
The midterm covers Equilibrium, Acids and Bases, Thermochemistry, and the first part of Thermodynamics up to deltaG.
- Fri Feb 07, 2020 7:15 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 4D.23 homework help
- Replies: 4
- Views: 144
Re: 4D.23 homework help
This problem is requiring the use of Hess’s law and the knowledge that enthalpy is a state function that can be manipulated.
- Tue Feb 04, 2020 12:53 pm
- Forum: Calculating Work of Expansion
- Topic: Knowing which equation to use
- Replies: 3
- Views: 124
Knowing which equation to use
How do we know when to use the different work equations? I believe that both occur at constant pressure; however, when do we know which equation to use?
- Mon Feb 03, 2020 5:05 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: -w = q
- Replies: 5
- Views: 283
Re: -w = q
For isothermal expansion, no net heat is lost or absorbed from the system. Because the pressure and volume of the system change very slowly over time, the energy released by work is pushed back into the system as heat. As a result, the net energy of the system is 0 resulting in -w = q.
- Mon Feb 03, 2020 5:02 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Temperature
- Replies: 14
- Views: 522
Re: Temperature
A negative delta H is exothermic as energy is released because the reactants have a higher amount of energy in comparison to the products. This results in the reaction releasing energy as the products are in a lower energy and more stable state.
- Mon Feb 03, 2020 5:01 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: endo vs exo
- Replies: 8
- Views: 176
Re: endo vs exo
Forming a chemical bond always requires energy, therefore the process is endothermic and delta H is positive. In contrast, the breaking of a chemical bond is the opposite and is exothermic so delta H is negative.
- Mon Feb 03, 2020 5:00 pm
- Forum: Calculating Work of Expansion
- Topic: units
- Replies: 9
- Views: 186
Re: units
Work (w) is in joules. The "w" used for calculating entropy is number of states.
- Mon Feb 03, 2020 4:59 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Vocabulary
- Replies: 3
- Views: 198
Re: Vocabulary
Standard reaction enthalpies signify the enthalpy of a whole reaction. In contrast, enthalpies of formation indicate the required energy needed to form a product from reactants. Standard enthalpies of formation are used to produce the standard reaction enthalpies.
- Mon Jan 27, 2020 12:11 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Signs for enthalpy
- Replies: 8
- Views: 446
Re: Signs for enthalpy
Enthalpy means the amount of heat transferred. In an exothermic reaction heat is released, therefore the enthalpy is negative. It is the reverse for an endothermic reaction.
- Mon Jan 27, 2020 12:09 pm
- Forum: Phase Changes & Related Calculations
- Topic: revere reactions
- Replies: 7
- Views: 152
Re: revere reactions
In biology, photosynthesis and cellular respiration are reverse reactions. Cellular respiration is exothermic in that it produces ATP while photosynthesis is endothermic as it requires sunlight to proceed. Similarly, the reverse of all chemical reactions has the opposite form of heat (either release...
- Mon Jan 27, 2020 12:05 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Units for temperature?
- Replies: 11
- Views: 486
Re: Units for temperature?
The specific heat refers to the increasing of energy in joules per unit of temperate. Both Kelvin and Celsius can be used as this unit of temperature. The unit of Kelvin means degree celsius + a constants (273.15). As a result, the units of Kelvin are the same as Celsius, but they are shifted up a s...
- Mon Jan 27, 2020 12:03 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Negative pH
- Replies: 9
- Views: 286
Re: Negative pH
Negative pH's can occur if the acid is so strong that the -log of the concentration of the hydronium ions in the solution results in a negative logarithm. This only occurs for super concentrated strong acids.
- Mon Jan 27, 2020 12:01 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Exothermic reaction
- Replies: 18
- Views: 639
Re: Exothermic reaction
An exothermic reaction means that the reaction is releasing heat to the surroundings. As a result of the increase in heat, the temperature of the rxn also increases. For an endothermic reaction, the reaction absorbs heat, so the temperature decreases.
- Mon Jan 20, 2020 10:01 pm
- Forum: Polyprotic Acids & Bases
- Topic: Deprotonation
- Replies: 3
- Views: 185
Re: Deprotonation
For polyphonic acids, only the first Ka is significant as the removal of the first hydrogen results in the biggest change in pH. Each succeeding removal of hydrogen does not have as much effect on the pH.
- Mon Jan 20, 2020 9:58 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Does order matter?
- Replies: 5
- Views: 240
Re: Does order matter?
The order does not matter as K represents a fixed ratio between the products and reactants. What does matter is the stoicometric coefficients as they affect both the K expression and ICE tables.
- Mon Jan 20, 2020 9:57 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Converting K to Kc
- Replies: 4
- Views: 257
Re: Converting K to Kc
If you are given values in Molarity, use Kc. If you are given values in pressure units, use Kp. Kc and Kp have the same equation and mean the same thing depending on what types of values are plugged into the expression.
- Mon Jan 20, 2020 9:55 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: pH sig figs
- Replies: 9
- Views: 406
Re: pH sig figs
I believe that it is two sig figs after the decimal place because pH + pOH = 14.00. Because, the sig fig rules for addition and subtraction indicate that your result can only be as accurate as the least precise digit, there are two sig figs after the decimal point.
- Mon Jan 20, 2020 9:53 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH and pOH in Reactions
- Replies: 3
- Views: 179
Re: pH and pOH in Reactions
In the equation ammonia is the base and water is the acid. When they react, only hydroxide will be sufficiently prevalent and the conjugate acid, ammonium, will be produced. This reaction further requires the use of a Kb to determine the equilibrium concentrations.
- Mon Jan 13, 2020 1:30 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kw calcuation
- Replies: 5
- Views: 188
Re: Kw calcuation
The Kw equation follows the previous logic of setting up K expressions. Pure solids and liquids are not included in the expression as they are in such excess that there equilibrium concentration is negligible. This results in Kw = [H3O+][OH-] as the molar concentration of hydronium and hydroxide are...
- Mon Jan 13, 2020 1:27 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Increase pressure by half the volume
- Replies: 3
- Views: 114
Re: Increase pressure by half the volume
If pressure is increased by halving the volume, then the reaction will shift to the side with the fewest number of moles, ie. the path of least resistance, in order to minimize the effects of this pressure increase following the ideas of Le Chatlier's principle.
- Mon Jan 13, 2020 1:25 pm
- Forum: Ideal Gases
- Topic: Topics for Test 1
- Replies: 17
- Views: 642
Re: Topics for Test 1
I think that it is essential to understand the basic principles behind equilibrium and equilibrium expressions as they are going to be fundamental ideas throughout the rest of the course.
- Mon Jan 13, 2020 1:22 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Solid and Liquid
- Replies: 5
- Views: 180
Re: Solid and Liquid
Solids and liquids are not included in the K expression as they do not change their concentrations in a reaction as they are pure substances. Essentially, their value is 1 resulting in the K expression only including aqueous solutions.
- Mon Jan 13, 2020 1:21 pm
- Forum: Ideal Gases
- Topic: R constant
- Replies: 6
- Views: 240
Re: R constant
R is used in the ideal gas law expression, PV=nRT. A specific R constant is used as a result of the given units in the problem. For example, if pressure has units of atm, R has a value of .0821 (L x atm)/(mol x K)
- Thu Jan 09, 2020 4:39 pm
- Forum: Ideal Gases
- Topic: What elements are closer to being "ideal"?
- Replies: 2
- Views: 68
Re: What elements are closer to being "ideal"?
By "ideal" do you mean stable? If so, the noble gases are the most ideal and nonreactive as they have a full valence shell allowing them to be incredibly stable. As a result, they often do not form bonds with other molecules as they are content with their full octet.
- Mon Jan 06, 2020 10:20 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Hw Problem 5G2(d)
- Replies: 1
- Views: 80
Re: Hw Problem 5G2(d)
Gibbs free energy (delta G) represents how spontaneous a reaction is ie. how likely is it to proceed in a certain direction. It also represents the maximum amount of energy in a system that can do reversible work at a certain temperature and pressure. Therefore, if the Gibbs free energy is greater t...
- Mon Jan 06, 2020 10:13 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium Expression
- Replies: 2
- Views: 137
Re: Equilibrium Expression
I believe that they apply to all equillibriums including homogenous or heterogenous equillibrium. Since the K expression only includes aqueous solutions, the solids or pure liquids in the chemical equation will not be used. However, the K equation can be used for all reactions at equilibrium. I hope...
- Mon Jan 06, 2020 10:11 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Units in Bars
- Replies: 4
- Views: 172
Re: Units in Bars
I believe that bars are a unit of pressure and are used when calculating Kp. Since Kp is a unit-less ratio, there is no need to convert to atm or any other units of pressure as the units will cancel.
- Mon Jan 06, 2020 10:09 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Very Large K
- Replies: 12
- Views: 2528
Re: Very Large K
K stands for the equilibrium constant and represents the fixed ratio between products and reactants under specific conditions. If K is large, there is a higher percentage of products in the equilibrium solution in comparison to reactants. This emphasizes that the forward reaction is therefore strong...
- Mon Jan 06, 2020 10:06 pm
- Forum: Ideal Gases
- Topic: Dynamic Equilibrium
- Replies: 10
- Views: 357
Re: Dynamic Equilibrium
During a dynamic equilibrium, a reaction is still occurring. However, the rates of the forward and reverse reactions are occurring at the same rate resulting in a net 0 rate. A reaction is never static as collisions continue to occur between atoms/molecules to form products/reactants.