Search found 58 matches

by Hannah Romeo 1J
Sat Mar 14, 2020 5:56 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: What was your favorite chem topic?
Replies: 24
Views: 190

Re: What was your favorite chem topic?

Thermochemistry! Also catalysts and kinetics are super cool :)
by Hannah Romeo 1J
Fri Mar 13, 2020 4:36 am
Forum: Balancing Redox Reactions
Topic: OH vs H
Replies: 12
Views: 116

Re: OH vs H

No because H+ is only used in acidic solutions.
by Hannah Romeo 1J
Tue Mar 10, 2020 4:04 pm
Forum: Administrative Questions and Class Announcements
Topic: Review Sessions for Final Exam
Replies: 2
Views: 70

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
by Hannah Romeo 1J
Mon Mar 09, 2020 12:51 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: cubic equations, assumption
Replies: 3
Views: 47

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.
by Hannah Romeo 1J
Mon Mar 09, 2020 12:50 pm
Forum: General Rate Laws
Topic: Formula for Individual Reactant Order
Replies: 1
Views: 17

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.
by Hannah Romeo 1J
Mon Mar 09, 2020 12:08 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 3
Views: 28

Re: Intermediates

I think they would give us the slow and fast steps and then have us identify the intermediates, catalysts, and overall reaction.
by Hannah Romeo 1J
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: 84

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.
by Hannah Romeo 1J
Mon Mar 09, 2020 12:05 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: k' vs kr
Replies: 13
Views: 75

Re: k' vs kr

K’ is the rate of the reverse reaction which equals Kr
by Hannah Romeo 1J
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: 76

Re: biological examples

I think electroylsis is a pretty big one as I am pretty sure it is used in ATP production.
by Hannah Romeo 1J
Mon Mar 02, 2020 6:41 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: inert conductor
Replies: 2
Views: 17

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.
by Hannah Romeo 1J
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: 32

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.
by Hannah Romeo 1J
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: 16

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.
by Hannah Romeo 1J
Mon Mar 02, 2020 6:18 am
Forum: Student Social/Study Group
Topic: Test 2 Homework Problems, Etc
Replies: 6
Views: 58

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.
by Hannah Romeo 1J
Mon Feb 24, 2020 9:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode/ Cathode
Replies: 3
Views: 33

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.
by Hannah Romeo 1J
Mon Feb 24, 2020 9:54 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Platinum
Replies: 5
Views: 56

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.
by Hannah Romeo 1J
Mon Feb 24, 2020 9:53 am
Forum: Administrative Questions and Class Announcements
Topic: Test 2
Replies: 5
Views: 73

Re: Test 2

Yes, Test 2 was moved to week 9 and covers the second page of Unit 4 and all of Unit 5.
by Hannah Romeo 1J
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: 33

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.
by Hannah Romeo 1J
Mon Feb 24, 2020 9:51 am
Forum: Administrative Questions and Class Announcements
Topic: Extra Credit
Replies: 17
Views: 199

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.
by Hannah Romeo 1J
Mon Feb 24, 2020 9:45 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Gibs free energy
Replies: 3
Views: 37

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.
by Hannah Romeo 1J
Mon Feb 17, 2020 7:56 am
Forum: Balancing Redox Reactions
Topic: Acidic conditions- relevant?
Replies: 1
Views: 14

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.
by Hannah Romeo 1J
Mon Feb 17, 2020 7:54 am
Forum: Balancing Redox Reactions
Topic: Why do we split equations?
Replies: 12
Views: 69

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.
by Hannah Romeo 1J
Mon Feb 17, 2020 7:52 am
Forum: Administrative Questions and Class Announcements
Topic: HW7
Replies: 14
Views: 87

Re: HW7

Work on/submit problems from the end of Outline 4 and beginning of Outline 5.
by Hannah Romeo 1J
Mon Feb 17, 2020 7:51 am
Forum: Balancing Redox Reactions
Topic: Oxidation Number Rules
Replies: 7
Views: 57

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.
by Hannah Romeo 1J
Mon Feb 17, 2020 7:49 am
Forum: General Science Questions
Topic: Content on Test 2
Replies: 10
Views: 105

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.
by Hannah Romeo 1J
Mon Feb 10, 2020 9:30 am
Forum: Ideal Gases
Topic: density
Replies: 5
Views: 104

Re: density

Density is mass/volume (g/cm^3) and can be substituted into the ideal gas equation using algebra.
by Hannah Romeo 1J
Mon Feb 10, 2020 9:29 am
Forum: Ideal Gases
Topic: Kc vs Kp
Replies: 43
Views: 418

Re: Kc vs Kp

You use Kc when you have concentrations in molarity snd use Kp when you have partial pressures.
by Hannah Romeo 1J
Mon Feb 10, 2020 9:28 am
Forum: Ideal Gases
Topic: ideal gases
Replies: 13
Views: 215

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.
by Hannah Romeo 1J
Mon Feb 10, 2020 9:27 am
Forum: Calculating Work of Expansion
Topic: Constant Volume and Pressure Values
Replies: 8
Views: 57

Re: Constant Volume and Pressure Values

I would say to know that Cp=Cv + R so you can quickly derive it to save time.
by Hannah Romeo 1J
Mon Feb 10, 2020 9:26 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm
Replies: 12
Views: 107

Re: Midterm

The midterm is on Wednesday from 6-8 pm in halls around campus depending on your lecture and last name.
by Hannah Romeo 1J
Mon Feb 10, 2020 9:25 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm Material
Replies: 13
Views: 120

Re: Midterm Material

The midterm covers Equilibrium, Acids and Bases, Thermochemistry, and the first part of Thermodynamics up to deltaG.
by Hannah Romeo 1J
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: 46

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.
by Hannah Romeo 1J
Tue Feb 04, 2020 12:53 pm
Forum: Calculating Work of Expansion
Topic: Knowing which equation to use
Replies: 3
Views: 35

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?
by Hannah Romeo 1J
Mon Feb 03, 2020 5:05 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: -w = q
Replies: 5
Views: 69

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.
by Hannah Romeo 1J
Mon Feb 03, 2020 5:02 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Temperature
Replies: 14
Views: 81

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.
by Hannah Romeo 1J
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: 36

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.
by Hannah Romeo 1J
Mon Feb 03, 2020 5:00 pm
Forum: Calculating Work of Expansion
Topic: units
Replies: 9
Views: 69

Re: units

Work (w) is in joules. The "w" used for calculating entropy is number of states.
by Hannah Romeo 1J
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: 37

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.
by Hannah Romeo 1J
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: 51

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.
by Hannah Romeo 1J
Mon Jan 27, 2020 12:09 pm
Forum: Phase Changes & Related Calculations
Topic: revere reactions
Replies: 7
Views: 47

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...
by Hannah Romeo 1J
Mon Jan 27, 2020 12:05 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Units for temperature?
Replies: 11
Views: 63

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...
by Hannah Romeo 1J
Mon Jan 27, 2020 12:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Negative pH
Replies: 9
Views: 63

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.
by Hannah Romeo 1J
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: 102

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.
by Hannah Romeo 1J
Mon Jan 20, 2020 10:01 pm
Forum: Polyprotic Acids & Bases
Topic: Deprotonation
Replies: 3
Views: 61

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.
by Hannah Romeo 1J
Mon Jan 20, 2020 9:58 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Does order matter?
Replies: 5
Views: 36

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.
by Hannah Romeo 1J
Mon Jan 20, 2020 9:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Converting K to Kc
Replies: 4
Views: 47

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.
by Hannah Romeo 1J
Mon Jan 20, 2020 9:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pH sig figs
Replies: 9
Views: 44

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.
by Hannah Romeo 1J
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: 76

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.
by Hannah Romeo 1J
Mon Jan 13, 2020 1:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kw calcuation
Replies: 5
Views: 41

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...
by Hannah Romeo 1J
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: 22

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.
by Hannah Romeo 1J
Mon Jan 13, 2020 1:25 pm
Forum: Ideal Gases
Topic: Topics for Test 1
Replies: 17
Views: 158

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.
by Hannah Romeo 1J
Mon Jan 13, 2020 1:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solid and Liquid
Replies: 5
Views: 32

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.
by Hannah Romeo 1J
Mon Jan 13, 2020 1:21 pm
Forum: Ideal Gases
Topic: R constant
Replies: 6
Views: 47

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)
by Hannah Romeo 1J
Thu Jan 09, 2020 4:39 pm
Forum: Ideal Gases
Topic: What elements are closer to being "ideal"?
Replies: 2
Views: 14

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.
by Hannah Romeo 1J
Mon Jan 06, 2020 10:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Hw Problem 5G2(d)
Replies: 1
Views: 33

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...
by Hannah Romeo 1J
Mon Jan 06, 2020 10:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Expression
Replies: 2
Views: 43

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...
by Hannah Romeo 1J
Mon Jan 06, 2020 10:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Units in Bars
Replies: 4
Views: 50

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.
by Hannah Romeo 1J
Mon Jan 06, 2020 10:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Very Large K
Replies: 12
Views: 128

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...
by Hannah Romeo 1J
Mon Jan 06, 2020 10:06 pm
Forum: Ideal Gases
Topic: Dynamic Equilibrium
Replies: 10
Views: 89

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.

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