Search found 56 matches

by Hui Qiao Wu 1I
Sun Mar 15, 2020 2:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic and voltaic cells
Replies: 5
Views: 67

Re: Galvanic and voltaic cells

The opposite of a galvanic cell is an electrolytic cell. Galvanic cell is spontaneous which electrolysis is not.
by Hui Qiao Wu 1I
Sun Mar 15, 2020 2:04 pm
Forum: Balancing Redox Reactions
Topic: oxidation numbers
Replies: 4
Views: 72

Re: oxidation numbers

There are some basic ones that you'll just have to remember:
hydrogen is +1 when bound to nonmetal but is -1 when bound to a metal
oxygen in the form of O^2 is -1; all other forms are -2
by Hui Qiao Wu 1I
Sun Mar 15, 2020 1:59 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells
Replies: 2
Views: 65

Re: Concentration Cells

You make the one with the lower concentration the product and figure out if it's oxidation or reduction.
by Hui Qiao Wu 1I
Sun Mar 15, 2020 1:56 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst K vs Q
Replies: 5
Views: 79

Re: Nernst K vs Q

The major difference between the two is if the rxn is at equilibrium or not. If you use K, then you are taking into consideration that the rxn is at equilibrium. If a rxn is at equilibrium, certain factors would be affected like E.
by Hui Qiao Wu 1I
Sun Mar 15, 2020 1:52 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: lnQ
Replies: 4
Views: 64

Re: lnQ

Yes, you would still apply the coefficients as the power.
by Hui Qiao Wu 1I
Sun Mar 15, 2020 1:46 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: spontaneity
Replies: 4
Views: 68

Re: spontaneity

When delta g is negative, it is saying that there is available energy for the reaction to happen. So it is spontaneous.
by Hui Qiao Wu 1I
Sun Mar 08, 2020 10:17 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Intermediate Species
Replies: 9
Views: 27

Re: Intermediate Species

It is a specie that first gets produced and then later used as a reactant.
by Hui Qiao Wu 1I
Sun Mar 08, 2020 10:05 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 8
Views: 48

Re: Catalysts

They somehow affect the orientation of the substrate it binds to, helping it to achieve the proper orientation.
by Hui Qiao Wu 1I
Sun Mar 08, 2020 9:58 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Pre Equillibrium
Replies: 2
Views: 22

Re: Pre Equillibrium

As a forward rxn is happening, the products are accumulating. Since thee are so many products, the rxn also wants to reverse the direction to try to get rid of the products (I am not sure if the rxn actually reverses the direction or it is just a state it wants to achieve). Therefore, this whole sit...
by Hui Qiao Wu 1I
Wed Mar 04, 2020 3:44 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Strongly Reducing vs Oxidizing
Replies: 2
Views: 25

Re: Strongly Reducing vs Oxidizing

Reducing agents refer to the substance being oxidized. If the problem gives you several different reduction rxns, you have to do a little inverse thinking. The more positive the standard reduction potential is, the more likely that rxn will happen. However, that rxn is a reduction rxn. If reduction ...
by Hui Qiao Wu 1I
Wed Mar 04, 2020 3:29 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Figuring out n
Replies: 15
Views: 100

Re: Figuring out n

Write out half rxns
Balance half rxns
Combine the two half rxns (when combining the two rxns, you should be canceling out electrons. The number of electrons, do not add up the number of electrons from both rxns, is your n).
by Hui Qiao Wu 1I
Wed Mar 04, 2020 3:20 pm
Forum: Balancing Redox Reactions
Topic: Both Oxidizing and Reducing Agent
Replies: 4
Views: 57

Re: Both Oxidizing and Reducing Agent

If the species was reduced, then it is the oxidizing reagent, and if it was oxidized, it is the reducing reagent.
Think of them as the opposite.
by Hui Qiao Wu 1I
Mon Mar 02, 2020 12:17 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst
Replies: 10
Views: 98

Re: Nernst

E = Eo -(RT/nF) ln Q
There are also other equations you can derive from this equation that can be considered as the Nernst equation.
by Hui Qiao Wu 1I
Mon Mar 02, 2020 12:08 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Free Energy and Cell Potential Relationship
Replies: 3
Views: 33

Re: Free Energy and Cell Potential Relationship

When you're given the value of delta G or cell potential and are asked to find the other, you can use the equation mentioned in the previous comment.
by Hui Qiao Wu 1I
Mon Mar 02, 2020 12:04 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Reduced/Oxidized based on Ecell
Replies: 6
Views: 95

Re: Reduced/Oxidized based on Ecell

Maybe you can look at the oxidation numbers.
by Hui Qiao Wu 1I
Mon Mar 02, 2020 12:01 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Value of K
Replies: 2
Views: 36

Re: Value of K

My TA said that if E knot is positive, k is greater than 1 and when E knot is negative, k is less than 1. But I don't know if k would equal to 0 is E knot is 0.
by Hui Qiao Wu 1I
Sun Feb 23, 2020 12:44 pm
Forum: Balancing Redox Reactions
Topic: Steps to Balance a Basic Solution
Replies: 2
Views: 24

Re: Steps to Balance a Basic Solution

In basic solution: 1. Identify what is being reduced and oxidized 2.Balance half-reactions by: a. balance elements other than oxygen and hydrogen b. balance the oxygens by adding H2O c. balance the hydrogens by adding H+ d. cancel H+ by adding OH- e. balance the charge of each reaction by adding ele...
by Hui Qiao Wu 1I
Sun Feb 23, 2020 12:37 pm
Forum: Balancing Redox Reactions
Topic: Redox in Acidic/Basic Solutions
Replies: 3
Views: 35

Re: Redox in Acidic/Basic Solutions

The only difference when balancing a redox reaction in a basic solution compared to an acidic solution is that in basic solution, you would have to do the extra step of canceling the H+ with the OH- at the end (everything else is the same).
by Hui Qiao Wu 1I
Sun Feb 23, 2020 12:27 pm
Forum: Balancing Redox Reactions
Topic: Oxidation number of H
Replies: 6
Views: 60

Re: Oxidation number of H

I was taught that if hydrogen is bound to a metal, it's -1; if bound to a nonmetal, it's +1.
by Hui Qiao Wu 1I
Sun Feb 23, 2020 12:26 pm
Forum: Balancing Redox Reactions
Topic: Oxidation States
Replies: 7
Views: 53

Re: Oxidation States

Hydrogens are +1 if bound to nonmetals or -1 if bound to metals.
If oxygen is seen as peroxide (O2), then it's -1; if in any other compounds, it's -2
by Hui Qiao Wu 1I
Sun Feb 23, 2020 12:21 pm
Forum: Balancing Redox Reactions
Topic: What is Being Reduced?
Replies: 10
Views: 60

Re: What is Being Reduced?

It might be better to include Fe3+ is being reduced to Fe2+, just to show that you know which iron is being reduced. In addition, some problems specifically ask you to include which species is reduced or oxidized and from what oxidation number to what.
by Hui Qiao Wu 1I
Sun Feb 16, 2020 2:18 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: 3/2R & 5/2R
Replies: 9
Views: 135

Re: 3/2R & 5/2R

mcat/ncat also incorporates Cv and Cp sometimes.
by Hui Qiao Wu 1I
Fri Feb 14, 2020 4:54 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal Reversible
Replies: 6
Views: 64

Re: Isothermal Reversible

I remember a UA mentioned that isothermal is always reversible but reversible does not always mean isothermal; I think that is what he said.
by Hui Qiao Wu 1I
Fri Feb 14, 2020 4:50 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: State functions
Replies: 5
Views: 92

Re: State functions

Rather than remembering all the state functions, just remember which ones are not because there are fewer of them. Heat and work are not state functions while the rest are. For intensive/ extensive properties, it might be easier to remember the definition of each rather than remembering all the exam...
by Hui Qiao Wu 1I
Sun Feb 09, 2020 11:41 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Microstates
Replies: 6
Views: 52

Re: Microstates

A microstate is the possible arrangements of the molecule.
by Hui Qiao Wu 1I
Sun Feb 09, 2020 11:38 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy equation
Replies: 2
Views: 26

Re: Entropy equation

You use this equation if only heat and temperature are given in the problem. If you do not have enough information to solve for entropy with the other equations involving constant pressure, temperature, or volume, this might be the one to use.
by Hui Qiao Wu 1I
Sun Feb 09, 2020 11:35 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Constant T,P,V
Replies: 4
Views: 48

Re: Constant T,P,V

A good strategy is to write out the given values, like what is volume1 and volume2. Usually, if there is only one temperature or volume or pressure, you will know that that is the one staying constant.
by Hui Qiao Wu 1I
Sun Feb 09, 2020 11:32 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Important conditions
Replies: 3
Views: 46

Re: Important conditions

I think it's also good to know about reversible and irreversible reactions, and how to differentiate between the two.
by Hui Qiao Wu 1I
Sun Feb 09, 2020 11:28 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Intensive vs. extensive, state vs. non state
Replies: 6
Views: 62

Re: Intensive vs. extensive, state vs. non state

I am not sure what you mean by intensive vs. extensive states but if you are referring to the intensive and extensive properties, they are:

Intensive
color, temperature, texture, density
Extensive
mass/weight, length, volume
by Hui Qiao Wu 1I
Sat Feb 08, 2020 9:23 am
Forum: Phase Changes & Related Calculations
Topic: General Phase Change Calculations
Replies: 6
Views: 49

Re: General Phase Change Calculations

There are important differences between the two situations. One has a temperature change while the other one has a constant temperature. Therefore, the equations need to take these differences into consideration, resulting in different equations.
by Hui Qiao Wu 1I
Sat Feb 08, 2020 9:04 am
Forum: Calculating Work of Expansion
Topic: Irreversible Expansion Explained
Replies: 7
Views: 79

Re: Irreversible Expansion Explained

Adding on to the balloon analogy, for me, reversible is slowly blowing air into the balloon so it "expands" or releasing air so it "compresses;" it can go both ways. Irreversible, on the other hand, is blowing the balloon so fast that it pops, so there is no way of going back.
by Hui Qiao Wu 1I
Sun Feb 02, 2020 10:16 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Extensive/Intensive Property
Replies: 4
Views: 33

Re: Extensive/Intensive Property

An intensive property is not dependent on the amount of a substance, like color and temperature. The extensive property, on the other hand, is dependent on the amount of a substance, like weight.
by Hui Qiao Wu 1I
Sun Feb 02, 2020 9:58 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: When to leave out reactants/products from enthalpy calculations
Replies: 4
Views: 37

Re: When to leave out reactants/products from enthalpy calculations

To add on, the most stable forms won't affect enthalpy change only when calculating the enthalpy of formation.
by Hui Qiao Wu 1I
Sun Feb 02, 2020 9:56 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law vs Bond Enthalpies vs Standard Enthalpies of Formation
Replies: 7
Views: 43

Re: Hess's Law vs Bond Enthalpies vs Standard Enthalpies of Formation

Usually, they will explicitly say to use bond enthalpy or standard enthalpy of formation in the problem. Bond enthalpies usually give you a chart with the different bond and their enthalpy values.
by Hui Qiao Wu 1I
Wed Jan 29, 2020 3:37 pm
Forum: Phase Changes & Related Calculations
Topic: Heating Curve for Water - Steam
Replies: 2
Views: 32

Re: Heating Curve for Water - Steam

Yes, you are correct. Phase change requires a lot of energy in the form of heat, that energy is so great that when it is released (touches skin), it causes severe burns.
by Hui Qiao Wu 1I
Wed Jan 29, 2020 3:26 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4A.9
Replies: 4
Views: 49

Re: 4A.9

Your change in temperature for copper should be final temperature-100, not the other way around.
by Hui Qiao Wu 1I
Wed Jan 29, 2020 3:06 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Closed Systems
Replies: 13
Views: 88

Re: Closed Systems

Yes, you are right. For the volume specifically, you are either doing work on the system or the system is doing work on the surrounding.
by Hui Qiao Wu 1I
Wed Jan 22, 2020 4:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6E.1
Replies: 1
Views: 28

Re: 6E.1

Since it's aqueous, it's reacting with water. Set up the reaction as HSO4 + H2O double arrow H3O + SO4^2-. Find [H3O+] with an ICE table, then take the -log of the concentration to get the pH.
by Hui Qiao Wu 1I
Wed Jan 22, 2020 4:00 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acids and Bases pka and pkb
Replies: 8
Views: 56

Re: Acids and Bases pka and pkb

The lower the pKb, the stronger the base. The lower the pKa, the stronger the acid.
by Hui Qiao Wu 1I
Wed Jan 22, 2020 3:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6D 13
Replies: 1
Views: 37

Re: 6D 13

I believe you will have to use the table they gave to you for the value of k. Then set up the ice table with your reaction. Since these compounds are aqueous, they are reacting with water. After you have found the [OH-] or[H+], take the -log of the concentration to get pH or pOH. After you have foun...
by Hui Qiao Wu 1I
Wed Jan 22, 2020 3:37 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5J 5: increase in pressure
Replies: 4
Views: 59

Re: 5J 5: increase in pressure

For B): First, you would not take solids into consideration when adding up the coefficients on each side. H2O has one mole on the reactants side. H2 and CO each have 1 mole on the products side; together, it's two moles. Since pressure increases, the volume decreases, meaning it will favor the side ...
by Hui Qiao Wu 1I
Wed Jan 22, 2020 3:31 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Buffers
Replies: 3
Views: 26

Re: Buffers

He said that buffers help resist change. Our body is only equipped to function under a limited range of conditions. The buffers help our mechanisms stay in that optimal range.
by Hui Qiao Wu 1I
Wed Jan 22, 2020 3:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Conjugate Seesaw
Replies: 3
Views: 33

Re: Conjugate Seesaw

The conjugate seesaw is referring to the conjugate acid and conjugate base of acid and base, the compound a base or acid turns into after donating or accepting hydrogen. A problem can give you the concentration of a conj. base or acid and some other information and ask you to use that information to...
by Hui Qiao Wu 1I
Sun Jan 19, 2020 9:15 am
Forum: Ideal Gases
Topic: R constant in Ideal Gas Law
Replies: 4
Views: 37

Re: R constant in Ideal Gas Law

When you plug in all the variables in the pv=nRT equation, you want to make sure all the units cancel out. The correct unit should give you only moles or some kind of pressure unit at the end (after the cancellation of units).
by Hui Qiao Wu 1I
Sun Jan 19, 2020 9:12 am
Forum: Ideal Gases
Topic: Ideal gas law and [P]/[R]
Replies: 3
Views: 30

Re: Ideal gas law and [P]/[R]

You can also us pv=nRT when concerting from concentration to pressure; it goes both ways.
by Hui Qiao Wu 1I
Wed Jan 15, 2020 3:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Conjugate Seesaw and Kw
Replies: 3
Views: 42

Re: Conjugate Seesaw and Kw

Rather than thinking everything is about Kw, why not try thinking that it's all these useful information we can get out of Kw. We can know about Ka/Kb, [H30]/[OH], or even the pH/pOH of an acid/base. In a way, all these values are connected. Kw=Ka x Kb and Ka and Kb connects back to the [H30] and [O...
by Hui Qiao Wu 1I
Wed Jan 15, 2020 12:00 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K units
Replies: 10
Views: 81

Re: K units

Explaining in a non-chemistry way, K is the ratio of products over reactants. And ratios are just numbers; they don't have units.
by Hui Qiao Wu 1I
Tue Jan 14, 2020 11:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5H.2
Replies: 2
Views: 43

Re: 5H.2

My solution manual only includes answers for odd problems, so I don't know how to explain the 2.5 * 10^7. Plus, there were three reactions to the problem, which one were you talking about? But the problem is connecting back to the topics that if a reaction is reversed, then the K would be the invers...
by Hui Qiao Wu 1I
Tue Jan 14, 2020 11:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acids and Bases
Replies: 3
Views: 42

Re: Acids and Bases

I remember Lavelle saying that when one concentration increases, the other concentration decreases (but didn't catch why). So when you multiply the two, they still give you 1.0 x 10^-14. In addition, the concentration affects the intensity of the reaction happening, not the ratio of products over re...
by Hui Qiao Wu 1I
Sat Jan 11, 2020 10:49 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Significant Figures
Replies: 8
Views: 86

Re: Significant Figures

I would say consider both the K constant and initial concentrations because you used both pieces of information in order to figure your answer. Sig figs are determined by all the numbers you used in a problem.
by Hui Qiao Wu 1I
Sat Jan 11, 2020 10:46 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K vs. Q
Replies: 10
Views: 77

Re: K vs. Q

Yup, like everybody else has said, K is for when you know that the reaction is in equilibrium and Q is when you are not sure if the reaction is in equilibrium.
by Hui Qiao Wu 1I
Sat Jan 11, 2020 10:33 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook question 5I.15
Replies: 1
Views: 35

Re: Textbook question 5I.15

Use the equilibrium constant K =[P]/[R] to find the [NH3]. Since NH4HS is a solid, we wouldn't include it in the equation as [R]. The [NH3] is .400/2.0 which is 0.2. Then you plug in the numbers: (1.6 x10^-4) = .2([H2S]). Therefore, the [H2S] is 8 x 10^4.
by Hui Qiao Wu 1I
Sat Jan 11, 2020 9:57 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Hw 5I.1
Replies: 4
Views: 48

Re: Hw 5I.1

Technically, you can use the ICE table for this problem, but it will take more time and work. ICE tables provides other information like the change in concentrations due to the process of the reaction.
by Hui Qiao Wu 1I
Sat Jan 11, 2020 9:52 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5G1
Replies: 2
Views: 43

Re: 5G1

I wouldn't recommend using equilibrium reaction and constant interchangeably in this case because one is the reaction itself and the other is the ration of products and reactants. Like Jacey said, the constant is [P]/[R}, which depends on the equation. The equilibrium equation would be affected by t...
by Hui Qiao Wu 1I
Sat Jan 11, 2020 9:44 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Knowing it's an Equilibrium Reaction
Replies: 4
Views: 41

Re: Knowing it's an Equilibrium Reaction

I think that the double arrow is the only way to recognize an equilibrium equation, unless otherwise specified in the problem. Another characteristic of equilibrium equations is that their concentrations have to remain constant.

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