Search found 62 matches

by Xingzheng Sun 2K
Thu Mar 14, 2019 10:04 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units of k
Replies: 5
Views: 119

Re: Units of k

The unit of k for a zero-order reaction is mol L-1 s-1; for a first-order reaction is s-1; For a second-order reaction is L mol-1 s-1.
by Xingzheng Sun 2K
Thu Mar 14, 2019 9:31 pm
Forum: General Rate Laws
Topic: intermediate molecules
Replies: 3
Views: 61

Re: intermediate molecules

Intermediate molecules are not included in general rate laws because only reactants are, but they can be included if you break down the reaction mechanism and look into the rate for each step.
by Xingzheng Sun 2K
Fri Mar 08, 2019 4:23 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Ecell and pH
Replies: 3
Views: 68

Re: Ecell and pH

I think E'cell is the standard E which is the same as E°. It is a fast way in my opinion because otherwise, you need to calculate pH from lnQ.
by Xingzheng Sun 2K
Fri Mar 08, 2019 4:19 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E˚ vs E
Replies: 13
Views: 184

Re: E˚ vs E

E and E°can be calculated by the formula E = E°- (RT/nF) lnQ.
by Xingzheng Sun 2K
Fri Mar 08, 2019 4:17 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E° is 0 for Concentration Cells
Replies: 3
Views: 59

Re: E° is 0 for Concentration Cells

Standard E = 0 only when there is the same material on both sides. Otherwise, you will need to calculate by subtracting the right side by the left side.
by Xingzheng Sun 2K
Fri Mar 08, 2019 4:14 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6th edition 14.35
Replies: 3
Views: 65

Re: 6th edition 14.35

I think the correct equation for this is In3+ (aq) + e- -----> In2+ (aq). This is from my solution manual.
by Xingzheng Sun 2K
Fri Mar 08, 2019 4:07 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Electrochemistry
Replies: 3
Views: 89

Re: Electrochemistry

Because the actual reaction going on is the reverse of formation of Tl3+, resulting in the standard Gibbs Free energy being the opposite.
by Xingzheng Sun 2K
Fri Mar 08, 2019 3:46 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Q: Partial Pressures and Concentration?
Replies: 4
Views: 91

Re: Q: Partial Pressures and Concentration?

For the calculation of Q and K, the equation is that Q = (The concentration x pressure of Products)/(The concentration x pressure of reactants) in the case there are two or more products or reactants which each contains both concentration and pressure.
by Xingzheng Sun 2K
Wed Feb 27, 2019 4:03 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cell Inert Component
Replies: 1
Views: 50

Galvanic Cell Inert Component

When we are asked to put a reaction equation into a cell diagram, how do we know if an inert component such as Pt should be included? Or it will always be mentioned in the question (since some question does not mention Pt but the ask has it)?
by Xingzheng Sun 2K
Wed Feb 27, 2019 3:56 am
Forum: Balancing Redox Reactions
Topic: Gibbs Free Energy
Replies: 2
Views: 60

Re: Gibbs Free Energy

First, you need to write down the half-oxid and half-red equations for the reaction. When you balance it out, I find the electron flow of the reaction which is the number of e- being canceled on each side. Use this number as n to find the △G with △G= -nFE.
by Xingzheng Sun 2K
Wed Feb 27, 2019 3:52 am
Forum: Balancing Redox Reactions
Topic: Oxidizing and Reducing Agent
Replies: 4
Views: 65

Re: Oxidizing and Reducing Agent

Yes. When an element in reactant is both oxidized and reduced in two products, it is both agents.
by Xingzheng Sun 2K
Sat Feb 23, 2019 6:40 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity
Replies: 8
Views: 127

Re: Spontaneity

△G determines whether a reaction can happen spontaneously. Negative △G is spontaneous, and positive △G is not. It is also related to which way of reaction can be more stable. The lower △G is, the more stable it is.
by Xingzheng Sun 2K
Sat Feb 23, 2019 6:36 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Change in Gibbs Free Energy
Replies: 3
Views: 62

Re: Change in Gibbs Free Energy

△G with Degree means it is the standard Gibbs free energy. Without a degree is not standard. It can be calculated by △G = standard△G + RTlnQ.
by Xingzheng Sun 2K
Thu Feb 21, 2019 3:58 am
Forum: Phase Changes & Related Calculations
Topic: joules conversion factor
Replies: 7
Views: 183

Re: joules conversion factor

The conversion from atm L to J is given on the formula sheet for the tests.
by Xingzheng Sun 2K
Thu Feb 21, 2019 3:57 am
Forum: Phase Changes & Related Calculations
Topic: Signs in work equations
Replies: 2
Views: 71

Re: Signs in work equations

I think the sign of work always depends on if the system does the work or work is done to the system. Once it is determined, the sign of work is figured out.
by Xingzheng Sun 2K
Thu Feb 21, 2019 3:54 am
Forum: Phase Changes & Related Calculations
Topic: heat of a phase change
Replies: 5
Views: 92

Re: heat of a phase change

During the phase change, the heat is called latent heat. The formula is q=mL (L is latent heat capacity).
by Xingzheng Sun 2K
Thu Feb 21, 2019 3:50 am
Forum: Phase Changes & Related Calculations
Topic: heat units
Replies: 3
Views: 71

Re: heat units

I think since C is in J/g, the final answer should be in J.
by Xingzheng Sun 2K
Thu Feb 21, 2019 3:48 am
Forum: Phase Changes & Related Calculations
Topic: Isothermal
Replies: 9
Views: 190

Re: Isothermal

Normally it is told that the system is isothermal if it is important for solving the problem.
by Xingzheng Sun 2K
Thu Feb 21, 2019 3:47 am
Forum: Phase Changes & Related Calculations
Topic: Phase Change and Temperature
Replies: 3
Views: 72

Re: Phase Change and Temperature

The change in temperature means that the kinetic energy of molecules is changing. While in the phase change, the substance is changing its potential energy. Thus the temperature does not change.
by Xingzheng Sun 2K
Thu Feb 21, 2019 3:43 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: units
Replies: 7
Views: 165

Re: units

Can the unit for Pressure be other than atm?
by Xingzheng Sun 2K
Thu Feb 21, 2019 12:32 am
Forum: Phase Changes & Related Calculations
Topic: Steam vs Boiling Water
Replies: 8
Views: 191

Re: Steam vs Boiling Water

Because the process of boiling water intakes energy, and when it becomes steam, the steam has more heat than water.
by Xingzheng Sun 2K
Wed Feb 20, 2019 11:49 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Systems
Replies: 6
Views: 190

Re: Systems

Simply, an open system means both matter and energy can exchange; A closed system can exchange energy but not matter. An isolated system does not exchange either matter or system.
by Xingzheng Sun 2K
Wed Feb 20, 2019 11:36 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Graphs
Replies: 2
Views: 72

Re: Graphs

There can be graphs of △H △S and △G. I think the graphs will mainly function to show the change of values.
by Xingzheng Sun 2K
Wed Feb 20, 2019 11:33 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: q=mCdeltaT
Replies: 11
Views: 391

Re: q=mCdeltaT

mC represents the specific heat capacity is measured in per unit of mass; nC means the specific heat capacity is measured per mole.
by Xingzheng Sun 2K
Wed Feb 20, 2019 3:34 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Direction of a Reaction
Replies: 8
Views: 185

Re: Direction of a Reaction

If K is not given, we probably can calculate the K using given information such as concentration. If not, we can not compare K vs Q.
by Xingzheng Sun 2K
Wed Feb 20, 2019 3:32 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ignoring x validity
Replies: 6
Views: 183

Re: ignoring x validity

That is what we are supposed to do. The formula to calculate x is given on the formula sheet, and it always works for solving the x.
by Xingzheng Sun 2K
Wed Feb 20, 2019 3:29 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: increasing pressure, what happens to concentration?
Replies: 10
Views: 179

Re: increasing pressure, what happens to concentration?

When pressure is increased, the reaction wants to do something to reduce the effects. Lowering the number of molecules can decrease the pressure which reduce the effect.
by Xingzheng Sun 2K
Wed Feb 20, 2019 3:25 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Midterm Ice Table
Replies: 6
Views: 136

Re: Midterm Ice Table

The questions on the midterm should not be solved using approximations. Also, I think there is a statement by the question saying no approximation allowed.
by Xingzheng Sun 2K
Wed Feb 20, 2019 3:22 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reverse Reaction
Replies: 8
Views: 120

Re: Reverse Reaction

For reverse reactions, it is important to calculate the K value, which k=[P]/[R].
by Xingzheng Sun 2K
Wed Feb 20, 2019 3:20 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Midterm
Replies: 4
Views: 112

Re: Midterm

I think we need to know strong acids and bases, and others are just weak.
by Xingzheng Sun 2K
Wed Feb 20, 2019 3:17 am
Forum: Ideal Gases
Topic: 5% rule
Replies: 12
Views: 245

Re: 5% rule

I think it simply means that if x (the change) is less than 5% than it is ok. It is important that the formula x=(-b+/-(b2-4ac)^1/2)/2a always work.
by Xingzheng Sun 2K
Wed Feb 20, 2019 3:12 am
Forum: Ideal Gases
Topic: atm vs. bar?
Replies: 23
Views: 416

Re: atm vs. bar?

So which one is the right unit for the equation PV=nRT?
by Xingzheng Sun 2K
Mon Dec 03, 2018 9:46 pm
Forum: Air Pollution & Acid Rain
Topic: Acid Rain
Replies: 9
Views: 735

Re: Acid Rain

One more thing to know is that rain is normally acidic, and the acid rain is when rain is too acidic (more than normal).
by Xingzheng Sun 2K
Mon Dec 03, 2018 9:38 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Sigma and Pi Bond with Hybridization
Replies: 2
Views: 132

Sigma and Pi Bond with Hybridization

I understand the number of the bond (single, double and triple) results in the type of bond. Can anyone tell me the relationship between the type of bond (sigma and pi) and its hybridization orbital?
by Xingzheng Sun 2K
Mon Dec 03, 2018 9:27 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: ph vs pOH
Replies: 5
Views: 89

Re: ph vs pOH

The pH is the concentration of H3O+ and calculated by -log[H3O+], whereas the pOH is the concentration of OH- and calculated by -log[OH-]
by Xingzheng Sun 2K
Mon Dec 03, 2018 9:03 pm
Forum: Hybridization
Topic: Hybridization
Replies: 5
Views: 95

Re: Hybridization

Yes, because the Tetrahedral shape has 4 bonds, which is 4 regions of electron density, resulting in an sp3 hybrid orbital.
by Xingzheng Sun 2K
Mon Dec 03, 2018 8:57 pm
Forum: Hybridization
Topic: Hybrid Orbitals
Replies: 3
Views: 74

Re: Hybrid Orbitals

Yes, the number of regions of electron density include bond and lone pairs, which is equal to hybrid orbitals.
by Xingzheng Sun 2K
Mon Dec 03, 2018 8:51 pm
Forum: Hybridization
Topic: tetrahedral
Replies: 5
Views: 92

Re: tetrahedral

The tetrahedral shape has 4 bonds, which in order 1, 2, 3, 4 bonds form s, sp, sp2 and sp3 hybridization.
by Xingzheng Sun 2K
Mon Dec 03, 2018 8:45 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Seesaw shape
Replies: 3
Views: 99

Re: Seesaw shape

Because of the existence of a lone pair, the bond angles of seesaw shape should be <120 and <90 degrees. I guess less than 180 degrees will work too.
by Xingzheng Sun 2K
Mon Dec 03, 2018 8:38 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: bond angle
Replies: 6
Views: 116

Re: bond angle

For trigonal planer, the bond angle is exactly 120 degrees. For other shapes, since the lone pair has a stronger force, the bond angle can be slightly smaller than the original angle.
by Xingzheng Sun 2K
Mon Dec 03, 2018 8:29 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: polarity
Replies: 11
Views: 148

Re: polarity

Molecules with one pair of electrons are polar, but as for two pairs or more, it depends on the shape and if the elements are the same. The graph on the textbook of VSEPR type VS polarity would help.
by Xingzheng Sun 2K
Wed Nov 14, 2018 7:30 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Dipole Dipole Forces
Replies: 3
Views: 140

Re: Dipole Dipole Forces

The interaction potential energy equation is expressed by (-a1a2)/(r to the sixth). Therefore, the determinations would be the charges of molecules and the distance between them. The distance is more significant because of the 6th power.
by Xingzheng Sun 2K
Wed Nov 14, 2018 7:21 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Bond energy value signs
Replies: 3
Views: 126

Re: Bond energy value signs

Energy is needed to break a bond and is released to form a bond. You also can understand by looking at the energy equation which starts with a negative sign.
by Xingzheng Sun 2K
Wed Nov 14, 2018 7:12 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: States of matter and forces
Replies: 3
Views: 102

Re: States of matter and forces

There is no definite determination on which force results in which state of matter because it depends on the element. However, the stronger the intermolecular force is, the more likely it will be solid; the weaker it is, the more to be gas.
by Xingzheng Sun 2K
Tue Nov 06, 2018 10:17 am
Forum: Electronegativity
Topic: Electronegativity
Replies: 4
Views: 87

Re: Electronegativity

When you are asked to calculate the difference of electronegativity, the values will be given. More importantly, you need to know how to compare each element in a periodic table to figure out, for example, which bond has more ionic or covalent characteristics.
by Xingzheng Sun 2K
Tue Nov 06, 2018 10:09 am
Forum: Bond Lengths & Energies
Topic: Lengths of Bonds
Replies: 9
Views: 170

Re: Lengths of Bonds

Because the double bond has a stronger attraction between the atoms, which pulls to form a shorter bond than a single bond.
by Xingzheng Sun 2K
Tue Nov 06, 2018 10:06 am
Forum: Lewis Structures
Topic: Parenthesis for Ions' Lewis Structures
Replies: 2
Views: 70

Parenthesis for Ions' Lewis Structures

In the answer key, I found that when we draw a Lewis structure for an ion, we need to put parenthesis after drawing the diagram and the write the charge on the up right corner. I wonder if it is a necessary step or just a better representation?
by Xingzheng Sun 2K
Wed Oct 31, 2018 6:42 am
Forum: Resonance Structures
Topic: How to tell when an molecule is resonant?
Replies: 7
Views: 298

Re: How to tell when an molecule is resonant?

This is a good question because the example given in lecture C6H6 has two possible structures, while indeed they are just one turning around. I believe it is still a resonance for the reason that it can also be seen as the change of single bond and double bond of the Cs in the structure.
by Xingzheng Sun 2K
Wed Oct 31, 2018 6:32 am
Forum: Lewis Structures
Topic: Central Atom
Replies: 13
Views: 219

Re: Central Atom

For the Lewis structure, we always choose the atom with the lowest ionization energy as the central atom. Therefore it is C in this case.
by Xingzheng Sun 2K
Wed Oct 31, 2018 6:29 am
Forum: Ionic & Covalent Bonds
Topic: Covalent Bonds
Replies: 16
Views: 276

Re: Covalent Bonds

No, because metals tend to form cations and nonmetals tend to form anions.
by Xingzheng Sun 2K
Thu Oct 25, 2018 4:14 am
Forum: DeBroglie Equation
Topic: equation definition
Replies: 5
Views: 249

Re: equation definition

De Broglie equation describes the status of a single quantum, which includes the mass and velocity. Therefore, the object has to be in motion.
by Xingzheng Sun 2K
Thu Oct 25, 2018 4:11 am
Forum: *Black Body Radiation
Topic: Black Body Radiation
Replies: 4
Views: 270

Re: Black Body Radiation

Will the concept of Black Body Radiation be tested?
by Xingzheng Sun 2K
Thu Oct 25, 2018 2:07 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Spherical Polar Coordinates
Replies: 1
Views: 65

Spherical Polar Coordinates

In the textbook, there is a part in chapter 2 describing spherical polar coordinates, but I do not think our professor covered that in classes. Is it a required material for the test?
by Xingzheng Sun 2K
Tue Oct 16, 2018 1:12 am
Forum: Properties of Light
Topic: E=hv
Replies: 13
Views: 201

Re: E=hv

Since electromagnetic radiation acts like particles, E in this equation stands for the energy per photon.
by Xingzheng Sun 2K
Tue Oct 16, 2018 1:02 am
Forum: Photoelectric Effect
Topic: Homework Ch. 1 Question 25; 6th Edition
Replies: 4
Views: 161

Re: Homework Ch. 1 Question 25; 6th Edition

The question is: Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by (a) an excited sodium atom when it generates a photon; (b) 5.00 mg of sodium atoms emitting light at this wavelength; (c) 1.00 mol of sodium atoms emitting light at th...
by Xingzheng Sun 2K
Tue Oct 16, 2018 1:00 am
Forum: Photoelectric Effect
Topic: Energy Unit of keV
Replies: 1
Views: 99

Energy Unit of keV

In homework problem 1.23, the energy is in the unit of keV. I wonder what is its relation to joules and how often do we use it.
by Xingzheng Sun 2K
Fri Oct 12, 2018 4:14 am
Forum: Limiting Reactant Calculations
Topic: Limiting Reagent
Replies: 10
Views: 418

Re: Limiting Reagent

I would say you do the three reagents together. Find the moles of each one first and figure out which one is the smallest. That is the limiting reagent.
by Xingzheng Sun 2K
Fri Oct 12, 2018 4:12 am
Forum: Empirical & Molecular Formulas
Topic: Empirical & Molecular Formulas
Replies: 11
Views: 604

Re: Empirical & Molecular Formulas

Yes, they can be the same when the molecule, or the molecular formulas, is at the simplest form, then it is the empirical formula.
by Xingzheng Sun 2K
Fri Oct 12, 2018 4:02 am
Forum: SI Units, Unit Conversions
Topic: Homework for Week 2
Replies: 16
Views: 297

Re: Homework for Week 2

I have the same question that if my discussion is on Friday, can I still do the homework from the previous chapter?
by Xingzheng Sun 2K
Fri Oct 05, 2018 3:01 am
Forum: Balancing Chemical Reactions
Topic: Balancing reactions tips
Replies: 29
Views: 759

Re: Balancing reactions tips

From my experiences, I usually start with the element that is the least common to the most common or easiest. By meaning the easiest, for example, H2 can be the one because it will be balanced easily so that I leave it for the latest. After you have the fixed number of the least common element, try ...
by Xingzheng Sun 2K
Fri Oct 05, 2018 2:49 am
Forum: Significant Figures
Topic: Scientific Notation
Replies: 7
Views: 118

Re: Scientific Notation

I would say scientific notation is not required except the question asks. It is a way to make your answer clear, so it is up to you to use it or not for most questions as long as you get the right result.
by Xingzheng Sun 2K
Fri Oct 05, 2018 2:36 am
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student [ENDORSED]
Replies: 96
Views: 48128

Re: Advice from a Medical Student [ENDORSED]

This post is very useful for a biology student like me. Thank you very much!

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