Search found 53 matches

by Wenxin Fan 1J
Thu Mar 15, 2018 9:51 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Steps
Replies: 2
Views: 78

Re: Slow Steps

Yes, you need to identify the slow step to see if it fits the experimentally observed rate law. However, you may not always be told which step is the slow step so you should try to see which step would work as the slow step if you apply what you know about the characteristics of a slow step and if y...
by Wenxin Fan 1J
Thu Mar 15, 2018 9:48 am
Forum: *Enzyme Kinetics
Topic: Enzymes in rate law
Replies: 4
Views: 214

Re: Enzymes in rate law

In most cases, catalysts will not be included in the rate law since it is not usually involved in the slow, rate determining step.
by Wenxin Fan 1J
Thu Mar 15, 2018 9:44 am
Forum: First Order Reactions
Topic: Integrated Rate Laws
Replies: 4
Views: 250

Re: Integrated Rate Laws

Integrated rate laws applies to reactions other than first order reactions as well. The ln[A] vs t, 1/[A] vs T are both from integrated rate laws.
by Wenxin Fan 1J
Thu Mar 15, 2018 9:39 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: mechanisms
Replies: 3
Views: 190

Re: mechanisms

To show the mechanism you just need to write and identify the slow step and ensure thsn the series of steps results in the overall equation and supports the experimentally determined rate law.
by Wenxin Fan 1J
Wed Mar 14, 2018 7:05 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: to find k
Replies: 4
Views: 191

Re: to find k

In problems where the experimental results are given, the k value calculated should be the same for each trial, but in actual experimentation the results will not be as accurate and precise so you would average them.
by Wenxin Fan 1J
Wed Mar 14, 2018 7:03 pm
Forum: General Rate Laws
Topic: Stoichiometric coefficients and order
Replies: 5
Views: 179

Re: Stoichiometric coefficients and order

The coefficients are helpful when using elementary steps to try to determine the reaction mechanism, but the actual rate law can only be determined through experimentation.
by Wenxin Fan 1J
Mon Mar 05, 2018 10:46 pm
Forum: Second Order Reactions
Topic: Order reactions
Replies: 6
Views: 394

Re: Order reactions

The order of the reaction is the addition of the exponents in the rate law equation. The different orders help you to determine the rate of the reactions in reference to the consumption of reactants. The order is an important aspect in the rate law.
by Wenxin Fan 1J
Mon Mar 05, 2018 10:44 pm
Forum: General Rate Laws
Topic: Rate laws and integrated rate laws
Replies: 3
Views: 122

Re: Rate laws and integrated rate laws

The primary difference is that the integrated rate law utilizes the initial rate and is a function of time.
by Wenxin Fan 1J
Mon Mar 05, 2018 10:41 pm
Forum: General Rate Laws
Topic: 15.3 Rate Laws Depending on concentrations of products
Replies: 3
Views: 101

Re: 15.3 Rate Laws Depending on concentrations of products

Use reactants when dealing with reaction rate problems for this class.
by Wenxin Fan 1J
Sun Feb 25, 2018 8:34 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: figuring out n and m
Replies: 3
Views: 143

Re: figuring out n and m

You must use experimental data to calculate n and m. All the necessary information should be given to you so that you can ultimately calculate n and m.
by Wenxin Fan 1J
Sun Feb 25, 2018 8:33 pm
Forum: General Rate Laws
Topic: Rate law equations
Replies: 3
Views: 122

Re: Rate law equations

They are the same. They are only written using different variables but they ultimately represent the same thing.
by Wenxin Fan 1J
Sun Feb 25, 2018 8:31 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Positive Slope???
Replies: 4
Views: 141

Re: Positive Slope???

For right now the tangent line will be positive since we are primarily looking at forward reactions as reactants proceed to products.
by Wenxin Fan 1J
Sun Feb 18, 2018 11:05 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Gold and Nitric Acid
Replies: 2
Views: 114

Re: Gold and Nitric Acid

That is one way to tell. You can look at the standard reduction potentials for the two half reactions to see what the sign of E˚ would be to determine if the reaction is spontaneous in one direction or the other.
by Wenxin Fan 1J
Fri Feb 16, 2018 10:26 am
Forum: Balancing Redox Reactions
Topic: Half-Reactions on Test 2
Replies: 5
Views: 156

Re: Half-Reactions on Test 2

Yeah, you aren't going to be required to memorize standard reduction potentials or other values found in the appendix.
by Wenxin Fan 1J
Fri Feb 16, 2018 10:16 am
Forum: Balancing Redox Reactions
Topic: Oxidized vs oxidizing agent
Replies: 5
Views: 117

Re: Oxidized vs oxidizing agent

Usually, the molecule/atom that has been reduced (gains electrons) is the oxidizing agent and the molecules that has been oxidized (loses electrons) is the reducing agent. This makes sense since redox-reactions involve an exchange of electrons between different atoms/compounds.
by Wenxin Fan 1J
Sat Feb 10, 2018 5:57 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy being a state function
Replies: 2
Views: 71

Re: Entropy being a state function

Yes, since entropy is a state function the two types of reactions would result in the same answer.
by Wenxin Fan 1J
Sat Feb 10, 2018 5:55 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Units Confusion [ENDORSED]
Replies: 3
Views: 118

Re: Units Confusion [ENDORSED]

Use dimensional analysis to track your units and see which ones cancel out in your problem.
by Wenxin Fan 1J
Sat Feb 10, 2018 5:46 pm
Forum: Balancing Redox Reactions
Topic: Oxidation vs. reduction
Replies: 8
Views: 156

Re: Oxidation vs. reduction

An oxidation equation is when an element has a lower oxidation number in the reactants compared to the products and/or when there are electrons in the products side of the equation. A reduction equation is when the electrons are found on the left side of the equation and/or when the oxidation number...
by Wenxin Fan 1J
Sun Feb 04, 2018 11:36 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Higher Molar Entropy
Replies: 4
Views: 138

Re: Higher Molar Entropy

Molar entropy is the amount of entropy change resulting from the formation of one mol of its substance from its simplest/purest components. It can be calculated using the molar entropy values of other components in an equation. The more disordered a phase is the more entropy. Gasses have the most an...
by Wenxin Fan 1J
Sun Feb 04, 2018 11:33 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Thermal and positional disorder
Replies: 2
Views: 141

Re: Thermal and positional disorder

Thermal motion and positional disorder are aspects of entropy that can be used to describe the amount of entropy or be used to compare the entropy that an object has.
by Wenxin Fan 1J
Sun Feb 04, 2018 11:30 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: pressure and free energy
Replies: 2
Views: 78

Re: pressure and free energy

Questions will normally specify if pressure has changed or if a reaction is not at standard conditions. That is when you would use that version of the gibbs free energy equation.
by Wenxin Fan 1J
Sat Jan 27, 2018 11:43 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Systems in practice
Replies: 4
Views: 156

Re: Systems in practice

Systems can only be completely isolated in theory. Most "isolated" systems are more similar to closed systems in real life.
by Wenxin Fan 1J
Sat Jan 27, 2018 11:42 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Pressure Internal vs. External
Replies: 2
Views: 101

Re: Pressure Internal vs. External

Work is the ability to move/push against an external force/pressure, which is why P external is used. In chemistry we view work from the point of view of the system.
by Wenxin Fan 1J
Sat Jan 27, 2018 11:38 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: exothermic vs endothermic [ENDORSED]
Replies: 7
Views: 262

Re: exothermic vs endothermic [ENDORSED]

It depends on the context of the problem but water is considered the surroundings if something is placed in the water. However, the amount of energy absorbed by a calorimeter can be used to calculate heat released to the surroundings as well.
by Wenxin Fan 1J
Sun Jan 21, 2018 10:50 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Bomb Calorimeters
Replies: 2
Views: 93

Re: Bomb Calorimeters

Questions should specify but most combustion reactions where heat is calculated should occur in a bomb calorimeter.
by Wenxin Fan 1J
Sun Jan 21, 2018 10:45 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 7
Views: 209

Re: Bond Enthalpies

More stable bonds have more negative (less) potential energies, which means more energy is required to break the bonds. Therefore bonds with greater potential energy (less negative) are less stable and require less energy to break.
by Wenxin Fan 1J
Sun Jan 21, 2018 6:32 pm
Forum: Phase Changes & Related Calculations
Topic: Heating Curve Calculation Confusion
Replies: 3
Views: 147

Re: Heating Curve Calculation Confusion

When temperature changes for a substance use the equation q=mCdeltaT and when the desired or required temperature is met and the substance changes phase use the values for delta H of vaporization or melting to find the heat . Add all the values together
by Wenxin Fan 1J
Fri Jan 12, 2018 8:51 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 788485

Re: Post All Chemistry Jokes Here

What do chemists call a benzene ring with iron atoms replacing the carbon atoms?


A ferrous wheel.
by Wenxin Fan 1J
Fri Jan 12, 2018 12:57 pm
Forum: Phase Changes & Related Calculations
Topic: Expansion and change in pressure
Replies: 4
Views: 164

Re: Expansion and change in pressure

When the internal heat of the system decreases because work is done on the surroundings by the system (heat released), the molecules in the system has less kinetic energy, resulting in less movement and less pressure. Volume and pressure are inversely related if heat is not a factor.
by Wenxin Fan 1J
Fri Jan 12, 2018 11:48 am
Forum: Phase Changes & Related Calculations
Topic: Work done BY vs. Work done ON [ENDORSED]
Replies: 5
Views: 207

Re: Work done BY vs. Work done ON [ENDORSED]

Work done on the system results in a positive value for joules while work done by the system results in a loss of heat of the system (negative) and into the surroundings.
by Wenxin Fan 1J
Wed Jan 10, 2018 4:06 pm
Forum: Administrative Questions and Class Announcements
Topic: Pre reqs for Chem 14B
Replies: 1
Views: 122

Pre reqs for Chem 14B

I passed out of 31A and 31B because of AP exams. However, I have decided to take the LS 30 series for math. Do I still meet the pre-reqs for the course if I am not taking 30B but have passed out of 31B?
by Wenxin Fan 1J
Fri Dec 08, 2017 10:13 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Volume vs Pressure
Replies: 1
Views: 91

Volume vs Pressure

Is there a difference between changing volume and changing pressure? Changing pressure does not always result in a shift because the addition of an inert gas has no effect, but does changing volume always result in a shift in the system?
by Wenxin Fan 1J
Fri Dec 08, 2017 10:07 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Sigma and Pi bonds
Replies: 1
Views: 210

Sigma and Pi bonds

I am confused by the notation when you determine the hybridization of bonds and lone pairs
an example was this: sigma(C2sp2, C2sp2) <=from the practice final exam on chem community
How would you write the notation if a double bond existed in the same place? Why is there a 2 in front of sp2?
by Wenxin Fan 1J
Wed Nov 29, 2017 2:34 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc and Kp [ENDORSED]
Replies: 1
Views: 105

Kc and Kp [ENDORSED]

If a question contains a chemical formula that only consists of gasses, will it be acceptable to write the equilibrium constant or expression as either Kc or Kp if it does not specify. The book had examples of both. Is there a go-to if the question does not specify? For example, chapter 11 question ...
by Wenxin Fan 1J
Wed Nov 29, 2017 1:11 am
Forum: Naming
Topic: 17.29 a [ENDORSED]
Replies: 1
Views: 114

17.29 a [ENDORSED]

Why is [Fe(CN)6]-4 hexacyanoferrate(II) instead of hexacyanidoferrate(II)? Shouldn't it be cyanido instead of cyano? are both correct? Table 17.4 says CN- is cyanido but can also be iso-cyano.

Please help!
by Wenxin Fan 1J
Mon Nov 27, 2017 9:42 am
Forum: Naming
Topic: Roman numeral placement
Replies: 4
Views: 175

Re: Roman numeral placement

The Roman numeral represents the oxidation number for a transition metal and should go right after the name of the metal.
by Wenxin Fan 1J
Mon Nov 27, 2017 9:40 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Some clarification about ligands
Replies: 5
Views: 185

Re: Some clarification about ligands

A ligand is a Lewis base that bonds to a transition metal central atom. It doesn't refer to the entire compound.
by Wenxin Fan 1J
Fri Nov 17, 2017 9:44 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Sigma and Pi Bonds
Replies: 3
Views: 217

Re: Sigma and Pi Bonds

Sigma bonds are the single bonds shared between two atoms. Pi bonds are the additional bond in double bonds. A double bond has 1 sigma and 1 pi bond. The distinction is how the orbitals are oriented in relation to another.
by Wenxin Fan 1J
Fri Nov 17, 2017 9:42 pm
Forum: Hybridization
Topic: Hybridization
Replies: 6
Views: 233

Re: Hybridization

Hybridization is basically the fusion of two orbitals to to form a new set of orbitals to hold electrons.
by Wenxin Fan 1J
Thu Nov 09, 2017 3:22 pm
Forum: Trends in The Periodic Table
Topic: first and second ionization energies [ENDORSED]
Replies: 3
Views: 233

Re: first and second ionization energies [ENDORSED]

After the initial electron is removed, the nuclear attraction on the electrons of the atom increases due to decreased electron electron repulsion. Making it more difficult to remove another electron.
by Wenxin Fan 1J
Thu Nov 09, 2017 3:19 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Unpaired Electrons [ENDORSED]
Replies: 3
Views: 258

Re: Unpaired Electrons [ENDORSED]

You need to follow the Pauley exclusion principle and hund's rule. Electrons must fill all the orbitals in a sub shell once before pairing up with an electron the orbitals. Knowing this rule will help you to determine how many electrons are unpaired.
by Wenxin Fan 1J
Wed Nov 01, 2017 12:04 pm
Forum: Dipole Moments
Topic: Polarity vs Non-Polarity
Replies: 3
Views: 275

Re: Polarity vs Non-Polarity

Based on Lewis structures you can see the arrangement if atoms in reference to each other. Looking at the bonding between atoms in the structure can also be used to determine the 3d structure of the molecule. These characteristics can be used to determine polarity by using the VSEPR theory in conjun...
by Wenxin Fan 1J
Wed Nov 01, 2017 11:07 am
Forum: Lewis Structures
Topic: Elements that have extended octets
Replies: 3
Views: 153

Re: Elements that have extended octets

Any element in and past the 3rd period has hybridizable d orbitals that can form a new set of orbitals to hold more than 8 valence electrons.
by Wenxin Fan 1J
Fri Oct 27, 2017 3:50 am
Forum: Trends in The Periodic Table
Topic: d-block elements
Replies: 1
Views: 162

Re: d-block elements

D block elements are transition metals which do not always have the same oxidation number. The oxidation number will usually be specified. Sometimes +2 or +1 will be written, but the oxidation number can also be shown in a compound name, usually in Roman numerals. There are a few exceptions that alw...
by Wenxin Fan 1J
Fri Oct 27, 2017 3:47 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: d and s blocks
Replies: 16
Views: 573

Re: d and s blocks

You write the electron configuration in the order of the principle quantum number "n". The n value of the d sub shell is n-1 compared to the s and the p subshell. Therefore, d is written first.
by Wenxin Fan 1J
Sun Oct 22, 2017 7:48 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: XYZ [ENDORSED]
Replies: 4
Views: 214

Re: XYZ [ENDORSED]

The XYZ system just helps to categorize the different electrons into their respective subsets in the p-orbital.
Wenxin Fan-1H
by Wenxin Fan 1J
Sun Oct 22, 2017 7:42 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Post Module Q. 14
Replies: 3
Views: 204

Re: Post Module Q. 14

The answer is D because the uncertainty principle refers to objects with momentum (m x v). Therefore, the answers involving stationary objects are not applicable.

Wenxin Fan- 1H
by Wenxin Fan 1J
Wed Oct 11, 2017 10:15 pm
Forum: Properties of Light
Topic: Calculating the wavelength of light [ENDORSED]
Replies: 5
Views: 284

Re: Calculating the wavelength of light [ENDORSED]

Since both h and c are constants, you can use the equation to either find E, energy or lambda, wavelength.
-Wenxin Fan 1H
by Wenxin Fan 1J
Wed Oct 11, 2017 10:07 pm
Forum: Einstein Equation
Topic: E=hv and ΔE=hv
Replies: 3
Views: 247

Re: E=hv and ΔE=hv

In chemistry the delta sign usually symbolizes change (in chemical equations it can show the application of heat). Therefore ΔE=hv is the equation for the change in energy while E=hv is just an energy calculation.
-Wenxin Fan 1H
by Wenxin Fan 1J
Wed Oct 11, 2017 10:04 pm
Forum: Properties of Electrons
Topic: Atomic Spectra and Energy Levels
Replies: 2
Views: 323

Re: Atomic Spectra and Energy Levels

The reason the spectrum lines are put in those categories or groups is because they share the same lower principle energy level (n=).
-Wenxin Fan 1H
by Wenxin Fan 1J
Thu Oct 05, 2017 1:37 am
Forum: Limiting Reactant Calculations
Topic: Percent Yield [ENDORSED]
Replies: 5
Views: 391

Re: Percent Yield [ENDORSED]

A high percent yield means that there were fewer outside errors in the application of a chemical reaction. You want the actual yield to be as close to the theoretical yield as possible to allow for more accurate predictions and calculations. High yield may indicate that there are fewer impurities in...
by Wenxin Fan 1J
Thu Oct 05, 2017 1:31 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E.29 part b HELP
Replies: 3
Views: 205

Re: E.29 part b HELP

There are 2 moles of Cl- for every mole of CuCl2. Therefore you just multiply the moles of CuCl2 from part A by 2. You yet 8.34x10^-2 moles Cl-

-Wenxin Fan 1H
by Wenxin Fan 1J
Thu Oct 05, 2017 1:24 am
Forum: SI Units, Unit Conversions
Topic: Limiting Reagents [ENDORSED]
Replies: 8
Views: 466

Re: Limiting Reagents [ENDORSED]

Problems might ask for a reactant that is in excess. Also, when working a problem with a given amount (either in moles or in grams) of each reactant, you should always check to see which is limiting in order to determine the theoretical yield. Many problems won't explicitly ask you to identify a lim...

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