Search found 53 matches
- Thu Mar 15, 2018 9:51 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Slow Steps
- Replies: 2
- Views: 404
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...
- Thu Mar 15, 2018 9:48 am
- Forum: *Enzyme Kinetics
- Topic: Enzymes in rate law
- Replies: 4
- Views: 759
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.
- Thu Mar 15, 2018 9:44 am
- Forum: First Order Reactions
- Topic: Integrated Rate Laws
- Replies: 4
- Views: 713
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.
- Thu Mar 15, 2018 9:39 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: mechanisms
- Replies: 3
- Views: 642
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.
- Wed Mar 14, 2018 7:05 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: to find k
- Replies: 4
- Views: 648
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.
- Wed Mar 14, 2018 7:03 pm
- Forum: General Rate Laws
- Topic: Stoichiometric coefficients and order
- Replies: 5
- Views: 1147
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.
- Mon Mar 05, 2018 10:46 pm
- Forum: Second Order Reactions
- Topic: Order reactions
- Replies: 6
- Views: 1109
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.
- Mon Mar 05, 2018 10:44 pm
- Forum: General Rate Laws
- Topic: Rate laws and integrated rate laws
- Replies: 3
- Views: 602
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.
- Mon Mar 05, 2018 10:41 pm
- Forum: General Rate Laws
- Topic: 15.3 Rate Laws Depending on concentrations of products
- Replies: 3
- Views: 489
Re: 15.3 Rate Laws Depending on concentrations of products
Use reactants when dealing with reaction rate problems for this class.
- 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: 548
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.
- Sun Feb 25, 2018 8:33 pm
- Forum: General Rate Laws
- Topic: Rate law equations
- Replies: 3
- Views: 582
Re: Rate law equations
They are the same. They are only written using different variables but they ultimately represent the same thing.
- Sun Feb 25, 2018 8:31 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Positive Slope???
- Replies: 4
- Views: 696
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.
- Sun Feb 18, 2018 11:05 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Gold and Nitric Acid
- Replies: 2
- Views: 845
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.
- Fri Feb 16, 2018 10:26 am
- Forum: Balancing Redox Reactions
- Topic: Half-Reactions on Test 2
- Replies: 5
- Views: 740
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.
- Fri Feb 16, 2018 10:16 am
- Forum: Balancing Redox Reactions
- Topic: Oxidized vs oxidizing agent
- Replies: 5
- Views: 722
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.
- 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: 323
Re: Entropy being a state function
Yes, since entropy is a state function the two types of reactions would result in the same answer.
- Sat Feb 10, 2018 5:55 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Units Confusion [ENDORSED]
- Replies: 3
- Views: 476
Re: Units Confusion [ENDORSED]
Use dimensional analysis to track your units and see which ones cancel out in your problem.
- Sat Feb 10, 2018 5:46 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation vs. reduction
- Replies: 8
- Views: 881
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...
- 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: 874
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...
- 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: 457
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.
- Sun Feb 04, 2018 11:30 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: pressure and free energy
- Replies: 2
- Views: 354
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.
- Sat Jan 27, 2018 11:43 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Systems in practice
- Replies: 4
- Views: 523
Re: Systems in practice
Systems can only be completely isolated in theory. Most "isolated" systems are more similar to closed systems in real life.
- Sat Jan 27, 2018 11:42 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Pressure Internal vs. External
- Replies: 2
- Views: 994
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.
- Sat Jan 27, 2018 11:38 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: exothermic vs endothermic [ENDORSED]
- Replies: 7
- Views: 1150
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.
- Sun Jan 21, 2018 10:50 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Bomb Calorimeters
- Replies: 2
- Views: 341
Re: Bomb Calorimeters
Questions should specify but most combustion reactions where heat is calculated should occur in a bomb calorimeter.
- 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: 830
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.
- Sun Jan 21, 2018 6:32 pm
- Forum: Phase Changes & Related Calculations
- Topic: Heating Curve Calculation Confusion
- Replies: 3
- Views: 356
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
- Fri Jan 12, 2018 8:51 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3715114
Re: Post All Chemistry Jokes Here
What do chemists call a benzene ring with iron atoms replacing the carbon atoms?
A ferrous wheel.
A ferrous wheel.
- Fri Jan 12, 2018 12:57 pm
- Forum: Phase Changes & Related Calculations
- Topic: Expansion and change in pressure
- Replies: 4
- Views: 388
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.
- Fri Jan 12, 2018 11:48 am
- Forum: Phase Changes & Related Calculations
- Topic: Work done BY vs. Work done ON [ENDORSED]
- Replies: 5
- Views: 610
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.
- Wed Jan 10, 2018 4:06 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Pre reqs for Chem 14B
- Replies: 1
- Views: 266
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?
- 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: 240
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?
- Fri Dec 08, 2017 10:07 am
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: Sigma and Pi bonds
- Replies: 1
- Views: 425
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?
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?
- Wed Nov 29, 2017 2:34 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kc and Kp [ENDORSED]
- Replies: 1
- Views: 264
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 ...
- Wed Nov 29, 2017 1:11 am
- Forum: Naming
- Topic: 17.29 a [ENDORSED]
- Replies: 1
- Views: 238
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!
Please help!
- Mon Nov 27, 2017 9:42 am
- Forum: Naming
- Topic: Roman numeral placement
- Replies: 4
- Views: 571
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.
- Mon Nov 27, 2017 9:40 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Some clarification about ligands
- Replies: 5
- Views: 639
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.
- Fri Nov 17, 2017 9:44 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: Sigma and Pi Bonds
- Replies: 3
- Views: 641
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.
- Fri Nov 17, 2017 9:42 pm
- Forum: Hybridization
- Topic: Hybridization
- Replies: 6
- Views: 650
Re: Hybridization
Hybridization is basically the fusion of two orbitals to to form a new set of orbitals to hold electrons.
- Thu Nov 09, 2017 3:22 pm
- Forum: Trends in The Periodic Table
- Topic: first and second ionization energies [ENDORSED]
- Replies: 3
- Views: 653
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.
- Thu Nov 09, 2017 3:19 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Unpaired Electrons [ENDORSED]
- Replies: 3
- Views: 523
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.
- Wed Nov 01, 2017 12:04 pm
- Forum: Dipole Moments
- Topic: Polarity vs Non-Polarity
- Replies: 3
- Views: 666
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...
- Wed Nov 01, 2017 11:07 am
- Forum: Lewis Structures
- Topic: Elements that have extended octets
- Replies: 3
- Views: 430
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.
- Fri Oct 27, 2017 3:50 am
- Forum: Trends in The Periodic Table
- Topic: d-block elements
- Replies: 1
- Views: 521
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...
- Fri Oct 27, 2017 3:47 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: d and s blocks
- Replies: 16
- Views: 2218
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.
- Sun Oct 22, 2017 7:48 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: XYZ [ENDORSED]
- Replies: 4
- Views: 2226
Re: XYZ [ENDORSED]
The XYZ system just helps to categorize the different electrons into their respective subsets in the p-orbital.
Wenxin Fan-1H
Wenxin Fan-1H
- Sun Oct 22, 2017 7:42 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Post Module Q. 14
- Replies: 3
- Views: 615
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
Wenxin Fan- 1H
- Wed Oct 11, 2017 10:15 pm
- Forum: Properties of Light
- Topic: Calculating the wavelength of light [ENDORSED]
- Replies: 5
- Views: 1006
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
-Wenxin Fan 1H
- Wed Oct 11, 2017 10:07 pm
- Forum: Einstein Equation
- Topic: E=hv and ΔE=hv
- Replies: 3
- Views: 1522
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
-Wenxin Fan 1H
- Wed Oct 11, 2017 10:04 pm
- Forum: Properties of Electrons
- Topic: Atomic Spectra and Energy Levels
- Replies: 2
- Views: 662
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
-Wenxin Fan 1H
- Thu Oct 05, 2017 1:37 am
- Forum: Limiting Reactant Calculations
- Topic: Percent Yield [ENDORSED]
- Replies: 5
- Views: 6103
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...
- Thu Oct 05, 2017 1:31 am
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: E.29 part b HELP
- Replies: 3
- Views: 464
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
-Wenxin Fan 1H
- Thu Oct 05, 2017 1:24 am
- Forum: SI Units, Unit Conversions
- Topic: Limiting Reagents [ENDORSED]
- Replies: 8
- Views: 1089
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...