Search found 48 matches

by Rex Lee 1C
Wed Mar 09, 2016 12:10 pm
Forum: *Cycloalkenes
Topic: Halocycloalkenes
Replies: 1
Views: 448

Re: Halocycloalkenes

Double bonds/triple bonds will always take numbering priority over substituents, but not functional groups.
by Rex Lee 1C
Sun Mar 06, 2016 10:54 pm
Forum: General Rate Laws
Topic: 2011 Final, Question 4A
Replies: 3
Views: 607

Re: 2011 Final, Question 4A

The reason that the rate=k[A]^n is because we integrate \frac{-d[A]}{dt} = k[A]^n First, we separate the variables, getting \frac{d[A]}{[A]^n}=-kdt Then, we integrate: \int \frac{d[A]}{[A]^n}=-k\int dt This is the same as \int \[A]^{-n}d[A]=-k\int dt When integrating, one takes the fraction of the v...
by Rex Lee 1C
Sun Mar 06, 2016 10:19 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Enzymes
Replies: 2
Views: 453

Re: Enzymes

I think that the book is trying to say that by placing the molecules in a more favorable orientation, the delta S will be smaller (less negative) because the reactants' entropy is decreasing by less since they are more ordered than they would be if there were no catalyst present. "Less negative...
by Rex Lee 1C
Sat Mar 05, 2016 12:15 pm
Forum: *Aldehydes
Topic: Naming functional groups
Replies: 1
Views: 953

Re: Naming functional groups

What's important in this structural formula is the ending -CHO. This implies that there is an oxygen and hydrogen attached to a carbon which is attached to the rest of the chain. However, since this is only 3 bonds and to get carbon a formal charge of zero, we double bond the oxygen. Now it is clear...
by Rex Lee 1C
Thu Mar 03, 2016 9:05 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: First and Second Order
Replies: 1
Views: 311

Re: First and Second Order

The Arrhenius equation does not depend on the order of the reaction, rather it gives the relationship between a reaction's activation energy and rate constant with the help of values including the gas constant, temperature, and the pre-exponential factor
by Rex Lee 1C
Sun Feb 28, 2016 10:02 pm
Forum: *Alkanes
Topic: Second number in structure
Replies: 2
Views: 344

Re: Second number in structure

The -2 is in reference to dimethyl. Because it is "di", there are two methyl groups on that molecule 2,2 describes where they are. In this case, carbon 2 contains two methyl groups
by Rex Lee 1C
Sun Feb 28, 2016 12:34 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: HW 15.63
Replies: 2
Views: 441

Re: HW 15.63

A better way to do a problem like this would be to use the equation ln(\frac{k'}{k}) = \frac{E_{A}}{R}(\frac{1}{T}-\frac{1}{T'}) This way, you can plug in the known vale of k as "k", 38 for Ea, 8.314 for R, (25+273) for T, and (37+273) for T'. This will give you k'
by Rex Lee 1C
Sun Feb 28, 2016 12:26 pm
Forum: *Alkanes
Topic: Numbering Cs
Replies: 1
Views: 322

Re: Numbering Cs

You look at the series of possible numbers for the substituents and find the arrangement that allows the lowest numbers. For example: 1,2,6 is better than 1,3,4 even though the sum of the first is greater. 1,3,5,6 is better than 1,3,6,7 Never look at sums, just the values of the numbers, whichever h...
by Rex Lee 1C
Sun Feb 28, 2016 1:26 am
Forum: *Alkenes
Topic: Naming Priorities
Replies: 2
Views: 555

Re: Naming Priorities

Functional Groups always take priority over double/triple bonds
by Rex Lee 1C
Sat Feb 20, 2016 2:01 pm
Forum: *Electrophilic Addition
Topic: Breaking double bonds
Replies: 1
Views: 1482

Re: Breaking double bonds

In this case, the pi bond between the two carbons is acting as a nucleophile which will be electrostatically attracted to the Hydrogen of HBr (since Br is highly electronegative and makes the hydrogen side of the molecule positive). When this pi bond breaks, the sigma bond between the two C's is sti...
by Rex Lee 1C
Tue Feb 16, 2016 11:56 am
Forum: Second Order Reactions
Topic: Questions 15.23c
Replies: 1
Views: 403

Re: Questions 15.23c

The reaction order does not necessarily correspond to the value of the stoichiometric coefficients for the reactants. The only time they are equal if if they give you (and specify that) it is an elementary reaction or step.
by Rex Lee 1C
Tue Feb 16, 2016 11:51 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetic Control
Replies: 2
Views: 528

Re: Kinetic Control

Reactions are either thermodynamically controlled or kinetically controlled. Thermodynamically controlled means that you would expect the reaction to occur based on a favorable energy difference between reactants and products, i.e. if ∆G˚ is negative, you would expect it to be spontaneous. Kinetical...
by Rex Lee 1C
Sat Feb 13, 2016 9:53 am
Forum: Zero Order Reactions
Topic: Zero, First, and Second Order Reactions
Replies: 1
Views: 629

Re: Zero, First, and Second Order Reactions

Zero, First, and Second Order Reactions refer to the dependence of the reaction's rate on the initial concentration of reactant(s). For a zero order, the rate of reaction does not depend at all on the reactant's concentration. For first order, it is directly dependent on concentration (for example d...
by Rex Lee 1C
Tue Feb 09, 2016 12:47 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagrams
Replies: 1
Views: 368

Re: Cell diagrams

You put Pt(s) in the cell diagram when the anode or the cathode needs an electrode for the transfer of electrons (and does not have an electrode already incorporated as in Zn(s) in the oxidation to Zn2+). Basically, whenever the redox reaction incorporates a change between a gas and a liquid or a li...
by Rex Lee 1C
Tue Feb 09, 2016 12:43 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Ka
Replies: 1
Views: 406

Re: Ka

Ka is simply the equilibrium constant for an acid, which implies that K will be of the (general) form
by Rex Lee 1C
Tue Feb 09, 2016 12:41 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells and Midterm Questions
Replies: 2
Views: 470

Re: Galvanic Cells and Midterm Questions

They most likely will not be labeled, however, the anode is drawn on the left and oxidation is taking place there while the cathode is drawn on the right and is the site of reduction
by Rex Lee 1C
Thu Feb 04, 2016 12:47 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Enthalpy Fusion and Enthalpy Vaporization
Replies: 2
Views: 447

Re: Enthalpy Fusion and Enthalpy Vaporization

Temperature never changes during a phase change (like fusion or vaporization) because all of the energy that is supplied to the sample goes into breaking the bonds and not raising the temperature. In other words, all of the energy goes to breaking the bonds that hold molecules or atoms together and ...
by Rex Lee 1C
Tue Feb 02, 2016 1:25 pm
Forum: Balancing Redox Reactions
Topic: Standard Reduction Potential
Replies: 1
Views: 322

Re: Standard Reduction Potential

Because standard reduction potentials (E˚) are an intensive property, that is, it doesn't matter how much is present, the values will always stay the same (although you do have to reverse the sign if you reverse the reaction)
by Rex Lee 1C
Fri Jan 29, 2016 2:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electromotive Force
Replies: 1
Views: 297

Re: Electromotive Force

Electromotive Force is the electrical potential for a reaction. (denoted as ℰ or E). It's measured in volts and it represents the maximum potential difference because once the reaction starts to "react", the potential difference between the anode and cathode side becomes smaller, so at tim...
by Rex Lee 1C
Thu Jan 28, 2016 10:11 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67 Inquiry
Replies: 1
Views: 265

Re: 8.67 Inquiry

The reason why the values are different is because the solutions manual is calculating the ∆H of reaction of methanol from elements in their standard states. Your equation is a completely different reaction (with CO), and different reactions have different ∆H's.
by Rex Lee 1C
Thu Jan 28, 2016 10:08 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 3
Views: 518

Bond Enthalpies

Bond enthalpies are the energy required to break a bond, so the bonds that are broken should stay positive, while the bonds that are formed need to be negated (since forming bonds releases energy). The addition of these positive (broken bonds) and negative (formed bonds) values are the ∆H of reaction.
by Rex Lee 1C
Thu Jan 28, 2016 10:03 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Physical Significance of Gibbs Free Energy
Replies: 1
Views: 4783

Re: Physical Significance of Gibbs Free Energy

Gibbs Free Energy represents the energy that is free to do useful work for a spontaneous process. In other words, it is the max work done by a process at constant T and P.
by Rex Lee 1C
Thu Jan 28, 2016 10:00 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: q = deltaH
Replies: 1
Views: 482

Re: q = deltaH

q=∆H whenever the reaction takes place under constant pressure. Enthalpy (∆H), by definition, is the heat absorbed or released by a reaction under constant pressure.
by Rex Lee 1C
Thu Jan 21, 2016 12:25 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity
Replies: 1
Views: 288

Re: Heat Capacity

Specific heat capacities are intrinsic properties that do not change as long as the substance remains in the same phase while energy is being transferred. So, liquid water has a specific heat capacity of 4.184 J/g˚C, no matter if it is 10˚C or 90˚C. However, the specific heat for solid water is diff...
by Rex Lee 1C
Fri Jan 15, 2016 12:54 am
Forum: Phase Changes & Related Calculations
Topic: Heating Curve
Replies: 3
Views: 605

Re: Heating Curve

The lines for enthalpy of fusion and vaporization are always horizontal, because when a phase change is occurring, all of the energy going into the sample is being used to break bonds between atoms/molecules and none is used for raising temperature. The steepness of lines that represent the liquid, ...
by Rex Lee 1C
Thu Jan 14, 2016 11:55 pm
Forum: Calculating Work of Expansion
Topic: Converting units
Replies: 1
Views: 408

Re: Converting units

Atm x cm^3 can be converted to atm•L (because 1 cm^3 is equal to 1 mL). From there, convert your value in atm•L using the conversion 101.325 J/(atm•L), and the work will be in units of Joules.
by Rex Lee 1C
Thu Jan 07, 2016 9:22 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond enthalpy and Enthalpy change
Replies: 1
Views: 354

Re: Bond enthalpy and Enthalpy change

Using bond enthalpies is a way to calculate the total change in enthalpy for a reaction. This works because bonds are broken (requires energy) and they are formed (releases energy), so the balance between them is the ∆H. If more energy is required to break reactant bonds than product bonds release, ...
by Rex Lee 1C
Fri Dec 04, 2015 12:37 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Solving for x in Problem 12.59 a
Replies: 1
Views: 372

Re: Solving for x in Problem 12.59 a

The approximation is made because the Kb for Ammonia (1.8e-5) is so small. Because of this, the x value that you would get when you solved the quadratic would be very small in relation to the starting concentration. Since the x value is so small, you can reduce (0.057-x) to 0.057 in the denominator ...
by Rex Lee 1C
Wed Dec 02, 2015 12:03 pm
Forum: Identifying Acidic & Basic Salts
Topic: differentiating between the two
Replies: 2
Views: 502

Re: differentiating between the two

To determine whether a salt is basic or acidic, look at the ions in salt. If one of the ions is the conjugate base of a weak acid, it will make the solution basic. If one is a conjugate acid of a weak base, it will make the solution acidic. For example NaCH3COO will be a basic solution because CH3CO...
by Rex Lee 1C
Sat Nov 28, 2015 1:43 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: HW Question 12.69 and 12.71
Replies: 1
Views: 440

Re: HW Question 12.69 and 12.71

In the problems where Kw is used, the compounds given are the salts of a conjugate weak acid or a weak base. Therefore, the Ka or Kb of the ion that performs salt hydrolysis can be calculated by dividing Kw by the Ka/Kb of its conjugate acid or base (i.e. the Ka of ammonium ion can be found by divid...
by Rex Lee 1C
Sat Nov 28, 2015 1:36 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Stronger Acid
Replies: 1
Views: 438

Re: Stronger Acid

To determine which acid is stronger, simply look at the Ka values for each of the species. The one with the larger Ka value will be more acidic, and therefore a stronger acid. This is because a larger Ka corresponds to greater product concentrations and the products of placing an acidic species in w...
by Rex Lee 1C
Fri Nov 20, 2015 8:18 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Protonation?
Replies: 1
Views: 2021

Re: Protonation?

Protonation is the addition of a proton (H+) to a species. A good example is a water molecule (acting as an acid) transferring a proton to a base. Like NH_{3} + H_{2}O \rightleftharpoons NH_{4}^{+} + OH^{-} . Calculating the percent protonation in this case would be done by dividing the concentratio...
by Rex Lee 1C
Fri Nov 20, 2015 6:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Converting from Moles to Pressure
Replies: 3
Views: 611

Re: Converting from Moles to Pressure

Yes, using PV=nRT, calculate the partial pressure of each gas based on the number of moles of each gas and plug them into the equilibrium expression. However, take note of how you solve for the molar values, because when using an ICE box, you should try to keep the units in either molarity or pressu...
by Rex Lee 1C
Fri Nov 20, 2015 10:36 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Writing Molarity of IONS as Logarithms: Solving Logarithms
Replies: 2
Views: 623

Re: Writing Molarity of IONS as Logarithms: Solving Logarith

The -11.8 was found by solving the logarithm " -log(1.7 * 10^(-12))". Plugging this into the calculator will give you -11.8. In general, solving logarithms in this form means finding the exponent of 10 that will give you the number after the log. So, this solved for the exponent of ten tha...
by Rex Lee 1C
Fri Nov 13, 2015 5:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating Equilibrium partial pressure
Replies: 1
Views: 969

Re: Calculating Equilibrium partial pressure

Looking at the equation, we can see that the solid NH4HS will not be a part of the equilibrium expression, because its concentration cannot change (it's a solid). Therefore, K=[NH3][H2S]. Since both of these gases have a molar coefficient of one, there will be equal concentrations of each at equilib...
by Rex Lee 1C
Mon Nov 09, 2015 6:26 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Temperature vs Pressure and Concentration
Replies: 1
Views: 415

Re: Temperature vs Pressure and Concentration

Temperature affects K values because K is related to the Gibbs Free Energy ( \Delta G ) of a reaction. ( \Delta G ) is changed by temperature because of thermochemical equations, and also related to K by the relationship \Delta G=-RTlnK . Therefore, temperature changes the equilibrium constant. Conc...
by Rex Lee 1C
Fri Nov 06, 2015 3:48 pm
Forum: Naming
Topic: Ligands and Transition Metal Bonding
Replies: 2
Views: 460

Re: Ligands and Transition Metal Bonding

Ligands form coordinate covalent bonds to transition metals because the ligands have lone pairs that can be donated (as a lewis base) to the TM. It is called a coordinate covalent bond because both of the electrons in the covalent bond come from one atom (the ligand) and the TM can accept them becau...
by Rex Lee 1C
Sun Nov 01, 2015 8:54 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Molecular Orbitals/Paramagnetism and Diamagnetism
Replies: 1
Views: 800

Re: Molecular Orbitals/Paramagnetism and Diamagnetism

Diamagnetism occurs when all of the electrons in a given compound are paired with each other, Paramagnetism is when a compound has one or more unpaired electrons in its molecular orbital.

Diamagnetic materials are repelled my magnetic fields, and paramagnetic ones are attracted
by Rex Lee 1C
Tue Oct 27, 2015 11:47 am
Forum: Resonance Structures
Topic: Homework 3.119
Replies: 1
Views: 389

Re: Homework 3.119

There is only one bond length because when we talk about resonance, we are talking about the phenomena in which electrons that "belong" to the double bond are delocalized throughout the molecule. Therefore in ozone, the electrons that comprise both the double and single bonds are not restr...
by Rex Lee 1C
Fri Oct 23, 2015 10:56 am
Forum: Hybridization
Topic: Usage of Hybridization
Replies: 1
Views: 348

Re: Usage of Hybridization

Hybridization is used to make all the orbitals in which electrons on the central atom are shared the same energy. For example, methane requires four bonds of equal energy around the central carbon. The carbon has two electrons in the 2s and two electrons in the 2p orbitals. To allow for four equal b...
by Rex Lee 1C
Fri Oct 16, 2015 4:08 pm
Forum: Octet Exceptions
Topic: Determining which elements are octet exceptions
Replies: 4
Views: 1535

Re: Determining which elements are octet exceptions

Octet exceptions occur because of the use of electrons in d orbitals. Therefore, elements with access to d orbitals can be exceptions to the octet rule. Most commonly, this includes elements like Phosphorus and Sulfur.
by Rex Lee 1C
Fri Oct 16, 2015 4:02 pm
Forum: Ionic & Covalent Bonds
Topic: Carbon and Oxygen- Electron Affinity
Replies: 2
Views: 2545

Re: Carbon and Oxygen- Electron Affinity

Carbon has a higher electron affinity than Oxygen because it is easier to place an electron in the ground state C atom than a ground state O atom. This is because C's electron configuration is [He]2s^{2}2p^{2} whereas O's is [He]2s^{2}2p^{4} . Therefore, the C atom has two electrons in the 2p with p...
by Rex Lee 1C
Sun Oct 11, 2015 11:15 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Quiz 1 Preparation #3
Replies: 3
Views: 839

Re: Quiz 1 Preparation #3

"Find the uncertainty in the position of a marble of mass 1.5 g given that its speed is known to within ±0.55 m.s^-1." Would we need to use the Δp=m x Δv formula to solve for Δp? Then use the Δp that we received and plug it into the Heisenberg Uncertainty Equation to obtain Δx, which is t...
by Rex Lee 1C
Thu Oct 08, 2015 6:00 pm
Forum: Photoelectric Effect
Topic: Quiz 1 Prep. Fall 2013 Question 10
Replies: 1
Views: 344

Re: Quiz 1 Prep. Fall 2013 Question 10

To solve this problem, use the equation h\nu = \phi + E_{K} where \phi represents the threshold energy. In the first part of this problem the minimum frequency to eject an electron is given. Multiplying this by Planck's constant gives you the threshold energy for the atom ( \phi ). In the second par...
by Rex Lee 1C
Tue Oct 06, 2015 7:50 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Elements with +2 charge
Replies: 1
Views: 425

Re: Elements with +2 charge

In the review problems for E:23, How do you calculate the amount (in moles) Cu^2+ ions in 3.00 g of CuBr2? First, convert CuBr_{2} into moles. Looking at the chemical formula, there is one atom of Cu for every formula unit of CuBr_{2} . Therefore, the amount of moles of Cu^{2+} in the sample is the...
by Rex Lee 1C
Fri Oct 02, 2015 3:44 pm
Forum: Properties of Light
Topic: Atomic Spectra
Replies: 1
Views: 675

Re: Atomic Spectra

The lines that make up a series all start at some higher energy level and fall to the same lower one. For example the Balmer series lines all end at n=2. So some lines may be the result of an electron falling from n=3 --> n=2, or n=5 --> n=2, etc. (as long as the initial level is n>2 and the final i...
by Rex Lee 1C
Thu Oct 01, 2015 12:44 am
Forum: Properties of Electrons
Topic: Energy Levels and Emission
Replies: 2
Views: 514

Re: Energy Levels and Emission

The jumps of electrons represent the transition states for the energy levels of the absorption/emission spectrum. In the same sense that it requires more energy to promote an electron from n=1 to n=3 (because the difference in energy is greater than it would be from n=2 to n=3), a more energetic pho...
by Rex Lee 1C
Wed Sep 30, 2015 10:51 am
Forum: Properties of Light
Topic: Rydberg Formula
Replies: 7
Views: 2170

Re: Rydberg Formula

The Rydberg Formula arranged for frequency, as stated in the question, can be used whenever the problem asks for the energy/wavelength/frequency of the photon released when an electron falls/is excited from one energy level to another. After plugging in the values for the energy levels, you get the ...

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