Search found 27 matches

by Justin_Yi_1J
Tue Mar 14, 2017 4:05 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 202
Views: 63420

Re: Saying Thank You to Dr. Lavelle

Dear Dr. Lavelle, Thank you so much for providing all these chemistry resources to us. You have worked tirelessly for us and I truly apprecitate all the thought you put into everything you have done for our class. Despite the challenges in your personal life, you made the class an amazing experience...
by Justin_Yi_1J
Thu Mar 09, 2017 11:31 am
Forum: *Free Energy of Activation vs Activation Energy
Topic: HW #4.40
Replies: 2
Views: 665

Re: HW #4.40

An approach to this is looking at the formula for rate constant, k = Ae^{\frac{-Ea}{RT}} = \frac{A}{e^{\frac{Ea}{RT}}} . We see that the rate constant can never equal 0. So, if we see a very small rate constant, we can say that the reaction does not occur. In the question, we are given the values fo...
by Justin_Yi_1J
Thu Mar 09, 2017 11:10 am
Forum: *Free Energy of Activation vs Activation Energy
Topic: Standard Gibbs Free Energy of Activation
Replies: 1
Views: 527

Re: Standard Gibbs Free Energy of Activation

In order to bring reactants together to undergo a chemical reaction, energy must be put into the system to do the work necessary to perform the reaction. Gibbs free energy is a measure of the energy in a system that is available to do work. A system must gain energy to do the work of the reaction, s...
by Justin_Yi_1J
Sun Mar 05, 2017 6:17 pm
Forum: Administrative Questions and Class Announcements
Topic: Quiz 3 Winter 2017
Replies: 183
Views: 15481

Re: QUiz 3

for number 8 on Quiz 3, I'm not understanding why Br2 acts as an electrophile. Can someone explain please? The reason Br 2 can act as an electrophile is due to electron-electron repulsion. Typically, Br 2 is a non-polar species. However, when it encounters the pi electrons of an alkene at a high en...
by Justin_Yi_1J
Thu Mar 02, 2017 4:14 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Determining Step
Replies: 1
Views: 239

Re: Rate Determining Step

There are four ways to tell that Lavelle has given: 1. It is given (e.g. this is the slow step) 2. The rate constant for one reaction is larger than the other. k 1 >> k 2 means the first elementary step is faster than the second. 3. The step with the most amount of bonds broken is the slow step. Thi...
by Justin_Yi_1J
Thu Mar 02, 2017 4:00 pm
Forum: *Free Energy of Activation vs Activation Energy
Topic: Catalysts/Enzymes regarding Entropy
Replies: 1
Views: 527

Re: Catalysts/Enzymes regarding Entropy

A way to think about it is using the equation ΔG° ‡ = ΔH° ‡ - TΔS° ‡ . Since a catalyst/enzyme will place the substrates into a more ordered state so that the substrates can more readily react, ΔS° ‡ will be higher with a catalyst than when there is no catalyst present. When ΔS° ‡ is higher, ΔG° ‡ l...
by Justin_Yi_1J
Thu Mar 02, 2017 3:39 pm
Forum: *Alkanes
Topic: "R" in Reference to Alkane to Alkyl Naming
Replies: 1
Views: 240

Re: "R" in Reference to Alkane to Alkyl Naming

An R is a generic alkyl group substituent. So for example, an alkane of length n might be expressed as having an R group attached to one of its carbons. In the case of something like 2-methyl-pentane, the R is the methyl group on the 2nd carbon. Methyl is methane with a removed H, allowing it to bon...
by Justin_Yi_1J
Thu Feb 23, 2017 4:19 pm
Forum: Second Order Reactions
Topic: Slow and Fast Steps [ENDORSED]
Replies: 2
Views: 476

Re: Slow and Fast Steps [ENDORSED]

If the mechanism is a slow step followed by a fast step, then the rate law of the slow step is the overall rate law. However, we must go through a different processes if the initial elementary is not slow. That is because any elementary step after the initial step will have an intermediate. So a slo...
by Justin_Yi_1J
Thu Feb 23, 2017 3:53 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Knowing the number of reaction mechanisms
Replies: 1
Views: 180

Re: Knowing the number of reaction mechanisms

We will most likely be given the information that the reaction goes through multiple steps. It is not like we will be asked to know exactly what steps the reaction has if we are just given the chemical equation. We will either be given a mechanism or given enough information that writing a mechanism...
by Justin_Yi_1J
Wed Feb 22, 2017 2:48 pm
Forum: General Rate Laws
Topic: Differential Rate Law Versus Integrated Rate Law
Replies: 1
Views: 276

Re: Differential Rate Law Versus Integrated Rate Law

The integrated rate law is useful for finding the concentration after a certain time if the initial concentration and the rate constant is known. The integrated rate law can be found by getting the specific solution to the separable differential equation \frac{\mathrm{d} [R]}{\mathrm{d} t} = \textup...
by Justin_Yi_1J
Wed Feb 15, 2017 8:57 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: If gibbs free energy of formation for water is negative, why is the formation of water not spontaneous?
Replies: 2
Views: 443

Re: If gibbs free energy of formation for water is negative, why is the formation of water not spontaneous?

It has to do with the kenetics of the reaction. Lavelle said in lecture the first day of kenetics the example of the diamonds turning to graphite. The reaction has a negative Gibbs Free energy, but it never occurs in real life.

H2 and O2 to H2O is a similar case.
by Justin_Yi_1J
Thu Feb 09, 2017 3:37 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Inert electrodes?
Replies: 2
Views: 266

Re: Inert electrodes?

I just reread the question and noticed the second half about what metal to use. Select a metal that does not easily react but conducts, such as platinum or gold for example.
by Justin_Yi_1J
Thu Feb 09, 2017 3:35 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Inert electrodes?
Replies: 2
Views: 266

Re: Inert electrodes?

You need to use an inert electrode when the species that you are having in the redox reaction is not a good conductor of electrons. For example, when using hydrogen gas, the gas can be in contact with an inert electrode of platinum metal. The metal will conduct the electrons to or from the hydrogen ...
by Justin_Yi_1J
Thu Feb 02, 2017 3:58 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Van't Hoff Equation
Replies: 1
Views: 297

Re: Van't Hoff Equation

Yes, you must raise both sides of the equation to the e power to cancel out the natural log.
by Justin_Yi_1J
Thu Jan 26, 2017 3:51 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy Equation Related to S(universe)
Replies: 1
Views: 251

Re: Gibbs Free Energy Equation Related to S(universe)

What the relationship S surr = - \frac{Hsys}{T} is saying is that as the system becomes more ordered, the surroundings must be getting more disordered. S = \frac{Hsys}{T} , as we learned in class. The equation basically is proving the 1st law of thermodynamics which says the total internal energy of...
by Justin_Yi_1J
Thu Jan 19, 2017 10:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HW 8.57
Replies: 2
Views: 372

Re: HW 8.57

To hydrogenate it means to add hydrogen to the molecule. You see in the given reaction H2 is added to the C2H2, making it C2H2. The pi bond breaks between the carbons and the electrons pair with the hydrogen diatomic molecules that also have their bonds broken.
by Justin_Yi_1J
Thu Jan 12, 2017 10:34 pm
Forum: Calculating Work of Expansion
Topic: 8.93 Substituting PdeltaV=nRT into w=PdeltaV
Replies: 1
Views: 337

Re: 8.93 Substituting PdeltaV=nRT into w=PdeltaV

Yeah that is the correct reasoning. Work is done by change in volume and one way to change volume is by changing the amount of moles.
by Justin_Yi_1J
Thu Dec 01, 2016 3:24 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: molecular form
Replies: 1
Views: 264

Re: molecular form

This is because it is a weak acid and it only partially disassociates, that is the majority (about 100:1 according to Lavelle) stays as the acetic acid. This is because the Ka is small, so the products (the conjugate base and a proton) are far less than the acetic acid. One reason why the acid favor...
by Justin_Yi_1J
Tue Nov 22, 2016 11:53 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Strong Acids
Replies: 3
Views: 368

Re: Strong Acids

The strength of an acid also has to do with its conjugate base anion's stability. If the anion is more stable after the loss of a proton, the acid is more likely to disassociate. In that case of strong acids, the loss of a proton creates a monoatomic anion, which is very stable and therefore it dona...
by Justin_Yi_1J
Thu Nov 17, 2016 9:57 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Difference between Pressure and compression/expansion?
Replies: 5
Views: 2030

Re: Difference between Pressure and compression/expansion?

When expansion or compression occurs, the system will try to minimize the change. If it is compressed, the pressure increases. To counteract this, the system shifts to the side with less moles of gas in order to minimize the change in pressure. Vice-versa for expansion.
by Justin_Yi_1J
Wed Nov 09, 2016 4:20 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: heteronuclear diatomic molecules
Replies: 1
Views: 230

Re: heteronuclear diatomic molecules

This is because the difference in energy of the subshells of each of the atoms will cause the pi molecular orbitals to be lower in energy than the sigma molecular orbital. The interaction between the sigma and pi orbitals will cause the pi to be a lower energy state. I believe it has something to do...
by Justin_Yi_1J
Wed Nov 09, 2016 4:09 pm
Forum: Properties of Light
Topic: Question 3B on the Fall 2016 Midterm [ENDORSED]
Replies: 3
Views: 413

Re: Question 3B on the Fall 2016 Midterm [ENDORSED]

The key thing your response did not touch on is the fact that each photon corresponds to a singular measure of energy, in other words light is quantized. You mentioned a photon is a particle and has wavelength like a wave, but in order to make the leap to quantized energy you must state the frequenc...
by Justin_Yi_1J
Thu Nov 03, 2016 7:09 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Splitting Energy
Replies: 2
Views: 363

Re: Splitting Energy

Splitting energy is the difference in energy between the bonding and antiboding states. It is represented by the distance between the two states in the MO diagrams.
by Justin_Yi_1J
Thu Oct 27, 2016 7:58 pm
Forum: Trends in The Periodic Table
Topic: Quiz 2 Question 1 Wording [ENDORSED]
Replies: 5
Views: 539

Re: Quiz 2 Question 1 Wording [ENDORSED]

I do not believe you would need to know the exact numerical values, just a sense of the trend.
by Justin_Yi_1J
Fri Oct 21, 2016 1:00 pm
Forum: Ionic & Covalent Bonds
Topic: Order or formula
Replies: 2
Views: 246

Re: Order or formula

In general, the molecular formula should not affect the Lewis structure. For example, writing CO 2 or, going against convention, O 2 C would not change the Lewis structure for the molecule. The central atom is still C because it has the higher electron affinity in this case. The only time the formul...
by Justin_Yi_1J
Thu Oct 06, 2016 8:18 pm
Forum: Photoelectric Effect
Topic: Question 1.33 (c) from the textbook [ENDORSED]
Replies: 2
Views: 469

Re: Question 1.33 (c) from the textbook [ENDORSED]

So if I understand you correctly, the objective of part c is to find the wavelength of the light that causes the emission of the electron. So in order do this, take the energy you found from part b. This is the threshold energy or work function. The energy of the absorbed photon that caused the elec...
by Justin_Yi_1J
Thu Sep 29, 2016 9:05 pm
Forum: SI Units, Unit Conversions
Topic: Review Principal L39
Replies: 1
Views: 301

Re: Review Principal L39

So the first step in using the information gathered in step A to answer part B is to see if the empirical formula (SnO 2 ) is the same as the molecular formula, and if not, find out what the molecular formula is. To do so, we must find the mass of the sample contained in the crucible. This is found ...

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