Search found 33 matches

by Masih Tazhibi 2I
Sat Mar 17, 2018 11:15 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 907921

Re: Post All Chemistry Jokes Here

What's an Organic Chemist's greatest fear?

A BACKSIDE ATTACK!
by Masih Tazhibi 2I
Sat Mar 17, 2018 11:05 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 907921

Re: Post All Chemistry Jokes Here

This quarter is moving so fast! I really need to get it in........Kinetic control
by Masih Tazhibi 2I
Sat Mar 17, 2018 10:54 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetically controlled reactions
Replies: 3
Views: 402

Re: Kinetically controlled reactions

Suppose you have two possible products, A and B. If A is kinetically favorable, it means that it has a lower activation energy, and a higher rate constant. If B is thermodynamically favorable, it means that as a product, it resides at a lower energy state, and thus is more stable. The problem is, th...
by Masih Tazhibi 2I
Sat Mar 17, 2018 1:31 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Step Determining Overall Rate
Replies: 3
Views: 132

Re: Slow Step Determining Overall Rate

The slow step always determines the rate of the reaction. The problem is that when the slow step is not the first step in the rxn, the experimentally observed rate law doesn't always seem to match the rate law obtained by the slow step. This is because the slow step rate might include the concentrat...
by Masih Tazhibi 2I
Tue Mar 13, 2018 10:29 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-Equilibirum Approach
Replies: 1
Views: 46

Re: Pre-Equilibirum Approach

The pre equilibrium approach is used when the slow or rate determining step in a mechanism is not the first step, and thus you can't simply write out a rate law and be done. This is because writing out the rate law for the second step will not consider the concentrations of reactants in step 1, but ...
by Masih Tazhibi 2I
Tue Mar 13, 2018 10:17 pm
Forum: Van't Hoff Equation
Topic: Confusion on different versions of the Van't Hoff equation?
Replies: 4
Views: 322

Re: Confusion on different versions of the Van't Hoff equation?

You can use either version of the equation. It was discussed in class that scientists just prefer not having negative signs in their equations if they can avoid it, so they sometimes reframe the equation to that end. However, both are perfectly fine as long as you keep your k and T values consistent.
by Masih Tazhibi 2I
Tue Mar 13, 2018 10:15 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Adsorption
Replies: 4
Views: 180

Re: Adsorption

Adsorption occurs when you have a heterogenous catalyst being used, that is, a catalyst that is in a different phase than the reactants. Usually, adsorption occurs when your catalyst is a solid, and the reactants, rather than going inside or being absorbed by the catalyst, simply sit on top of it as...
by Masih Tazhibi 2I
Sat Mar 10, 2018 12:07 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Kinetic information [ENDORSED]
Replies: 3
Views: 109

Re: Kinetic information [ENDORSED]

Reaction mechanisms are found experimentally, and are very similar to putting together a puzzle. You know through experimental data that a mechanism will create the final reaction, but you need to (through trial and error) figure out how the initial reaction gets to its final form. Creating a mechan...
by Masih Tazhibi 2I
Sat Mar 10, 2018 12:04 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation [ENDORSED]
Replies: 7
Views: 235

Re: Arrhenius Equation [ENDORSED]

I have heard that when plugging in values for Ea, you want to convert the units to joules, or else your answer will be incorrect. Is this because R is in J/mol*k?
by Masih Tazhibi 2I
Sat Mar 10, 2018 12:01 am
Forum: First Order Reactions
Topic: slope
Replies: 3
Views: 250

Re: slope

The slope of the first order reaction can be found through assessing the integrated rate law. The first order integrated rate law is ln(A)=-kt+ln(Ao), which is in the linear y=mx+b form. As such, the slope is -k.
by Masih Tazhibi 2I
Sat Mar 03, 2018 1:33 pm
Forum: Zero Order Reactions
Topic: Difference between zero, first, second [ENDORSED]
Replies: 3
Views: 146

Re: Difference between zero, first, second [ENDORSED]

Lucian did a fantastic job explaining the rate orders here. I would also like to add that experimentally, you determine rate orders by isolating the impact of one reactant at a time on the overall reaction rate. If you have two reactants, you would keep one constant and change the concentration of t...
by Masih Tazhibi 2I
Sat Mar 03, 2018 1:26 pm
Forum: General Rate Laws
Topic: Test 3
Replies: 5
Views: 156

Re: Test 3

As has already been stated, knowing the derivations really adds another layer of depth to your understanding of the topic. It's great to have an equation sheet to give you the formulas, and for most of the problems you do it's nice to have them on demand, but knowing the way these equations came abo...
by Masih Tazhibi 2I
Sat Mar 03, 2018 1:21 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: How to tell difference btwn thermo and kinetics [ENDORSED]
Replies: 7
Views: 307

Re: How to tell difference btwn thermo and kinetics [ENDORSED]

Another key point is that thermodynamics really buckled down on the initial and final states of a system, dealing mostly with state functions and just looking at relative changes in work, energy, and entropy. What seems to be the most different about kinetics is that it focuses on the very path port...
by Masih Tazhibi 2I
Sun Feb 25, 2018 2:49 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: kinetics
Replies: 5
Views: 256

Re: kinetics

One of the big things that I've noticed is that thermodynamics was heavily concerned with state functions, that is, the initial and final relative states of a system without respect to the path the reaction took. I think Kinetics is concerned with the very path dependency that thermodynamics ignored...
by Masih Tazhibi 2I
Sun Feb 25, 2018 2:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electromotive Force
Replies: 3
Views: 161

Re: Electromotive Force

When we are calculating cell potential, it is usually a means of calculating the Gibbs Free Energy of the redox reaction taking place. This is the maximum work that the cell can do in the form of electrical energy, which is what we use these cells for in the first place.
by Masih Tazhibi 2I
Sun Feb 25, 2018 2:42 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Initial rates
Replies: 5
Views: 206

Re: Initial rates

We also use the initial values because it makes our calculations a lot simpler. This is because you only have to consider the reactant concentrations, rather than taking into account both products and reactants, as well as the extent of both the forward and reverse reactions.
by Masih Tazhibi 2I
Sun Feb 18, 2018 10:46 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells
Replies: 5
Views: 187

Re: Concentration Cells

..Also, as the concentrations of the two half reactions change, the voltage also changes
by Masih Tazhibi 2I
Sun Feb 18, 2018 10:43 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cells
Replies: 2
Views: 84

Re: Galvanic cells

In general I think for the purposes of this class you are looking for the transfer of electrons from one half reaction to the next. There would thus be two cells in system.
by Masih Tazhibi 2I
Sun Feb 11, 2018 11:05 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 2nd law -- conceptual
Replies: 3
Views: 136

Re: 2nd law -- conceptual

The idea behind this law is that the universe is always heading towards some increase in entropy. The entropy of the surroundings plus the entropy of the system is greater than zero because in a spontaneous process, the system has not reached thermal equilibrium. Since Entropy is Q/T, having the sam...
by Masih Tazhibi 2I
Sun Feb 11, 2018 10:59 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Number of Bonds and Entropy
Replies: 3
Views: 115

Re: Number of Bonds and Entropy

I think in general, there are a couple things to look at when comparing molecules. The first is the state each molecule occupies, as we know that Sgas>Sliquid>Ssolid. Additionally, it is important to compare the relative size of the molecule, as an increase in the number of bonds and electrons leads...
by Masih Tazhibi 2I
Sat Feb 10, 2018 8:44 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: negative entropy [ENDORSED]
Replies: 3
Views: 152

Re: negative entropy [ENDORSED]

It is actually possible to have a negative change in entropy, but we don't typically see those in what we are dealing with. However, you do see negative entropies quite frequently in aqueous ions. It's just good to know they are out there, but the main thing you should know about entropy is that it ...
by Masih Tazhibi 2I
Sun Feb 04, 2018 5:52 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: deltaS question
Replies: 7
Views: 246

Re: deltaS question

The 3/2 and 5/2 is for ideal gases that have different properties. For gases that are not ideal, you use the one without Cp.
by Masih Tazhibi 2I
Sun Feb 04, 2018 5:50 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Question about Change in Gibb's Free Energy
Replies: 4
Views: 116

Re: Question about Change in Gibb's Free Energy

A big trend in thermodynamics is that it is hard to conceptualize and analyze these concepts in and of themselves, as some quantity. It is much more useful to analyze concepts like enthalpy, entropy, and Gibbs free energy as relative quantities, where you look at changes with respect to differing co...
by Masih Tazhibi 2I
Sun Feb 04, 2018 5:46 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Delta U (Concept Clarification)
Replies: 6
Views: 162

Re: Delta U (Concept Clarification)

While the internal energy is zero, the gas is expanding against a vacuum which has no resistance.
by Masih Tazhibi 2I
Sun Jan 28, 2018 4:04 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy based on initial temp
Replies: 3
Views: 84

Re: Entropy based on initial temp

Changes in entropy are based on the equation q/T. It intuitively makes sense that if you held q constant in both cases, lets say 100J, the change in entropy would be less with a higher temperature. For example, 100J/200K is greater than 100J/500k. This is logical because adding a constant amount of ...
by Masih Tazhibi 2I
Sun Jan 28, 2018 3:55 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Practice Example 9.5
Replies: 1
Views: 83

Re: Practice Example 9.5

In this problem, you have both the volume changing and the temperature changing. Thus, there are two different factors impacting the total change in entropy. The first is positional entropy, due to a change in the volume. This entropy change takes into account the increase or decrease in entropy whe...
by Masih Tazhibi 2I
Sun Jan 28, 2018 3:49 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Sign of ΔS
Replies: 3
Views: 160

Re: Sign of ΔS

The sign for the change in entropy comes from the q value in the numerator. Thus, if your system is releasing heat, the change in entropy of the system is decreasing, and vice versa.
by Masih Tazhibi 2I
Sat Jan 20, 2018 3:51 pm
Forum: Calculating Work of Expansion
Topic: Integral from Today's Lecture
Replies: 3
Views: 134

Re: Integral from Today's Lecture

The integral is to show the more scientifically accurate way of writing your PdeltaV equation. They essentially are doing the same thing in a nonreversible expansion, but when things change, it is good to know conceptually where the integral is coming from, and how it could further be applied. I wou...
by Masih Tazhibi 2I
Sat Jan 20, 2018 3:48 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Concept Clarification
Replies: 3
Views: 133

Re: Concept Clarification

Yes, adding matter would increase the internal energy of a system, because there are more substances to react in the system. Taking matter out of the system would limit the extent of reaction you would have had if the matter was not removed.
by Masih Tazhibi 2I
Sat Jan 20, 2018 3:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard enthalpies on test 1 [ENDORSED]
Replies: 7
Views: 311

Re: Standard enthalpies on test 1 [ENDORSED]

It's important to also know that the reason diatomic molecules have standard enthalpies of formation at zero is not because they are diatomic in and of itself, but it is a consequence of the fact that diatomic elements are pure substances. For example, molecules like C(s) or K(s) or O2 etc., are all...
by Masih Tazhibi 2I
Thu Jan 11, 2018 8:24 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 2
Views: 85

Re: Bond Enthalpies

Another important thing to note is that the bond enthalpies have a role in determining the overall Enthalpy of the reaction. If you take the summation of the enthalpies of bonds broken, and subtract from that value the summation of the enthalpies of bonds formed, you get the total enthalpy of the re...
by Masih Tazhibi 2I
Wed Jan 10, 2018 9:27 pm
Forum: Phase Changes & Related Calculations
Topic: qp=deltaH
Replies: 8
Views: 386

Re: qp=deltaH

For all intents and purposes, I think it is just important to know the concept behind their interchangeability. q is used to describe values of released or absorbed heat, and using the subscript p to create "qp" just means you are looking at the change in heat at a constant pressure. This ...
by Masih Tazhibi 2I
Wed Jan 10, 2018 9:21 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy is a state property
Replies: 13
Views: 450

Re: Enthalpy is a state property

It is also important to know that a state property is independent of how the substance was prepared. Good examples of state properties include things like altitude, pressure, volume, temperature. Note that when looking at these values, it isn't important to track the path they have taken; with tempe...

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