Search found 39 matches

by Connor Kelligrew 2D
Thu Mar 08, 2018 12:06 am
Forum: First Order Reactions
Topic: Simpler way to calculate change in concentrations
Replies: 2
Views: 86

Re: Simpler way to calculate change in concentrations

No, you would not be penalized. That method is good and completely legitimate. I like it too. In fact, in the homework I noticed another trend in second order reactions that I do not believe would be penalized either, since it is just manipulating equations and finding trends. Here it is if I rememb...
by Connor Kelligrew 2D
Thu Mar 08, 2018 12:00 am
Forum: Second Order Reactions
Topic: Second Order
Replies: 3
Views: 255

Re: Second Order

Both changes in concentration can be described by the half-life of a second order reaction: t_{1/2} = \frac{1}{k[A]_{0}} Since the initial concentration of A is in the denominator, the time it takes different initial concentrations to decay to half of their original concentration is dependent upon t...
by Connor Kelligrew 2D
Wed Mar 07, 2018 11:52 pm
Forum: General Rate Laws
Topic: Coefficients
Replies: 5
Views: 175

Re: Coefficients

I believe that these coefficients do not affect how we write the rate laws for first and second order reactions. It would affect the unique rate of the reaction and finding the rates of consumption/production for one reactant/product in terms of another reactant/product's rate of consumption/product...
by Connor Kelligrew 2D
Sat Mar 03, 2018 8:23 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 900786

Re: Post All Chemistry Jokes Here

What did C14 do for Valentine's Day?

He went carbon dating!
by Connor Kelligrew 2D
Sat Mar 03, 2018 3:52 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 900786

Re: Post All Chemistry Jokes Here

What do you do with a dead chemist?

Barium
by Connor Kelligrew 2D
Sat Mar 03, 2018 3:48 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 900786

Re: Post All Chemistry Jokes Here

I don't trust atoms...

I heard they make up everything
by Connor Kelligrew 2D
Sat Feb 24, 2018 4:46 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Q of eqn [ENDORSED]
Replies: 2
Views: 130

Re: Q of eqn [ENDORSED]

As long as the reactants and products are not in the liquid or solid state, their concentrations and/or pressures affect the reaction quotient, Q, and the direction the reaction will proceed in to reach equilibrium. Both pressure and concentration can be included in the formula for the reaction quot...
by Connor Kelligrew 2D
Sat Feb 24, 2018 4:42 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate constant (k)
Replies: 4
Views: 155

Re: Rate constant (k)

The rate constant K, is constant for a particular reaction at a particular temperature So yes, you're right; it may change with a temperature change, but usually these rate constants are measured by scientists in a lab setting, where temperature remains controlled. K is a very idealized constant bec...
by Connor Kelligrew 2D
Sat Feb 24, 2018 4:35 pm
Forum: General Rate Laws
Topic: Reaction Rate and Spontaneity
Replies: 5
Views: 321

Re: Reaction Rate and Spontaneity

I agree with both the other answers, spontaneity != reaction rate and vice versa
by Connor Kelligrew 2D
Tue Feb 13, 2018 1:02 pm
Forum: Calculating Work of Expansion
Topic: Calculating work in Reversible and Irreversible Pathways
Replies: 1
Views: 96

Re: Calculating work in Reversible and Irreversible Pathways

-PdeltaV is for irreversible expansion and -nRTlnV2/V1 is for reversible expansion.
by Connor Kelligrew 2D
Tue Feb 13, 2018 12:47 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Boltzmann Equation
Replies: 2
Views: 85

Re: Boltzmann Equation

It is important to specifically note that because when dealing with actual, complex molecules, it is difficult to know the exact number of microstates, W. It is often the case that we do not know the exact number of microstates, but that is okay because if we can estimate it, then we will still obta...
by Connor Kelligrew 2D
Tue Feb 13, 2018 12:18 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Practice Midterm [ENDORSED]
Replies: 5
Views: 392

Re: Practice Midterm [ENDORSED]

Also if you search thoroughly enough on chemistry community there are past exam questions that students post about after they finished their exam, and even if they’re old they’re valuable to look at
by Connor Kelligrew 2D
Sat Feb 10, 2018 9:40 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 900786

Re: Post All Chemistry Jokes Here

What is the show cesium and iodine were watching together?

CSI
by Connor Kelligrew 2D
Sat Feb 10, 2018 9:38 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 900786

Re: Post All Chemistry Jokes Here

The first rule of thermodynamics is you don't talk about thermodynamics
by Connor Kelligrew 2D
Sat Feb 10, 2018 9:37 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 900786

Re: Post All Chemistry Jokes Here

Thermodynamics:

First Law: You can't get anything without working for it.

Second Law: The most you can accomplish by work is to break even.

Third Law: You can't break even.
by Connor Kelligrew 2D
Tue Jan 23, 2018 8:14 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Reaction Enthalpy units
Replies: 1
Views: 82

Re: Standard Reaction Enthalpy units

I believe the unit is kJ for the whole reaction because you cannot specify it to kJ/mol since each substance may have a different stoichiometric ratio, resulting in kJ/2mol, 2mol*kJ/mol... etc.
by Connor Kelligrew 2D
Tue Jan 23, 2018 8:10 pm
Forum: Administrative Questions and Class Announcements
Topic: When can we pick up our finals from Chem 14A?
Replies: 3
Views: 315

Re: When can we pick up our finals from Chem 14A?

Final exams will be available 3rd week Winter quarter from 4006 Young Hall.
by Connor Kelligrew 2D
Tue Jan 23, 2018 8:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.65
Replies: 6
Views: 203

Re: 8.65

They added the first reaction to half of the second reaction, and I am referring to the two reactions they provide in the problem.

Personally I would avoid dealing with fractions in these calculations if possible, and would not approach the problem like this.
by Connor Kelligrew 2D
Sat Jan 20, 2018 6:25 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 900786

Re: Post All Chemistry Jokes Here

How do you tell the difference between a chemist and a train conductor?

Have them read "unionized"
by Connor Kelligrew 2D
Sat Jan 20, 2018 5:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard reaction enthalpies
Replies: 1
Views: 67

Re: Standard reaction enthalpies

For this question, you can use the standard enthalpies of formation from Appendix 2A to calculate the standard reaction enthalpy, which is one of the methods to calculating a standard reaction enthalpy. Imagine that to carry out the reaction we convert the reactants into the elements in their most s...
by Connor Kelligrew 2D
Sat Jan 20, 2018 10:45 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Problem 8.65
Replies: 3
Views: 107

Re: Problem 8.65

For your first question: It is because they preferred to write the chemical equation for forming 1 mole of N_{2}O_{5} first and then work their way towards that. You do not have to solve the problem this way, it is just how the textbook prefers to do it. For your second question: You actually can so...
by Connor Kelligrew 2D
Sat Dec 02, 2017 11:32 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: strength
Replies: 2
Views: 167

Re: strength

If it was two acids you could calculate the pH values and compare, whichever is lowest is a stronger acid. If it was two bases you could calculate the pH values and compare, whichever is higher is a stronger base. If it was an acid and a basic you could calculate the pH of the acid and the pOH of th...
by Connor Kelligrew 2D
Sat Nov 25, 2017 11:18 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape Memorization
Replies: 6
Views: 271

Re: Molecular Shape Memorization

I mean, unless you can memorize the basic shapes and then derive the rest by removing bonds and adding lone pairs of electrons and figure out the bond angle to maximize distance without memory, then yes it would have to simply be memorized.
by Connor Kelligrew 2D
Sat Nov 25, 2017 11:10 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Expanded octet
Replies: 6
Views: 228

Re: Expanded octet

Also if an atom is at a lower energy, more stable state when an expanded octet is applied to one of the elements in the atom. So a quick lewis structure can double check if an element uses and expanded octet
by Connor Kelligrew 2D
Sat Nov 11, 2017 9:55 pm
Forum: Resonance Structures
Topic: Resonance Structure vs. Isomer
Replies: 1
Views: 173

Re: Resonance Structure vs. Isomer

I believe the difference between a resonance structure and an isomer is resonance forms only differ in the arrangement of electrons while isomers differ in both the arrangement of atoms and electrons. As for chirality, I believe that is a special type of isomer and it is when two molecules are mirro...
by Connor Kelligrew 2D
Sat Nov 11, 2017 9:43 pm
Forum: Ionic & Covalent Bonds
Topic: Covalent Bonding: Polar and Non-polar
Replies: 6
Views: 372

Re: Covalent Bonding: Polar and Non-polar

Well, a polar covalent bond is a covalent bond between atoms that have partial electric charges. The chance of these partial electric charges occurring increases as the difference in the electronegativity between the atoms increases. An example is HCl. So two atoms in a covalent bond with a high ele...
by Connor Kelligrew 2D
Sat Nov 04, 2017 8:17 pm
Forum: Electronegativity
Topic: ELECTRON AFFINITY
Replies: 7
Views: 553

Re: ELECTRON AFFINITY

Also note that the atom wants to reach a stable, full valence shell, so whether that is easier by losing or gaining electrons will lead to a lower or higher electron affinity respectively.
by Connor Kelligrew 2D
Sat Nov 04, 2017 8:12 pm
Forum: Administrative Questions and Class Announcements
Topic: 14B and 14BL
Replies: 3
Views: 231

Re: 14B and 14BL

14BL is titration and spectroscopy I heard, and I’ve also read it doesn’t matter either way.
by Connor Kelligrew 2D
Sat Oct 28, 2017 11:59 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2.85
Replies: 5
Views: 212

Re: 2.85

Hello! If you remember the diagram Dr. Lavelle drew in lecture showing the different energy levels an electron in a Hyrdrogen atom can occupy, the n=1,2,3,... lines he drew correspond to the energy levels of the atomic orbitals of Hyrdogen with principal quantum numbers n=1,2,3,... Note that the ene...
by Connor Kelligrew 2D
Sat Oct 28, 2017 9:09 pm
Forum: Administrative Questions and Class Announcements
Topic: Nov 9th Midterm
Replies: 1
Views: 199

Re: Nov 9th Midterm

Hi! It seems they're already posted at https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/Midterm_Review_Sessions_14A.pdf
Which is on the main 14A page at the link "Midterm Review Sessions and Rooms"
by Connor Kelligrew 2D
Thu Oct 19, 2017 12:19 pm
Forum: Photoelectric Effect
Topic: Finding the number of photons
Replies: 2
Views: 285

Re: Finding the number of photons

Using E=h\upsilon and c=\lambda\upsilon you get: E=\frac{hc}{\lambda} Using that you can get the energy per photon of light emitted with the given wavelength of 1850 nm. Then: \frac{E_{total}}{E_{photon}} would give the number of photons generated in 1.0 s, since it is the energy emitted in 1.0 s di...
by Connor Kelligrew 2D
Thu Oct 19, 2017 11:52 am
Forum: Properties of Electrons
Topic: 1.57
Replies: 3
Views: 258

Re: 1.57

For tests, should we know that 486 nm represents blue light, 700 nm is red, and so on? At office hours, Dr. Lavelle said we should know that roughly 400nm-700nm is visible light, 700 nm is red and 400 nm is violet and ultraviolet light is lower than 400nm and infrared light is higher than 700 nm. I...
by Connor Kelligrew 2D
Wed Oct 18, 2017 5:29 pm
Forum: DeBroglie Equation
Topic: Homework 1.13/ Rydberg
Replies: 3
Views: 181

Re: Homework 1.13/ Rydberg

Personally, I would use the equation Dr. Lavelle used in class to avoid confusing myself:

Where:

That way I never have to deal with and
by Connor Kelligrew 2D
Wed Oct 18, 2017 5:19 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: E-p distribution
Replies: 2
Views: 137

Re: E-p distribution

Since is rho, the electron density, I agree with the other reply saying he meant electron density distribution.
by Connor Kelligrew 2D
Thu Oct 12, 2017 10:36 pm
Forum: Properties of Light
Topic: converting units ( keV )
Replies: 2
Views: 179

Re: converting units ( keV )

1 keV * \frac{1000eV}{1 keV} * \frac{1.602*10^{-19}C}{1e} eV stands for electron-volt. So in order to convert from keV, first you convert it to eV which is like any other unit with the kilo- prefix, then you multiply it by the charge of an electron. Couloumb (C) times Volt (V) makes a J so that sho...
by Connor Kelligrew 2D
Thu Oct 12, 2017 10:22 pm
Forum: Photoelectric Effect
Topic: Constants that need to be memorized
Replies: 6
Views: 294

Re: Constants that need to be memorized

My TA asked Dr Lavelle and confirmed that the constants and equations will be provided for the test.
by Connor Kelligrew 2D
Thu Oct 12, 2017 10:15 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectroscopy Post-Assessment Q28
Replies: 2
Views: 167

Re: Atomic Spectroscopy Post-Assessment Q28

In order to get the wavelength, you calculate 1 meter divided by 1,650,763.73 wavelengths:


The problem is saying there are 1,650,763.73 wavelengths in a meter, so the division simply obtains the very small portion of a meter that each wavelength is.
by Connor Kelligrew 2D
Thu Oct 05, 2017 3:27 am
Forum: Molarity, Solutions, Dilutions
Topic: G25 homework problem
Replies: 7
Views: 419

Re: G25 homework problem

I don't still don't really get how to do this problem. Can someone explain how to do it more? Well I started by reading the problem and seeing I have the molarity and the volume of the solution. So I can use the equation: M= \frac{n}{V} I want to find the moles of X in the solution, so I will switc...

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