CHEMISTRY COMMUNITY

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

What did C14 do for Valentine's Day?

He went carbon dating!

Connor Kelligrew 2D

What do you do with a dead chemist?

Barium

Connor Kelligrew 2D

I don't trust atoms...

I heard they make up everything

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

I agree with both the other answers, spontaneity != reaction rate and vice versa

Connor Kelligrew 2D

-PdeltaV is for irreversible expansion and -nRTlnV2/V1 is for reversible expansion.

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

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

Connor Kelligrew 2D

What is the show cesium and iodine were watching together?

CSI

Connor Kelligrew 2D

The first rule of thermodynamics is you don't talk about thermodynamics

Connor Kelligrew 2D

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.

Connor Kelligrew 2D

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.

Connor Kelligrew 2D

Final exams will be available 3rd week Winter quarter from 4006 Young Hall.

Connor Kelligrew 2D

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.

Connor Kelligrew 2D

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

Have them read "unionized"

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

Sure. Here ya go:

https://lavelle.chem.ucla.edu/wp-conten ... ns_14A.pdf

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

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.

Connor Kelligrew 2D

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

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

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.

Connor Kelligrew 2D

14BL is titration and spectroscopy I heard, and I’ve also read it doesn’t matter either way.

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

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"

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

Personally, I would use the equation Dr. Lavelle used in class to avoid confusing myself:
$\Delta E=E_{final}-E_{initial}$
Where:
$\Delta E=-\frac{hR}{(n_{final})^{2}}+\frac{hR}{(n_{initial})^{2}}$
That way I never have to deal with $n_{1}$ and $n_{2}$

Connor Kelligrew 2D

Since $\rho$ is rho, the electron density, I agree with the other reply saying he meant electron density distribution.

Connor Kelligrew 2D

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...

Connor Kelligrew 2D

My TA asked Dr Lavelle and confirmed that the constants and equations will be provided for the test.

Connor Kelligrew 2D

In order to get the wavelength, you calculate 1 meter divided by 1,650,763.73 wavelengths:
$\frac{1 meter}{1,650,763 wavelengths}$

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.

Connor Kelligrew 2D

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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